NORSOK STANDARD
M-101 Edition 5, October 2011
Structural steel fabrication
This NORSOK standard is developed with broad petroleum industry participation by interested parties in the Norwegian petroleum industry and is owned by the Norwegian petroleum industry represented by The Norwegian Oil Industry Association (OLF) and The Federation of Norwegian Industry. Please note that whilst every effort has been made to ensure the accuracy of this NORSOK standard, neither OLF nor The Federation of Norwegian Industry or any of their members will assume liability for any use thereof. Standards Norway is responsible for the administration and publication of this NORSOK standard. Standards Norway Strandveien 18, P.O. Box 242 N-1326 Lysaker NORWAY Copyrights reserved
Telephone: + 47 67 83 86 00 Fax: + 47 67 83 86 01 Email:
[email protected] Website: www.standard.no/petroleum
NORSOK standard M-101
Edition 5, October 2011
Foreword
5
Introduction
5
1
Scope
6
2
Normative and informative references 2.1 Normative references 2.2 Informative references
6 6 7
3
Terms, definitions and abbreviations 3.1 Terms and definitions 3.2 Abbreviations
7 7 7
4
Selection of steels 4.1 Design classes 4.2 Selection of steel quality level
8 8 8
5
Qualification of welding procedures and welders 5.1 Welding procedure specification (WPS) 5.2 Qualification of welding procedures 5.3 Welding procedure qualification record (WPQR) - Range of approval 5.4 Examination of the test weld 5.5 Welder and welding operators qualifications
8 8 8 9 10 12
6
Fabrication and welding requirements 6.1 General 6.2 Drawings for fabrication 6.3 Welding coordination 6.4 Welding inspection and qualification of welding inspectors 6.5 Forming 6.6 Assembly 6.7 Preparation for coatings 6.8 Preparation and fit-up of weld bevels 6.9 Welding processes 6.10 Welding consumables 6.11 Preheat and interpass temperature 6.12 Production welding 6.13 Post weld heat treatment (PWHT) 6.14 Grinding 6.15 Peening
12 12 12 12 13 13 13 15 15 15 15 15 16 16 17 17
7
Production tests
17
8
Fabrication tolerances
17
9
Non-destructive testing (NDT) 9.1 General 9.2 Qualification of non-destructive testing (NDT) operators 9.3 Extent of visual examination and non-destructive testing (NDT) 9.4 Visual examination and finish of welds 9.5 Radiographic testing 9.6 Ultrasonic testing 9.7 Magnetic particle and penetrant testing 9.8 Acceptance criteria
17 17 18 19 20 20 20 21 21
10
Repair Definitions Correction of welds containing defects Repair by welding Repair welding procedure Correction of distortion
24 24 25 25 25 25
Annex A (Informative) Details for high fatigue utilisation
26
Annex B (Informative) Correlation between steel quality level, MDS number and steel grade/designations
28
10.1 10.2 10.3 10.4 10.5
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Annex C (Normative) Qualification of welding consumables by data sheets
30
Annex D (Normative) Welding consumable documented by batch testing
32
Annex E (Normative) Fabrication tolerances
33
Annex F (Informative) Weld inspection, typical check points
57
Annex G (Normative) Components in stainless steel and Ni-alloys
59
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Foreword The NORSOK standards are developed by the Norwegian petroleum industry to ensure adequate safety, value adding and cost effectiveness for petroleum industry developments and operations. Furthermore, NORSOK standards are, as far as possible, intended to replace oil company specifications and serve as references in the authorities’ regulations. The NORSOK standards are normally based on recognised international standards, adding the provisions deemed necessary to fill the broad needs of the Norwegian petroleum industry. Where relevant, NORSOK standards will be used to provide the Norwegian industry input to the international standardisation process. Subject to development and publication of international standards, the relevant NORSOK standard will be withdrawn. The NORSOK standards are developed according to the consensus principle generally applicable for most standards work and according to established procedures defined in NORSOK A-001. The NORSOK standards are prepared and published with support by The Norwegian Oil Industry Association (OLF), The Federation of Norwegian Industry, Norwegian Shipowners’ Association and The Petroleum Safety Authority Norway. NORSOK standards are administered and published by Standards Norway. Annex A, B and F are informative. Annexes C, D, E and G are normative.
Introduction Edition 5 of this NORSOK standard has been necessary due to an extensive change in referenced international standards. In addition new annexes have been included. Some corrections and improvements have also been implemented
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1
Edition 5, October 2011
Scope
This NORSOK standard covers the requirements for fabrication and inspection of offshore steel structures with SMYS < 500 MPa and with a minimum design temperature down to -14 C. NOTE 1
Lower minimum design temperatures require project specific evaluations. For special application steels with SMYS up to 690 MPa may be used.
NOTE 2
For highly fatigue utilized structures, more severe requirements may apply, and these will be shown on the design drawings.
2
Normative and informative references
The following standards include provisions and guidelines which, through reference in this text, constitute provisions and guidelines of this NORSOK standard. Latest issue of the references shall be used unless otherwise agreed. Other recognized standards may be used provided it can be shown that they meet the requirements of the referenced standards.
