NBW-515-001-WTG Steel Specification R10_20150921 ()

Intended for

Nobelwind NV/SA

Document type

Specification

Date

August 2015

Document Number

NBW-515-001

Version

10

BELWIND II OFFSHORE WIND

FARM - DETAILED DESIGN

SPECIFICATION - WTG STEEL

SPECIFICATION

BELWIND II OFFSHORE WIND FARM - DETAILED DESIGN

SPECIFICATION - WTG STEEL SPECIFICATION

Ramboll

240 Blackfriars Road

London SE1 8NW

United Kingdom

T +44 (0)20 7631 5291

F +44 (0)20 7323 4645

www.ramboll.co.uk/energy

Version 10

Date 2015-08-17

Made by NHOWA

Checked by BWYSO

Approved by BWYSO

Description Issued for Certification

Ref 61033923

Document ID 476349-1 / NBW-515-001

Belwind II Offshore Wind Farm - Detailed Design

Specification - WTG Steel Specification

476349-1 / NBW-515-001

VERSION TABLE

Version Date Made by Checked by Approved by Description

10 17.08.2015 NHOWA BWYSO BWYSO Issued for Certification

9 12.08.2015 NHOWA BWYSO CWINK Issued for Information

8 13.07.2015 CWINK HMACK CWINK Issued for Information

7 09.07.2015 JFAGA CWINK CWINK Issued for Information

6 09.07.2015 JFAGA CWINK CWINK Issued for Information

5 28.04.2015 NHOWA CWINK CWINK Issued for Information

4 20.03.2015 NHOWA CWINK CWINK Issued for Information




VERSION HISTORY

Version 1 First Issue

Version 2 General - Update based on Client’s comments.

Section 1.4 – Updated to explicitly define the skirt as part of primary steel.

Section 2 – Execution class detailed.

Section 3.3 – Properties of steel above LAT of thickness greater than 80 mm removed.

Section 3.6 – Material certification requirements added.

Section 4.1 – Weld quality explicitly stated.

Section 5.1 – Requirements general to both primary and secondary moved.

Section 6.1 – Reference made to EN 1090-2 for tolerance requirements.

Section 7.1 – Reference made to DNV-OS-J101 for reduction in inspection requirements

based on previous quality.

Version 3 General - Update based on Client’s comments.

Section 5.3 – Bolt requirements for thread locking, bolt hole dimensions and bolt over

length updated.

Section 6.3 – Primary steel flanges updated to include run out tolerance.

Section 7.2– Option for ultrasonic testing instead of radiographic inserted.

Version 4 General – Update based on Client’s comments.

Section 5.2 – Bolt tolerances updated.

Section 6.3 – Flange tolerances reference drawings.

Version 5 General – Update based on Certifier’s comments.

4.2.6 – C curve updated to C1 curve for ground circumferential weld.

Version 6

General – Update based on Certifier’s comments.

4.2.6 – C curve for ground circumferential weld.

Section 5.2.1 - 5.2.3 Updated

Section 6.2.5 updated based on ovality and MP Length

Section 6.5 removed



476349-1 / NBW-515-001

Section 7.3.3 updated

Version 7

Section 6.2.5 corrected

Version 8 Section 6.3.3 corrected

Version 9 1.4 – Reference to drawing numbers added.

Table 3-2 – Additional plate sizes added.

3.5.5 – Requirements for stainless steel added.

3.5.6 – Requirements for stainless steel added.

4.1.4 – Reference to geometry best practices included.

4.1.5 – Requirements for welding stainless steel added.

4.2.4 – Requirements in weld holding time removed.

4.2.13 – PWHT requirement added.

4.2 – Weld dimensions requirements added.

4.3.11– Requirement for one sided welds added.

Section 5 – References to ‘studs’ changed to ‘bolts’.

5.2.5 – Standards modified.

5.2.17 – Requirements for grease caps removed.

6.1.5 – Tolerance requirement added.

Table 6-1 – Deviation from standard noted.

6.2.5 – Ovality, length and end perpendicularity requirements modified.

6.3.5 – Requirement for flange face perpendicularity tolerance definitively stated.

7.2.3 – Reworded.

7.2.4 – Weld inspection requirements modified.

7.3.3 – Reworded.

Version 10 Section 4.2 – Weld width tables updated and moved to appendix.

Section 0 – New section. Weld width tables moved from Section 4 to Appendix A and

updated.

1.1.1 – Weld width clause added.

4.2.18 – Plate chamfering requirement added.



