Nomenclatura

Small or medium-scale focused research project (STREP) proposal SST Call 1

FP7-SST-RTD-1

“MARINE INSPECTION ROBOTIC ASSISTANT SYSTEM”

MINOAS 233715

WP 1 – Task 1.1 Analysis and task assessment during a vessel inspection D1.1 - Definition of the Inspection Plan / Definition of Acceptance Criteria

PERFORMING ORGANISATION RINA SPA

REV. DATE

DESCRIPTION PAGES CHECKED APPROVED

0 August 2009 1 November 2009 More detailed drawings have been addedd 2 November 2009 Input and summary tables added by Glafcos 3 December 2009 Guideline on surveys requirement by RINA 4 February 2010 IACS Guidelines added 63 5 February 2010 Survey Tasks Re-engineering 67

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Index 1. General ................................................................................................................................................4

2. Classification Requirements – Lloyd’s Register ......................................................................5

2.1. Lloyd's Register Hull Survey requirements.................................................. 5

2.2. Double hull oil tankers – Close up survey.................................................... 5

2.3. General dry cargo ships - Close-up Survey .................................................. 6

2.4. Double skin bulk carriers - Close-up Survey................................................ 7

3. Tank nomenclature and configuration – LR..............................................................................8

3.1. Tank configurations and nomenclature – Bulk Carrier................................. 8

3.1.1. Single skin - bulk carrier ..................................................................... 8

3.1.2. Transverse section – bulk carrier .......................................................... 9

3.1.3. Transverse watertight bulkhead – bulk carrier .....................................10

3.1.4. Transverse watertight bulkhead – bulk carrier with nomenclature........11

3.2. Tank configuration and nomenclature – Oil tankers....................................12

3.2.1. Design of oil tanker types....................................................................12

3.2.2. Mid section of double hull oil tanker ...................................................13

3.2.3. Transverse bulkhead – oil tanker .........................................................14

3.2.4. Transverse bulkhead nomenclature– oil tanker ....................................14

3.2.5. Double oil tanker – construction..........................................................15

4. RINA Class Requirements............................................................................................................ 16

4.1. General principles of Classification ............................................................16

4.2. Maintenance of Class .................................................................................16

4.3. Thickness measurement..............................................................................16

4.4. Number and Locations of measurements ....................................................18

4.5. Acceptance criteria for thickness measurement...........................................21

4.5.1. Local and Global strength criteria........................................................21

4.5.2. Buckling strength criterion ..................................................................30

4.5.3. Pitting .................................................................................................30

5. Tank nomenclature and configuration – RINA...................................................................... 33

6. Common structural defects - LR ................................................................................................ 40

6.1. Structural defect table.................................................................................40

6.2. Critical Sections – Cargo Holds..................................................................42

7. IACS Guidelines for the use of remote survey techniques.................................................. 47

7.1. General.......................................................................................................47

7.2. Conditions..................................................................................................47

7.3. Procedures..................................................................................................47

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8. Best practices and technical operative experience.............................................................. 48

Introduction..........................................................................................................48

8.1. Ultrasonic Testing ......................................................................................48

8.2. Corrosion ...................................................................................................50

8.3. Ultrasonic Thickness Measurement initiation .............................................51

8.3.1. Execution procedure of UTM..............................................................52

8.3.2. Surface Preparation .............................................................................53

8.3.3. Measurement execution.......................................................................54

8.3.4. Measurement Logging and Inspection .................................................55

8.4. Reporting ...................................................................................................55

8.5. On board survey completion.......................................................................55

8.6. Thickness measurement - Reporting ...........................................................56

9. Synthesis of class requirements (RINA).................................................................................. 57

10. Synthesis of class requirements – LR ....................................................................................... 63

10.1. Special survey.........................................................................................63

10.2. Special survey – Preparations..................................................................63

10.3. Special survey – Typical hull inspection .................................................64

10.4. Docking survey - Shell examination........................................................64

11. Survey Tasks Re-engineering..................................................................................................... 65

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1. General T1.1 – ‘Analysis and task assessment during a vessel inspection’ of WP1 will provide as outcome specific guidelines under which the ship inspection will be executed utilizing the system proposed by MINOAS. The guidelines will be in the form of a list of instructions / suggestions towards the inspector on the procedures to be followed during the phases a) of a vessel inspection and b) repair-marking. During the phase (a) of the project, T1.1 will define the areas that are going to be inspected and the type of the measurements that is required by the robots. The traditional inspection protocol, will act as basic guideline for T1.1. Furthermore, a specific work-plan is required as outcome that will indicate: • the number and the type of the measurements that are needed. The wall thickness

measurements and the image grabbing are considered as prerequisite/ basic tasks. • the frequency in which the measurements are going to be taken. Taking under

consideration that the vessel’s walls and overall structure cover vast areas of metallic surfaces, the measurements will be taken according to a predefined spatial distribution.

• the critical sections of the vessel, that require a more elaborate examination. Under phase (b) of the project, T1.1 will extract the criteria upon which specific areas of the vessel are in need of repair. These areas will be marked by the robots, indicating the exact locations of intervention for the repair/ maintenance crew. This study will produce specification on the number and the sequence of action required under a MINOAS-type inspection and will provide input for the corresponding tasks that study the technological aspects of the related tasks, such as the way the robots are deployed, the way they communicate with the central controller, etc.- T1.4-T1.8. The results of T1.1 will be documented under D1.1 – ‘Definition of the Inspection Plan / Definition of Acceptance Criteria’ and will include results and comparison on the effort minimization achieved within MINOAS related to the traditional inspection procedures.

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2. Classification Requirements – Lloyd’s Register 2.1. Lloyd's Register Hull Survey requirements In the following, Lloyd’s Register Class procedures and requirements for the hull inspection and survey are detailed. The requirements and the frequency of survey of cargo hold is dependent on the age of the ship and ship type which focuses on close up survey, overall survey, and thickness measurements aimed at detecting fractures, buckling, corrosion and other types of structural deterioration. The following tables shows LR rule requirements for the survey of double hull tanker and bulk carriers during special survey.Table below gives details. 2.2. Double hull oil tankers – Close up survey

Table 1: Close up survey for Double Hull oil tankers

Special Survey I (Ships 5 years old)

Special Survey II (Ships 10 years old)

Special Survey III (Ships 15 years old)

Special Survey IV (Ships 20 years old and

over)

(1) One web frame ring in a complete ballast tank, see Notes 1 and 3

(2) One deck transverse in a cargo tank, see Notes 4 and 12

(3) One transverse bulkhead in a complete ballast tank, see Notes 1 and 6

(4) One transverse bulkhead in a cargo centre tank, see Notes 2 and 7

(5) One transverse bulkhead in a cargo wing tank, see Note 7

(1) All web frame rings in a complete ballast tank,see Notes 1 and 3

(2) The knuckle area and the upper part (approx. 5 m) of one web frame ring in each remaining ballast tank, see Note 8

(3) One deck transverse in two cargo tanks, see Note 4

(4) One transverse bulkhead in each complete ballast tank, see Notes 1 and 6

(5) One transverse bulkhead in two cargo centre tanks, see Notes 2 and 7

(6) One transverse bulkhead in a cargo wing tank, see Note 7

(1) All web frame rings in all ballast tanks, see Note 3

(2) All web frame rings in a cargo tank, see Note 9

(3) One web frame ring in each remaining cargo tank, see Note 9

(4) All transverse bulkheads– in all cargo and ballast tanks, see Notes 5 and 6

(5) As considered necessary by the Surveyor, see Note 10

(1) As Special Survey III

(2) Additional transverse areas if deemed necessary by the Surveyor, see Note 10

NOTES

(1) Complete ballast tank means double bottom tank plus the double side tank and the double deck tank, as applicable, even if these are separate.

(2) Where there are no centre tanks, the transverse bulkheads in wing tanks are to be subject to Close-up Survey.

(3) Web frame ring in a ballast tank includes the vertical web in side tank, hopper web in hopper tank, floor in double bottom tank and deck transverse in a double deck tank and adjacent structural members. In

(6) Transverse bulkhead complete in ballast tanks, including girder system and adjacent structural members including longitudinal bulkheads, girders in double bottom tanks, inner bottom plating, hopper side, connecting brackets.

(7) Transverse bulkhead lower part in cargo tanks, including girder system, adjacent structural members (including longitudinal bulkheads) and internal structure of lower stool, where fitted.

(8) The knuckle area and the upper part (approximately 5 m), including adjacent structural members. Knuckle area is the area of the web frame around the connections of the

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peak tanks a web frame means a complete transverse web frame, including adjacent structural members.

(4) Deck transverse including adjacent deck structural members (or external structure on deck in way of the tank, where applicable).

(5) Transverse bulkhead complete in cargo tanks, including girder system, adjacent structural members (including longitudinal bulkheads) and internal structure of lower and upper stools, where fitted.

sloping hopper plating to the inner hull bulkhead and the inner bottom plating, up to 2 m from the corners both on the bulkhead and the double bottom.

(9) Web frame ring in cargo tank includes deck transverse, longitudinal bulkhead vertical girder and cross ties, where fitted, and adjacent structural members.

(10) Additional complete transverse web frame ring.

(11) Ballast tanks includes peak tanks.

(12) Within the mid 0,5 length of the tank.

2.3. General dry cargo ships - Close-up Survey

Table 2: Close up survey for dry cargo ships




Special Survey IV and subsequent (Ships 20 years old and over)

(1) Selected shell frames in one forward and one aft cargo hold and associated tween deck spaces.

(2) One selected cargo hold transverse bulkhead.

(3) All cargo hold hatch covers and coamings (plating and stiffeners).

(1) Selected shell frames in all cargo holds and tween deck spaces.