2.1
Normative references
BS 7448, Part 1, BS 7910, DNV RP D404, IIW International Welder, EN 287-1, EN 473, EN 1011- (all parts), EN 1011-3,
Fracture mechanics toughness tests Guide on methods for assessing the acceptability of flaws in fusion welded structures Unstable fracture Minimum requirements for education, training and qualification of welding personnel Qualification test of welders – Fusion welding – Part 1: Steels Qualification and certification of NDT personnel – General principles Welding – Recommendation for welding of metallic materials - (all parts) Welding – Recommendation for welding of metallic materials – Part 3: Arc welding of stainless steels
EN 1090-1:2009 + EN 1090-1:2009/AC:2010, Execution of steel structures and aluminium structures – Part 1: Requirements for conformity assessment of structural components EN 10204, Metallic products – Types of inspection documents EN 10225, Weldable structural steels for fixed offshore structures – Technical delivery conditions ISO 2553, Welded, brazed and soldered joints – Symbolic representation on drawings ISO 3452-1, Non-destructive testing – Penetrant testing – Part 1: General principles ISO 3690, Welding – Determination of hydrogen indeposited weld metal arising from the use of covered electrodes for welding mild and low alloy steels ISO 3834-2, Quality requirements for welding of metallic materials – Part 2: Comprehensive quality requirements ISO 6520-1, Welding and allied processes – Classification of geometric imperfections in metallic materials – Part 1: Fusion welding ISO 6847, Welding consumables – Deposition of a weld metal pad for chemical analysis ISO 8062:1994, Castings – System of dimensional tolerances and machining allowances ISO 9016, Destructive tests on welds in metallic materials – impact tests – Test specimen location, notch orientation and examination ISO 9606-4, Approval testing of welders – Fusion welding – Part 4: Nickel and nickel alloys ISO 9712, Non-destructive testing – Qualification and certification of personnel ISO 14731, Welding coordination – Tasks and responsibilities ISO 14732, Welding personnel – Approval testing of welding operators for fusion welding ISO 15607, Specification and qualification of welding procedures for metallic materials – General rules ISO 15609-1, Specification and qualification of welding procedures for metallic materials – Welding procedure specification – Part 1: Arc welding ISO 15614-1, Specification and qualification of welding procedures for metallic materials – Welding procedure test – Part 1: Arc and gas welding of steels and arc welding of nickel and nickel alloys ISO/TR 15608, Welding – Guidelines for a metallic materials grouping system
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Welding consumables – Test methods – Part 1: Test methods for all-weld metal test specimens in steel, nickel and nickel alloys General requirements for the competence of testing and calibration laboratories Non-destructive testing of welds – Radiographic testing of fusion-welded Non-destructive testing of welds – Visual testing of fusion welded joints. Non-destructive testing of welds – Magnetic particle testing. Non-destructive testing of welds – Ultrasonic testing of welded joints. Non-destructive testing of welds – Ultrasonic testing – Testing of welds in austenitic steels and nickel-based alloys Material data sheets for structural steel Design of steel structures Welding and inspection of piping Welding. Rules for approval of welding inspectors
ISO 15792-1, ISO 17025, ISO 17636, ISO 17637, ISO 17638, ISO 17640, ISO 22825, NORSOK M-120, NORSOK N-004, NORSOK M-601, NS 477,
2.2
Informative references
EN 10025-(all parts), EN 10210-(all parts), EN 10219-(all parts), ISO 3834-3,
3
Edition 5, October 2011
Hot rolled products of structural steels – (all parts) Hot finished structural hollow sections of non-alloy and fine grain steels – (all parts) Cold formed welded structural hollow sections of non-alloy and fine grain steels – (all parts) Quality requirements for welding of metallic materials – Part 3: Standard quality requirements
Terms, definitions and abbreviations
For the purposes of this NORSOK standard, the following terms, definitions and abbreviations apply.
3.1
Terms and definitions
3.1.1 shall verbal form used to indicate requirements strictly to be followed in order to conform to this NORSOK standard and from which no deviation is permitted, unless accepted by all involved parties 3.1.2 should verbal form used to indicate that among several possibilities one is recommended as particularly suitable, without mentioning or excluding others, or that a certain course of action is preferred but not necessarily required 3.1.3 may verbal form used to indicate a course of action permissible within the limits of this NORSOK standard 3.1.4 can verbal form used for statements of possibility and capability, whether material, physical or casual
3.2
Abbreviations
AFC BS CEV
approved for construction British Standard carbon equivalent value (IIW, International Institute of Welding Formula
CEV
C
CTOD DAC DNV EN (pr EN) EWF FCAW
crack tip opening displacement distance amplitude curve Det Norske Veritas European Standard (proposal for EN) European Welding Federation flux cored arc welding
Mn Cr Mo V Ni Cu 6 5 15
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NORSOK standard M-101 FSH HAZ HDM IIW IW IWT IWE IWI ISO MDS MSF MT NDT OD Pcm
full screen height heat affected zone hydrogen content, deposit metal International Institute of Welding International Welder International Welding Technologist International Welding Engineer International Welding Inspector International Organization for Standardization material data sheet main support frame magnetic particle testing non destructive testing outside diameter carbon equivalent (cold cracking susceptibility)
Pcm
C
PT PWHT RT SAW SMYS SQL SS UT VT WPS WPQR
penetrant testing post weld heat treatment radiographic testing submerged arc welding specified minimum yield strength steel quality level stainless steel ultrasonic testing visual testing welding procedure specification welding procedure qualification record
4 4.1
Edition 5, October 2011
Si Mn Cu Cr Ni Mo V 5B 30 20 60 15 10
Selection of steels Design classes
The design classes will be decided by the designer and shall form the basis for selection of SQL. Reference is made to NORSOK N-004.
4.2
Selection of steel quality level
The steel quality level will be decided by the designer in compliance with NORSOK N-004. Annex B gives the correlation between the steel quality levels I, II, III and IV, and designations on equivalent steels given in NORSOK M-120. Selection of a better steel quality level in fabrication than the minimum required by the designer shall not lead to more stringent requirements in fabrication.
5
Qualification of welding procedures and welders
5.1
Welding procedure specification (WPS)
Specification and qualification of welding procedures for metallic materials shall be in accordance with ISO 15607. WPS shall be established in accordance with ISO 15609-1.
