The OCIMF and IACS positions relating to

secondary venting. – An update.David Savage SIRE Training and Development manager.

Secondary Venting

SOLAS

International Convention for the Safety of Life at Sea Chapter II-2

Construction - Fire protection, fire detection and fire extinction

Part C Part C

Suppression of fire

Regulation 11

Structural integrity - 6

Protection of cargo tank structure against pressure or vacuum in tankers

6.3.2. Secondary means for pressure/vacuum relief

A secondary means of allowing full flow relief of vapour, air or inert gas mixtures to prevent over-pressure or under-pressure in the event of failure of the arrangements in paragraph 6.1.2. Alternatively, pressure sensors may be fitted in each tank protected by the arrangement required in paragraph 6.1.2, with a monitoring system in the ship’s cargo control room or the arrangement required in paragraph 6.1.2, with a monitoring system in the ship’s cargo control room or the position from which cargo operations are normally carried out. Such monitoring equipment shall also provide an alarm facility which is activated by detection of over-pressure or under-pressure conditions within a tank.

The IACS position

Secondary Means of Venting Cargo Tanks

(Reg. II-2/4.5.3.2.2 and Reg. II-2/11.6.3.2)

1. A P/V breaker fitted on the IG main may be utilised as the required secondary means

of venting.

2. The height requirements of Reg. II-2/4.5.3.4.1 and 11.6.2 and the requirements for

Venting

IACS UI SC140 (October 1998) (Rev. 1 June 1999) (Rev. 2 Nov 2005)

2. The height requirements of Reg. II-2/4.5.3.4.1 and 11.6.2 and the requirements for

devices to prevent the passage of flame of Reg. II-2/4.5.3.3 are not applicable to the

P/V breaker provided the settings are above those of the venting arrangements

required by Reg. II-2/11.6.1.

3. Where the venting arrangements are of the free flow type and the masthead

isolation valve is closed for the unloading condition, the IG systems will serve as the

primary under pressure protection with the P/V breaker serving as the secondary

means.

Secondary Means of Venting Cargo Tanks

(Reg. II-2/4.5.3.2.2 and Reg. II-2/11.6.3.2)

4. Inadvertent closure or mechanical failure of the isolation valves required by SOLAS

Reg. II-2/4.5.3.2.2 and the FSS Code, Ch. 15, 2.3.2.2 need not be considered in

Secondary Venting

IACS UI SC140 (October 1998) (Rev. 1 June 1999) (Rev. 2 Nov 2005)

Reg. II-2/4.5.3.2.2 and the FSS Code, Ch. 15, 2.3.2.2 need not be considered in

establishing the secondary means since:

a) The valves are operated under the control of the responsible ships officer and a

clear

visual indication of the operational status of the valves is required by SOLAS Reg. II-

2/4.5.3.2.2, as amended, and

b) The possibility of mechanical failure of the valves is remote due to their simplicity.

Vessel Date Description of Incident

KHANNUR 10-Sep-01

Reported through Lloyds Hotline that vessel experienced overpressurisation of her cargo tank of LNG in No.4 tank

during discharging operation at everett, Boston. As a result some cracking was caused in the tank.

KRONVIKEN 12-Feb-02

Reported through Loyds Hotline that vessel sustained steel damage due to over pressurisation of the cargo tank

system, will require some 360 tonnes of steel renewals.

GOLDEN DREAM 26-Sep-02

It has been reported that the vessel had a cargo tank explosion due to over pressurization while N2 purging of cargo

tanks.

Explosion occurred in No.3 cargo tank of asphalt tanker Asphalt Victory (17840 gt, built 1983), bound Providence, R.I.,

2001 - ONWARDS - OVER PRESSURISATION INCIDENT

Some Incidents since 2001

ASPHALT VICTORY 14-May-03

at 1424, local time, May 12, 50 miles south-east of Providence. Explosion caused by over-pressurisation of tank and

caused a rupture.