(2) One transverse bulkhead in each cargo hold, including stiffening system.

(3) Forward and aft transverse bulkhead in one side ballast tank, including stiffening system.

(4) One transverse web with associated plating and framing in two representative water ballast tanks of each type (i.e. topside, hopper side, side tank or double bottom tank).


(6) Selected areas of all deck plating and underdeck structure inside the line of hatch openings between cargo hold hatches.

(7) Selected areas of inner bottom plating.

(1) All shell frames in the forward lower cargo hold and 25% of shell frames in each remaining cargo hold and tween deck spaces, including their end attachments and adjacent shell plating.

(2) All cargo hold transverse bulkheads, including stiffening system.

(3) All transverse bulkheads in ballast tanks, including stiffening system.

(4) All transverse webs with associated plating and framing in each water ballast tank.


(6) All deck plating and underdeck structure and inside the line of hatch openings between cargo hold hatches.

(7) All areas of inner bottom plating.

(1) All shell frames in all cargo holds and tween deck spaces, including their end attachments and adjacent shell plating.

(2) All cargo hold transverse bulkheads, including stiffening system.

(3) All transverse bulkheads in ballast tanks, including stiffening system.

(4) All transverse webs with associated plating and framing in each water ballast tank.


(6) All deck plating and underdeck structure inside the line of hatch openings between cargo hold hatches.

(7) All areas of inner bottom plating.

NOTES

1. Close-up survey of cargo hold transverse bulkheads to be carried out at the following areas:

(i) Immediately above the inner bottom and immediately above the tween decks, as applicable.

(ii) Mid-height of the bulkhead for the holds without tween decks.

(iii) Immediately below the main deck plating and tween deck plating.

2. Ballast tank includes peak tanks.

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2.4. Double skin bulk carriers - Close-up Survey Ore carriers are excluded.

Table 3: Close up survey for double skin bulk carriers




Special Survey IV (Ships 20 years old and

over)

(1) 1 transverse web with associated plating and longitudinals in 2 representative water ballast tanks of each type. This is to include the foremost topside and double side ballast tanks on either side

(2) 2 selected cargo hold transverse bulkheads including internal structure of upper and lower stools, where fitted

(3) All cargo hold hatch covers and coamings (plating and stiffeners)

(1) 1 transverse web with associated plating and longitudinals in each water ballast tank

(2) Forward and aft transverse bulkheads, including stiffening system, in a complete ballast tank, see Note 1

(3) 25% of ordinary transverse web frames in the foremost double side tanks

(4) One transverse bulkhead in each cargo hold including internal structure of upper and lower stools, where fitted


(6) All deck plating and underdeck structure inside line of hatch openings between all cargo hold hatches

(1) All transverse webs with associated plating and longitudinals in each water ballast tank

(2) All transverse bulkheads in ballast tanks, including stiffening system

(3) 25% of ordinary transverse web frames in all double side tanks

(4) All cargo hold transverse bulkheads including internal structure of upper and lower stools, where fitted



(1) All transverse webs with associated plating and longitudinals in each water ballast tank

(2) All transverse bulkheads in ballast tanks, including stiffening system

(3) All ordinary transverse web frames in all double side tanks

(4) All cargo hold transverse bulkheads including internal structure of upper and lower stools, where fitted



NOTES

(1) Complete ballast tank means topside tank, hopper tank, double bottom tank and double side tank, even if these are separate.

(2) Ballast Tank includes peak tanks.

(3) Close-up survey of transverse bulkheads to be carried out at four levels:

Level (a) Immediately above the inner bottom and immediately above the line of gussets (if fitted) and shedders for ships without lower stool.

Level (b) Immediately above and below the lower stool shelf plate (for those ships fitted with lower stools), and immediately above the line of the shedder plates.

Level (c) About mid-height of the bulkhead.

Level (d) Immediately below the upper deck plating and immediately adjacent to the upper wing tank and immediately below the upper stool shelf plate for those ships fitted with upper stools, or immediately below the topside tanks.

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3. Tank nomenclature and configuration – LR

The following gives and interpretation for the location and critical sections mentioned in the survey requirements. 3.1. Tank configurations and nomenclature – Bulk Carrier The purpose of carrying out structural survey of any tank is to determine the

extent of corrosion wastage and structural defects present in the tank and verify suitability of the structure to continue in offering the strength needed for continous efficient operation of vessels.

To help achieve this and to identify key locations in the tank that might warrant special attention, it is paramount to understand the terms mentioned within the rule requirements. The following cross section diagrams depict the locations described in the LR rules and provides familiarisation with the configurations within the cargo holds of oil tankers and bulk carriers.

3.1.1. Single skin - bulk carrier

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3.1.2. Transverse section – bulk carrier

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3.1.3. Transverse watertight bulkhead – bulk carrier

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3.1.4. Transverse watertight bulkhead – bulk carrier with nomenclature

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3.2. Tank configuration and nomenclature – Oil tankers 3.2.1. Design of oil tanker types

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3.2.2. Mid section of double hull oil tanker

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3.2.3. Transverse bulkhead – oil tanker

3.2.4. Transverse bulkhead nomenclature– oil tanker

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3.2.5. Double oil tanker – construction

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4. RINA Class Requirements In the following RINA Class procedures and requirements for the structural inspection and survey are detailed. 4.1. General principles of Classification In RINA Rules Pt A Ch 2 Sec 1 – ‘Assignment of Class’, general principles for class assignment are provided both for new buildings and for ship classed under construction. 4.2. Maintenance of Class The maintence of Class foresees that ships are submitted to Class renewal survey, Intermediate class survey and Annual survey and Bottom survey. The relevant criteria are provided in RINA Rules Pt A Ch 2 Sec 2. 4.3. Thickness measurement • The extent, determination of location, acceptance criteria for ship constructed

after 1 June 2000 • The thickness measurements are a prominent factor in the determination and

extent of the repair and the renewal of the ship structure. • The relevant criteria are provided in RINA Rules Pt A Ch 2 App 2.

In the following table 4 the reference to rule requirements are detailed

Table 4: Reference to Rule requirements related to thickness measurements

TYPE OF SERVICE

NOTATION CLASS RENEWAL INTERMEDIATE ANNUAL

all service notations except those in

other rows

Ch 3, Sec 5, [2.5] and Ch 3, Sec 5, Tab 2: systematic

measurements and suspect areas

Where substantial corrosion is found, the extent of thickness

measurements may be increased to the Surveyor’s satisfaction, using Ch 3, Sec 5, Tab 3 as

guidance

Ch 3, Sec 4, Tab 1 : thickness measurements to be taken if

deemed necessary by the Surveyor Where substantial

corrosion is found, the extent of thickness measurements may

be increased to the Surveyor’s satisfaction,

using Ch 3, Sec 5, Tab 3 as guidance

Ch 3, Sec 3, [2.4.1]: areas of substantial corrosion identified

at previous surveys

Where substantial corrosion is found, the extent of

thickness measurements may be increased

to the Surveyor’s satisfaction, using

Ch 3, Sec 5, Tab 3 as guidance

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bulk carrier ESP ore carrier ESP

Ch 4, Sec 2, [4.1] and Ch 4, Sec 2, [4.5] : planning and

general requirements Ch 4, Sec 2, Tab 5 :

measurements of elements subjected to close-up survey

Ch 4, Sec 2, Tab 6 : extent of systematic thickness

measurements

Ch 4, Sec 2, Tab 7 to Ch 4, Sec 2, Tab 11, according to

the different locations, where substantial corrosion is found

Ch 4, Sec 2, Tab 3 for cargo holds Ch 4, Sec 2, Tab 4 for

salt ballast tanks

Ch 4, Sec 2, Tab 7 to Ch 4, Sec 2, Tab 11, according to the different locations, where

substantial corrosion is found

Ch 4, Sec 2, Tab 1, note (2) for cargo holds and when deemed necessary by the

Surveyor

Ch 4, Sec 2, [2.3.2] for salt ballast tanks and when

deemed necessary by the Surveyor



oil tanker ESP combination

carrier/OBO ESP combination

carrier/OOC ESP



measurements of elements subjected to close-up survey


measurements Ch 4, Sec 3, Tab 4 to Ch 4,

Sec 3, Tab 7, according to the different locations, where


Ch 4, Sec 3, Tab 1 for both cargo and salt ballast tanks



Ch 4, Sec 3, [2.3.2] limited to salt ballast tanks and when deemed necessary by the

Surveyor



oil tanker ESP double hull

Ch 4, Sec 4, [4.1] and Ch 4, Sec 4,

[4.4]: planning and general requirements

Ch 4, Sec 4, Tab 2: measurements of elements

subjected to close-up survey Ch 4, Sec 4, Tab 3: extent of

systematic thickness measurements

Ch 4, Sec 4, Tab 4 to Ch 4, Sec 4, Tab 8, according to the

different locations, where substantial corrosion is found

Ch 4, Sec 4, Tab 1 for both cargo

and salt ballast tanks Ch 4, Sec 4, Tab 4 to Ch 4, Sec

4, Tab 8, according to the different locations, where


Ch 4, Sec 4, [2.3.2] limited to salt

ballast tanks and when deemed necessary by the

Surveyor Ch 4, Sec 4, Tab 4 to Ch 4, Sec

4, Tab 8, according to the different locations, where


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chemical tanker ESP



measurements of elements subjected to close-up survey Ch 4, Sec 5, Tab 3 : extent of

systematic thickness measurements

Ch 4, Sec 5, Tab 4 to Ch 4, Sec 5, Tab 7, according to the

different locations, where substantial corrosion is found

Ch 4, Sec 5, Tab 1 for both cargo and salt ballast tanks



Ch 4, Sec 5, [2.3.2] limited to salt ballast tanks and when deemed necessary by the