5.2
Qualification of welding procedures
Welding procedures used for structures requiring steel quality level I and II for all strength levels and steel quality level III for SMYS 355 MPa shall be qualified in accordance with ISO 15614-1 and the additional requirements in this NORSOK standard.
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The qualification is primarily valid for the workshop performing the welding tests, and other workshops under the same technical and quality management. It may also be transferred to and used by a subcontractor, provided the principles of ISO 3834-2 and ISO 14731 are implemented and documented. Requirements to components in stainless steel and Ni-alloys are given in Annex G. The WPQR documentation shall include the material certificates for the base material and filler materials applied in the weld qualification test. PWHT report and chart shall be included in the WPQR.
5.3
Welding procedure qualification record (WPQR) - Range of approval
5.3.1 For welding of steels in all strength classes The WPQR is valid within the limitations specified in ISO 15614-1, with the following clarifications and modifications: a) control of heat input according to ISO 15614-1, 8.4.8, shall apply. If an approval testing have been performed at both a high and a low heat input level (all specified mechanical testing to be performed for both high and low heat input), then all intermediate heat inputs are also qualified; b) when the steel to be welded has a Pcm 0,21, or a carbon content C 0,13 %, then an increase of more than 0,02 Pcm units or 0,03 CEV (IIW formula) units over the value on the approval test shall require a new qualification test; c) a change from wrought (rolled, forged) steel to cast steel or converse; d) for all strength levels for SQL I and II and for SMYS > 400 MPa for SQL III, a change in delivery condition (normalised, thermomechanically controlled processed or quenched and tempered); e) a change in microalloying element or manufacturing technique for steel with SMYS 400 MPa; f) a decrease in groove angle of more than 10° . For groove angles less than 30°, the limitation is +20°/- 0°; g) a qualification of fillet welds carried out on plate thickness equal to or greater than 30 mm, applies for all plate and throat thicknesses. Single layer fillet welds qualifies multi-layer, but not the converse; h) qualification of WPS with manual welding methods 135 and 136 applies also for partly mechanized and mechanized welding, but not vice versa; i) CTOD testing shall be included in the qualification of welding procedures for weldments with a plate thickness above 50 mm for all strength levels for steel quality level I and II and for SMYS > 400 MPa for steel quality level III. CTOD testing shall be included in the qualification of welding procedures for weldments with a plate thickness below and equal 50 mm if requested by the designer for the specified steel quality level. CTOD testing shall be executed from as welded and PWHT weld assemblies as applicable, covering the following combined conditions: 1) full penetration buttweld with K-, or half V -groove as deemed most representative for the actual fabrication. V and X groove are acceptable for weld metal test; 2) a welding procedure representing the maximum heat input to be used in fabrication; 3) maximum joint thickness (within 10 %). Assemblies shall be made and tested for the actual combination of steel manufacturer, welding process and welding consumable (brand) used, except welding consumables used for root passes only, provided these are removed completely by gouging and grinding. NOTE The changes specified in d) and e) above need not require re-qualification if HAZ properties for the material to be welded have been documented from the steel manufacturer for relevant thicknesses and heat input ranges. If sufficient documentation from the steel manufacturer is not available, a change of material shall require re-qualification of a reduced number of procedures. The number of procedures to be re-qualified shall be sufficient to verify that the HAZ properties of the new material is comparable with that used for the previous qualifications.
5.3.2 For welding of steels with SMYS 500 MPa In addition to the requirements given in 5.3.1 the following additional requirements apply for welding of steels with SMYS > 500 MPa: a) a change in steel manufacturer; b) CTOD testing as described in 5.3.1 i) shall be executed for thicknesses above 30 mm; c) stress relieving if required/specified by designer.
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5.4
Edition 5, October 2011
Examination of the test weld
5.4.1 General The type and number of tests shall be in accordance with Table 1. Testing shall be performed in accordance with ISO 15614-1 and the additional requirements given below. The test weld shall be 100 % examined for both surface and volumetric defects with the relevant NDT methods. The soundness of the weld shall comply with Clause 9. Test laboratories shall have a quality system in compliance with ISO 17025 or equivalent.
Table 1
Type and number of tests
Mechanical testing Joint configuration Buttwelds (Tubulars and plates) T-joints (plates) d
Tubular joints
d
Fillet welds
Joint thickness mm t ≤ 50 t 50
Tensile test
Bend a tests
2 2
4 4
t ≤ 50 t 50 t ≤ 50 t 50 All
Charpy Vnotch tests 4 sets 6 sets b
c c c c
4 sets 6 sets b 4 sets 6 sets
Hardness and e macro 1 1 2 2 2 2 2
CTOD
See 5.3.1 i), 5.3.2 b) and 5.4.4 f
a
Bend tests shall consist of 2 face and 2 root bend specimen for t < 12 mm and 4 side bend specimens for t 12 mm. b If the dimensions of the joint does not allow Charpy V-notch testing, the Charpy V-notch properties shall be documented on a butt weld joint made with the same consumable and same base material, and welding parameters and thickness within the range qualified for the joint. c It shall be documented on a butt weld test that the welding consumable used will have sufficient tensile strength. d T-joints on plates qualify for tubular joints, and vice versa. e For welds on submerged structures with cathodic protection, the hardness limits in NORSOK M001 shall apply in addition to the requirements of ISO 15614-1. f For T-joints with t > 50 mm, CTOD testing shall be documented on a buttweld.
5.4.2 Charpy V-notch testing Sampling of Charpy V-notch impact tests shall be carried out in accordance with ISO 9016, with the notch in the positions listed below. All specimens shall be machined with the notch through the thickness, 2 mm below the surface of the material. Designation in parenthesis refers to Figure 1 and Table 2 in ISO 9016.
Notch in centre of weld (VWT 0/2). Notch in fusion line (VHT 0/2). Notch in HAZ, 2 mm from fusion line (VHT 2/2). Notch in HAZ, 5 mm from fusion line (VHT 5/2).
