DNV-OS-C401

OFFSHORE STANDARDDNV-OS-C401

FABRICATION AND TESTING OF OFF-SHORE STRUCTURES

JANUARY 2001DET NORSKE VERITAS

FOREWORDDET NORSKE VERITAS (DNV) is an autonomous and independent foundation with the objectives of safeguarding life, prop-erty and the environment, at sea and onshore. DNV undertakes classification, certification, and other verification and consultancyservices relating to quality of ships, offshore units and installations, and onshore industries worldwide, and carries out researchin relation to these functions.DNV Offshore Codes consist of a three level hierarchy of documents: Offshore Service Specifications. Provide principles and procedures of DNV classification, certification, verification and con-

sultancy services. Offshore Standards. Provide technical provisions and acceptance criteria for general use by the offshore industry as well as

the technical basis for DNV offshore services. Recommended Practices. Provide proven technology and sound engineering practice as well as guidance for the higher level

Offshore Service Specifications and Offshore Standards.DNV Offshore Codes are offered within the following areas:

A) Qualification, Quality and Safety MethodologyB) Materials TechnologyC) StructuresD) SystemsE) Special FacilitiesF) Pipelines and RisersG) Asset Operation

Amendments October 2002 and April 2002This Code has been amended, but not reprinted in October 2002 and April 2002. The changes are incorporated in the Web, CDand printable (pdf) versions. The amendments are shown in red colour in the Web and CD versions.All changes affecting DNV Offshore Codes that have not been reprinted, are published separately in the current Amendmentsand Corrections, issued as a printable (pdf) file.Comments may be sent by e-mail to [email protected] subscription orders or information about subscription terms, please use [email protected] information about DNV services, research and publications can be found at http://www.dnv.com, or can be obtained from DNV,Veritasveien 1, N-1322 Hvik, Norway; Tel +47 67 57 99 00, Fax +47 67 57 99 11.

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Offshore Standard DNV-OS-C401, January 2001Contents Page 3CONTENTS

CH. 1 INTRODUCTION ................................................ 5

Sec. 1 Introduction........................................................... 7

A. General....................................................................................7A 100 Introduction....................................................................... 7A 200 Objective........................................................................... 7A 300 Organisation of contents ................................................... 7

B. Normative References ............................................................7B 100 General.............................................................................. 7B 200 Offshore service specifications and rules ......................... 7B 300 Offshore Standards ........................................................... 7B 400 Other references................................................................ 7

C. Informative References...........................................................7C 100 General.............................................................................. 7

D. Definitions .............................................................................. 8D 100 Verbal forms ..................................................................... 8D 200 Terms ................................................................................ 8D 300 Abbreviations.................................................................... 8D 400 Latin symbols.................................................................... 8D 500 Greek symbols .................................................................. 9

CH. 2 TECHNICAL PROVISIONS ............................ 11

Sec. 1 Welding Procedures and Qualification ofWelders................................................................. 13

A. General..................................................................................13A 100 Scope...............................................................................13A 200 Welding processes ..........................................................13

B. Welding Procedures..............................................................13B 100 General............................................................................13B 200 Preliminary welding procedure specification, pWPS.....13B 300 Welding procedure qualification record, WPQR............13B 400 Welding procedure specification, WPS.......................... 13B 500 Welding procedure tests..................................................13

C. Welding Procedure Tests, C-Mn Steel andLow Alloy Steel....................................................................13

C 100 Butt welds on plates........................................................13C 200 Butt welds on tubes.........................................................15C 300 Full penetration T-, Y-, and K- joints .............................16C 400 Tubular joints..................................................................16C 500 Fillet welds......................................................................17C 600 Re-testing........................................................................17C 700 Validity of qualified welding procedures .......................17

D. Welding Procedure Tests, Aluminium .................................19D 100 General............................................................................19D 200 Butt welds .......................................................................20D 300 Fillet welds......................................................................21D 400 Re-testing........................................................................21

E. Welding Procedure Tests, Stainless Steel.............................22E 100 General............................................................................22E 200 Supplementary requirements for austenitic

stainless steel...................................................................22E 300 Supplementary requirements for ferritic-austenitic

stainless steel...................................................................22

F. Qualification of Welders ...................................................... 22F 100 General............................................................................22F 200 Standards for qualification testing ..................................23

G. Testing ..................................................................................23G 100 General............................................................................23G 200 Tensile testing at ambient temperature ...........................23

Sec. 2 Fabrication and Tolerances............................... 25

A. General..................................................................................25A 100 Objective and scope........................................................ 25B. Fabrication Planning.............................................................25B 100 General............................................................................ 25B 200 Quality system and workmanship................................... 25C. Inspection..............................................................................25C 100 General............................................................................ 25

D. Material Identification, Cutting and Forming.......................25D 100 Material identification .................................................... 25D 200 Cutting and forming........................................................ 25

E. Tolerances.............................................................................26E 100 Misalignments................................................................. 26E 200 Fairness and straightness ................................................ 26

F. Assembly, Welding, Heat Treatment and Repairs................29F 100 Assembly and welding.................................................... 29F 200 Post weld heat treatment (PWHT).................................. 30F 300 Repairs ............................................................................ 30

Sec. 3 Testing of Welds ................................................. 32

A. General..................................................................................32A 100 Scope............................................................................... 32

B. Destructive Testing...............................................................32B 100 Fracture mechanics (FM) testing .................................... 32C. Non-Destructive Testing (NDT)...........................................33C 100 General............................................................................ 33C 200 NDT procedures.............................................................. 33C 300 Personnel qualification ................................................... 33C 400 Extent of NDT ................................................................ 33C 500 Acceptance criteria for NDT .......................................... 35

Sec. 4 Other Tests.......................................................... 37

A. General..................................................................................37A 100 Scope............................................................................... 37

B. Testing of Watertightness .....................................................37B 100 General............................................................................ 37

C. Structural Tests .....................................................................37C 100 General............................................................................ 37

Sec. 5 Corrosion Protection Systems ........................... 38

A. General..................................................................................38A 100 Scope............................................................................... 38A 200 General............................................................................ 38A 300 Application of coating .................................................... 38A 400 Fabrication and installation of sacrificial anodes ........... 38A 500 Fabrication and installation of impressed

current systems ............................................................... 38

Sec. 6 Miscellaneous ...................................................... 39

A. Use General ..........................................................................39A 100 Scope............................................................................... 39

B. Bolts ......................................................................................39B 100 Bolts and nuts ................................................................. 39

C. Mechanical Fastening ...........................................................39C 100 Contact surfaces in slip resistant connections ................ 39DET NORSKE VERITAS

G 300 Bend testing ....................................................................23 CH. 3 CERTIFICATION AND CLASSIFICATION 41

Offshore Standard DNV-OS-C401, January 2001Page 4 ContentsSec. 1 General ................................................................ 43

A. Introduction .......................................................................... 43A 100 Scope...............................................................................43

B. Specific Certification and Classification Requirements....... 43B 100 General ............................................................................43B 200 Basic requirements ..........................................................43

B 300 Welding shops and -contractors......................................43B 400 Welding consumables .....................................................43B 500 Welding procedures and qualification of welders...........43B 600 Corrosion protection systems..........................................43

C. Records and Documentation.................................................43C 100 General ............................................................................43DET NORSKE VERITAS

OFFSHORE STANDARDDNV-OS-C401FABRICATION AND TESTING OF OFFSHORE STRUC-TURES

CHAPTER 1

INTRODUCTION

CONTENTS PAGE

Sec. 1 Introduction ................................................................................................................................ 7DET NORSKE VERITASVeritasveien 1, N-1322 Hvik, Norway Tel.: +47 67 57 99 00 Fax: +47 67 57 99 11

Offshore Standard DNV-OS-C401, January 2001Ch.1 Sec.1 Page 7SECTION 1INTRODUCTION

A. GeneralA 100 Introduction101 This standard contains requirements for fabrication andtesting of offshore structures.

A 200 Objective201 The objectives of this standard are to: provide an internationally acceptable standard to ensure

the quality of all welding operations used in offshore fab-rication, through identifying appropriate welding proce-dures, welder qualifications and test methods

serve as a technical reference document in contractualmatters between purchaser and contractor

serve as guideline for designer, purchaser and contractor specify minimum requirements for welding operations

subject to DNV certification and classification.A 300 Organisation of contents301 Ch.2 Sec.1 to Ch.2 Sec.6 give common requirementsthat are considered applicable to all types of offshore units andinstallations.