Surveyor



liquefied gas carrier


general requirements

Ch 4, Sec 6, Tab 2 : measurements of elements

subjected to close-up survey


measurements

Ch 4, Sec 6, Tab 1 : thickness measurements to be

taken if deemed necessary by the Surveyor

Ch 4, Sec 6, [2.1.6] and limited to salt ballast tanks

and when deemed necessary by the

Surveyor

4.4. Number and Locations of measurements Table 5 provides explanations and/or interpretations for the locations and number

of points to be measured Table 5: Interpretations of rule requirements for the locations and number of points to

be measured A) SYSTEMATIC MEASUREMENTS

ITEM INTERPRETATION FIGURE

Selected plates on deck, tank top, bottom, double bottom and

wind-and- water

“Selected” means at least a single point on one out of three plates, to be chosen on representative areas

of average corrosion No figure

All deck, tank top and bottom plates and wind-and-water

strakes

At least two points on each plate to be taken either at each

1/4 extremity of plate or at representative areas of average corrosion

No figure

Transverse section Refer to the definition given in Sec 2, [2.2.5]

Fig 1 for general cargo ships Fig 2 for bulk carriers Fig 3 for oil tankers

For other ship types, see [3.2.1]

Cargo hold hatch covers and coamings

Fig 4 for ships fitted with hold hatch covers and

coamings

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Bulkheads on ships other than bulk carriers, oil tankers, chemical

tankers and liquefied gas carriers (for these ships refer to B) and C)

CLOSE-UP SURVEYS AND RELATED MEASUREMENTS)

“Selected bulkheads” means at least 50% of the bulkheads

Fig 5 for general cargo ships. It may also apply to

other ship types (see [3.2.1])

Selected internal structure such as floors and longitudinals,

transverse frames, web frames, deck beams,

‘tweendecks, girders

The internal structural items to be measured in each space internally surveyed are to be at least 20% within the cargo area and 10% outside the cargo

area

Fig 6 for general cargo ships. It may also apply to

other ship types (see [3.2.1])

Transverse section of deck plating outside line of cargo hatch

openings (for bulk carriers, ore carriers and combination carriers)

Two single points on each deck plate (to be taken either at each 1/4 extremity of plate or at

representative areas of average corrosion) between the ship sides and hatch coamings in the

transverse section concerned

No figure

One section of deck plating for the full beam of the ship within the cargo area (for oil tankers,

chemical tankers and liquefied gas carriers)

Two single points on each deck plate (to be taken either at each 1/4 extremity of plate or at

representative areas of average corrosion) in the transverse section concerned

No figure

B) CLOSE-UP SURVEYS AND RELATED MEASUREMENTS (for oil tankers, chemical tankers, gas carriers and combination carriers)


Web frame ring (for oil tankers and combination carriers)

Refer to the definition given in Ch 4, Sec 3, Tab 2. “Adjacent structural members” means plating and

stiffeners of deck, bottom, double bottom, sides and longitudinal bulkheads in the vicinity of the

web frame ring

Extent of areas is shown as (1) in Ch 4, Sec 3, Fig 1

Locations of points are given in Fig 10

Transverse section (for chemical tankers and liquefied gas

carriers)

Refer to the definitions given in Ch 4, Sec 5, Tab 2 and Ch 4, Sec 6, Tab 2.

“Adjacent structural members” means plating and stiffeners of deck, bottom, double bottom, sides and longitudinal bulkheads in the vicinity of the web

frame ring

No figure

Deck transverse

This is the upper part of the web frame ring including the adjacent structural members (see

meaning given above). For chemical tankers it may be fitted on deck, i.e. outside the tank



Deck and bottom trans- verses (for oil tankers)

Refer to the definition given in Ch 4, Sec 3, Tab 2 Extent of areas is shown as (2)

and (5) in Ch 4, Sec 3, Fig 1

Transverse bulkhead “Complete” means the whole bulkhead including stringers and stiffeners and adjacent structural

members as defined above



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“Lower part” means lower part of bulkhead up to 1/4 of ship’s depth or 2 metres above the lower

stringer, whichever is the greater (stringers, stiffeners and adjacent structural members



All plating and internal structures (for chemical tankers

and liquefied gas carriers)

Refer to the definitions given in Ch 4, Sec 5, Tab 2 and Ch 4, Sec 6, Tab 2

No figure

C) CLOSE-UP SURVEYS AND RELATED MEASUREMENTS (for b ulk and ore carriers)


Frames in cargo holds

25% of frames: one out of four frames should preferably be chosen throughout the cargo hold length on each side “Selected frames” means at

least 3 frames on each side of cargo holds



Transverse bulkheads in cargo holds

Refer to the definition given in Ch 4, Sec 2, Tab 5 Two selected bulkheads: one is to be the bulkhead

between the two foremost cargo holds and the second may be chosen in other positions

Areas of measurements are shown in

Ch 4, Sec 2, Fig 2 Locations of points are given

in Fig 8

One transverse bulkhead in each cargo hold

This means that the close-up survey and related thickness measurements are to be performed on one

side of the bulkhead; the side is to be chosen based on the outcome of the overall survey of both sides. In the event of doubt, the Surveyor may also

require (possibly partial) close-up survey on the other side

Areas of measurements are shown in

Ch 4, Sec 2, Fig 2 Locations of points are given

in Fig 8

Transverse bulkheads in one topside/side ballast tank

The ballast tank is to be chosen based on the history of ballasting among those prone to have the most

severe conditions


Transverse webs in ballast tanks

Either of the representative tanks of each type (i.e. topside or hopper or side tank) is to be chosen in

the forward part “Associated plating and longitudinals” means adjacent plating and

longitudinals of deck, bottom, side shell, slope, hopper and longitudinal bulkhead, as applicable



Areas of deck plating inside line of hatch openings

“Selected” means at least a single point on one out of three plates, to be chosen on representative areas

of average corrosion

All deck plating means at least two points on each plate to be taken either at each 1/4 extremity of

plate or at representative areas of average corrosion


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4.5. Acceptance criteria for thickness measurement The acceptance criteria for the minimum thicknesses are divided into: � criteria on local and global strength

� criteria on buckling strength � criteria on pitting Each measured structural item is to be checked against the following criteria, as far as applicable. Where any of the criteria are not met, reinforcements, repairs and renewals are to be carried out as appropriate.

4.5.1. Local and Global strength criteria Local and global strength criteria are given for the following ship types:

� general cargo ships � bulk carriers � Oil tankers. These criteria may also be used for other ship types taking into consideration the equivalence or similarity of structural elements and their contribution to local and/or global strength. The evaluation of ship longitudinal strength is based on the prerequisite that fillet welding between longitudinal members and deck, side and bottom plating is maintained effective so as to keep continuity of hull structures. Each structural item to be assessed is illustrated in a typical transverse section (see fig 1 for general cargo ships, fig 2 for bulk carriers, fig 3 for oil tankers). These structural items are grouped according to their position and contribution to the local or global strength of the ship (see tab 6 for general cargo ships, tab 7 for bulk carriers, tab 8 for oil tankers). Each structural item is to be assessed according to four different criteria which vary with regard to the domain under which it is considered, namely:

a) An isolated area, which is meant as a part of a single structural item. This criterion takes into consideration very local aspects such as grooving of a plate or web, or local severe corrosion; however, it is not to be used for pitting for which separate criteria are considered

b) An item, which is meant as an individual element such as a plate, a stiffener, a web, etc. This criterion takes into consideration the average condition of the item, which is assessed by determining its average thickness using the various measurements taken on the same item

c) a group of items, which is meant as a set of elements of the same nature (plates, longitudinals, girders) contributing either to the longitudinal global strength of the ship in a given zone or to the global strength of other primary transverse

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elements not contributing to the ship longitudinal strength, e.g. Bulkheads, hatch covers, web frames

d) a zone, which is meant as all and only longitudinal elements contributing to the longitudinal strength of the ship; in this regard, the three main zones are defined as deck zone, neutral axis zone and bottom zone. This criterion takes into consideration the average condition of all groups of items belonging to the same zone.

Figure 1 : General cargo ship: layout of items to be assessed

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Figure 2: Bulk carrier: layout of items to be assessed

Figure 3 : Oil tanker: layout of items to be assessed

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Table 6: Local and global acceptance criteria for general cargo ships (given in % of

wastage)

Group of items

Description of items

1 Isolated

area

2 Item

3 Group

4 Zone

ITEMS CONTRIBUTING TO THE LONGITUDINAL STRENGTH (TR ANSVERSE SECTION)

DECK ZONE (1) - - - 10

1

Hatch coaming

underdeck girder web

underdeck girder flange

- 25 20

- 20 15

10 - -

- - -

2 Upperdeck plating, deck stringer plates and sheer strakes

30 20 10 -

3

Deck longitudinals

web

flange

- 30 25

- 20 15

10 - -

- - -

NEUTRAL AXIS ZONE (1) - - - 15

4 Side shell plating 25 20 15 -

5

‘Tweendeck hatch girder

web flange

- 25 20

- 20 15

15 - -

- - -

6 ‘Tweendeck plating 30 20 15 -

7

‘Tweendeck longitudinals

web flange

- 30 25

- 20 15

15 - -

- - -

BOTTOM ZONE (1) - - - 10

8 Bilge and bottom strakes and keel plate 25 20 10 -

9 Bottom girders 25 20 10 - (1) Each zone is to be evaluated separately.

(2) If continuous, to be included in item 1. (3) For deep tank bulkheads, the values “average of item” and “average of group” are to be increased by 5 (%).