For welds with a joint thickness T 50 mm or more, two additional sets of Charpy V-notch tests shall be taken from the root area, with the notch in the following positions: notch in centre of weld (VWT 0/b); notch in fusion line (VHT 0/b). The test temperature and energy requirements shall comply with Table 2.
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NORSOK standard M-101 Table 2
Edition 5, October 2011
Charpy impact test temperatures and energy requirements for welding procedure qualifications.
Material thickness (mm)
t 12 12 < t 25 25 < t 50 t > 50 Energy a requirement a
Steel quality level II
I SMYS 400
SMYS 500
SMYS 400
°C
400< SMYS 500 °C
°C
0 -20 -40 -40 36 J
-20 -40 -40 -40 42 J
-20 -40 -40 -40 60 J
III SMYS 500
°C
400< SMYS 500 °C
SMYS 500
°C
355 SMYS 500 °C
0 0 -20 -40 27 J
-0 -20 -40 -40 42 J
-20 -40 -40 -40 60 J
-0 0 -20 -40 27 J
0 -20 -40 -40 42 J
°C
The minimum average value is given in the table. No individual value shall be less than 70 % of the minimum average value. Reduction factors of energy requirements for subsize specimens shall be 5/6 for 7,5 mm and 2/3 for 5 mm.
5.4.3 Transverse tensile testing Testing shall be carried out in accordance with ISO 15614-1. The fracture shall be located outside the weld metal, i.e. maximum 20 % of the fracture surface shall consist of weld metal/HAZ. 5.4.4 Crack tip opening displacement (CTOD) testing The CTOD-technique with the Bx2B through-thickness notched type specimen according to BS 7448, Part 1, should be used. Three valid test specimens shall be obtained for each test position. CTOD-testing of welds shall be carried out with the fatigue notch tip positioned in the coarse grained region of the heat affected zone and in the weld metal. For HAZ, determination of the actual location of the fatigue crack tip shall be performed after testing, see EN 10225. NOTE Test assemblies may be given hydrogen diffusion treatment prior to testing, and specimens may be precompressed.
If not specified otherwise, the test temperature for design temperature down to -14 °C shall be -10 °C for splash zone or above, 0 °C for submerged parts. Other test temperature may be prescribed by the designer. The requirement for minimum CTOD value shall be prescribed by the designer. If not specified, the requirement for minimum CTOD value shall be as for the steel purchase order. CTOD-testing of HAZ can be omitted if relevant CTOD properties in HAZ have been documented previously in accordance with requirements in this NORSOK standard, provided the requirements for the essential variables are met. CTOD-testing of weld metal can be omitted if relevant CTOD properties in weld metal have been documented previously in accordance with requirements in this NORSOK standard, provided the requirements for the essential variables are met. The required fracture toughness level shall be decided in design for joints when steel quality level I and II are required. Testing is normally not requested for structures with plate thickness below 40 mm for SMYS 500 MPa or for structures with plate thickness below 25 mm for SMYS > 500 MPa.
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5.5
Edition 5, October 2011
Welder and welding operators qualifications
The welders shall be certified by an accredited body according to EN 287-1 and/or ISO 9606-4. Welding operators shall be certified according to ISO 14732. rd
For tack welders, an internal test according with EN 287-1 and/or ISO 9606-4 is accepted without use of 3 part.
For welding in inspection category C, D and E, diploma as IW-International Welder (fillet- plate-pipe welder) within actual welding method and material may be accepted, see IIW, Minimum requirements for the education, training, examination and qualification of welding personnel. For welding of single sided acute angled tubular joints with < 70º, welders shall be qualified with a realistic joint, representing the minimum angle to be used in production.
6
Fabrication and welding requirements
6.1
General
All welding work shall be according to recommendations given in relevant part of the EN 1011-series. The manufacturer shall have an implemented and documented quality system according with ISO 3834-2. For fabrication of structural steel in inspection category D and/or E, ISO 3834-3 may be accepted (used). All types of inspection/examination shall be performed by personnel other than those performing and being responsible for the production work. The fabricator shall apply a weld numbering system for identification on all shop drawings and as reference in all documentation.
6.2
Drawings for fabrication
Symbolic presentation of welds shall be according to ISO 2553. Welds in inspection category A and B shall have unique weld number. Welds in inspection category C,D and E may be group numbered, but only within the same node/essential member and same drawing sheet. The shop drawings shall have enough information to enable correct selection of WPS. The following information shall be used as relevant:
material type/grade and grouping number (ISO/TR 15608); dimension (outside diameter and wall thickness); PWHT requirements, if relevant; required toe grinding; etc.
6.3
Welding coordination
All welding coordination shall be according to ISO 14731. The manufacturer shall appoint a responsible authorized welding coordinator. The responsible welding coordinator shall be qualified as an IWE, see ISO 14731, Annex A. The responsible welding coordinator may delegate welding coordination activities at fabrications sites to an IWT, see ISO 14731. If only fabrication/welding in inspection category D and/or E, an IWT may be accepted. All other personnel who are carrying out one or more welding activities according to ISO 14731, Annex B, are welding coordinators. The level of technical knowledge, tasks, responsibility and authority shall be identified for each person/function in a job description.