B. Normative ReferencesB 100 General101 The references given in Table B1, Table B2 and TableB3 include provisions, which through reference in this textconstitute provisions for this standard.

B 200 Offshore service specifications and rules201 The offshore service specifications and rules given inTable B1 are referred to in this standard.

B 300 Offshore Standards301 The offshore standards given in Table B2 are referred toin this standard.

B 400 Other references

this standard.

C. Informative ReferencesC 100 General101 The documents listed in Table C1 include acceptablemethods for fulfilling the requirements in the standard and maybe used as a source of supplementary information. Other rec-ognised documents as listed below may be used provided it isshown that they meet or exceed the level of safety of the actualstandards.

Table B1 DNV Offshore Service Specifications and rulesReference TitleDNV-OSS-101 Rules for Classification of Offshore Drilling and

Support UnitsDNV-OSS-102 Rules for Classification of Floating Production

and Storage UnitsRules for Classification of Ships

Table B2 DNV Offshore StandardsReference TitleDNV-OS-B101 Metallic MaterialsDNV-OS-C101 Design of Offshore Steel Structures, General

(LRFD method)DNV-OS-C201 Structural Design of Offshore Units (WSD meth-

od)

Table B3 Other referencesReference TitleANSI/AWSD1.1

Structural Welding Code - Steel

ASME Section IX, Welding and Brazing QualificationsNon-Interfiled (Boiler and Pressure VesselCodes)

ASTM G48 Standard Test Methods for Pitting and CreviceCorrosion Resistance of Stainless Steels and Re-lated Alloys by Use of Ferric Chloride Solution

ASTM E562 Standard Test Method for Determining VolumeFraction by Systematic Manual Point Count

BS 7448-2 Fracture mechanics toughness tests. Method fordetermination of KIc, critical CTOD and criticalJ values of welds in metallic materials

EN 287 Approval testing of welders - Fusion weldingEN 1418 Welding personnel Approval testing of welding

operators for fusion welding and resistance weldsetters for fully mechanized and automatic weld-ing of metallic materials

IACS Shipbuilding and Repair Quality Standard, PartA - Shipbuilding and repair Quality Standard forNew Construction and Part B - Repair QualityStandard for Existing Ships

ISO 148 Steel - Charpy impact test (V-notch)ISO 898 Mechanical properties of fasteners made of car-

bon and alloy steelISO 6507-1 Metallic materials - Vickers hardness test - Part

1: Test methodISO 8501-1 Preparation of steel substrates before application

of paints and related products -- Visual assess-ment of surface cleanliness - Part 1: Rust gradesand preparation grades of uncoated steel sub-strates and of steel substrates after overall remov-al of previous coatings

ISO 9001:2000 Quality management systems - RequirementsISO 9606 Approval testing of welders - Fusion weldingISO 10042 Arc-welded joints in aluminium and its weldable

alloys - Guidance on quality levels for imperfec-tions

NACE MR0175 Sulphide Stress Cracking Resistant Metallic Ma-terials for Oilfield Equipment - Item No. 21302

Table C1 DNV Recommended Practices and ClassificationNotesReference TitleDNV-RP-C203 Fatigue Strength Analysis of Offshore Steel

StructuresClassification Buckling Strength AnalysisDET NORSKE VERITAS

401 The other references given in Table B3 are referred to in Note 30.1

Offshore Standard DNV-OS-C401, January 2001Page 8 Ch.1 Sec.1D. DefinitionsD 100 Verbal forms101 Shall: Indicates a mandatory requirement to be followedfor fulfilment or compliance with the present standard. Devia-tions are not permitted unless formally and rigorously justified,and accepted by all relevant contracting parties.102 Should: Indicates a recommendation that a certaincourse of action is preferred or particularly suitable. Alterna-tive courses of action are allowable under the standard whereagreed between contracting parties but shall be justified anddocumented.103 May: Indicates a permission, or an option, which is per-mitted as part of conformance with the standard.104 Can: Can-requirements are conditional and indicate apossibility to the user of the standard.105 Agreement, or by agreement: Unless otherwise indicat-ed, agreed in writing between contractor and purchaser.

D 200 Terms201 Purchaser: The owner or another party acting on his be-half, who is responsible for procuring materials, componentsor services intended for the design, construction or modifica-tion of a structure.202 Contractor: A party contractually appointed by the pur-chaser to fulfil all, or any of, the activities associated with fab-rication and testing.203 Welding procedure: A specified course of action to befollowed in making a weld, including reference to materials,welding consumables, preparation, preheating (if necessary),method and control of welding and post-weld heat treatment (ifrelevant), and necessary equipment to be used.204 Welding procedure specification: A document provid-ing in detail the required variables of the welding procedure toensure repeatability.205 Preliminary welding procedure specification (pWPS):A tentative welding procedure specification, which is assumedto be adequate by the manufacturer or contractor, but whichhas not been qualified.206 Welding procedure test: The making and testing of astandardised test piece, as indicated in the pWPS, in order toqualify a welding procedure specification.207 Welding procedure qualification record (WPQR): Arecord comprising all necessary data needed for qualificationof a pWPS.208 Qualified welding procedure specification (WPS): Awelding procedure specification, which has been qualified byconforming to one or more, qualified WPQRs.209 Non-destructive testing (NDT): Visual inspection, radi-ographic testing, ultrasonic testing, magnetic particle testing,penetrant testing and other non-destructive methods for reveal-ing defects and irregularities.

D 300 Abbreviations301 The abbreviations given in Table D1 are used in thisstandard.

D 400 Latin symbols401 The following Latin symbols are used:

Table D1 AbbreviationsAbbreviation In fullAC Alternating currentANSI American National Standards InstituteASME American Society of Mechanical EngineersASTM American Society for Testing of MaterialsAWS American Welding Society

BS British Standard (issued by British Standard Institu-tion)