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Cont’d

Group of items


1 Isolated

area

2 Item

3 Group

4 Zone

10

Bilge and bottom longitudinals

web

flange

- 30 25

- 20 15

10 - -

- - -

11 Inner bottom plating 30 20 10 -

12

Inner bottom longitudinals

web flange

- 30 25

- 20 15

10 - -

- - -

OTHER ITEMS

13 Hatch coaming plating (2) 25 20 - -

14 Hatch coaming brackets 30 25 - -

15 Hatch cover top plating 25 20 15 -

16 Hatch cover skirt plating 30 20 - -

17 Hatch cover stiffeners 30 20 - -

18

Transverse bulkheads (3) plating

stringer web

stringer flange

stiffener web

stiffener flange

brackets

30 30 25 30 25 30

20 20 15 20 15 20

15 - - - - -

- - - - - -

19

Side frames

web

flange

brackets

30 25 30

20 15 20

- - -

- - -

20

Deck/’tweendeck frames

web

flange

30 25

20 15

- -

- -

21 Floors

plating

30

20 -

-

22

Forward and aft peak bulkheads

plating

stiffener web

stiffener flange

30 30 25

20 20 15

15 - -

- - -

(1) Each zone is to be evaluated separately.

(2) If continuous, to be included in item 1.

(3) For deep tank bulkheads, the values “average of item” and “average of group” are to be increased by 5 (%).

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Table 7 : Local and global acceptance criteria for bulk carriers (given in % of wastage) (1/7/2005)

Group of items


1 Isolated

area

2 Item

3 Group

4 Zone

ITEMS CONTRIBUTING TO THE L ONGI TUDIN AL STRENGTH (TRANSVERSE SECTI ON) DECK ZONE (1) - - - 10

1 Strength deck plating, deck stringer, sheer strake and part of side shell plating in way of top side tanks 25 20 10 -

2 Deck longitudinals web flange

- 25 20

- 20 15

10 - -

- - -

3 Side shell longitudinals in way of top side tanks web flange

- 25 20

- 20 15

10 - -

- - -

4 Top side tank sloped plating, including horizontal and vertical strakes

25 20 10 -

5 Longitudinals connected to top side tank sloped plating web flange

- 25 20

- 20 15

10 - -

- - -

NEUTRAL AXIS ZONE (1) - - - 15 6 Side shell plating 25 20 15 -

BOTTOM ZONE (1) - - - 10 7 Bilge and bottom plating and keel plate 25 20 10 -

8 Bilge and bottom longitudinals web flange

- 25 20

- 20 15

10 - -

- - -

9 Bottom girders 25 15 10 -

10 Inner bottom plating and hopper tank sloped plating 25 20 10 -

11

Longitudinals connected to inner bottom and hopper tank sloped plating web flange

-

25 20

-

20 15

10 - -

- - -

OTHER ITEMS

12 Hatch coaming plating (2) (5) 25 20 - -

13 Hatch coaming brackets (5) 30 25 - -

14 Hatch cover top plating (4) (6) 25 20 15 -

15 Hatch cover skirt plating (4) (6) 25 20 - -

16 Hatch cover stiffeners (4) (6) 25 20 - -

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17 Transverse bulkheads (3) plating stiffener web stiffener flange

25 25 20

20 20 15

15 - -

- - -

18 Side shell frames web flange brackets

25 20 20

20 15 15

- - -

- - -

19 Topside and hopper tank web frames web flange

25 20

20 15

- -

- -

20 Floors plating

25

15

-

-

21

Forward and aft peak bulkheads plating stiffener web stiffener flange

25 25 20

20 20 15

15 - -

- - -

(1) Each zone is to be evaluated separately. (2) If continuous, to be included in item 1. (3) For vertically corrugated transverse bulkheads in cargo holds:

• For ships indicated in Ch 6, Sec 2, [1.1] which are to comply with the retroactive requirements according to the schedule given in Ch 6, Sec 2, [1.2], the bulkhead between the two foremost cargo holds is to be assessed based on the criteria given in Ch 6, Sec 2, [1.3].

• For ships indicated in Pt E, Ch 4, Sec 3, [7.1.1], contracted for construction on or after 1 July 1998, all bulkheads are to be repaired by steel renewal where the gauged thickness is less than t + 0,5 mm, where t net is the thickness obtained by applying the strength criteria given in Pt E, Ch 4, Sec 3, [7.1]. However, where the gauged thickness is within the range t net + 0,5 mm and t net + 1,0 mm, coating (applied in accordance with the coating Manufacturer’s requirements) or annual gauging may be adopted as an alternative to steel renewal.

(4) For ships indicated in Ch 1, Sec 2, [4.3.2], contracted for construction before 1 January 2004, the renewal criteria of all cargo hatch covers are as follows: • for single skin hatch covers and for the plating of pontoon covers, steel renewal is required where the gauged thickness is less than

tnet + 0,5 mm. Where the gauged thickness is within the range tnet + 0,5 mm and tnet + 1,0 mm, coating (applied in accordance with the

coating Manufacturer’s requirements) or annual gauging may be adopted as an alternative to steel renewal. For the internal structure of pontoon hatch covers, thickness gauging is required when plating renewal is to be carried out or when this is deemed necessary, at the discretion of the Surveyor, on the basis of the plating corrosion or deformation condition. In these cases, steel renewal for the internal structures is required where the gauged thickness is less than tnet.

(5) For ships indicated in Ch 1, Sec 2, [4.3.2] to Ch 1, Sec 2, [4.3.7], contracted for construction on or after 1 January 2004, the renewal criteria of forward and side hatch coamings on exposed decks in position 1, as defined in ILCC, are as follows: • steel renewal is required where the gauged thickness is less than tnet + 0,5 mm. Where the gauged thickness is within the range

tnet + 0,5 mm and tnet + 1,0 mm, coating (applied in accordance with the coating Manufacturer’s requirements) or annual gauging may be

adopted as an alternative to steel renewal. Coating is to be maintained in good condition, as defined in Sec 2, [2.2.11]. (6) For ships indicated in Ch 1, Sec 2, [4.3.2] to Ch 1, Sec 2, [4.3.7], contracted for construction on or after 1 January 2004, the renewal

criteria of all cargo hatch covers are as follows: • for single skin hatch covers and for the plating of double skin hatch covers, steel renewal is required where the gauged thickness

is less than tnet + 0,5 mm. Where the gauged thickness is within the range tnet + 0,5 mm and tnet + 1,0 mm, coating (applied in

accordance with the coating Manufacturer’s requirements) or annual gauging may be adopted as an alternative to steel renewal. Coating is to be maintained in good condition, as defined in Sec 2, [2.2.11].

For the internal structure of double skin hatch covers, thickness gauging is required when plating renewal is to be carried out or when this is deemed necessary, at the discretion of the Surveyor, on the basis of the plating corrosion or deformation condition. In these cases, steel renewal for the internal structures is required where the gauged thickness is less than tnet.

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Table 8 : Local and global acceptance criteria for oil tankers (given in % of wastage)

Group of items


1 Isolated area

2 Item

3 Group

4 Zone

ITEMS CONTRIBUTING TO THE LONGITUDINAL STRENGTH (TR ANSVERSE SECTION)

DECK ZONE (1) - - - 10

1 Deck plating, deck stringer, sheer strake and longitudinal bulkhead upper strake (2)

25 20 10 -

2

Deck and sheer strake longitudinals

web

flange

- 25 20

- 20 15

10 - -

- - -

3

Deck longitudinal girders

web

flange

- 25 20

- 20 15

10 - -

- - -

4

Longitudinals connected to long. bulkhead upper strake (2) web

flange

- 25 20

- 20 15

10 - -

- - -

NEUTRAL AXIS ZONE (1) - - - 15

5 Side shell plating (2) 25 20 15 -

6

Side shell longitudinals and stringers (2) web flange

- 25 20

- 20 15

15 - -

- - -

7 Longitudinal bulkhead plating 25 20 15 -

8 Longitudinal bulkhead longitudinals and stringers web flange

- 25 20

- 20 15

15 - -

- - -

BOTTOM ZONE (1) - - - 10

9 Bilge and bottom strakes, longitudinal bulkhead lower strake and keel plate (2) 25 20 10 -

10 Bilge and bottom longitudinals (2) web flange

- 25 20

- 20 15

10 - -

- - -

11

Longitudinals connected to longitud. bulkhead lower strake

web

flange

- 25 20

- 20 15

10 - -

- - -

12

Bottom girders

web

flange

- 25 20

- 20 15

10 - -

- - -

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Cont’d OTHER ITEM S

13

Deck transverse web frame

web flange brackets / stiffeners

25 20 25

20 15 20

- - -

- - -

14

Side shell web frame

web

flange brackets / stiffeners

25 20 25

20 15 20

- - -

- - -

15

Longitudinal bulkhead web frame

web


25 20 25

20 15 20

- - -

- - -

16

Bottom transverse web frame

web


25 20 25

20 15 20

- - -

- - -

17

Cross tie

web

flange

brackets / stiffeners

25 20 20

15 15 15

- - -

- - -

18

Transverse bulkheads (3) plating

stringer web

stringer flange

stiffener web

stiffener flange

25 25 20 30 25

20 20 15 20 15

15 - - - -

- - - - -

(1) Each zone is to be evaluated separately. (2) For double hull oil tankers, the structural elements of the inner skin (plating, longitudinals, girders, bulkheads) are to be included

in the corresponding elements of the outer skin. (3) Including swash bulkheads, forward and aft peak bulkheads.

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4.5.2. Buckling strength criterion This criterion is applicable to ships having a length greater than 120 metres.

In addition to the evaluation of structural elements according to the local and global strength criteria, the structural items contributing to the longitudinal strength of the ship, such as deck and bottom plating, deck and bottom girders, etc., are also to be assessed with regard to their buckling strength. The values shown in Tab 9 are not to be exceeded. The minimum thickness will be specially considered for ships built with excess hull girder section modulus.