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6.4
Edition 5, October 2011
Welding inspection and qualification of welding inspectors
Welding inspector’s tasks and responsibilities is to be familiar with all standards, rules and specifications, and continuously verify that all requirements and adequate parts in ISO 3834-2 are implemented and followed. Welding inspection shall be performed before, during and after welding according to typical check points listed in Annex F. All inspections shall be reported to the responsible welding coordinator. The inspection frequency shall be sufficient to report weekly quality status during fabrication based on welding inspection reports. Prior to fabrication start-up, contractor shall implement a system for recording of quality status. Causes for non-conformance shall be immediately investigated and corrective action shall be taken to prevent further occurrence. Non-conformance shall require documented investigation/action by the responsible welding coordinator. Welding inspectors shall be qualified according to NS 477 or EWF/IIW rules for approval of IWI-International Welding Inspector
6.5
Forming
Cold forming of steel (i.e. forming below 250 C) shall be carried out within the deformation range recommended by the steel manufacturer. For steel quality level I and II, the deformation limit without documentation of mechanical properties is 5 %. If the deformation is more than the above given limits, either heat treatment shall be performed, or strain ageing tests shall be carried out according to the following requirements: the material shall be permanently strained locally to the actual deformation; the material shall be artificially aged at 250 C for 1 h; one set of 3 impact test specimens shall be tested from the base material in the strained plus artificially aged condition. The notch shall be located within the plastically strained portion of the material, in the part of the cross section which have received the highest strain; the impact testing temperature shall be as specified for the actual steel grade in question; the Charpy-V impact value shall comply with the minimum requirements for the steel grade and shall not be more than 25 % lower than the impact value for the material before deformation and strain ageing. If forming is performed at temperature above 250 C, it shall be documented that the base material properties, weldability, weldmetal and HAZ properties satisfy the actual MDS and this NORSOK standard. The percentage strain due to forming is defined as follows:
Percent strain 6.6
Wall thickness x 100 % Forming mid thickness diameter
Assembly
6.6.1 General In tubular joints, circumferential and longitudinal weld joints should not be placed in the shaded areas shown in Figure 1, unless otherwise shown on design drawings.
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W1
W1
W1
W1
W2
W2
W2
W2
W
3
D
Longitudinal welds
Circumferential welds
W1 = 75 mm or minimum 2 times chord thickness W2 = 150 mm or minimum D/4 W3 = 600 mm or minimum D Figure 1
Prohibited location of welds in tubular joints
6.6.2 Splices Splices shall not be located in areas, noted as restricted on design drawings. 6.6.3 Tapering Tapering shall be in accordance with the requirements given in relevant standards or drawings. If no other requirements are specified, a tapering of 1:4 should be used. 6.6.4 Bolting connection Bolting material shall comply with requirements in NORSOK M-001. Holes shall be made by machine drilling. 6.6.5 Seal/blind-compartments. Crevices and areas which become inaccessible after fabrication or assembly shall be sealed off from the outside atmosphere. Seal welds shall have a throat thickness of at least 3 mm. Where steel items shall be hot dip galvanised, hollow sections shall be ventilated. 6.6.6 Temporary cut-outs Temporary cut-outs shall not be located in restricted areas as shown on design drawings. Temporary cut outs shall have a corner radius not less than 100 mm. Temporary cut-outs shall be closed by refitting the same or an equivalent plate and employing the same welding, inspection and documentation procedures and requirements that govern the structural part in question. 6.6.7 Straightening of structural members Members distorted by welding shall be straightened according to a detailed work instruction. The base material properties shall satisfy the specified requirements after straightening. Maximum temperature for straightening shall not exceed the temperature limit recommended by the steel manufacturer, but it shall in no case be higher than 600 C.
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6.6.8 Doubler plates All temporary attachments which shall be flame cut or welded under water shall be attached to the structure by using doubler plates. All attachments in the splash zone shall be attached to the structure by using doubler plates.
6.7
Preparation for coatings
Edges of plates and structural shapes which are intended to be coated shall be rounded to approximately 2 mm radius, unless otherwise indicated on fabrication drawings.
6.8
Preparation and fit-up of weld bevels
Permanent backing strips are not accepted, unless shown in fabrication drawings. Buttering shall be welded in accordance with applicable WPS. The WPS shall be supported by a butt weld WPQR. The responsible NDT-coordinator/personnel shall be notified every time buttering is performed in any groove. Maximum buttering is limited to t/2, maximum 20 mm in the joint. Tack welds shall normally have a length of minimum 100 mm. For material thickness less or equal to 25 mm, tack length may be minimum 4 x plate thickness.
6.9
Welding processes
The welding processes listed in ISO 15614-1 are acceptable.
6.10 Welding consumables The manufacturers shall ensure that welding consumables applied for joints where steel quality level I, II and III are required, meet the requirements for mechanical properties as specified for the welding procedure qualification, in both as welded and (where applicable) PWHT condition. This may be achieved through (alternatively): batch testing including chemical analysis and mechanical properties, see Annex D; an established and reliable system of batch certification against accepted supplier data sheets, see Annex C; for steels with SMYS > 500 MPa, Annex D is mandatory. Except for solid wires such consumables shall be classified by the supplier as extra low hydrogen, i.e. HDM 5 ml/100 g weld metal. For self shielded flux cored wire HDM 8 ml/100 g may be accepted, provided preheating temperature and post weld holding temperature and time is assessed to avoid hydrogen cracking. Hydrogen testing shall be according to ISO 3690 or equivalent. For all steels with SMYS > 500 MPa special precautions shall be taken to verify that selected consumables comply with hydrogen requirements. Stricter requirements than given above may be relevant. Prequalification with mock-up structures shall apply if there is a risk for high restraint in welding or erection. Consumables for joints in steel quality level III (with SMYS < 355 MPa) and IV and for joining stainless to carbon steel shall be selected with due consideration of base material properties, thickness and weldability, to ensure sufficient weld strength, toughness and homogenity. Such consumables shall be delivered with EN 10204, type 2.2, certificate, as a minimum. All welding consumables shall be individually marked. When certification according to Annex C is used, welding consumables (except welding fluxes) shall be supplied with an inspection certificate type 3.1 in accordance with EN 10204, including a statement of compliance with the welding consumable data sheet and the chemical composition of the weld deposit (elements of the data sheet). Welding fluxes shall be supplied with a test report (EN 10204, type 2.2), declaring conformity with the approved product type.