CE Carbon equivalentC-Mn Carbon manganeseCTOD Crack tip opening displacementDAC Distance amplitude curveDC Direct currentDNV Det Norske VeritasECA Engineering critical assessmentEN European de NormalisationFM Fracture mechanicsHAZ Heat affected zoneIACS International Association of Classification Socie-

tiesISO International Organisation for StandardisationMAG Metal active gas (welding)MIG Metal inert gas (welding)NACE National Association of Corrosion EngineersNDT Non-destructive testingPWHT Post weld heat treatmentpWPS Preliminary welding procedure specificationRP Recommended practiceSMAW Shielded metal arc weldingSMYS Specified minimum yield stressTIG Tungsten inert gas (welding)WM Weld metal or DepositWPQR Welding procedure qualification recordWPS Welding procedure specificationWPT Welding production test

a = size of test specimenb = size of test specimend = diameter of round tensile test specimendf = distance from the plane of the fatigue pre-crack

to the fusion linee = plastic deformationhT = test pressure heighthop1 = vertical distance from the load point to the posi-

tion of maximum filling heighths3 = vertical distance from the load point to the top of

the tankhp0 = height corresponding to valve opening pressure

when exceeding the general valuehop2 = vertical distance from the load point to the posi-

tion of maximum filling height. For tanks adja-cent to the sea that are situated below theextreme operational draught (TE), hop2 is notnormally to be taken as being less than TE

hD2 = pressure head due to flow through pipesle = equivalent parameter for conical shellslmin = breadth of test assembly plateslr = length of template or rodr = nominal radius of the shellra = actual distance from the centre of the sphere to

the shell wallre = equivalent parameter for conical shells

Table D1 AbbreviationsAbbreviation In fullDET NORSKE VERITAS

BM Base material

Offshore Standard DNV-OS-C401, January 2001Ch.1 Sec.1 Page 9D 500 Greek symbols501 The following Greek symbols are used:

ra = actual distance from the cylinder axis to the shellwall

s = distance between stiffeners or girderst = thicknesst1 = wall thickness of the greater tube (can)t2 = wall thickness of the smaller tube (brace)A = diameter used in wrap around bending testC = diameter of roller in bend testD = outside diameterD1 = outside diameter of the greater tube (can)D2 = outside diameter of the smaller tube (brace)KV = impact energy requirementLo = length of test area in test specimensLmin = length of test assembly platesN = number ofR = radius

Rc = forming radiusT = thickness of plate in bend testW = width of weld

= tubular joint angle = measure of deformation compared to theoretical ge-

ometryi = length of area with acceptable location of the fa-

tigue pre-crack = Poisson's ratio1 = largest compressive principal membrane stress2 = principal membrane stress normal to 1 = ratio between principal stresses.DET NORSKE VERITAS

Offshore Standard DNV-OS-C401, January 2001Page 10 Ch.1 Sec.1DET NORSKE VERITAS

OFFSHORE STANDARDDNV-OS-C401FABRICATION AND TESTING OF OFFSHORE STRUC-TURES

CHAPTER 2

TECHNICAL PROVISIONS

CONTENTS PAGE

Sec. 1 Welding Procedures and Qualification of Welders.................................................................. 13Sec. 2 Fabrication and Tolerances ...................................................................................................... 25Sec. 3 Testing of Welds ...................................................................................................................... 32Sec. 4 Other Tests ............................................................................................................................... 37Sec. 5 Corrosion Protection Systems .................................................................................................. 38Sec. 6 Miscellaneous........................................................................................................................... 39DET NORSKE VERITASVeritasveien 1, N-1322 Hvik, Norway Tel.: +47 67 57 99 00 Fax: +47 67 57 99 11

Offshore Standard DNV-OS-C401, January 2001Ch. 2 Sec.1 Page 13SECTION 1WELDING PROCEDURES AND QUALIFICATION OF WELDERS

A. GeneralA 100 Scope101 This section specifies requirements for welding proce-dures and welding procedure tests for C-Mn steel and low alloysteel, aluminium, austenitic stainless steels and ferritic-auste-nitic (duplex) stainless steels as well as qualification of weld-ers.

A 200 Welding processes201 Welding may be performed with the following processesunless otherwise specified:

manual metal arc welding (metal arc welding with coveredelectrode)

self-shielded tubular-cored arc welding submerged arc welding with one wire electrode submerged arc welding with strip electrode metal inert gas welding, (MIG) welding metal active gas welding, (MAG) welding tubular-cored metal arc welding with active gas shield tubular-cored metal arc welding with inert gas shield tungsten inert gas arc welding, (TIG) welding plasma arc welding.

B. Welding ProceduresB 100 General101 A welding procedure specification shall as a minimumcontain the following information as relevant for the weldingoperation:

material: standard, grade and modification nominal thickness or diameter range (dimensions) welding process joint or groove design with tolerances welding position(s) and direction of progression welding consumables: trade name, electrode or wire diam-

eter, shielding gas, flux and recognised classification welding sequence: number and order of passes or layers electrical parameters: voltage range, current range, polari-

ty travel speed- and heat input ranges preheat and interpass temperatures post weld heat treatment parameters details on cleaning processes employed and restrictions if

any.

B 200 Preliminary welding procedure specification,pWPS201 A pWPS shall be prepared for each new welding proce-

dure test. The pWPS shall specify the ranges for all relevantparameters.202 The pWPS shall be submitted for review and acceptanceby the purchaser prior to commencing the welding proceduretest.

B 300 Welding procedure qualification record, WPQR301 The WPQR shall be a record of the parameters used dur-ing the welding procedure test and subsequent non-destructive,destructive and corrosion test results. The WPQR shall be sub-mitted for review and acceptance prior to start of production.

B 400 Welding procedure specification, WPS401 A WPS is a specification based on a WPQR and shall beaccepted by purchaser in accordance with those requirements.The WPS shall be the pWPS revised to reflect the welding var-iables qualified by the welding procedure test.

B 500 Welding procedure tests501 When a welding procedure specification is required tobe qualified by welding procedure tests, the welding shall beperformed based upon the accepted pWPS and by applying thetype of welding equipment to be used during production weld-ing. The conditions shall be representative of the actual work-ing environment for the work shop or site where the productionwelding will be performed.

C. Welding Procedure Tests, C-Mn Steel andLow Alloy Steel

C 100 Butt welds on plates101 The test assembly may consist of two plates welded to-gether. As far as possible the plates shall have a size that cansimulate the heat transfer during the production welding. Formanual or semiautomatic welding, a test assembly accordingto Fig.1 shall be carried out with:

For automatic welding, the dimensions shall be:

Edge preparation and fit-up shall be as detailed in the pWPS.The plates shall be joined and held by tack welds to provide thecorrect gap for the edge preparation used. 50 mm of each endof the test piece shall be discarded.

lmin = 300 mmLmin = 350 mm

lmin = 400 mmLmin = 1000 mmDET NORSKE VERITAS

Offshore Standard DNV-OS-C401, January 2001Page 14 Ch. 2 Sec.1Figure 1Test assembly for butt welds on plates

102 NDT shall be carried out in accordance with the specifi-cation given for the production welding in question. The extentof the testing shall be as follows:

100% visual inspection 100% radiographic or ultrasonic testing 100% surface crack detection (dye penetrant or magnetic

particle testing).The soundness of the weld shall comply with requirementsgiven in Sec.3 C.103 The following mechanical tests are required from eachassembly (see Fig.2): 2 tensile tests (flat specimen transverse to the weld) 1 root and 1 face bend tests when t 20 mm and 2 side

bend tests when t > 20 mm 4 (6) sets of Charpy V-notch tests with the notch location

as given in 107 1 macrosection test (metallographic examination + hard-

ness measurements).104 Specimens for transverse tensile testing shall be in ac-cordance with G, type B.The tensile strength shall not be below the specified minimumtensile strength for the steel grade in question.

Figure 2Sampling of test specimens on plates

105 Transverse side bend, root bend and face bend speci-mens shall be machined to the dimensions shown in G300.For a mixed or heterogeneous butt joint longitudinal bend testspecimens may replace transverse bend test specimens.The test specimens shall be bent on a mandrel with diameter4 t, where t is the thickness of the specimen, except for extrahigh strength steel grades NV 550, NV 620 and NV 690 wherethe diameter shall be 5 t.The bending angle shall be at least 120. After bending, thetest specimens shall not reveal any open defects in any direc-tion greater than 3 mm. Defects appearing at the corners of atest specimen during testing may be ignored in the evaluation,if not associated with obvious defects.106 The macrosection shall include about 10 mm of unaf-fected base material and shall be prepared and etched on oneside to clearly reveal the fusion line and the HAZ. Cracks andlack of fusion are not accepted.The welded joints shall have a regular profile with smoothtransitions to the base materials and without significant or ex-cessive reinforcement.107 The Charpy V-notch specimens shall be machined in ac-cordance with the requirements given in DNV-OS-B101. Foursets of three specimens each shall be sampled 2 mm below thesurface of the parent material and transverse to the weld. 12Charpy V-notch specimens shall be localised in the weldedjoint as follows: 3 specimens with the notch along the weld metal cen-

trelineDET NORSKE VERITAS

3 specimens with the notch in the fusion line

Offshore Standard DNV-OS-C401, January 2001Ch. 2 Sec.1 Page 15 3 specimens with the notch in the HAZ, 2 mm from the fu-sion line

3 specimens with the notch in the HAZ, 5 mm from the fu-sion line.