Table 9: Buckling strength criterion

MATERIAL (ReH) ITEMS

RATIO 235 315 355 and 390

Bottom and deck plates s / t 56,0 51,0 49,0

Longitudinals flat bar web hw / tw 20,0 18,0 17,5

Flanged longitudinals / girders web hw / tw 56,0 51,0 49,0

Flanged longitudinals / girders symmetrical flange bf / tf 34,0 30,0 29,0

Flanged longitudinals / girders asymmetrical flange bf / tf 17,0 15,0 14,5

Symbols:

ReH : minimum yield stress of the material, in N/mm2; s : longitudinal spacing, in mm; t : actual plate thickness, in mm;

hw : web height, in mm; tw : web thickness, in mm; bf : flange breadth, in mm; tf : flange thickness, in mm;

4.5.3. Pitting The maximum acceptable depth for isolated pits is 35% of the as-built thickness. For areas with different pitting intensity, the intensity diagrams shown in Fig 4 are to be used to identify the percentage of affected areas.

For areas having a pitting intensity of 50% or more, the maximum acceptable average depth of pits is 20% of the as-built thickness. For intermediate values between isolated pits and 50% of affected area, the interpolation between 35% and 20% is made according to Tab 10. In addition, the thickness outside the pits in the area considered is to be assessed according to the local and global strength criteria and to the buckling strength criterion. Application of filler material (plastic or epoxy compounds) is recommended as a means to stop or reduce the corrosion process, but it is not considered an acceptable repair for pitting exceeding the maximum allowable wastage limits. Welding repairs may be accepted when performed in accordance with procedures agreed with the Society

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PITTING INTENSITY (%)

MA XI MUM ACCEPTABLE AV ERAGE

PITTING DEPTH (% of the as-built thickness)

Isolated 35,0

5 33,5

10 32,0

15 30,5

20 29,0

25 27,5

30 26,0

40 23,0

50 20,0

Table 10: Pitting intensity and corresponding maximum acceptable average depth of

pitting

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Figure 4: Pitting intensity diagrams (from 1% to 50% intensity)

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5. Tank nomenclature and configuration – RINA The following Figures are given to facilitate the visualization of requirements given in the table. These figures show typical arrangements of cargo ships, bulk carriers and oil tankers. Figures are not intended to cover all the different cases. However, the figures provided here may be used as a guidance for ships other than those here illustrated.

Figure 5: Transverse section of a general cargo ship

Measurements are to be taken on both port and starboard sides of the selected transverse section

Measure Point Symbol

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Figure 6: Transverse section of a bulk carrier

Measurements are to be taken on both port and starboard sides of the selected transverse section

Figure 7: Transverse section of an oil tanker Measurement are to be taken on both port and starboard sides of the selected transverse section

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Figure 8: Locations of measurements on hatch covers and coamings

(valid for all ships fitted with hatch covers and coamings)

(1) Three sections at L/4, L/2, 3L/4 of hatch cover length, including: • one measurement of each hatch cover plate and skirt plate • measurements of adjacent beams and stiffeners • one measurement of coaming plates and coaming flange, each side (2) Measurements of both ends of hatch cover skirt plate, coaming plate and coaming flange (3) One measurement of one out of three hatch coaming brackets and bars, on both sides and both ends

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Figure 9: Locations of measurements on bulkheads of general cargo ships

Cargo hold bulkhead/watertight floor plating to be measured as per main view One stiffener out of three to be measured as per view A - A

Figure 10: Locations of measurements on selected internal structural elements of general cargo ships

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Figure 11: Locations of measurements on structural members in cargo holds and ballast tanks of bulk carriers

Figure 12: Locations of measurements on cargo hold transverse bulkheads of bulk carriers

Measurements to be taken in each shaded area as per views A - A and B – B

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Figure 13: Locations of measurements on transverse bulkheads of topside, hopper and double bottom tanks of bulk carriers

Measurements to be taken in each vertical section as per view A - A

Figure 14: Locations of measurements on web frame rings and longitudinal elements of oil tankers

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Figure 15: Locations of measurements on tranverse bulkheads of oil tankers

(1) : Corrugated bulkhead (2) : Plane bulkhead Measurements are to be taken in a similar way on the centre tank bulkheads Measurements are to cover the different thicknesses of strakes over the height of the bulkhead Measurements are to be taken of the adjacent structural members

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6. Common structural defects - LR When dealing with any hull damage, defect or failure consideration needs to be given to the location of the damage and its extent, as well as severity, age, size, type and general condition of the ship. These factors will influence the nature and extent of any repairs. Hull defects are in many cases preventable with timely maintenance and an understanding of their causes. Understanding the typical causes of defects is important as it will also help to locate defects. The following can be used to define, group into category the type of hull defect which can be found in the hull of a ship.

1. Structural overload 2. Design related 3. Workmanship related 4. Vibration related 5. Corrosion 6. Pitting

It is important to state here that structural damages and deterioration imply deficiencies caused by: o excessive corrosion o design faults o material defects or bad workmanship o navigation in extreme weather conditions o loading and unloading operations, water ballast exchange at sea o wear and tear o Contact (with quay side, ice, touching underwater objects, etc.

This is not as a direct consequence of accidents such as collisions, groundings and fire/explosions as deficiencies are normally recognized as material wastage, fractures or cracks, deformations etc 6.1. Structural defect table The table below gives a brief description of these defects.

Table 11 : Common Structural defect

Defect category Definition

Structural overload is caused by placing greater stress on the ship than it was designed for.

This category of defect may be the result of the following:

• Grounding

Structural overload

• Collision

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• Contact (for example with the quay or with tugs)

• Operational overload (for example; poor loading sequence, too high a rate of loading, variable ballast levels during loading)

Overload due to heavy weather (heavy weather damage) may also be considered to fall into this category.

Design related defects resulting from:

• Differences between the actual loads experienced by the structure compared with the theoretical loads used for design

• The design tolerances having been exceeded

• Applicable standards not having been complied with

• Inadequacies in the initial design and in particular the detail design.

Design related

• This category of defect is characterised by the defect having no apparent cause and by it repeatedly re-occurring following repair as per the original design.

Regardless of the quality of the design, poor workmanship results in defects.

Workmanship related defects include those defects caused by any of the following:

• Use of sub-standard materials

• Poor alignment

• Poor welding

• Poor finishing and/or omissions

Workmanship related

• Initial deformations.

Vibration related Fatigue defects resulting from hydrodynamic or mechanically induced vibration

The type of corrosion encountered in a location will fall into one of the following types:

• General wastage

• Localised corrosion.

Local coating breakdowns are more likely in:

• Areas which are hard to access and therefore maintain

• Areas such as erection joints where weld profiles may be less smooth (particular attention should be paid to such areas in ballast tanks)

• Areas of higher stresses.

Corrosion

It should be noted that corrosion rates are accelerated in areas of higher stresses (corrosion under stress). In turn, the more a structure corrodes the greater are the stresses on the remaining sound structure and therefore the corrosion rate increases. Conversely, if the stresses in an area are reduced the rate of corrosion is also reduced.

Pitting Pitting defects generally caused by corrosion.

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The various types of deficiencies and where they may occur will be discussed in more details. 6.2. Critical Sections – Cargo Holds The following areas where structural defects might occur should have special attention at during survey: (a) Cargo Tanks • Main deck deckhead: corrosion and fractures. • Buckling in web plate of the underdeck web frame and fractures at end of

bracket toes. • Transverse bulkhead horizontal stringers: fractures in way of cut-outs and at

end bracket toe connections to inner hull and longitudinal bulkhead. • Longitudinal bulkhead transverse web frames: fractures at end bracket toe • Connection to inner bottom. • Necking effect of longitudinal web plating at longitudinal bulkhead plating. • For plane transverse bulkheads, transverse bulkhead vertical stiffeners • connected to inner bottom: for vertically corrugated bulkheads, corrugation • connection to lower shelf plate and bulkhead plating connection to inner

bottom: • Fractures caused by misalignment and excessive fit-up gap. • Transverse bulkheads at the forward and after boundaries of the cargo space: • Fractures in way of inner bottom. • Pitting and grooving of inner bottom plating.

(b) Double Hull Ballast Spaces • Main deck deckhead: corrosion and fractures. • Inner hull plate and stiffener: coating breakdown. • Buckling of the web plate in the upper and lower part of the web frame. • Fractures at the side shell longitudinal connection to web frames due to

fatigue. • Corrosion and fractures at knuckle joints in inner hull at forward and after

parts of ship. • Corrosion and fractures at the juncture where the sloped inner hull is

connected to the inner bottom. • Fractures at side and inner hull longitudinal connections to transverse

bulkheads due to fatigue and/or high relative deflections. • Inner bottom deckhead corrosion at inner bottom. • Bottom corrosion wastage. • Cracks at inner bottom longitudinal connection to double bottom floor web

plating. • Fractures at inner bottom and bottom longitudinal; connection to transverse • Watertight floor due to high relative defections.

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Figure 16 : Common Critical Sections

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Figure 17: Typical fracturing at the connection of transverse bulkhead structure – Bulk carriers

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7. IACS Guidelines for the use of remote survey techniques On may 2004 the International Association of the Classification Societies (IACS) proposed a guideline regarding the use of remote survey techniques. The contents of this guideline are following detailed: 7.1. General � Remote Inspection Technique methods may be used to facilitate the required

internal examinations, including close-up surveys and gaugings required with close-up surveys. The methods applied for Remote Inspection Techniques are to provide the survey results normally obtained for the Surveyor.

� Confirmatory close-up surveys are to be carried out by the Surveyor at selected locations where close up surveys are required to verify the results of the Remote Inspection Technique methods. Proposals for use of Remote Inspection Technique methods are to be submitted to the Classification Society for approval in advance of the survey. The Classification Society will review the proposal and approve the arrangements including minimum requirements for confirmatory close-up surveys.