6.11 Preheat and interpass temperature Preheating above 50 °C should be achieved by electric heating elements. Cutting torches are not allowed for preheating. NORSOK standard
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The minimum interpass temperature shall not drop below the minimum required preheat temperature. If not otherwise stated in the WPS, and qualified by the WPQR, the maximum interpass temperature shall not exceed 250 C measured at the edge of the groove. For C- and C/Mn-steels, a maximum interpass temperature of 250 C may be used, even if a lower temperature was recorded on the WPQR. The preheat temperatures used during repair welding should be minimum 50 C higher than the preheat used for the original weld. NOTE Production welding of high strength steels with SMYS > 500 MPa is normally more sensitive to hydrogen cracking than experienced during welding for qualification. Special precautions, including preheating temperature, minimum holding temperature and extended post weld holding temperature for 24 h or more, shall be taken into consideration.
6.12 Production welding 6.12.1 General Welding shall be carried out in accordance with the WPS and applicable drawings. The applicable WPS shall be given directly to the welder and be available at the site of welding at all times A collection of WPS`s on walls or boards are only for general information and not accepted used for welding. Butt welds in joints where steel quality level I and level II for all strength levels, or steel quality level III for SMYS > 400 MPa are required shall, whenever possible, be welded from both sides. If any welding is conducted after PWHT, the PWHT shall be repeated. For joints in inspection category A, the ”straight” edges of K- and half V-butt weld grooves shall have a groove º angle of at least 10 , unless it is documented that possible defects can be detected by the UT technique used. º For K-grooves, the 10 should be machined from the root to each plate surface. Any occurrence of cracking during production welding shall be investigated. Welding should be suspended until the cause of cracks and defects has been identified and measures taken to prevent their reoccurrence. Cracks or other persistent weld defects may lead to revision and requalification of the WPS. 6.12.2 Attachments Temporary attachments as lifting lugs, lugs for scaffolding and assembly, supports for cables, equipment, ladders or other fabrication and erection aids should be removed. If indicated on design drawings that removal (full or partial) is not required, the temporary attachments may be left as is, or removed only partially. All welding of attachments shall comply with the requirements for the structure to which they are attached. Temporary attachments shall be cut minimum 3 mm from the base metal and ground. The ground area shall be visually examined and magnetic particle/penetrant tested (as relevant) in accordance with the inspection category in question. 6.12.3 Stainless steel components Permanent or temporary structural elements, attachments or penetration sleeves in stainless steel materials may be selected for various purposes. Requirements for welding and inspection of stainless outfitting structures shall follow similar classification principles as for other structural steel elements, see annex G. All welding and inspection of welds to carbon steel structures shall as a minimum comply with the requirements for the structure to which they are attached. Welding consumables shall be selected in accordance with G.4.
6.13 Post weld heat treatment (PWHT) PWHT shall be required for structural welds in steel quality level I or level II, or quality level III with yield strength Re > 400 MPa, when the nominal thickness as defined in ISO 15614-1, exceeds 50 mm, unless adequate fracture toughness can be documented in the as welded conditions. For restrained joints of complicated design, PWHT may be required for smaller thicknesses, independent of steel quality level. PWHT shall be carried out in accordance with a procedure which shall include NORSOK standard
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heating rate, cooling rate, soaking temperature and time, heating facilities, insulation, control devices, recording equipment, configuration of structure to be PWHT or details if local PWHT shall be carried out, number and location of thermocouples to be used during PWHT.
The holding time and temperature shall be as recommended by the steel manufacturer. The temperature difference between different parts of the structure during soaking time shall not exceed 30 C within the heated area. Double sided heating shall be used as far as possible. The temperatures shall be continuously and automatically recorded on a chart.
6.14 Grinding When grinding is specified on design drawings or is instructed as a corrective action, the grinding shall be performed according to a detailed procedure. Grinding tools, direction, surface roughness and final profile shall be specified. Reference samples for typical joints and sections may be prepared and used for acceptance of treated welds. Typical examples for requirements for grinding of joints are given in A.1.
6.15 Peening Weld improvement by peening shall be performed in accordance with detailed procedures. Normally pregrinding of a groove will be required to assure correct location of peening area. Tools for grinding and peening, surface roughness and profile of grinding as well as peening shall be specified. Tools for check and measurements shall be described and shall be available during operations. Documentation of correct performance shall include macrophotography. Typical examples of requirements for peening of joints are given in A.2.
7
Production tests
Production tests shall be selected on weldments in critical regions to verify that the specified requirements have been meet. Minimum one test coupon is required from each applied welding process. Test coupons shall be welded in a manner which realistically simulates the actual production welding, normally as extension of the production weld, and meet the requirements for welding procedure approval tests. CTOD testing is not required for production testing. If a production test fails, the reason for the failure shall be determined and remedial action implemented.
8
Fabrication tolerances
Fabrication tolerances shall be in accordance with Annex E, unless otherwise specified on drawings.