VALLE DI CASTIGLIA 21-May-03

Report received from MSINSPECT: Vessel had a condiiton of class which indicates vessel tank got overpressurised and

vessel structure suffered substantial deformity.

R.M.K. 54 01-Jul-03

Operators informed that M.T. "Serra Theresa", IMO 9254965, was involved in a tank expansion incident, due to

overpressurisation, during blow through of shore line after loading.

ALESSANDRO F 12-Sep-03

From VIQ evaluation - Two conditions imposed to the class due to deformations, the second of these deformations,

between frames 72 and 78, was caused due to slight tank overpressure.

LOUGH FISHER 17-Sep-03

From VIQ evaluation on 16th Sept 2003 - The vessel experienced an oil spill incident in March 2003 and as a result of

shutting down incorrect valves with subsequent overpressurisation, some distortion the bulkheads, stringers and web

frame brackets .

BOW FORTUNE 03-Oct-03 From VIQ evaluation - Tank overpressurisation causing structural damage during a loading operation

Unacceptable Sire report:

CHEMBULK

HONGKONG 19-Jan-05

Unacceptable Sire report:

There was no class documentation available onboard concerning the repairs made following an over pressurization of

No: 3 stb. cargo tank that occurred in August 2003. The vessel only had shipyard specifications.

Incident w

ERMAN S 03-Mar-05

From SIRE evaluation

It was noted on the ESP file on board Structural Condition Evaluation Report & Survey report files that the vessel had

carried out extensive repairs on tanks No 2 starboard during recent dry dock, due to over pressurization .

WEB222 02-Apr-05 Spray (<1gal.water) of oil from hatch aft end of tk due to overpressurization

S30 02-Apr-05 TKM over pressured system, gasket failed, < 2qt.

GUANGZHOU

INTERNATIONAL 17-Oct-05

Reported by Operator - Maersk Bering had an incident of overpressurisation of cargo tanks during loading operation

whereby the deck tranverse girders on top of No. 5 cargo tanks have buckled and become deformed. The Maersk

Bering was loading Gas oil at time of incident.

Loading LCO. A pressure surge/overpressurisation in the main cargo line ruptured an expansion bellows joint, with a

Some Incidents since 2001 (Continued)

CAP CAMARGUE 29-Nov-05

Loading LCO. A pressure surge/overpressurisation in the main cargo line ruptured an expansion bellows joint, with a

spray of cargo on deck and overboard. Emergency shutdown activated. Crew mobilised to contain and clean up spill.

Quantity not established.

FS SOLENE 09-Mar-06

Vessel loading HCO Slurry. Vessel suffered overpressurisation of No 3 stbd cargo tank, with level at about 60% full. No

injuries, no pollution, no leakage to ballast tanks. Vessel sustained distortion of trunk and fracture of welding on

external supports.

MARISP 19-Jun-06

EMRUSH - mt Marisp had a cargospill during loading Hydro Crackate at Esso botlek. As per master vsl requested

max loadrate of 1200 cbm/h, during cargospill loadrate was 1800 cbm/h which caused overpressure in tank. Cargospill

appr. 20 ltrs on deck / 1 lt in water.

BOW SANTOS 24-Apr-07

Reported by Baton Rouge Terminal - Bow Santos has experienced a tank breach (deck fracture) due to N2

overpressurization at BAYTANK terminal.

OCIMF SIRE Vessel Inspection Questionnaire Inspector guidance

Secondary Venting – What the VIQ 08 Edition says…

8.30 Are SOLAS secondary venting requirements being complied with?

A secondary means of full flow relief of vapour, air or inert gas mixtures shall be

provided to prevent overpressure or under-pressure in the event of failure of the

primary venting arrangements.