7.2. Conditions � Use of Remote Inspection Technique method may be restricted or limited where

there is a record or indication of abnormal deterioration or damage to structure. This method may not be applicable if there are recommendations for repairs. It may also be inapplicable if conditions affecting the class of the vessel are found during the course of the survey. If the Remote Inspection Technique method reveals damage or deterioration that requires attention, the Surveyor may require close-up survey without the use of Remote Inspection Techniques to be undertaken.

7.3. Procedures � The inspection is to be carried out by a qualified technician with adequate

knowledge of hull structure inspection under the surveillance of a Surveyor. The attending Surveyor(s) are to be fully informed of the firm’s proposed inspection plan.

� The Surveyor shall be satisfied with the method of live pictorial representation and the method of positioning of the technician on the structure. Two-way communication between the Surveyor and technician is to be provided. Means of thickness gauging and non-destructive testing may be required in conjunction with use of Remote Inspection Technique methods.

� The structure to be examined using Remote Inspection Technique methods is to be sufficiently clean to permit meaningful examination. Tanks are to be thoroughly cleaned including removal, from tank internal surfaces, of all loose accumulated corrosion scale, if present.

� If divers are used for Remote surveys, the visibility in the tank is to be good to allow for a meaningful examination.

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8. Best practices and technical operative experience Introduction 8.1. Ultrasonic Testing The need for surveys and fault diagnosis in a wide field of industrial applications has lead to the development of various Non Destructive Testing (NDT) techniques and equipment for specific type of fields [www.ndt.org]. Thickness measurements of metal constructions are essential for the verification of the structures integrity as is also the demand for fast and reliable testing of large constructions. The most widely used techniques for non destructive thickness measurements in industry are listed in the sequel (a detailed analysis may be found in http://www.ndt-ed.org/EducationResources/CommunityCollege/communitycollege.htm). • Ultrasonic Testing (UT) with piezoelectric transducer • Electromagnetic Acoustic Transducer (EMAT) • Magnetostictive • Laser induced ultrasonic

All methods use the measurement of the time of travel of ultrasound within the material with known acoustic properties for the calculation of its thickness. The use of piezoelectric transducers is widely used for its easy creation of ultrasounds within the specimen although good contact with the specimen is required since the ultrasound is induced through mechanical coupling of probe to the material.

The piezoelectric material is usually excited with an impulse and its response is a short narrow-band oscillation. Its frequency is well defined by the used probe and is usually in the range of 1 to 20MHz, where higher frequencies lead to increased resolution in the expense of increased attenuation. The probes vibration is coupled to

Figure 18: Piezoelectric Probes and active material (SiO2)

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the steel part and the ultrasound travels through the specimen. For its detection the opposite effect is used by the same piezoelectric element or a different receiver. Typical waveforms appear in the following figure.

The main drawback of piezoelectric transducers is the need of contact of the active element to the part under test, especially when the material is corroded or covered with paint as is the usual case in marine industry. For cancelling the effect of the additional delay caused by paint or other layers between the active element and the material, the multi – echo method is used. Instead of measuring the time between the transmitted tone burst and the first echo, the time between 2nd and 3rd echo are measured.

Figure 19: Transmitter (top) and receiver (bottom) waveforms

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8.2. Corrosion A qualitative categorization as appear in “Ultrasonic thickness gauging for hull surveys”, ABS Academy, 1995 is: • Pitting Corrosion. Localized corrosion occurring on bottom plating, other

horizontal surfaces and at structural details that trap water. • General Corrosion. Appears as non – protective, friable rust which can

uniformly occur on tank internal surfaces that are uncoated. The rust scale breaks off, exposing fresh metal to corrosive attack.

• Grooving Corrosion. Localized, linear corrosion which occurs at structural intersections where water collects and flows.

• Weld Metal Corrosion. Defined as preferential corrosion of the weld deposit. Most likely cause is galvanic action with the base metal. More likely in manual welds than machine welds.

For the quantization of the corrosion it is common to visually compare the area with various Measle charts, depending on corrosion type (localized, scattered or linear). A list of examples follows.

Figure 20: Echo timing

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8.3. Ultrasonic Thickness Measurement initiation As a general rule the Class surveyor, considering the Class Rules for the particular type of ship, dictates for the survey type. After the ships preparation by the ship yards, the UT operator and the appointed Class surveyor examine the ship's plans and its history regarding former surveys, modifications and repairs that may had, and also the kind of cargo that used to transfer. Depending on ship's load conditions, former UT

Figure 21: Examples of corrosion quantization

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measurements and repairs, it is possible to isolate the critical parts of the ship's structure that need maintenance. Considering the practical inability for examining the whole ship's structure and parts, this is a valuable pre-process stage that its main aim is to minimize the metal surfaces and parts that need to be examined, thus minimizing surveys time, while maintaining safety rules. However this process encapsulates in a significant degree the experience of the Class surveyor and the UT operator, rendering the survey not factual. The UT operator before proceeding with the main stage of the survey, that is the thickness measurements of the defined locations, must ensure the following conditions are met for the personnel’s safety

1. Informing of captain and/or chief mate and other teams that may work on board, about the places that will be visited and the corresponding time schedule.

2. In enclosed, isolated and/or dangerous places the UTM technician must be accompanied of at least one more with adequate equipment.

3. Before entering inside any tank and void space, it is necessary to check the quantity of oxygen that is contained in space (>21% per volume), especially for fuel tanks and cargo tanks (tankers) must be covered the criterions that mentioned at the “International Safety Guide for oil Tankers and Terminals” (ISGOTT: Ch.10 – “Entry into & work in enclosed spaces”. During stay inside tanks must be provided adequate ventilation. At the entrance of the tank must remain a crew member, responsible of the safety of those inside.)

4. The UTM technician must never enter inside cargo holds during loading/unloading and ballast tanks during ballasting / deballasting.

5. Lighting must be natural where available, i.e. by opening hatch covers in cargo holds or all small hatches in way of a tank. When natural light is not enough or not available, the crew must provide the appropriate means (i.e. cargo lights) for satisfactory lighting. UTM technician must always carry a personal waterproof torchlight in enclosed spaces with artificial lighting.

6. Protection of means of access. 7. Means of escape & proceedings of rescue. 8. When the time schedule of spaces to be visited is being prepared,

consideration must be taken of the existing temperature levels (i.e. at hot climates (tropics) visiting exposed spaces during noontime must be avoided).

8.3.1. Execution procedure of UTM

After the initiation process the UT operator proceeds to the thickness measurements. The preparation of the surface for the measurements to be accurate is the most time and effort consuming operation. Since the majority of thickness measurement equipment use ultrasonic waves, the ultrasonic probe (transmitter / receiver) must be in good contact with the specimen, so that the waves may pass from the probe to the steel plate easily without great loss and reflections for an accurate and reliable measurement. The most common tasks for the measurement execution are ordered as:

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8.3.2. Surface Preparation i. Visual inspection of the area to be surveyed. An evaluation of corrosion is

made empirically and with guidance of the Classes manuals the number and location of required point measurements are estimated. Also a first time schedule assessment is noticed to the Owner representative and Class Surveyor.

ii. Cleaning of the spot to be measured from paint or rust by hammering (if considered necessary). It is usual for the steel plates of the ships structure to be corroded or pitted, thus having a significant amount of brittle material above the structural steel that is not contributing to the structural integrity and mechanical loading. Even if a measurement is feasible, the added layers of brittle material may lead to misleading measurements since the extra layers are measured as structural steel.

iii. Cleaning as above but with the use of portable grinder (if necessary).

Figure 22: Grinding of corroded plate

iv. Rub out with rag.

Figure 23: Prepared surface

v. Apply a layer of couplant (grease, water, etc.). This layer acts as acoustic impedance matching between the UT probe and the steel part minimizing reflections from the contact area allowing the UT wave to travel through the steel part.

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Figure 24: Ultrasonic probe and use of acoustic couplant

8.3.3. Measurement execution

i. Take the spot thickness measurement on the structural member. The UT operator in most cases has in his disposal several type of UT probes for specific type of parts and corrosion. The use of such different equipment is based on his expertise and capabilities since e.g small dual element probes (separately transmitter / receiver) may require smaller amount of surface preparation whereas larger single element probes (transmitter and receiver in the same element) require larger clean surfaces but producing more reliable results.

ii. Record the thickness at the corresponding exact point on the prepared

drawings.

Figure 25: Measurement

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Figure 26: Measured points and marking for Class Surveyor's reference

iii. Repeat the above-described procedure for all measurements required to be taken, by the class surveyor.

8.3.4. Measurement Logging and Inspection

i. The measurements that will be recorded to UTM tables are the average of multiple readings thus giving a general indication of the plate concerned.

ii. In case of there is a deviation between e.g. a plate’s original thickness as came up from U.T. Measurements and same plate’s original thickness which derives from vessel’s drawings, then prior of any action, an immediate notification should be made to Owner’s Representative and LR attending Surveyor in order for him to conclude and/or consult timely for any further action.

iii. Re-test measuring instruments every three (3) hours of continuous operation for proper functioning and correct measurement indications.

8.4. Reporting During the measurement procedure the UT operator should manually log the data for the specific measured part to the corresponding drawing so as a representative thickness profile is created. The plans are then consulted for the original steel thicknesses of the particular part or any available former measurements and in case of large deviations or substantial corrosion the Owner Representative and Class surveyor should be informed before further actions are taken. In general the reporting operations required follow: 8.5. On board survey completion

1. The thickness measurements as taken and recorded are presented to Owner’s Representative and submitted in rough forms to the Class surveyor. Frequency of those presentations is at Class Surveyor discretion, but the best situation is in an every-day basis.