476349-1 / NBW-515-001

CONTENTS

1. INTRODUCTION 1 1.1 General 1 1.2 Background 1 1.3 Objective 1 1.4 Definitions 1 2. CODES AND STANDARDS 2 3. MATERIAL REQUIREMENTS 3 3.1 Basis of Selection 3 3.2 General 3 3.3 Primary Steel Plates 4 3.4 Primary Steel Flanges 4 3.5 Secondary Steel Items 5 3.6 Material Certification 6 4. FABRICATION AND WELDING 7 4.1 General 7 4.2 Primary Steel 7 4.3 Secondary Steel 8 5. BOLTING 10 5.1 General 10 5.2 Primary Steel Bolts for MP/TP Connection 10 5.3 Secondary Steel Bolts 11 6. TOLERANCES 13 6.1 General Tolerance Requirements 13 6.2 Primary Steel - Cans 13 6.3 Primary Steel – Flanges 15 6.4 Secondary 15 7. INSPECTION 16 7.1 General 16 7.2 Primary 16 7.3 Secondary 17 8. REFERENCES 18 9. APPENDIX A – WELD WIDTHS 1 9.1 General 1 9.2 MP Butt Weld Widths 1 9.3 TP Butt Weld Widths 2 9.4 Attachment Weld Widths 2



476349-1 / NBW-515-001

1. INTRODUCTION

1.1 General

This steelwork specification has been prepared by Ramboll on behalf of Nobelwind NV/SA.

1.2 Background

This Material Specification is made as part of the detailed design package for the WTG (Wind

Turbine Generator) support structures on the Belwind II Offshore Wind Farm project. The support

structures will be driven monopiles connected to a transition piece made ready for mounting of

the WTG tower structures once installed.

For the steelwork specification specific to the OHVS, please refer to NBW-515-501.

1.3 Objective

The objective of this Material Specification is to state the requirements for the steel materials

used for both the primary and secondary steel structures as well as requirements for the

fabrication, testing and surveying of the steel structures.

This specification should be read in conjunction with the WTG primary and secondary steel

drawings.

1.4 Definitions

Steelwork is categorised as either Primary Steelwork or Secondary Steelwork in line with DNV-

OS-J101.

Primary Steelwork comprises the main monopile and transition piece tubular and cylindrical

sections (including skirt), the interface flange between the tower and the transition piece, the

MP/TP connection flanges, and the transportation flange at the base of the transition piece.

All primary steelwork is detailed on the primary steelwork drawings – drawings numbered

61033923-NBW-519-WTG-PS-XX-XXX unless noted otherwise on the drawings.

Secondary Steelwork comprises all appurtenances attached to the Primary Steelwork including

but not limited to the boat landing, internal and external platforms, ladders, anode supports,

installation guides, etc.

All secondary steelwork is detailed on the secondary steelwork drawings – drawings numbered

61033923-NBW-519-WTG-SS-XX-XXX unless noted otherwise on the drawings.



476349-1 / NBW-515-001

2. CODES AND STANDARDS

2.1.1 The following codes and standards are to be observed for the design, procurement, fabrication and

testing of all steelwork items:

Standard Year Title

DNV-OS-J101 2014 Design of offshore wind turbines

DNV-OS-B101 2012 Metallic materials

DNV-OS-C401 2014 Fabrication and testing of offshore structures

EN 10025 2004 Hot rolled products of structural steels

EN 10029 2010 Hot rolled steel plates 3mm thick or above – Tolerances on

dimensions, shape and mass

EN 10163-2 2004 Delivery requirements for surface condition of hot-rolled steel

plates, wide flats and sections – Part 2: Plate and wide flats

EN 10164 2004 Steel products with improved deformation properties perpendicular

to the surface of the product. Technical delivery conditions

EN 10204 2004 Metallic products – Types of inspection documents

Table 2-1: Governing standards.

Additional standards are referenced throughout this document; a full list is given in the

References section.

2.1.2 In case of conflict between codes and specifications, the strictest code is to be used.

2.1.3 As a minimum requirement, all steel work is to be with Execution Class 3 (EXC 3) according to EN

1090-2. The following consequence, production and service categories are applicable:

• Consequence class – CC2

• Production class – PC2

• Service class – SC2



476349-1 / NBW-515-001

3. MATERIAL REQUIREMENTS

3.1 Basis of Selection

Material selection was made in accordance with DNV-OS-J101. Suitable grades were chosen

using this code and converted to the corresponding EN designation.

The primary steel structures were categorised as “Primary” and the secondary steel items as

“Secondary” in accordance with DNV OS-J101 Table 6-1.

The reference temperature above LAT is -10°C and the temperature below LAT is 0°C.

Steels with a yield strength of 355 MPa (nominal designation) are selected for both primary and

secondary items.

3.2 General

3.2.1 All steel items are required to have the properties in Table 3-1 according to EN 1993-1-1 3.2.6 and EN

10025-1 7.7.2.

Property Value Unit

Modulus of elasticity 210 x 103 MPa

Shear modulus 81 x 103 MPa

Poisson’s ratio 0.3 -

Coefficient of thermal expansion 12 x 10-3 K-1

Density 7850 kg m-3

Table 3-1: Material properties.

3.2.2 All testing to be performed in accordance with DNV-OS-B101, section 6.

3.2.3 Surface defects to be in accordance with EN 10163, with the maximum size as given below:

• MP: In accordance with EN 10163-2, Class B, subclass 3. Upon agreement, subclass 3 may be

upgraded to subclass 1 reviewed on a case by case evaluation.

• Surface defects at plate edges bordering circumferential welds are generally not

permitted, but may be accepted on a case by case evaluation.