The V-notch shall be perpendicular to the plate surface.For plate thickness t > 50 mm two additional sets of specimensshall be taken from the root area: one with the notch in centreof weld and one with the notch in the fusion line.For dissimilar metal joints and/or joints between cast or forgedand rolled materials, impact tests shall be carried out on testspecimens with notch in fusion line, 2 mm from fusion line and5 mm from fusion line in each parent material.The Charpy V-notch test temperature and the average value forabsorbed energy (KV) in weld metal, fusion line and HAZshall be the same as required for the base material in transversedirection (see DNV-OS-B101).For grades of improved weldability (see DNV-OS-B101), theCharpy V-notch test temperature and the average value for ab-sorbed energy in weld metal, fusion line and HAZ shall be thesame as required for the base material of the comparable nor-mal weldability grade in transverse direction.For ship-shaped units, the requirements given by the Rules forClassification of Ships Pt.2 Ch.3 Sec.2 B308 may be appliedas an alternative.108 In the case of reduced Charpy V-notch test specimens(10 mm x 7.5 mm and 10 mm x 5 mm), the impact energy val-ues to be obtained shall satisfy the requirements in Table C1.

109 The average impact requirements shall be satisfied foreach notch location, but one single value of three values fromspecimens from the same notch location may be below the av-erage requirements, but not below 70% of minimum average.110 Where the results from a set of three impact test speci-mens do not comply with the requirements, an additional set ofthree impact test specimens may be taken.The results obtained shall be combined with the original resultsto form a new average, which, for acceptance, shall be not lessthan the required value. Additionally, for these combined re-sults not more than two individual values shall be less than therequired average value, and of these, not more than one shallbe less than 70% of the average value.When the result of any test, other than impact test, fails to meetthe requirements, two further tests may be made from the samewelded joint. If both these additional tests are satisfactory, thetest is acceptable.111 The hardness testing shall be in accordance with ISO6507-1 or equivalent. The Vickers method (HV10) shall beused.Indentations shall be made along traverses in the weld, HAZand the parent metal approximately 1 mm below the surface.For each traverse a minimum of 3 indentations shall be madein the weld, HAZ (both sides) and parent metal (both sides).For HAZ the first indentation shall be placed as close to the fu-sion line as possible. For double sided welds, for fillet and T-butt welds one additional row of indentations shall be madethrough the root area.For material grades up to and including NV 460, a maximumhardness limit of 350 HV10 shall be met for welds in sub-merged structures exposed to cathodic protection. Hardness

Guidance note:For NV 500, NV 550, NV 620 and NV 690 grades a maximumhardness limit of 420 HV10 is recommended for welds in sub-merged structures exposed to cathodic protection.

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112 When a butt weld is made between two different materi-al grades, the test temperature and achieved impact energyshall comply with the minimum specified requirements for thelower steel grade.In the same way, the tensile strength to be obtained on thewelded assembly shall be in agreement with the requirementsrelating to the plate steel having the lower strength.As an example the test temperature, impact energy and tensilestrength for the butt welded joints given in Fig.3 are those re-quired for the plate of grade D in the left assembly and for theplate of grade E in the right assembly.

Figure 3Butt welded plate joints of different grades

C 200 Butt welds on tubes201 The test assembly shall be in accordance with Fig.4.

Figure 4Test assembly for butt welds on tubes

202 NDT shall be carried out in accordance with the specifi-cation given for the production welding in question. The extentof the testing shall be as follows:

Table C1 Impact energy requirement for sub-size specimensDimensions of Charpy V-notch test specimen Impact energy10 x 10 mm KV10 x 7.5 mm 5/6 KV10 x 5 mm 2/3 KV

a = minimum value 150 mmD = outside diameterDET NORSKE VERITAS

limits for higher grades shall be subject to agreement. 100% visual inspection

Offshore Standard DNV-OS-C401, January 2001Page 16 Ch. 2 Sec.1 100% radiographic or ultrasonic testing 100% surface crack detection (dye penetrant or magnetic

particle testing).The soundness of the weld shall comply with requirementsgiven in Sec.3 C.203 The following mechanical tests are required from eachassembly (see Fig.5): 2 tensile tests (flat specimen transverse to the weld) 1 root and 1 face bend tests when t 20 mm and 2 side

bend tests when t > 20 mm 4 (6) sets of Charpy V-notch tests with the notch location

as given in 107 macrosection test (metallographic examination + hardness

measurements).

Figure 5Sampling of test specimens on tubes

204 The results of mechanical testing shall comply with therelevant requirements given in C100.

C 300 Full penetration T-, Y-, and K- joints301 WPQT's for full penetration groove welds betweenplates at right angles or inclined, i.e. T- or Y- and K- configu-rations, shall cover a weld length of minimum 350 mm (seeFig.6).302 NDT shall be carried out in accordance with the specifi-cation given for the production welding in question. The extentof the testing shall be as follows:

100% visual inspection 100% ultrasonic testing 100% surface crack detection (dye penetrant or magnetic

particle testing).The soundness of the weld shall comply with requirementsgiven in Sec.3 C.

Figure 6Test assembly for full penetration T-joints

303 The following mechanical tests are required from eachassembly (see Fig.7): 4 (6) sets of Charpy V-notch tests with the notch location

as given in 107 macrosection test (metallographic examination + hardness

measurements).The results of mechanical testing shall comply with the rele-vant requirements given in C100.

Figure 7Sampling of test specimens on full penetration T-joints

C 400 Tubular joints401 The test assembly shall be in accordance with Fig.8.402 NDT shall be carried out in accordance with the specifi-cation given for the production welding in question. The extentof the testing shall be as follows:

100% visual inspection 100% ultrasonic testing 100% surface crack detection (dye penetrant or magnetic

particle testing).

a = 3 t, minimum value 150 mmb = 6 t, minimum value 350 mmDET NORSKE VERITAS

The soundness of the weld shall comply with requirements

Offshore Standard DNV-OS-C401, January 2001Ch. 2 Sec.1 Page 17given in Sec.3 C.

Figure 8Test assembly for tubular joints

403 The following mechanical tests are required from eachassembly (see Fig.9): Charpy V-notch tests sampled at 9 o'clock and with the

notch location as given in 107 two macrosection tests (metallographic examination +

hardness measurements) at 12 and 6 o'clock.404 The results of mechanical testing shall comply with therelevant requirements given in C100.405 Restrictions and testing for joint configuration involvingacute angles (less than 15) should be specified. AWS D1.1 isa good reference for structural welds.

C 500 Fillet welds501 The two plates are assembled and positioned edgewiseso as to constitute a tee-assembly with no clearance. As far aspossible the plates shall be of a sufficient size to ensure a rea-sonable heat distribution.For fillet welds the test assembly shall be as defined in Fig.9.