9
Non-destructive testing (NDT)
9.1
General
The inspection category shall be decided by the designer in accordance with NORSOK N-004, and shall be specified on the design drawings. Final inspection and NDT of structural steel welds shall not be carried out before 48 h after completion except where PWHT is required. The time delay may be reduced to 24 h for steel grades with SMYS of 355 MPa or lower, and for steel grades with SMYS of 420 MPa or lower for plate thicknesses below 40 mm, provided delayed cracking have not been observed for the materials and/or welding consumables in question. NORSOK standard
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When PWHT is performed, the final NDT shall be carried out when all heat treatment have been completed. Prior to fabrication start-up, contractor shall implement a system for recording of weld defect rates. The defect rates shall be recorded on a weekly basis for VT, MT, PT, UT and RT from each production area (geographically split in production areas at the same yard) and shall be reported together with the accumulated defect rate. The defect rate statistics shall be used as a tool in weld quality control. Causes for defects shall immediately be investigated and corrective actions shall be taken to prevent further occurrence. Cracks detected with any NDT method shall require documented investigation/action by the responsible welding engineer. The defects shall be reported with reference to the numbering system according with ISO 6520-1. At a weekly high defect rate or at repeated occurrence of planar defects, two trigger levels apply for extended NDT for welds in inspection category B, C and D. Two steps of actions apply within trigger level 2. Trigger level 1 If a defect rate for any method exceed 10 % for a single week the extent shall be increased to 100 % for all welds in question. Trigger level 2 If a defect rate for any method of 5 % to 10 % for a single week is observed the following two steps of extended NDT shall apply: Step 1. A defect rate for any NDT method exceeding 5 % (1 % for MT) for a single week require doubling of the extent of NDT according to the inspection category. Spot extent shall be increased to 20 %. Step 2. If the defect rate for the weld length where the extended NDT is taken in accordance with Step 1 above exceed 5 %, the extent shall be increased to 100 % for all welds in question The increased NDT extent shall cover welds of the same inspection categories, welded in the same period of time by the specific welder(s) and WPS when the high defect rate was produced, to assure that the weld quality is maintained also with the lower extent of NDT. Unless the causes for defects found leads to immediate and documented preventive actions, the higher level of extent of NDT shall be maintained until the weekly defect rate is well below 5 %. Generally, if the defect rate approaches 10 % during any stage in production welding, further welding should be held until investigations are completed and corrective actions implemented. A low defect rate may be used as basis for a reduction in the extent of NDT for inspection categories B, C and D, provided that a correct defect rate identification is prepared for each weld method, each NDT method b and each production area, see Table 3, table footnote .
The defect rate is defined as :
(Defect length x 100 %) (Length of tested parts of welds)
NOTE “Tested part of welds” means the part that is tested with the same NDT method. Defect rate shall be based on at least 5 welds or 1 m tested weld length.
NDT after repair shall not be included when calculating the defect rate.
9.2
Qualification of non-destructive testing (NDT) operators
Personnel responsible for all NDT activities shall be qualified according to EN 473, Level 3 (or ISO 9712) or rd equivalent 3 party certification scheme. NDT personnel performing visual inspection of welded joints shall be qualified in accordance with EN 473, VT rd level 2 or equivalent 3 party certification scheme. NS 477 latest revision may be used. rd
The NDT operator shall be qualified according to EN 473, level 2 or equivalent 3 party certification scheme.
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Operators simply producing radiographs and not performing evaluation, do not require level 2, but shall have sufficient training. Ultrasonic operators performing inspection of welds in duplex stainless steel material shall be specially rd trained and qualified for the purpose according to EN 473 or equivalent 3 party certification scheme When testing of castings or forgings, the NDT operator shall document experience with forged and cast products.
9.3
Extent of visual examination and non-destructive testing (NDT)
The required minimum extent of examination/testing is given in Table 3. Design drawings may show areas of welds where testing is mandatory. Testing performed shall be representative for the weld quality. Partial NDT shall normally be planed for on all shop drawings. Ultrasonic testing to reveal the presence of possible weld metal transverse cracking shall be included for butt welds with thickness more than 25 mm. The testing shall be performed on minimum 5 % of welds in inspection category A and B for SAW (12) and FCAW (131 and 136).
Table 3 Inspection category A a
B
C
a
a
D E
Minimum extent (in %) of non-destructive testing for structural welds Type of connection Buttweld T-connection Fillet/partial Buttweld T-connection Fillet/partial Buttweld T-connection Fillet/partial All connections All connections
Visual examination
Extent of testing %
%
RT
UT
MT
100 100 100 100 100 100 100 100 100 100 100
10 Spot -
100 100 c 20 b 50 b 50 bc 10 b 20 b 20 c spot -
100 100 100 b 100 b 100 b 100 b 20 b 20 b 20 spot -
Key Spot means 2 % to 5 %. a
Increased extent of NDT shall be as defined in relevant Trigger levels in 9.1. The required level of increased extent shall be maintained until a defect rate below 5 % is reestablished and documented.
b
The extent may be reduced to 50 % of the specified extent, based on experience and documented records with similar joints, provided the defect rate (see 9.1) for UT/RT is < 2,0 % and for MT is < 0,2 % during the last 100 m of weld. The last 100 m shall be continuously updated every week. If the defect rate exceeds the limits given above, the normal extent of NDT shall apply again. A possible reduction in the extent of NDT shall be considered separately for each welding method and each production area.
c
Applies only for partial penetration welds with a penetration depth greater than 12 mm.
When partial testing is defined for welds in an area, the testing shall be spread such that the most essential members and nodes are included in the inspection, and such that areas of welds most susceptible to weld defects are covered. The specified percentage to be tested in Table 3 refers to the total length of welds in each inspection category. NORSOK standard
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All WPSs used and welds representing all welding personnel involved in the fabrication shall be subject to NDT. During the initial fabrication the extent of UT and MT of inspection category B and C welds shall be intensified, normally to twice the level given in Table 3. This extent shall be maintained for a weld and test length sufficient to conclude that the weld repair percentage is at a reasonable level. The increased initial testing may be accounted for in the overall extent provided the initial testing confirms consistent good workmanship. In addition to what is listed in Table 3, the following shall apply for inspection category A and B: a) one film at each end for longitudinal welds of tubulars (including tubulars for nodes and stubs); b) where radiographic testing is required, intersection welds, and those locations where presence of defects is deemed to be most harmful, shall be tested; c) ultrasonic and radiographic testing shall not overlap, except when 100 % UT is specified. However, ambiguous imperfections revealed by UT shall in addition be tested by RT; d) ultrasonic testing is normally not applicable for thicknesses less than 10 mm. For such thicknesses, UT shall be replaced with RT. In general, RT should be considered if UT is not possible. Radiographic testing is normally not applicable for thicknesses above 40 mm.