• Surface defects in plates at or within 300 mm from locations of welded attachments are

generally not permitted, but may be accepted on a case by case evaluation.

• Any repair by grinding shall blend smoothly with the contour of the base material.

• TP: In accordance with EN 10163-2, Class B, subclass 3. Upon agreement, class B subclass 3

may be upgraded to class A subclass 1 reviewed on a case by case evaluation.

• Surface defects at plate edges bordering circumferential welds are generally not

permitted, but may be accepted on a case by case evaluation.

• Surface defects in plates at or within 300 mm from locations of welded attachments are

generally not permitted, but may be accepted on a case by case evaluation.

• Any repair by grinding shall blend smoothly with the contour of the base material.

3.2.4 Where EN 10025 steels are used, additional testing will be required for Longitudinal (L) and Transverse

(T) impact test values to comply with DNV-OS-B101, table C5.



476349-1 / NBW-515-001

3.3 Primary Steel Plates

3.3.1 All primary steel items are required to have the properties given in Table 3-2.

Location Steel Grade Thickness Min. Yield

Stress Temp

Charpy V-notch

minimum

- DNV EN mm MPa °C L /J T /J

Above

LAT

NV A36 S355N/M

t ≤ 16 355 0

34 24 16 < t ≤ 20

345 NV D36 20 < t ≤ 40 -20

NV E36 S355NL/ML

40 < t ≤ 50 335

-40

50 < t ≤ 63 41 27

63 < t ≤ 70 325

70 < t ≤ 80 50 34

Below

LAT

NV A36

S355N/M

t ≤ 16 355 0

34 24 16 < t ≤ 25

345

NV D36 25 < t ≤ 40

-20 40 < t ≤ 50

335

NV E36

S355NL/ML

50 < t ≤ 63

-40

41 27 63 < t ≤ 70

325 70 < t ≤ 80

50 34 80 < t ≤ 100 315

100 < t ≤ 120 295

Table 3-2: Primary steel grades.

3.3.2 Where a can spans LAT, the grade applicable for above LAT will be used.

3.3.3 N or NL steel can be substituted for M or ML steel respectively, if the mechanical properties can be

proven intact after welding, including the fracture toughness of the welded region. No hot forming of

S355M/ML steel is permitted.

3.3.4 Steel to be delivered with material certificate 3.1 according to EN 10204.

3.4 Primary Steel Flanges

3.4.1 Flanges to meet the specification given in Table 3-3.

3.4.2 If constructed from plates, the plate must also be Z35 according to EN 10164. No Z grade is required if

they are seamless hot rolled (forged) flanges.

Location Steel Grade Thickness Min. Yield Stress Min Charpy

- - mm MPa -

MP & TP S355NL - 325 50 J at -60°C

Table 3-3: Flange steel grades.



476349-1 / NBW-515-001

3.5 Secondary Steel Items

3.5.1 All plates and profiles items are required to have the properties given in Table 3-4.


Stress Temp Impact Energy

- DNV EN mm MPa °C L/J T/J

Above

LAT

NV A36 S355J2 t ≤ 16 355

0 34 24 16 < t ≤ 40 345

NV D36 S355K2 40 < t ≤ 50 335

-20 50 < t ≤ 60 335 41 27

Below

LAT

NV A36 S355J2

t ≤ 16 355

0 34 24 16 < t ≤ 40 345

40 < t ≤ 50 335

NV D36 S355K2 50 < t ≤ 60 335 -20 41 27

Table 3-4: Steel grades for secondary steel plates and profiles.

3.5.2 All hollow sections are required to have the properties given in Table 3-5.


Stress Temp Impact Energy

- DNV EN mm MPa °C L /J T /J

Above

LAT

NV A36 S355J2H t ≤ 16 355

0 34 24 16 < t ≤ 40 345

NV D36 S355K2H 40 < t ≤ 50 335

-20 50 < t ≤ 60 335 41 27

Below

LAT

NV A36 S355J2H

t ≤ 16 355

0 34 24 16 < t ≤ 40 345

40 < t ≤ 50 335

NV D36 S355K2H 50 < t ≤ 60 335 -20 41 27

Table 3-5: Steel grades for hollow sections for secondary steel.

3.5.3 All hollow sections are to be hot rolled.

3.5.4 Welded hollow sections are permissible providing orientation of the seam weld is considered in relation

to other structural welds.

3.5.5 The following stainless steel grades should be used in accordance with EN 10088, unless noted

otherwise on drawings:

• External locations: 1.4462

• Internal locations: 1.4404

3.5.6 All stainless steel parts shall be ordered with a smooth surface and free of scale, and must be produced

and handled in such a way as to exclude any ferrite contamination.



476349-1 / NBW-515-001

3.6 Material Certification

3.6.1 The material certificates given in Table 3-6 are to be provided in accordance with EN 10204.

Steel Category Charpy Test Temperature Material Certificate

Primary All 3.1

Secondary < 0°C 3.1

≥ 0°C 2.2

Table 3-6: Material certification.



476349-1 / NBW-515-001

4. FABRICATION AND WELDING

4.1 General

4.1.1 Details of any additional welds or modification to welds shown on the drawings to be submitted to the

Engineer for approval.