Figure 9

For manual and semi-automatic welding the length of the testpiece shall be:

For automatic welding the length shall be:

Weld and fit-up shall be as detailed in the pWPS.The test assembly shall be welded on one side only. For man-ual and semi-automatic welding, the stop and restart positionshall be included in the test length and shall be clearly markedfor subsequent examination.The ends of the specimen are exempted from examination overa length of 50 mm.502 NDT shall be carried out in accordance with the specifi-cation given for the production welding in question. The extentof the testing shall be as follows:

100% visual inspection 100% surface crack detection (dye penetrant or magnetic

particle testing).The soundness of the weld shall comply with the specified re-quirements given in Sec.3 C.If the stop and restart spot is included in the test length, specialattention shall be paid to this position with respect to profile,proper fusion and absence of crater defects.503 The following tests shall be performed:

two macrosection tests (metallographic examination,hardness measurements).

One of the macrosections shall be taken at the marked positionof the stop and restart (for more details see 106).For hardness testing, see 111.

C 600 Re-testing601 If the welding procedure test fails to comply with any ofthe requirements for NDT one extra test shall be welded andsubjected to the same testing. If this additional test does notmeet the relevant requirements, the actual pWPS shall be con-sidered as not qualified and a re-specification of the pWPSshall be made prior to a new welding procedure test.

C 700 Validity of qualified welding procedures701 The validity of a qualified welding procedure shall be re-stricted to the workshop or work site performing the qualifica-tion. Workshops, work site or workshop branches under thesame technical management and working in accordance withthe same QA-program and -procedures are considered as oneworkshop or work site.702 Qualification of a welding procedure remains valid pro-vided the parameters are kept within the qualified ranges of es-sential variable during production welding. The essentialvariables and qualified ranges are given in 703. When varia-tions outside the qualification ranges of essential variables oc-cur, the welding procedure qualification shall be consideredinvalid, and the WPS shall therefore be re-specified and re-qualified.703 A qualified welding procedure shall be used within theranges of the parameters of essential variables listed below.Base materialThe following changes shall lead to a new qualification:

a) In general, significant change of material properties whichwill obviously affect the weldability and mechanical prop-

a = minimum value 150 mmD1 = outside diameter of the greater tubular (can)t1 = wall thickness of the canD2 = outside diameter of the smaller tube (brace)t2 = wall thickness of the brace

Lmin = 350 mm

Lmin = 1000 mmDET NORSKE VERITAS

Test assembly for fillet welds erties.

Offshore Standard DNV-OS-C401, January 2001Page 18 Ch. 2 Sec.1Guidance note:When qualifying a welding procedure, it is recommended to usespecified material with highest carbon equivalent (CE) availablein the workshop or work site, especially when the thickness islarge.


b) More specifically, structural steels of both normal and im-proved weldability are grouped in three strength groups:

i) Normal strength steel, grades A, B, D and E or equiv-alent structural steels with tensile strength 400 to 520N/mm2.

ii) High strength steel, grades A 27, D 27, E 27, A 32, D32, E 32, F 32, A 36, D 36, E 36, F 36, A 40, D 40, E40, F 40 or equivalent structural steels with minimumspecified yield strength 265 to 390 N/mm2.

iii) Extra high strength steels, grades A-F 420, A-F 460,A-F 500, A-F 550, A-F 620, A-F 690 or equivalentstructural steels with minimum specified yieldstrength 420 to 690 N/mm2.

The qualification on steel grades of higher toughness require-ments will qualify the grades of lower toughness but not viceversa.

704 Thickness, is defined as follows:

a) For a butt weld:The base metal thickness, which for welds between dis-similar thickness is that of the thinner material.

b) For a fillet weld:The base metal thickness, which for welds between dis-similar thickness is that of the thicker material. However,for each thickness range qualified, as given in Table C2there is an associated range of qualified throat thickness.

c) For a set-on tubular joint:The thickness of the brace.

d) For a set-in or set-through tubular joint:The thickness of the can.

e) For a T-butt joint in plate:The thickness of the prepared plate (abutting member).

The requirements for qualified thickness range for butt weldsshall be as given in Table C2.

The requirements for qualified thickness range for single runfillet welds are in addition to the requirements of Table C2, thatthe throat thickness, tw, shall be in the range 0.75 tw to 1.5 tw.However, a test with a throat thickness 10 mm shall givequalification for all throat thicknesses 10 mm.Where a fillet weld is qualified by means of a butt weld test,the throat thickness range qualified shall be based on the thick-

ness of the deposited weld metal.Diameter of tubes and tubular jointsThe qualification of a welding procedure test on diameter Dshall include qualification for diameters in the following rang-es as given in Table C3.

Angle of tubular jointsA welding procedure test carried out on a tubular joint with an-gle shall qualify all tubular joint angles in the range of to90.Welding consumablesThe following changes shall lead to a new qualification:

any change in consumable classification change of consumable brand when impact testing is re-

quired at temperatures below 20C any significant change of mixture or composition (e.g.

change from argon or mixed gas to CO2 gas), flow rate,filling time and filling volume for shielding and purginggases.

Welding positionsThe following changes shall lead to a new qualification.

Change from one principal welding position (see Fig.10,Fig.11 and Fig.12) to another, unless complying with Ta-ble C4.

Figure 10Plate test positions

Table C2 Qualified thickness rangeThickness t in

mm of test pieceQualification range 1)

for single run or singlerun from both sides

for multi-run weldingand all fillet welds

t 12 0.8 t to 1.1 t up to 2 t12 < t 100 0.8 t to 1.1 t 0.5 t to 2 t

(maximum 150)t > 100 - 0.5 t to 1.5 t

1) The qualification range for vertical downward position is 0.5 t to 1.1 t

Table C3 Qualified range for tube and tubular jointDiameter of the test piece D

(mm) 1) 2)Qualification range

D < 168.3 0.5 D to 2 DD 168 0.5 D and plates

1) D is the outside diameter of the tube or outside diameter of the brace2) Qualification given for plates also covers tubes when the outside diam-

eter is greater than 500 mmDET NORSKE VERITAS

Offshore Standard DNV-OS-C401, January 2001Ch. 2 Sec.1 Page 19Figure 11Pipe test positions

Type of jointThe following changes shall lead to a new qualification:

change from fillet weld to butt weld change from two sided welding to one side (but not con-

verse) deletion of back gouging deletion of backing in cases where the backing material is

equivalent to the base material addition or deletion of ceramic (temporary) backing change from T-, Y- or K-joint to butt joint change from butt joint on plate to butt joint on tubular with

outside diameter less than 500 mm change of specified type of groove, root face and gap,

which may significantly affect penetration, fusion and de-lution of the weld.

Welding conditionThe following changes shall lead to a new qualification:

any change of welding process change from weaving to stringer bead technique or con-

verse change from multi-run welding to one-run welding change of type of welding current from A.C. to D.C. or

converse or change of polarity. For SMAW only, the cur-rent may be changed from A.C. to D.C. if recommendedby the electrode manufacturer

change in metal powder or wire addition beyond 10% change from spray arc to short arc or pulsed arc or vice

versa change beyond 25% in heat input any decrease in preheating temperature and any increase in

interpass temperature beyond 250C change of post weld heat treatment parameters except for

holding time, which may be adjusted as a function ofthickness.