9.4
Visual examination and finish of welds
The visual examination shall be carried out in accordance with ISO 17637.
9.5
Radiographic testing
Radiographic testing shall be carried out in accordance with ISO 17636, Class A. The general film density shall be ≥ 2,0. However, if X-ray are used, the minimum film density may be reduced to 1,5. Suspect planar indications discovered by RT shall be type determined, located and sized by UT.
9.6
Ultrasonic testing
Ultrasonic testing of welds in plate and tubular butt welds and double side welded tubular joints shall be performed in accordance with ISO 17640, examination level C. Reference blocks shall be made with thickness and side-drilled holes in accordance with Table 4. DAC reference curves shall be established. The effective test range of a DAC curve shall be determined by the point at which the curve has fallen to 25 % FSH, when it will be necessary to raise the curve using reflectors at increased depth. The reference block shall be from a steel type that is representative for the steel to be inspected. Where ultrasonic testing is to be performed on steel produced by controlled rolling or thermo mechanical treatment, reference blocks shall be produced both perpendicular to, and parallel to, the direction of rolling. The rolling direction shall be clearly identified. The actual refracted angle for each probe measured from the reference block or as measured on the actual object being examined, shall be used when plotting indications. Ultrasonic testing procedures shall be sufficiently detailed to ensure 100 % of the weld body and heat affected zones are examined for longitudinal defects. All indications exceeding -10dB DAC shall be investigated to the extent that they can be evaluated in terms of the acceptance criteria. For butt welds, (C and D) or (E and F) according to ISO 17640 shall be utilised for the detection of transverse imperfections, providing that the surface finish of the weld cap is sufficiently smooth and in accordance with clause 8 of ISO 17640.
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Alternatively techniques (X and Y) or (W and Z) according to ISO 17640 can be utilised by placing the probe alongside the weld connection, so that the beam forms a small angle with the centreline. If the surface finish adjacent to the weld is such that testing with an angle probe using techniques (C and D) or (E and F) along the centre line of the weld is judged to be the only reliable method of examination, than the weld cap is to be dressed smooth or ground flush with the parent material in accordance with clause 8 of ISO 17640. Scanning is in all cases to be performed from both sides of the weld and in both directions. The examination record shall include the position, the echo height, length, depth and type of indication. Table 4 Thickness of material to be examined mm 10 < t < 50 50 < t 815: ENiCrMo-3 or ERNiCrMo-3 Consumables for joining of dissimilar materials For welding of type 316L SS to carbon steel, consumables should be of type 309MoL, alternatively a nickel based alloy. For welding of higher alloyed stainless steels to carbon steel, the same or higher alloyed filler metal, as used for welding the stainless steel to itself, shall be used.
G.5
General fabrication requirements
Requirements for fabrication, welding and inspection of structural components in SS and Ni alloys shall follow the same classification principles as for other structural steel elements, as specified in this NORSOK standard. All fabrication shall be in accordance with recommendations given in EN 1011-3. Prefabrication of SS and Ni-alloys should be performed in a workshop, or parts thereof, which is reserved exclusively for those types of materials. Contamination of weld bevels and surrounding areas with low melting point metals such as copper, zinc, etc. are not acceptable. The welding processes listed in ISO 15614-1 are acceptable. Maximum interpass temperature shall be 150 °C. All welds shall be continuous. Intermittent welding is acceptable if the environment can be defined as dry and non-corrosive. Maximum cold forming shall be 10 % for austenitic SS, and 5 % for duplex SS and Ni alloys. For calculation of deformation rate, see 6.2. Straightening shall not be performed by application of heat. Welding of attachments in SS or Ni alloys to carbon steel structures shall comply with the requirements for the structure to which they are attached.
G.6
Non-destructive testing (NDT)
G.6.1
General
The inspection category shall be decided by the designer in accordance with NORSOK N-004, and shall be specified on the design drawings.
G.6.2
Qualification of NDT-operators
The requirements of 9.1 shall apply.
G.6.3
Extent of NDT
The minimum extent of examination is given in Table G.1. Design drawings may show areas of welds where examination is mandatory.
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Inspection category A
B
C
D E
G.6.4
Type of connection Buttweld T-connection Fillet/partial Buttweld T-connection Fillet/partial Buttweld T-connection Fillet/partial All connections All connections
Minimum extent of NDT (%)
Visual Examination % 100 100 100 100 100 100 100 100 100 100 100
Extent of testing % RT PT 100 50 20 -
100 100 100 100 100 100 20 20 20 2 to 5 -
Procedures and acceptance criteria
Visual inspection and finish of welds: shall be in accordance with 9.4 and 9.8; weld zones shall in addition be visually inspected on both sides of the weld (where access), and fulfil the following criteria: the oxidation levels showing light brown to brown colour are acceptable; oxidation levels showing a narrow band of dark brown colour and intermittent spots of blue colour are acceptable; darker or more extensive oxidation colours are not acceptable, and shall be chemically or mechanically removed. Radiographic testing shall be in accordance with 9.5 and 9.8. Radiographic testing may be replaced with ultrasonic examination for material thickness ≥ 12mm. Ultrasonic examination shall be performed in accordance with ISO 22825. Personnel shall be qualified as described in 9.2. Acceptance criteria shall be in accordance with 9.8.4. Penetrant testing shall be carried out in accordance with ISO 3452-1. Acceptance criteria shall be in accordance with 9.8.5.
G.7
Repair
Repair welding may only be carried out twice in the same area.
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