4.1.2 All ground welds to be ground flush to plate surface and must follow requirements in DNV-OS-J101

section 7.10.7.

4.1.3 Weld quality to be level B in accordance with EN ISO 5817.

4.1.4 The best practices regarding geometry detailed in section 5.1.9 of the Corrosion Strategy must be

followed.

4.1.5 Stainless steel to carbon steel welding should be carried out in accordance with EN 1090-2 and EN

1011-3.

4.2 Primary Steel

4.2.1 Welded connections are to be performed in accordance with DNV-OS-C401.

4.2.2 All welding edges to be in compliance with DNV-OS-C401. Weld edges to be dried with a flame torch,

or by preheating when necessary.

4.2.3 Preheat shall be extrapolated from the weld procedure qualifications (WPQ) and estimated using EN

1011-2 to make allowance for extra thickness or restraint or cooling parts.

4.2.4 Clause removed. Refer to 7.2.4.

4.2.5 Longitudinal welds must have an offset of 300 mm from any secondary steel work or cut outs.

4.2.6 Circumferential welds to be in accordance with DNVGL-RP-0005 Table A-9, as detailed below.

Item Detail category

Ground circumferential welds C

Non-ground circumferential welds D

Table 4-1: Circumferential detail categories.

4.2.7 Longitudinal welds to be in accordance with DNVGL-RP-0005 Table A-9, as detailed below.

Item Detail category

Ground longitudinal welds C

Non-ground longitudinal welds C

Table 4-2: Longitudinal detail categories.

4.2.8 When joining two plates of different thicknesses, the thicker plate must be bevelled at 1:4 to the

thickness of the thinner plate unless otherwise noted on the drawing.

4.2.9 Grinding of welds to be performed at locations is shown on primary steel drawings.



476349-1 / NBW-515-001

4.2.10 Cut-outs to be in accordance with Table A-1 in DNVGL-RP-0005, detail category B2.

4.2.11 No weld repairs are permitted on cut-outs.

4.2.12 Cut edges to have a fillet of 10% the plate thickness (minimum radius 5 mm) unless otherwise shown.

4.2.13 PWHT is not required.

4.2.14 MP butt welds are to have widths (refer to Figure A-1) no greater than is specified in Table A-1.

Maximum width of weld achieved per weld must be recorded and provided to the Client for as-built

structures.

4.2.15 TP butt welds are to have widths (refer to Figure A-1) no greater than is specified in Table A-2.

Maximum width of weld achieved per weld must be recorded and provided to the Client for as-built

structures.

4.2.16 The maximum weld width for plate thicknesses not listed above can be calculated by linear

interpolation within the ranges given.

4.2.17 The maximum weld widths for attachments butt welded (single and double sided) or fillet welded to

any primary steel no greater than specified in Table A-3. Maximum width of weld achieved per weld

must be recorded and provided to the Client for as-built structures.

4.2.18 For circumferential welds between plates of different thicknesses, the thicker plate shall be chamfered

to the thickness of the adjoining plate with a length to thickness ratio of 4:1 as indicated on the

drawings.

4.2.19 Maximum weld widths for butt welds between plates of different thicknesses shall be based on the

thinner plate thickness as specified in Appendix A.

4.3 Secondary Steel

4.3.1 Welded connections are to be performed in accordance with EN-1011-1, EN 1011-2 and EN ISO 9692.

4.3.2 For special weld shapes not covered by EN ISO 9692, only approved weld procedures according to

DNV-OS-C401 are allowed.

4.3.3 All secondary steelwork welded to the primary steel must comply with the weld requirements for

primary steel.

4.3.4 Weldings not specified on drawings must be performed as full penetration butt welds.

4.3.5 Fillet welds with no specification of dimensions are made with an effective measurement of not less

than a = 6 mm + corrosion allowance.

4.3.6 On the Transition Piece, there must be no overlap between primary welds and weld from secondary

steel. A minimum distance of 300 mm must be observed.

4.3.7 When joining two plates of different thicknesses, the thicker plate must be bevelled at 1:4 to the

thickness of the thinner plate unless otherwise noted on the drawing.

4.3.8 All hollow sections to be closed with 8 mm cap plates welded with a minimum a = 5 mm unless

otherwise noted on the drawing.



476349-1 / NBW-515-001

4.3.9 Connections between RHS profiles to be made according to Figure 4-1 unless otherwise noted on the

drawing.

Figure 4-1: Welding detail for RHS profiles.

4.3.10 Only soft stamping allowed for marking of plates, flanges and hollow sections. Minimum clearance of

300 mm from the plate edges, flanges and welded attachments.

4.3.11 For one sided welds it is required that the defect size in the weld root is maximum 2 mm such that the

joint may be classified F3 according to DNVGL-RP-0005. The fabricator must demonstrate to the

satisfaction of the Client, through track record or otherwise, that this requirement can be achieved.