Figure 12Positions of test plate for fillet welds

D. Welding Procedure Tests, AluminiumD 100 General101 Qualified welding procedures are required for all impor-tant structural joints. The procedure tests shall be representa-tive of the following:

the thickness and diameter range in question (see Table C2and Table C3)

each type of consumable and welding process welding position (see Table D1) joint and groove design number of passes preheat (if any)

Table C4 Qualified principal positions for butt welds and fillet welds, steel

Test weldJoint configuration 1)2) Principal positions

Qualified positions 3)Butt welds Fillet weldsPlates or tubes

Plates TubesButt welds on plates 2G + 3G1G2G3G4G All1G1G, 2G, 4G3G1G,

4GAll1G1G, 2GNot

applicable1GAll1F1F, 2F, 4F3F1F, 4F

Butt welds in tubes 2G + 5G = 6G1G2G5G All1G1G, 2G, 4GAll All1G1G, 2G1G, 5G All1F1F, 2F, 4FAllFillet welds 2F + 3F1F2F3F4F5F All1F1F, 2F, 4F3F1F, 2F,

4FAll1) Tubes with D > 500 mm are considered equivalent to plates (apply only to the can in tubular joints)2) Tubular joints shall be qualified separately3) The vertical downwards position shall be qualified separatelyDET NORSKE VERITAS

each base material or alloy and temper used in production volt-ampere characteristics

Offshore Standard DNV-OS-C401, January 2001Page 20 Ch. 2 Sec.1 shielding gas.

D 200 Butt welds201 Each test assembly consists of 2 plates with dimensions300 x 150 mm. The plates shall be joined with a longitudinalbutt weld. For extruded sections and pipes the assembly shallconsist of 2 sections each 150 mm long (see Fig.13 andFig.14).202 Weld and fit-up shall be as detailed in the pWPS. Weld-

ing consumables are those recommended in Table D2.203 If back-sealing run is specified, this run shall be laid inthe same position as for the respective weld.204 The welds shall be subjected to visual inspection, dyepenetrant testing and ultrasonic- or X-ray testing. The require-ments for quality level for imperfections shall be as given inISO 10042 level B.

205 Side-bend tests shall be carried out for thickness equal toand above 10 mm. Two bend specimens shall be taken fromeach of the welded assemblies.

Figure 13Location of test specimens for a butt weld on plate

206 For thickness below 10 mm one face bend and one rootbend test specimens shall be taken. The width shall be 30 mmand the thickness equal to the plate thickness. The diameter ofthe bending mandrel shall be as given in Table D3.

207 RequirementNo cracks or open defects exceeding 3 mm measured on theconvex surface after bending are accepted. Smaller cracks de-veloping from the edges of the specimens should not be con-sidered as significant, unless there is definite evidence thatthey result from inclusions or other defects.Wrap aroundbending as shown in Fig.15 is the preferred bending method.

Table D1 Qualified principal positions for butt welds and fillet welds, aluminiumTest weldJoint configuration Principal positions

Qualified positions1)Butt welds, plates Butt welds, tubes Fillet welds

Butt welds on plates 1G2G3G4G 1G1G, 2G, 3G1G, 2G,3GAll1G 1F1F, 2F, 3F1F, 2F, 3FAll

Butt welds in tubes 1G2G5G 1G1G, 2G, 3GAll 1G2G1G, 5G 1F1F, 2F, 3FAll

Fillet welds 1F2F3F4F5F 1F1F, 2F, 3F1F, 2F,3FAllAll1) The vertical downward position shall be qualified separately.

Table D2 Selection of suitable consumables for combinations of aluminium alloysBase metal alloy NV-5052, NV-5754 NV-5154,NV-

5454 NV-5086NV-5083NV-5383 NV-6060, NV-6061 NV-6063, NV-

6005A NV-6082NV-5052, NV-5754 NV-5154,

NV-5454 NV-5086 5356, 5556, 5183 5356, 5556, 5183 5356, 5556, 5183

NV-5083, NV-5383 5356, 5556, 5183 5183 1) 5356, 5556, 5183NV-6060, NV-6061 NV-6063,

NV-6005A NV-6082 5356, 5556, 5183 5356, 5556, 5183 5356, 5556, 5183

Note:All consumables are covered by the AWS specification. The prefix ER is omitted.

1) Other consumables may be used if allowable stresses are reduced.

Table D3 Former diameter for bend tests

Base metal alloyCondition

0, H111 H116, H32,H321, H34 T4 T5, T6

NV-5052, NV-5754NV-5154, NV-5454 4t 4t - -

NV-5086, NV-5083,NV-5383 6t 6t - -

NV-6060, NV-6061NV-6063, NV-6005ANV-6082

- - 6t 7tDET NORSKE VERITAS

Offshore Standard DNV-OS-C401, January 2001Ch. 2 Sec.1 Page 21Figure 14Location of test specimens for a butt weld in pipe

Figure 15Wrap around bending

208 One tensile specimen shall be taken from each of thewelded assemblies. The test specimen, 25 mm wide and withfull plate thickness and orientated transverse to the weld, isshown in Fig.16.

Figure 16Tensile test specimen

209 The tensile strength of the test specimens shall not beless than specified for the parent alloy in Table D4.210 One macrosection shall be prepared from the test assem-bly to reveal the weldment macro structure. The macrosection

shall be visually inspected using a magnification of 5 to 10X.The macrosection shall show a regular weld profile with asmooth transition to the base material without significant un-dercut or excessive reinforcement and show thorough fusionbetween adjacent layers of weld metal and base metal. Thereshall be no cracks, lack of fusion and incomplete penetration.

D 300 Fillet welds301 The two plates are assembled and positioned edgewiseso as to constitute a tee-assembly with no clearance. As far aspossible the plates shall be of a sufficient size to ensure a rea-sonable heat distribution.For fillet welds the test assembly shall be as defined in Fig.9.For manual and semi-automatic welding the length of the testpiece shall be:

For automatic welding the length shall be:

Weld and fit-up shall be as detailed in the pWPS.The test assembly shall be welded on one side only. For man-ual and semi-automatic welding, the stop and restart positionshould be included in the test length and shall be clearlymarked for subsequent examination.The ends of the specimen are exempted from examination overa length of 50 mm.302 NDT shall be carried out in accordance with the specifi-cation given for the production welding in question. The extentof the testing shall be as follows:

100% visual inspection 100% surface crack detection (dye penetrant).The soundness of the weld shall comply with ISO 10042 levelB.If the stop and restart spot is included in the test length, specialattention shall be paid to this position with respect to profile,proper fusion and absence of crater defects.303 The following tests shall be performed:

two macrosection tests (metallographic examination).One of the macrosections shall be taken at the marked positionof the stop and restart (for more details see C106).D 400 Re-testing401 If any of the tests do not satisfy the specified require-ments, new procedure tests in duplicate may be carried out.The results of both re-tests shall meet the specified require-ments, otherwise the test shall be rejected.

Guidance note:HAZ softening adjacent to weldsThe strength of a weldment is a function of the welding process,filler metal and the aluminium alloy in question. For design pur-poses it is assumed that the strength is reduced in HAZ. The ex-tent of the HAZ is assumed to have the same width as theweldment plus the plate thickness in each direction of the weld asshown in Fig.17.If the strength shall be measured for information, this shall becarried out on a gauge length 2 t + W of the weld (approximately3 t).

lmin = 300 mmLmin = 350 mm

lmin = 400 mmLmin = 1000 mmDET NORSKE VERITAS

Offshore Standard DNV-OS-C401, January 2001Page 22 Ch. 2 Sec.1Figure 17Extent of HAZ


E. Welding Procedure Tests, Stainless SteelE 100 General101 When welding procedure tests are required, the testsshall be performed in accordance with C and the supplementa-ry requirements stated in D200 and D300 (if not otherwisespecified herein).102 The welding procedure tests shall cover all relevant di-mensions, positions and material combinations. Details re-garding essential variables and validity of the procedure shallbe as described in C. Mechanical testing shall be as describedin C100, if not otherwise specified in D200 and D300.

E 200 Supplementary requirements for austenitic stain-less steel201 Impact testing is not required for design temperaturesabove 105C. If used at below 105C, the test temperatureshall be at minimum design temperature.202 If impact testing is required, the average impact valuefor the three specimens shall not be less than 34 J.203 When a butt weld is made between dissimilar materialgrades, both sides of the weld shall be impact tested.