2. Additional measurements in critical structural areas might be requested to be taken by the Class surveyor.

3. Where excessive diminution of the structure is found during the survey then this is to be brought to the attention of the Owners and Surveyors, also where the diminution of the structure is zero or minimal then this also to be brought to the Surveyors attention such that the extent of the measurements may be given further consideration.

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4. The measurement report or summary of the report is to be submitted to the attending Surveyor prior to the completion of the survey for verification and confirmation of completeness of the thickness survey. This is required in order to confirm that the recorded measurements are acceptable.

5. Upon completion of the aforementioned procedures and with the Class surveyor’s consent, the onboard survey is included.

6. Before departure, operator must submit to Owner’s Representative and Class Surveyor an electronic copy of Ultrasonic Thickness Measurements Report, considered as Preliminary Report.

7. Departure of UT operator. 8.6. Thickness measurement - Reporting Thickness measurements, depending on the vessel's type and associate Class, are reported in report forms. According to “Thickness Measurement & Close up Survey Guidance”, Revision 5.4 (April 2009) by LR, and in “Lloyd’s Register Thickness Measurements v.3.1” the report is to include the following (e.g. for single skin bulk carriers):

1. Table/index of contents. 2. Thickness Measurement report - General Particulars. 3. Drawings indicating the taken thickness, drafted with the use of CAD

programs. 4. Tables of results for the measured members. The tables are designed by

appropriate computer program. 5. The tabulated results 6. In general the final report is submitted to the attending surveyor prior of

vessel’s departure but in any case no later than 2 weeks after measurements is completed.

Upon completion of survey and delivery of report the survey file is to contain, apart of the information mentioned in paragraph 1, the following:

1. The rough drawings used onboard to mark the onsite. 2. Original thickness measurement booklet. 3. Any additional information and document considered being of useful future

reference. 4. Evidence of the final approved (stamped) report (i.e. fully stamped copy, copy

of the 1st (gen. par.) stamped page etc.). The described evidence is collected either directly by the surveyor or by the shipping company.

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9. Synthesis of class requirements (RINA) In order to synthetize the RINA requirements, the following guide on visual inspection and thickness measurments criteria in accordance with RINA rules is provided. Accordingly to RINA Requirements the Class Certificate is assigned to a ship upon a survey in order to verify whether it is eligible to be classed on the basis of the Rules of the Society. All RINA classed ships are submitted to surveys for the maintenance of the class during their operative life. In particular the surveys foreseen during the ship life are: � Class renewal survey (every 5 years); � Intermediate (every 2,5 years); � Annual survey (every year). � Bottom survey1 (two surveys in the 5 years class period)

In addition to the above periodical surveys, Classed ships are to be submitted to occasional surveys whenever the circumstances may require them. Procedures to be followed during a survey The general procedure of a survey consists in: � An overall survey (visual inspection) of the parts of the ship covered by the

rule requirements; � Checking by means of Thickness Measurements selected items covered by the

rule requirements. Overall survey and close-up survey An overall survey is a survey intended to report on the overall condition of the hull structure and determine the extent of additional close-up survey. A close-up is a survey where the details of structural components are within the close visual inspection range of the surveyor, i.e. normally within reach of hand.

1 Bottom survey means the examination of the outside of the ship’s bottom and related items. This examination may be carried out with the ship either in dry dock or afloat. (see RINA Rules Pt A Ch 2 Sec 2 item 5 and Pt A Ch 3 Sec 6)

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Thickness measurements (TM)

General aspects In general, thickness measurements are to be carried out under the responsibility of the Owner, in the presence of the Surveyor. The thickness measurements are to be witnessed by a Surveyor of the Society. The Surveyor is to be on board to the extent necessary to control the process. Prior to commencement of the intermediate and class renewal surveys, a meeting is to be held between the attending Surveyor(s), the Owner's representative(s) in attendance and the thickness measurement firm's representative(s) so as to ensure the safe and efficient execution of the surveys and thickness measurements to be carried out on board. Thickness measurements are to be carried out by a firm approved by the Society in accordance with the "Rules for the Certification of Service Suppliers".

The TM are a major part of surveys to be carried out for the maintenance of class, and the analysis of these measurements is a prominent factor in the determination and extent of the repairs and renewals of the ship’s structure.

Type of Thickness Measurements The thickness measurements required by the RINA Rules consist of:

1. systematic thickness measurements of different parts of the structure in order to assess the overall and local strength of the ship

2. thickness measurements of suspect areas 3. additional thickness measurements on areas determined as affected by

substantial corrosion.

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1. Systematic thickness measurements Criteria for the Systematic thickness measurements are provided in the following table. Table 12 : Interpretations of rule requirements for the locations and number of points

to be measured SYSTEMATIC MEASUREMENTS ITEM INTERPRETATION Selected paltes on deck, tank top, bottom, double bottom and wind-and-water

‘Selected’ means at least a single point on one out of three plates, to be chosen on representative areas of average corrosion

All deck, tank top and bottom plates and wind-and-water strakes

At least two points on each plate to be taken either at each ¼ extremity of plate or at representative areas of average corrosion

Transerve section Cargo hold hatch covers and coamings Bulkheads on ships other than bulk carriers, oil tankers, chemical tankers and liquefied gas carriers

‘Selected bulkheads’ means at least 50% of the bulkheads

Selected internal structure such as floors and longitudinals, transverse frames, web frames, deck beams, tweendecks, girders

The internal structure items to be measured in each space internally surveyed are to be at least 20% within the cargo area and 10% outside the cargo area

Transverse section of deck plating outside line of cargo hatch openings (for bulk carriers, ore carriers and combination carries)

Two single points on each deck plate (to be taken either at each ¼ extremity of plate or at representative areas of average corrosion) between the ship sides at hatch coamings in the transverse section concerned

One section of deck plating for the hull beam of the ship within the cargo area (for oil tankers, chemical tankers and liquefied gas carriers)

Two single points on each deck plate (to be taken either at each ¼ extremity of plate or at representative areas of average corrosion) in the transverse section concerned

2. Thickness Measurements of suspect areas Suspect areas are locations showing substantial corrosion and/or considered by the Surveyor to be prone to rapid wastage

3. Additional Thickness Measurements Additional measurements are foressen on areas determined as affected by substantial corrosion. Substantial corrosion is an extent of corrosion such that assessment of the corrosion pattern indicates a wastage in excess of 75% of allowable margins, but within acceptable limits. For ships built under the IACS Common Structural Rules,

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substantial corrosion is an extent of corrosion such that the assessment of the corrosion pattern indicates a gauged (or measured) thickness between tnet + 0,5mm and tnet. Criteria for the selection of additional thickenss measurements are provided in the table below.

Table 13 : Guidance for additional thickness measurements in way of substantial corrosion areas

Structural member Extent of measurements Pattern of measurements

Plating Suspect area and adjacent plates 5 point pattern over 1 square

metre

Stiffeners Suspect area 3 measurements each in line

across web and flange

Thickness measurement vs. type of suvey In the following table the thickness measurements foreseen for all type of surveys are provided.

TYPE OF SURVEY RENEWAL (5 years) INTERMEDIATE (2,5 years) Annual (every years) Systematic measurements Measurements on suspect areas Additional measurements

Measurements on suspect areas Additional measurements Other maeasurments at the surveyor satisfaction

Measurements on suspect areas Additional measurements

As far as the TM extension and location for the Renewal survey is concerned they are to be done in accordance to the requirements indicated in the following table.

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Table 14 : Requirements for thickness measurements at class renewal survey

Age of ship (in years at time of class renewal survey) (1) (2)

age < 5 5 < age < 10 10 < age <15 (4) age > 15 Suspect areas

Suspect areas Suspect areas Suspect areas

One transverse section of deck plating in way of a cargo space within 0,5 L amidship

Two transverse sections within 0,5 L amidship in way of two different cargo spaces (3)

A minimum of three transverse sections in way of cargo spaces within 0,5 L amidship (3)

Internals in forepeak and after peak tanks

Internals in forepeak and after peak tanks

All cargo hold hatch covers and coamings (plating and stiffeners)

All cargo hold hatch covers and coamings (plating and stiffeners)

All exposed main deck plating full length

Representative exposed superstructure deck plating (poop, bridge, and forecastle deck)

Lowest strake and strakes in way of tween decks of all transverse bulkheads in cargo spaces together with internals in way

All wind and water strakes, port and starboard, full length

All keel plates full length. Also, additional bottom plates in way of cofferdams, machinery space, and aft end of tanks

Plating of seachests. Shell plating in way of overboard discharges as considered necessary by the attending Surveyor

(1) Thickness measurement locations are to be selected to provide the best representative sampling of areas likely to be most exposed to corrosion, considering cargo and ballast history and arrangement and condition of protective coatings. (2) Thickness measurements of internals may be specially considered by the Surveyor if the hard protective coating is in GOOD condition. (3) For ships less than 100 metres in length, the number of transverse sections required at the class renewal survey for ships 10 < age <15 may be reduced to one, and the number of transverse sections required at subsequent class renewal surveys may be reduced to two (4) For ships more than 100 metres in length, at the class renewal surveys for ships 10 < age <15, thickness measurements of exposed deck plating within 0,5 L amidship may be required. ACCEPTANCE CRITERIA Acceptance criteria stipulate limits of wastage which are to be taken into account for reinforcements, repairs or renewals of steel structure. These limits are generally expressed for each structural item as a maximum percentage of acceptable wastage (W). When the maximum percentage of wastage is indicated, the minimum acceptable thickness (tmin) is that resulting from applying this percentage to the rule thickness (trule), according to the following formula:

tmin = (1-W/100)trule

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However, when the rule thickness is not available, the as-built thickness can be used. Only for criteria related to an item the Society may establish a list of renewal thicknesses taylored to the different structural items. In such a case these thicknesses are used in lieu of the minimum thicknesses calculated from the percentage of wastage. Each structural item is to be assessed according to four different criteria which vary with regard to the domain under which it is considered, namely: • an isolated area, which is meant as a part of a single structural item. This criterion

takes into consideration very local aspects such as grooving of a plate or web, or local severe corrosion; however, it is not to be used for pitting for which separate criteria are considered 4.5