476349-1 / NBW-515-001

5. BOLTING

5.1 General

5.1.1 All given bolt pre-tensioning relates to the residual bolt tension force.

5.1.2 At the date when operation and maintenance becomes the responsibility of the employer, all bolts

specified with preloading must be demonstrated to fulfil the required preload.

5.2 Primary Steel Bolts for MP/TP Connection

5.2.1 All bolts to be hexagon head bolts, sourced and converted by Rotabolt to a “rotabolt 2”.

5.2.2 Load certificate to be issued for each individual bolt.

5.2.3 All components of these "rotabolt 2" shall be so designed that they remain fully functional for the entire

design life, and the material and/or surface preparation is chosen so to inhibit corrosion

5.2.4 Clause removed Refer to 5.2.1.

5.2.5 Class of bolts to be 10.9 according to EN 1993-1-8. The recommendations for mechanical properties

given in ISO 898-1 should be extended to cover the larger size of the flange bolts in conjunction with

the guidelines given in DASt Richtlinie 021.

5.2.6 Bolt thread rolled before hot dip galvanising.

5.2.7 External threads should be sized to tolerance position h before coating in accordance with ISO 965-1 to

ISO 965-3.

5.2.8 Nut threads to be tapped after hot dip galvanizing.

5.2.9 Internal threads to be oversized to tolerance AZ in accordance with ISO 965-5.

5.2.10 Hexagon nut according to EN 14399-2. Tolerances adjusted for hot dip galvanizing as per ISO 10684.

5.2.11 Lubrication as per bolt/nut manufacturer and bolt tensioning contractor’s recommendations.

5.2.12 Washers to be designed and specified by installation contractor. Surface area must not be less than

hexagon nut.

5.2.13 Bolts, nuts and washers to be hot dip galvanized in accordance with ISO 10684. Zinc shall be in

accordance with ISO 1461.

5.2.14 The surface of the fastener before immersion in the molten zinc shall be clean and free from all

contaminants that would adversely affect the galvanising. Parts to be galvanised should be cleaned

using an inhibited acid, alkaline or mechanical process.

5.2.15 The bolt, nut and washer should be galvanized at a bath temperature of 455°C to 480°C.

5.2.16 Coating thicknesses in accordance with ISO 10584 (minimum coating thickness 40 µm).

5.2.17 Clause removed.



476349-1 / NBW-515-001

5.2.18 De-hydrogenation after galvanizing, via baking, should be performed so as to limit the risk of hydrogen

embrittlement.

5.3 Secondary Steel Bolts

5.3.1 All bolts are grade 8.8 meeting the requirements in EN 1090-2, EN 14399-1/2/3/5/6, system HR,

U.N.O.

5.3.2 All bolted connection must be delivered hot dip galvanized from the factory in accordance with EN

14399-3, U.N.O.

5.3.3 Washers are placed under nuts with plain washers per EN 14399-5 and under bolt head with plain

chamfered washers per EN 14399-6, U.N.O.

5.3.4 Two nuts per assembly U.N.O.

5.3.5 Chemical thread locking agent (Loctite or similar) to be used on outer nut.

5.3.6 Bolts to have an over length of at least three threads after nuts have been torqued.

5.3.7 Oversize washers are only permitted upon agreement with the engineer.

5.3.8 Washers must have smooth edges towards coated areas.

5.3.9 All bolts must have rolled threads.

5.3.10 Contractor to specify procedure for preloading of bolts for engineer approval, to be in accordance with

EN 1090-2.

5.3.11 Bolts for which a pre-tension is not specified are to be ‘hand-tight’ using an electric or pneumatic

impact wrench.

5.3.12 Stainless steel bolts shall be lubricated before tensioning per supplier recommendations.

5.3.13 When connecting carbon steel with stainless steel bolts, insulation washers and bush shall be installed

in the connection holes.

5.3.14 For pin and slip resistant connections, on a plate of thickness “t”, the thread length in the bearing area

must not exceed t/2 for double section joints and t/4 for single sections.

Figure 5-1: Thread lengths in pin and slip-resistant connections.



476349-1 / NBW-515-001

5.3.15 The following bolt hole sizes are to be used, U.N.O.

Bolt size Hole diameter

M12 DSHAFT +3 mm

M14

M16

DSHAFT + 4 mm M20

M24

M27 DSHAFT + 5 mm

Table 5-1: Bolt hole sizing.

5.3.16 All holes must be drilled.



476349-1 / NBW-515-001

6. TOLERANCES

6.1 General Tolerance Requirements

6.1.1 In general, the fabrication tolerances shall be accordance with DNV-OS-C401 and EEMUA 158. If better

production tolerances than specified can be achieved, this is recommended.

6.1.2 Any tolerances not covered in either DNV-OS-C401 or EEMUA 158 are to be in accordance with EN

1090-2.

6.1.3 Tolerances are to be achieved upon completion of fabrication of entire structure.

6.1.4 Plate tolerances on dimensions and shape to be in accordance with EN 10029 Class C.

6.1.5 Any tolerances stated on the drawings must be adhered to in addition to the requirements within this

specification.

6.2 Primary Steel - Cans

6.2.1 The TP skirt and MP shall have a full dimensional survey after fabrication to ensure that the fabrication

tolerances detailed within this document have been achieved.