E 300 Supplementary requirements for ferritic-auste-nitic stainless steel301 Impact testing shall be carried out at design temperatureor 20C, whichever is the lower. The average impact valuefor the three specimens shall not be less than 27 J.

grades, both sides of the weld shall be impact tested.303 Butt welds and fillet welds shall be corrosion tested ac-cording to ASTM G48, Method A. The test specimen shall bein the as welded state after normal weld cleaning operation.The test specimens shall be exposed to the solution at a con-stant temperature of 20C for 24 hours.The following test requirements shall be fulfilled:

no pitting attack shall be visible on the test face(s) general weight loss shall not be less than 4 g/m2.

Guidance note:Welds between ferritic-austenitic stainless steels and C- and C-Mn steels need not be subjected to corrosion test.


304 A microstructural examination comprising the weldmetal, heat affected zone and base metal is required for eachwelded assembly. The microstructure shall be suitably etchedand examined at 400X magnification and shall be free fromgrain boundary carbides and precipitates. The ferrite content inthe weld metal root and not re-heated weld cap shall be deter-mined in accordance with ASTM E562 and shall be in therange of 25 to 70%.

F. Qualification of WeldersF 100 General

t = Plate thicknessW With of weld

Table D4 Mechanical properties in the welded condition

Alloy Temper FillerTensile strength

Rm, minimum(N/mm2)Yield stress

in HAZ, Rp0,2 minimum(N/mm2)NV-50520 F, H111H32, H34 5356 170 65NV-5754 0, F, H111, H24 5356-5183 190 80

NV-5154A 0, H111 5356-5183 215 85NV-5454 0, F, H111, H34 5356-5183 215 85NV-5086 0, F, H111,H116, H32,

H345356-5183 240 100

NV-5083 0, F t < 6 mm0, F t > 6mmH116, H321H116,

H321

51835356-518353565183 270270270270 125115115125

NV-5383 0, H111, H116,H321 5183 290 140NV-6060 T5 5356-5183 95 65NV-6061 T4T5 or T6 5356-5183 165165 115115NV-6063 T5T6 5356-5183 100100 6565

NV-6005A T5 or T6 5356-5183 165 115NV-6082 T4T5 or T6 5356-5183 170170 110115DET NORSKE VERITAS

302 When a butt weld is made between dissimilar material 101 The welding processes for which qualifications are re-

Offshore Standard DNV-OS-C401, January 2001Ch. 2 Sec.1 Page 23quired include those which are designated as manual or partlymechanised welding. Welders shall pass a qualification test inaccordance with 200. Contractors are required to keep recordsof the welders' qualifications and, when required, furnish cop-ies of valid welders' certificates.

F 200 Standards for qualification testing201 Welders shall be tested according to a recognised stand-ard, e.g. EN 287, ISO 9606, ASME Section IX or ANSI/AWSD1.1.202 Welding operators using fully mechanised or fully auto-matic processes need generally not pass a qualification test.However, operators shall receive adequate training in settingor programming and operating the equipment. Appropriaterecords of training shall be maintained. Contractors may be re-quired to furnish valid qualification test certificates. EN 1418may be used as a reference.

G. TestingG 100 General101 Testing of welds shall be carried out as specified in 200to 300.

G 200 Tensile testing at ambient temperature201 For tensile testing of all-weld-metal and butt welds twodifferent types of test specimens may be used, round test spec-imens or flat test specimens (see Fig.18) as described below:A - Deposited metal tensile testNormally, round test specimens with the following dimensionsshall be used:

B - Butt weld tensile test for testing of the weld as a wholeFlat test specimens with the weld machined flush with the sur-face of the plate, shall be used. The dimensions shall be as fol-lows:

C - Butt weld tensile testFlat test specimens with the weld machined flush with the sur-face of the plate, shall be used. The dimensions shall be as fol-lows:

Figure 18Tensile test specimen

G 300 Bend testing301 Flat bend test specimens, as given in Fig.19 shall beused. Edges on tension side shall be rounded to a radius of 1 to2 mm.

Figure 19Bend test specimen

Figure 20Wrap around bend test

302 When the wrap around bend test, exemplified Fig.20 isused, e.g. for the side bend test of a weld, the length of the testspecimen shall be greater than the length 11a shown in Fig.19.303 For butt weld bend test specimens, the weld shall be ma-chined flush with the surface of the plate.304 For transverse face-bend and root-bend test specimensfor butt weld test the dimensions shall be as follows:

If the as rolled thickness t is greater than 25 mm, it may be re-duced to 25 mm by machining on the compression side of the

d = 10 mmLo = 50 mmLc = 60 mmR 5 mm

a = thickness of plate, tb = 25 mmL0 = LC = 3 t or 2 t + width of weld, whichever is the

greatestR = 25 mm

a = thickness of plate, tb = 30 mmLo = 6 mm + width of weld + 6 mmR = 50 mm

a = as rolled thickness t of the plateb = 30 mmDET NORSKE VERITAS

test specimen.

Offshore Standard DNV-OS-C401, January 2001Page 24 Ch. 2 Sec.1305 For transverse side-bend test specimens for butt weldtest the dimensions shall be as follows:

If t 40 mm, the side-bend test specimen may be subdivided,each part being at least 20 mm wide.306 When a longitudinal face-bend or root-bend weld test isrequired, a test specimen according to an appropriate standardwill be accepted.

a = 10 mmb = as rolled thickness t of the plateDET NORSKE VERITAS

Offshore Standard DNV-OS-C401, January 2001Ch. 2 Sec.2 Page 25SECTION 2FABRICATION AND TOLERANCES

A. GeneralA 100 Objective and scope101 This section gives requirements for fabrication and tol-erances of offshore structures.

B. Fabrication PlanningB 100 General101 As a prerequisite for fabrication, procedures, inspectionand test plans and work instructions for execution and controlof fabrication activities shall be established. The purpose of theprocedures and work instruction shall be:

to provide instructions and information regarding the re-quirements for and the principles of the work execution

to identify and document the responsibilities and plans forthe work execution in accordance with the project require-ments

to provide information to the purchaser on how the workis executed and controlled

to identify applicable procedures, test plans, work instruc-tions, acceptance criteria, hold points and documents to begenerated

to serve as basis for quality audits.

102 Relevant procedures, including information of pre-as-sembled items and the sequence of fabricating the parts intostructure, shall be prepared.

B 200 Quality system and workmanship201 Fabrication of structural members shall have a docu-mented and implemented quality system according to ISO9001 or equivalent. The extent of the quality management sys-tem shall be dependent on the size and type of the organisation,complexity and interaction of the processes and competence ofpersonnel.202 Workmanship shall be in accordance with E followingwritten procedures agreed upon.203 All work shall be skilfully and carefully executed withadequate control by the contractor. All faults and deficienciesshall be corrected before the material is coated with paints, ce-ment or similar. Repair work of significant extent shall bedemonstrated as acceptable to the purchaser.204 Prior to commencement of the work the contractor shallsubmit a plan for NDT, NDT procedures and documents forNDT inspectors certification for acceptance by the purchaser.The programme shall contain information and documents forplanning, controlling, reporting etc. Acceptance criteria forNDT shall be accepted by the purchaser if they are not speci-fied in relevant documents.

C. InspectionC 100 General101 Inspection shall be carried out in accordance with ac-cepted inspection and test plans to confirm that work is carriedout in accordance with established project procedures andplans such that all project requirements are complied with tothe satisfaction of the purchaser.

correct identification and documentation and use of mate-rials

qualification and acceptance of fabrication procedures andpersonnel

inspection of preparatory work (assembly, fit-up formwork, reinforcement etc.)

welding inspection inspection of fabrication work for compliance with speci-

fications and procedures witnessing NDT, control and testing inspection of repairs inspection of corrosion protection systems ensure functionality of examination or testing equipment

and of recording and/or measuring devices vital for correctfunctioning of equipment and machinery used in fabrica-tion.