Alternatively, pressure sensors may be fitted in each tank protected by the primary

venting arrangement with a monitoring system in the cargo control room or the

position from which cargo operations are normally carried out. Such monitoring

equipment shall also provide an alarm facility which is activated by detection of over-equipment shall also provide an alarm facility which is activated by detection of over-

pressure or under-pressure conditions within a tank. (SOLAS 2000 II-2/11.6.3.2)

Note: Class societies may accept a system that may not comply with the SOLAS

requirements for ‘Secondary means of full flow relief’.

In such cases the question should be answered ‘No’. A full description of the system as fitted

should be made as an observation to allow an assessment of acceptability to be made.

In the case of inerted vessels, if pressure sensors are provided as the means of secondary

protection, the alarm settings for the pressure sensors must be set to actuate when the

tank pressure reaches 10% greater than the normal actuation settings of the pressure

valves themselves.

In the case of the under-pressure settings, the pressure in a tank should never be

permitted to fall below zero and the pressure sensors should be set to alarm above zero.

Secondary Venting – Inerted vessels

(Side note: The reason for the latter guidance on the vacuum side is

because of the concerns relating to pyrophoric ignition in inerted tanks with

the introduction of air. In the event that the IG pressure falls to <50mm/WG,

the fans will stop and trip the cargo pumps.)

In the case of non-inerted vessels If pressure sensors are provided, the over-

pressure setting should be set to alarm at 10% greater than the normal

actuation settings of the pressure valves, and at a vacuum 10% greater than

the normal actuation settings of the vacuum valves.

In all cases, a description of the secondary venting arrangements should be

provided, in particular what vents or pressure/vacuum sensing systems are

available on each tank when the main inlet valve to IG/vent main is shut.

Secondary Venting – non-inerted tanks

available on each tank when the main inlet valve to IG/vent main is shut.

Where electronic pressure/vacuum sensors are provided, identify and record

whether the alarms are set to operate at the correct value or some other

value.

Secondary Venting – VRS Operations

VIQ 8.59 (C) If the vessel is operating with a vapour return line connected, are

appropriate transfer procedures in place?

Vessels equipped with vapour collection systems must be fitted with a pressure sensing

device that senses the pressure in the main vapour collection line, which:

(a) Has a pressure indicator located on the vessel where the cargo transfer is controlled;

and

(b) Has a high pressure and a low pressure alarm that:

(1) Is audible and visible on the vessel where cargo transfer is controlled;(1) Is audible and visible on the vessel where cargo transfer is controlled;

(2) Alarms at a high pressure of not more than 90 percent of the lowest pressure relief

valve setting in the cargo tank venting system; and

(3) Alarms at a low pressure of not less than four inches water gauge (0.144 psig) for an

inerted tankship, or the lowest vacuum relief valve setting in the cargo tank venting

system for a non-inerted tankship.

(CFR 46 39.20-13)

Note: Particular attention should be paid to

monitoring the pressure in the cargo tanks and the

associated line system. P/v valves, the ullaging

system and the level alarms should have been

Secondary Venting – VRS Operations

system and the level alarms should have been

thoroughly tested prior to the transfer commencing

and there should be awareness of the initial transfer

rate and maximum allowable transfer rates.

Typical OCIMF Member chartering requirements

Secondary Venting

Cargo tank venting MUST be through approved systems that

expel vapours clear of the tank deck area in accordance with

ISGOTT. It is strongly preferred that the secondary means of ISGOTT. It is strongly preferred that the secondary means of

providing protection against tank over/under pressurisation be

provided by full flow independent P/V valves and/or pressure

monitoring system fitted to each tank. These full flow P/V valves

should be so fitted that they cannot be isolated from the tanks

they protect and should be capable of allowing sufficient volume

of gas to prevent damage at the tank’s maximum

loading/discharge rates.