6.2.2 Survey results shall be made available a minimum of 10 days before transportation from the

fabrication yard.

6.2.3 The following tolerances must be achieved on the mis-alignment of primary steel plates, in accordance

with EN ISO 5817.

Item Tolerance

Misalignment of longitudinal welds 3 mm

Misalignment of circumferential welds 3* mm

Table 6-1: Primary steel weld tolerances. *Deviation from EN ISO 5817.

6.2.4 Records of the maximum misalignment to the nearest mm for each weld to be provided to the

Engineer.

6.2.5 Tolerances of the final size of rolled primary steel cans for the transition piece and monopile will be in

compliance with EEMUA-158 and below.

• Circumference – at or within 610 mm of a joint, the external circumference shall not differ from the

nominal external circumference by 30% of the wall thickness or 10 mm whichever is smaller.

Outside of this zone the tolerances can be increased by a factor of 1.5.

Ovality – ovality is defined as the difference between the maximum and minimum external (or

internal) diameters.

• Ovality shall not exceed the greater of 15 mm or 0.3% of nominal diameter for all cans in

the TP.

• Ovality shall not exceed the greater of 15 mm or 0.3% of nominal diameter for can

sections in the TP-MP overlap zone.

• Ovality shall not exceed the greater of 15 mm or 0.5% of nominal diameter for all other

cans in the MPs.



476349-1 / NBW-515-001

A minimum of 4 checks evenly spaced around the circumference at both ends and any

circumferential seams must be performed.

Figure 6-1: Ovality measurements.

• Out of roundness – out of roundness is defined as the difference between the actual form and the

ideal circular form of the section as measured using a 20° arc gauge. Out of roundness shall not

exceed 0.2% of the external diameter or 25% of the nominal wall thickness whichever is the

smaller.

Checks to be performed over a 360° sweep of the circumference at equal intervals of 20°.

Figure 6-2: Out of roundness measurements.

• Local straightness – local straightness is defined as the deviation of the plate from a straight

generator of length 3000 mm parallel to the true centre line of the tubular. The tolerance shall not

exceed 20% of wall thickness.

Checks to be performed at 20° intervals of arc.

• End perpendicularly – the ends of tubular and cones shall be cut perpendicular to the longitudinal

axis within a 6 mm tolerance.

• Out of straightness – out of straightness shall not exceed L/1200 where L is the finished length of

the complete structure.

• Total length – the total length of the fully fabricated MP shall be at nominal within ±100 mm.



476349-1 / NBW-515-001

6.3 Primary Steel – Flanges

6.3.1 Each flange shall have a full dimensional survey before and after welding onto the transition piece or

monopile. The method of survey shall be agreed with the Employer and the foundation designer. The

Employer shall be notified before each survey.

6.3.2 Survey results shall be made available a minimum of 10 days before transportation from the

fabrication yard.

6.3.3 The amount by which the middle TP flange and upper (interface) TP flange can be out of parallel shall

not exceed 4 mm.

6.3.4 The flanges shall be fabricated within the tolerances shown in drawing series 61033923-NBW-519-

WTG-PS-04.

6.3.5 The perpendicularity of the flange faces shall be within 2 mm with reference to the global longitudinal

axis, i.e. the flange faces must lie with two planes perpendicular to the longitudinal axis and separated

by 2 mm.

6.4 Secondary

6.4.1 In general, the fabrication tolerances shall be accordance with DNV-OS-C401.



476349-1 / NBW-515-001

7. INSPECTION

7.1 General

7.1.1 NDT to be undertaken according to DNV-OS-C401.

7.1.2 The final NDT examination has to be carried out after grinding, if grinding is applied.

7.1.3 A visual inspection must precede any weld inspection for detection of visible defects such as notches

scoriae, splatter, etc.

7.1.4 In accordance with DNV-OS-J101, if the fabrication quality is assessed by testing, or well known quality

from previous experience, the extent of inspection required for elements with structural category

primary may be reduced if agreed with the Client, but no less than category III.

7.2 Primary

7.2.1 The inspection categories for the primary steel are given below.

Item Inspection Category

Circumferential welds I

Longitudinal welds II

Flange welds I

Transportation flange weld II

All other primary steel welds I

Table 7-1: Inspection category for primary steel welds.

7.2.2 Minimum extent of inspection is to be as per Table 7-2.

Category Weld Type Visual Magnetic Radiography* Ultrasonic

Category I Butt 100% 100% 100% -

Category II Butt 100% 20% 10% -

Category II Fillet 100% 20% - -

Table 7-2: Inspection requirements, primary steel. *Refer to clause 7.2.3 for possibility for replacing radiographic testing with ultrasonic.

7.2.3 As stated in DNV-OS-C401, radiographic testing may be replaced by ultrasonic testing and vice versa,

when methodologically justifiable and agreed upon. Ultrasonic examination shall not be carried out on

welds with thickness < 10 mm. Testing of thicknesses as low as 8mm is acceptable subject to special

qualification to be agreed with the Client.