• an item, which is meant as an individual element such as a plate, a stiffener, a web, etc. This criterion takes into consideration the average condition of the item, which is assessed by determining its average thickness using the various measurements taken on the same item

• a group of items, which is meant as a set of elements of the same nature (plates, longitudinals, girders) contributing either to the longitudinal global strength of the ship in a given zone or to the global strength of other primary transverse elements not contributing to the ship longitudinal strength, e. g. bulkheads, hatch covers, web frames

• a zone, which is meant as all and only longitudinal elements contributing to the longitudinal strength of the ship; in this regard, the three main zones are defined as deck zone, neutral axis zone and bottom zone. This criterion takes into consideration the average condition of all groups of items belonging to the same zone

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10. Synthesis of class requirements – LR 10.1. Special survey Any damage in association with wastage over the allowable limits (including buckling, grooving, detachment or fracture), or extensive areas of wastage over the allowable limits, which affects or, in the opinion of the surveyor, will affect the vessel’s structural watertight or weathertight integrity, is to be promptly and thoroughly repaired. Areas to be considered for a typical bulk carrier are to include: • Side shell frames, • Their end attachments and adjacent shell plating, • deck structure and deck plating, • watertight bulkheads, • hatch covers and • Coamings.

Areas to be considered for a typical oil tanker carrier are to include: • bottom structure and bottom plating; • side structure and side plating; • deck structure and deck plating; • Watertight or oil-tight bulkheads.

10.2. Special survey – Preparations • Ships are required to be risk free before overall survey to ascertain any

significant corrosion, deformation, fractures, damages and other structural deterioration.

• Such preparation including the following • Provision for proper and safe access to tanks and spaces • Tanks and spaces to be gas free and properly ventilated • Permit to entry may be required ( minimum 24hrs ventilation) • All spaces to be cleaned including removal from surface of all lose

accumulated corrosion scale. • Clean spaces to be free from water, scale, dirt, oil residue etc to reveal

corrosion deformation, fracture and condition of protective coating. • Sufficient illumination to reveal any structural deformation • A communication system is to be arranged between the survey party in the

tank and the responsible officer on deck. • Where soft coatings have been applied, safe access is to be provided for the

Surveyor to verify the effectiveness of the coating and to carry out an assessment of the conditions of internal structures which may include spot removal of the coating. When safe access cannot be provided, the soft coating is to be removed.

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• Oxygen-meter, breathing apparatus, lifeline, riding belts with rope and hook and whistles together with instructions and guidelines on their use are to be made available during the survey.

• For oil tankers and chemical tankers, an explosimeter is to be provided

10.3. Special survey – Typical hull inspection The following are the general requirements for special survey and the list is not exhaustive of the full requirements but considers areas applicable to the hull. • Hull and related piping are to be in satisfactory condition fit for any another

new period of class of 5years subject to maintenance and operation and periodical surveys being carried out.

• One docking survey to coincide with special survey • Overall survey to be carried out to ascertain any significant corrosion,

deformation, fractures, damages and other structural deterioration. • All spaces within the hull and superstructure are to be examined • Internal of tanks are to be examined • For ballast water tanks, condition of the corrosion prevention system where

provided in the salt-water ballast tanks is to be examined. • Double bottom, deep, ballast, peak and other tanks, including cargo holds

assigned also for the carriage of salt water ballast, are to be tested with a head of liquid to the top of air pipes or to near the top of hatches for ballast/cargo holds.

• All bilge and ballasting piping systems are to be examined and operationally tested to working pressure to ensure tightness and condition remains satisfactory to the satisfaction of the surveyor.

• Areas of tanks and cargo holds where coatings are found in good condition, the extent of close up surveys may be specially considered.

10.4. Docking survey - Shell examination The following are the requirements for docking Survey:

• 2 dockings required in a 5 year period • Max interval of first docking not exceeding 3 years • One docking survey must coincide with special survey

One docking survey is to coincide with special survey

• Damages, nature of indents, position and sharpness • Cracks or fracture looking for dripping or weeping water/oil. • Pay attention at bilge keels/tunnel welds for cracks or fracture • Erosion/corrosion of welds, platings, stern appendages, sea chest • Condition of the shell coating

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11. Survey Tasks Re-engineering The extent of the Classification Requirements elaborated in the previous sections, sets the reasons for constructing an elaborated plan-methodology that needs to be followed during the re-engineering of the survey procedures. The adaptation of the existing rules that apply to each type of survey and each type and size of vessel will be the task within the framework of D1.2 – ‘Tentative Draft Rules for acceptance of a Hull Robot Inspection’, which will set up and clarify the rules applicable to survey tasks by making use of the holistic approach used by the means of MINOAS system. Results from the elaboration of the existing rules (traditional survey) show the variety of the cases needed to be examined in order to set up the specifications for the ongoing of the technical tasks – extraction of quantititative rather than qualitative criteria for the execution of tasks. It has been agreed upon, during the evolution of T1.1, that the amount of the information to be examined to extract the aforementioned specifications is large compared to the expected profits and is rather recommended to narrow down the extraction of the quantititative criteria needed by utilizing a specific application example - by choosing a specific vessel type and size. The criteria set out in order to reach a decision on the vessel type were:

a. the complexity of the structure is required to be the most challenging one – which means that the vessel type should include most (if not all) of the difficulties/obstacles that could be faced during a vessel survey by a robot, so that locomotion and reachability difficulties will be resolved within the work of this application example.

b. the size of the vessel is chosen based on the availability of the vessel that will host/accommodate the execution of the pilot testing and experimental verification of the results

c. the amount of information required for the surveyor to reach a decision has been kept to the mean expected values – met during most of the applications at hand. That is, the number of images & UT measurements has been chosen (through the choice of the vessel type & size) to be near the values expected in real-life applications – but it is expected that it will not be limited in other cases due to the availability of the resources (power supply is assumed to be available by the same metrics/values in all real – life applications).

This specialization intends solely to narrow down the specifications set down by the Classification Societies (following the traditional survey Requirements followed by humans) which will result in the formalization and the equipping of the robotic platforms. As the choice of the application example is made for the most generic case (the one that carries most of the difficulties to be faced when facing traditional surveys) it is expected that minimum or none adaptation of the methodology, the formulation of the platforms or other subsequent results will be needed – but will only

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remain as a matter of scaling down (or up) of the produced results to match up to the needs met in different applications in practice. It is has been agreed that the Consortium efforts will be focused on the requirements stemming from the structure of a PANAMAX - Bulk Carrier vessel type and that a draft inspection protocol will be assumed (that will also serve as an application example scenario) so that the sequence of tasks and the information flow will be clarified (& facilitated) for the needs of the subsequent tasks. It consists of three sequencially executed Phases, namely:

Phase A: 1st stage of video/image grabbing to provide an overall impression of

the vessel’ status and input for visual evaluation Phase B: 2nd stage of detailed video grabbing (up to surveyor’s satisfaction) – it

is identified in the following algorithmic implementation by making use of a looping condition.

Phase C: Execution of UT measurements at required locations (by the Classification Requirements & indicated positions by the surveyor)

The surveyor may go on-board during the final phase of the execution protocol at his/her own free-will to assess the results of both the previous phases and the execution of the last one.

The protocol formulation is given through the sequence of these steps:

1. Grabbing images/video from the entire vessel. The entire vessel will be covered by the robots (each locomotion ability used based on the activation area) that will transmit images/video to a control station within which the surveyor resides. This way he/she will have an overall view of the vessel’s status within a very short period of time

2. <Begin Loop>

a. Comparison of the images grabbed with images from DataBases that will produce the level of corrosion/pitting. The goal of the comparison will indicate the percentage of pitting through means of image processing tools. This pre-processing of the gathered information aims in assisting the surveyor in reaching decisions similar to ‘how many more and in which places do we need to take more UT measurements to reach conclusive results regarding the vessel’s structural integrity?’. It is foreseen that the images grabbed in the previous step will be part of the vessel’s archives and will be available for future comparisons in future surveys. In cases where this does not apply the images will be drawn from the Classes’ DataBases.

b. Extraction of ‘Hot-Spots’ areas where additive information (through UT means) will be required

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c. <Decision> - Able to reach results with the information at hand?

d. <No> - Grab more images from the ‘dark areas’ and iterate from the beginning of the loop.

e. <Yes> - Exit loop and continue

3. Perform the UT operations at the points indicated by the Classes as standard procedure and the additive ‘Hot-Spots’ extracted previously.

4. Logging. The entire volume of the data collected within the previous survey-tasks will be logged into archives, firstly to formulate/update the vessel’s own history archives and secondly to update the required information in the Classes Databases.

5. Post-Processing, statistical data will be produced and made available to the surveyor (on the extension of corrosion or the areas with extended pitting), graphical interpretation of the measurements, representation on 3D-CAD drawings, etc. that will facilitate the work of the surveyor and the documentation describing the survey results.

The procedural protocol aims in providing the overall tasks execution described in the Technical Annex (TA) in the form of an algorithm that will be clear and easy to follow by both the maritime experts and the robotic partners and will facilitate the decision making while resolving more detailed technical issues for the subsequent tasks. This protocol will act as a main guideline for all partners but is subject to changes if it is found nessecary during the evolution of the project.

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