SOLAS

Reg. II-2/4.5.3.2.2

and and

Reg. II-2/11.6.1

5.3.2.2. Where the arrangements are combined with other

cargo tanks, either stop valves or other acceptable means

shall be provided to isolate each cargo tank. Where stop

valves are fitted, they shall be provided with locking

arrangements which shall be under the control of the

responsible ship’s officer. There shall be a clear visual

indication of the operational status of the valves or other

acceptable means. Where tanks have been isolated, it shall acceptable means. Where tanks have been isolated, it shall

be ensured that relevant isolating valves are opened before

cargo loading or ballasting or discharging of those tanks is

commenced. Any isolation must continue to permit the flow

caused by thermal variations in a cargo tank in accordance

with regulation 11.6.1.1.

6.1. General

The venting arrangements shall be so designed and operated as to ensure that neither pressure nor vacuum in cargo tanks shall exceed design parameters and be such as to provide for:

.1. the flow of the small volumes of vapour, air or inert .1. the flow of the small volumes of vapour, air or inert gas mixtures caused by thermal variations in a cargo tank in all cases through pressure/vacuum valves; and

.2. the passage of large volumes of vapour, air or inert gas mixtures during cargo loading and ballasting, or during discharging.

6.2. Openings for small flow by thermal variations

. Openings for pressure release required by paragraph 6.1.1 shall: shall:

.1. have as great a height as is practicable above the cargo tank deck to obtain maximum dispersal of flammable vapours, but in no case less than 2 m above the cargo tank deck; and

.2. be arranged at the furthest distance practicable but not less than 5 m from the nearest air intakes and openings to enclosed spaces containing a source of ignition and from deck machinery and equipment which may constitute an ignition hazard. Anchor windlass and chain locker openings constitute an windlass and chain locker openings constitute an ignition hazard.

6.3. Safety measures in cargo tanks

6.3.1

Preventive measures against liquid rising in the venting system.

Provisions shall be made to guard against liquid rising in the venting system to a height which would exceed the design head of cargo tanks. head of cargo tanks.

This shall be accomplished by high-level alarms or overflow control systems or other equivalent means, together with independent gauging devices and cargo tank filling procedures. For the purposes of this regulation, spill valves are not considered equivalent to an overflow system.

6.3.2. Secondary means for pressure/vacuum relief

A secondary means of allowing full flow relief of vapour, air or inert gas mixtures to prevent over-pressure or under-pressure in the event of failure of the arrangements in paragraph 6.1.2. Alternatively, pressure sensors may be fitted in each tank protected by the arrangement required in paragraph 6.1.2, with a monitoring system in the ship’s in paragraph 6.1.2, with a monitoring system in the ship’s cargo control room or the position from which cargo operations are normally carried out. Such monitoring equipment shall also provide an alarm facility which is activated by detection of over-pressure or under-pressure conditions within a tank.

6.3.3. Bypasses in vent mains

. Pressure/vacuum valves required by paragraph 6.1.1 may

be provided with a bypass arrangement when they are

located in a vent main or masthead riser. Where such an

arrangement is provided there shall be suitable indicators

to show whether the bypass is open or closed. to show whether the bypass is open or closed.

6.3.4. Pressure/vacuum-breaking devices

. One or more pressure/vacuum-breaking devices shall be provided to prevent the cargo tanks from being subject to:

.1. a positive pressure, in excess of the test pressure of the cargo tank, if the cargo were to be loaded at the cargo tank, if the cargo were to be loaded at the maximum rated capacity and all other outlets are left shut; and

.2. a negative pressure in excess of 700 mm water gauge if cargo were to be discharged at the maximum rated capacity of the cargo pumps and the inert gas blowers were to fail.

• Such devices shall be installed on the inert gas main unless

they are installed in the venting system required by Regulation

4.5.3.1or on individual cargo tanks. The location and design of

the devices shall be in accordance with Regulation 4.5.3 and

paragraph 6.

All very well, but ask yourself this basic

question...

• What protection does the tank have if this valve is shut?

The extent of the problem today

Analysis of the SIRE database

(>6,000 vessels)

shows approximately 5% (approx 300 shows approximately 5% (approx 300

reports) “No” responses to Q8.30