7.2.4 Primary welds shall be held for 48 hours after completion before carrying out NDT. This may be

reduced to 24 hours if the fabricator can demonstrate to the satisfaction of the Client and Certifier that

controlled shop conditions and weld procedures are in place so as to controlling the risk of hydrogen

cracking. (refer to ref.[38])

7.2.5 Frequent repairs shall result in increased extent of NDT. The extent of NDT shall be increased in a

manner such that all relevant defects are discovered in the areas of concern and that representative

sampling is carried out on all welds.



476349-1 / NBW-515-001

7.3 Secondary

7.3.1 The inspection categories for the secondary steel are given below.

Item Inspection Category

Boat landing I

External platforms III

Internal platforms III

Attachments to primary steel I

Table 7-3: Inspection categories for secondary steel welds.

7.3.2 All parts which are protected by hot dip galvanising shall have 100% visual inspection and NDT after

the galvanization.

7.3.3 As stated in DNV-OS-C401, radiographic testing may be replaced by ultrasonic testing and vice versa,

when methodologically justifiable and agreed upon. Ultrasonic examination shall not be carried out on

welds with thickness < 10 mm. Testing of thicknesses as low as 8mm is acceptable subject to special

qualification to be agreed with the Client.

7.3.4 Minimum extent of inspection to be as per Table 7-4.

7.3.5 Magnetic particle inspection shall be performed prior to ultrasonic testing.

7.3.6 Cracks, lack of fusion or lack of penetration flaws characterised and confirmed by ultrasonic inspection

are not acceptable regardless of size or amplitude.

Category Weld Type Visual Magnetic Radiography* Ultrasonic

Category I Butt 100% 100% 100% -

Category I, Cross and T-joints Full pen. 100% 100% - 100%

Category I, Cross and T-joints Partial pen.

And fillet

100% 100% - -

Category III Butt 100% 5% 5% -

Category III, Cross and T-joints Full pen. 100% 5% - 5%

Category III, Cross and T-joints Partial pen.

And fillet

100% 5% - -

Table 7-4: Inspection requirements, secondary steel. *Refer to clause 7.3.3 for possibility for replacing radiographic testing with ultrasonic.



476349-1 / NBW-515-001

8. REFERENCES

[1] DNV-OS-J101, Design of Offshore Wind Turbine Structures, May 2014

[2] DNV-OS-C401, Fabrication and Testing of Offshore Structures, October 2014

[3] DNV-OS-B101, Metallic Materials, October 2012

[4] DNVGL-RP-0005, Fatigue design of offshore steel structures, June 2014

[5] DASt Richtlinie 021, Schraubenverbindungen aus feuerverzinkten Garnituren M 39 bis

M72 entspreschend DIN EN 14399-4, DIN EN 14499-6, 2013

[6] EN-1993-1-1, Eurcode 3: Design of steel structures – Part 1-1: General rules and rules

for buildings, 2005

[7] EN 1993-1-8, Eurcode 3: Design of steel structures – Part 1-8: Design of joints, 2005

[8] EN-1993-1-10, Eurocode 3: Design of steel structures – Part 1-10: Material toughness

and through-thickness properties

[9] EN 1011-3, Welding. Recommendations for welding of metallic materials. Arc welding of

stainless steels, 2000

[10] EN 1090-2, Execution of steel structures and aluminium structures. Technical

requirements for steel structures, 2008

[11] EN 10025-1, Hot rolled products of structural steels – Part1: General technical delivery

conditions

[12] EN-10025-2, Hot rolled products of structural steel – Part 2: Technical delivery

conditions for non-alloy structural steels

[13] EN-10025-3, Hot rolled products of structural steels – Part 3: Technical delivery

conditions for normalized/normalized rolled weldable fine grain structural steels, 2004

[14] EN-10025-4, Hot rolled products of structural steels – Part 4: Technical delivery

conditions for thermomechanical rolled weldable fine grain structural steels, 2004

[15] EN 10029, Hot-rolled steel plates 3mm thick or above – tolerances on dimensions and

shape, 2010

[16] EN-10164, Steel products with improved deformation properties perpendicular to the

surface of the product – Technical delivery conditions, 2004

[17] EN 10204, Metallic products – Types of inspection documents, 2004

[18] EN-10210-1, Hot finished structural hollow sections of non-alloy and fine grain steels –

Part 1: Technical delivery conditions, 2006

[19] EN 10210-1, Hot finished structural hollow sections of non-alloy and fine grain steels.

Technical delivery conditions, 2006

[20] EN 1011-1, Welding – recommendations for welding of metallic materials. General

guidance for arc welding, 2009

[21] EN 1011-2, Welding – recommendations for welding of metallic materials. Arc welding

of ferritic steels, 2001

[22] EN 10163-2, Delivery requirements for surface condition of hot-rolled steel plates, wide

flats and sections. Plate and wide flats, 2004

[23] EN 14399-2, High-strength structural bolting assemblies for preloading. Suitability test

for preloading, 2005

[24] EN 14399-3, High-strength structural bolting for preloading. System HR. Hexagon bolt

and nut assemblies, 2005

[25] EN 14399-5, High-strength structural bolting assemblies for preloading. Plain washers,

2005

[26] EN 14399-6, High-strength structural bolting assemblies for preloading. Plain chamfered

washers, 2005

[27] EN ISO 5817, Welding – fusion-welded joints in steel, nickel, titanium and their alloys

(beam welding excluded) – quality levels for imperfections, 2014

[28] ISO 989-1, Mechanical properties of fasteners made of carbon steel and alloy steel.

Part 1: Bolts, screws and studs with specified property classes - Coarse thread and fine

pitch thread, 2013



476349-1 / NBW-515-001

[29] ISO 965-1, General purpose metric screw threads. Tolerances, principles and basic

data, 2013

[30] ISO 965-3, General purpose metric screw threads. Tolerances deviations for

constructional screw threads, 1998

[31] ISO 965-5, General purpose metric screw threads. Tolerances limits of sizes for internal

screw threads to mate with hot dip galvanized external screw threads with maximum

size of tolerance position h before galvanizing, 1998

[32] ISO 9692-1, Welding and allied processes, 2013

[33] ISO 9712, Non-destructive testing – qualification and certification of NDT personnel,

2012

[34] ISO 10684, Hot dip galvanized coatings, 2004

[35] ISO 1461, Hot dip galvanized coatings on fabricated iron and steel articles.

Specifications and test methods, 2009

[36] EEMUA-158, Construction specification for fixed offshore structures in the North Sea,

The Engineering Equipment and Materials Users Association, September 2000

[37] NBW-511-002, Design Basis Part C2, Ramboll, December 2014

[38] NBW-515-501, OHVS Steel Specification, January 2015



476349-1 / NBW-515-001

APPENDIX A – WELD WIDTHS

A.1. General

The following sections present the weld widths for the MP primary steel, TP primary steel and

attachments to the primary steel. The naming of the weld dimensions is shown in Figure A-1.

Figure A-1: (Left) Butt weld geometry. (Right) Attachment weld geometry.

A.2. MP Butt Weld Widths

Plate Thickness

/mm

Weld Width /mm Plate Thickness

/mm

Weld Width /mm

Inside Outside Inside Outside

40 22.6 23.9 87 42.4 38.7

45 24.7 25.5 88 42.8 39.0

50 26.8 27.0 89 43.2 39.3

55 28.9 28.6 90 43.6 39.6

56 29.3 28.9 91 44.0 39.9

57 29.7 29.2 92 44.4 40.2

58 30.1 29.5 93 44.8 40.5

59 30.5 29.8 94 45.3 40.8

60 30.9 30.1 95 45.7 41.1

61 31.3 30.4 96 46.1 41.5

62 31.8 30.8 97 46.5 41.8

63 32.2 31.1 98 46.9 42.1

64 32.6 31.4 99 47.3 42.4

65 33.0 31.7 100 47.7 42.7

66 33.4 32.0 101 48.2 43.0

67 33.8 32.3 102 48.6 43.3

68 34.2 32.6 103 49.0 43.6

69 34.7 32.9 104 49.4 43.9

70 35.1 33.2 105 49.8 44.2

71 35.5 33.5 106 50.2 44.6

72 35.9 33.8 107 50.6 44.9

73 36.3 34.2 108 51.1 45.2

74 36.7 34.5 109 51.5 45.5

75 37.1 34.8 110 51.9 45.8



476349-1 / NBW-515-001

Table A-1: Required dimensions for MP butt welds.

A.3. TP Butt Weld Widths

Plate Thickness

/mm

Weld Width /mm Plate Thickness

/mm

Weld Width /mm

Inside Outside Inside Outside

40 42.2 39.8 66 59.4 55.4

45 45.5 42.8 67 60.1 56.0

50 48.8 45.8 68 60.7 56.6

55 52.1 48.8 69 61.4 57.2

60 55.4 51.8 70 62.1 57.8

61 56.1 52.4

62 56.8 53.0

63 57.4 53.6

64 58.1 54.2

65 58.8 54.8

Table A-2: Required dimensions for TP butt welds.

A.4. Attachment Weld Widths

Attachment

Thickness /mm

Single Sided

Weld Width /mm

Double Sided

Weld Width /mm

5 18.9 20.9

10 23.9 25.9

15 28.9 30.9

20 33.9 35.9

25 39.2 41.2

30 44.2 46.2

35 49.2 51.2

40 54.2 56.2

Table A-3: Required weld widths for attachment butt welds.

76 37.6 35.1 111 52.3 46.1

77 38.0 35.4 112 52.7 46.4

78 38.4 35.7 113 53.1 46.7

79 38.8 36.0 114 53.5 47.0

80 39.5 36.5 115 54.0 47.3

81 39.9 36.8 116 54.4 47.6

82 40.3 37.1 117 54.8 48.0

83 40.7 37.4 118 55.2 48.3

84 41.1 37.7 119 55.6 48.6

85 41.5 38.1 120 56.0 48.9

86 41.9 38.4 - - -

Documents

NBW-515-001-WTG Steel Specification R10_20150921 ()