102 Due consideration shall be given to the access and thetime required for adequate inspection during fabrication.103 High non-conformance rates in execution of the work orin the product itself shall call for special considerations. Suchspecial considerations may include, but not be limited to, in-creased inspection, re-qualification of personnel or otheragreed remedial actions.104 Inspectors shall be qualified according to a recognisedscheme and shall be able to provide documentation of profi-ciency.

D. Material Identification, Cutting and FormingD 100 Material identification101 A traceability system that ensures correct installationand documentation of the material grades or strength classesshall be established by the contractor throughout the prefabri-cation and installation process.Proper care shall be exercised during handling and storage topreserve identification of such material.

D 200 Cutting and forming201 The effect of work hardening shall be considered ifshearing is used for cutting of material. Special attention shallbe paid to the risk of cracked edges.202 Attention shall be paid to excessive local hardening andcarbon contaminations by thermal cutting. This may be re-duced by suitable heat treatment or removed by mechanicalmeans.

203 Forming and straightening of materials shall be per-formed according to procedures outlining the successive andcontrolled steps. Such procedures shall be controlled by in-spection.204 The degree of cold deformation of special and primarystructural elements shall be less than 5%. If the deformationexceeds 5%, either heat treatment or strain ageing tests shall becarried out according to an agreed procedure.

Guidance note:The plastic deformation e may be calculated by the following,simplified formulae:Single-curvature deformationCold rolling or pressing of plates to cylindrical forms:

et----100%=DET NORSKE VERITAS

The inspection shall cover items such as: D

Offshore Standard DNV-OS-C401, January 2001Page 26 Ch. 2 Sec.2Cold bending of straight pipes to bends:

Double curvature deformationForming of plates to spheres:


E. TolerancesE 100 Misalignments101 Allowable misalignment depends on extent of misalign-ment, stress level and type of loading as well as type and im-portance of the joint. See also DNV-RP-C203 Sec. 2.5.102 The maximum misalignments shall not exceed the val-ues given as standard values in IACS Shipbuilding and RepairQuality Standard, Part A Sec 7 without special consideration.Primary and Special is regarded as strength members andSecondary is regarded as other in the IACS Shipbuilding andRepair Quality Standard. Separate requirement to misalign-ment of non-continuos plates in special areas are given in 103.103 Misalignment of the non-continuous plates in cruciformjoints is not to exceed the values given in Fig.1 and Table E1.

Figure 1Alignment of cruciform joint

E 200 Fairness and straightness201 The tolerances shall not exceed the requirements givenas the standard values in IACS Shipbuilding and Repair Qual-ity Standard, Part A Sec.6 without special consideration.202 For compression members, the straightness of membersshall be in accordance with the buckling code applied in codecheck.203 Tolerances for compression members which are basedon calculations according to DNV Classification Note 30.1 orDNV RP-C202 shall not exceed the values given in Table E2.The buckling strength of a fabricated structure with larger im-perfections may be determined by use of the actually measuredimperfection.For ship shaped units complying with DNV-OS-C102, accept-able tolerances are given in IACS Shipbuilding and RepairQuality Standard.

t = material thicknessD = outside diameter of pipe or vesselRc = forming radius = Poisson's ratio (0.5 for plastic condition).

eD

2Rc---------100%=

et l v+( )

2Rc-----------------100%=

Table E1 Misalignment aStructural category Maximum misalignmentSpecial 0.15 t1Primary 0.33 t1Secondary 0.5 t1t1 is the smaller thickness of t1, t2 and t3DET NORSKE VERITAS

Offshore Standard DNV-OS-C401, January 2001Ch. 2 Sec.2 Page 27Table E2 Tolerances for compression membersDetail Tolerance Fig. CommentsBars and frames Max. out of straightness

= 0.0015 ll = unsupported length

Pillars, vertical col-umns

Max. inclination = 0.001 l

l = unsupported length

Stiffened plane plates.Stiffener or girderwebs relative to theplate plane.

Max. out of straightness = 0.0015 l

l = Unsupported length of thestiffener or girder

Stiffened plane plates.Stiffener or girderflanges relative to theweb plate


l = Unsupported length of theflange

Stiffened plane plates.Parallel stiffeners orgirders

Max. misalignment = 0.02 s

s = distance between parallelstiffeners or girders

Stiffened plane plates.Plates between stiff-eners or girders.

Max. out of plane displace-ment = 0.005 s

s = unsupported width of theplate panelDET NORSKE VERITAS

Offshore Standard DNV-OS-C401, January 2001Page 28 Ch. 2 Sec.2Circular cylindricalshells.

Max. deviation from thenominal radius measured atringstiffener or bulkhead = (ra - r) = 0.005 r

ra = actual distance from thecylinder axis to the shellwall.r = nominal radius of theshell

Circular cylindricalshells.Longitudinalstiffeners or girders.

Max out of straightness = 0.0015 l

l = Unsupported length of thestiffener or girder.

Circular cylindricalshells.Flanges of lon-gitudinal stiffeners orgirder webs.


l = Unsupported length of theflange

Circular cylindricalshells.Longitudinalstiffeners.

Max. misalignment = 0.02 s

s = stiffener spacing

Circular cylindricalshells.Local out ofroundness.Local outof straightness.

Max. imperfection A circular template or straightrod held anywhere on theshell.g = length of template orrod.The length of the circulartemplate shall be the smallestof:s, and s= stiffener spacing (of longi-tudinal stiffeners)l = distancebetween rings or bulk-headThe length of the straightrod shall be taken equal to thesmallest of:l and .

Conical shells The tolerance requirementsgiven for cylindrical shells areapplicable also for conicalshells.

Table E2 Tolerances for compression members (Continued)Detail Tolerance Fig. Comments

0.01g1 g r+-------------------=

1.15 l rt r2---

4 rtDET NORSKE VERITAS

Offshore Standard DNV-OS-C401, January 2001Ch. 2 Sec.2 Page 29F. Assembly, Welding, Heat Treatment andRepairs

F 100 Assembly and welding101 A fabrication sequence shall be established to ensurethat the structure can be assembled in a manner that allows forcontinuous inspection and control during all stages of thework.102 The welding sequence shall be such that the amount ofshrinkage, distortions and residual stresses are minimised.103 For butt welded joints of plates subjected to dynamicloading with thickness difference exceeding 4 mm, the thickerplate is normally to be tapered. The taper is generally not to ex-ceed 1:4. See Fig.2.

Figure 2Tapering of butt joints

104 All butt- and full penetration joints should be weldedfrom both sides. Before welding is carried out from the secondside, unsound weld metal shall be removed at the root by a suit-able method.105 Tubular members framing into joints shall be carefullycontoured to obtain accurate alignment. The bevel shall beformed providing a continuous transition from maximum tominimum bevel angle around the circumference. Generally,the fabrication shall be planned in such a manner that backwelding can be performed to the largest extent possible.106 Members to be welded shall be brought into correctalignment and held in position by clamps, other suitable devic-es or by tack welds until welding has been completed or pro-gressed to a stage where the holding devices or tack welds canbe removed without danger of distortion, shrinkage or crack-ing. Suitable allowances shall be made for distortion andshrinkage where appropriate.107 The use of permanent steel backing strips may be per-mitted after thorough corrosion evaluation and when properlyaccounted for in the design analysis.108 Corners of cut-outs shall be given appropriate radii min-imising local stress concentrations. Where temporary cut-outsare made, such cut-outs shall be made of sufficient size to al-low sound replacement.109 The fit-up shall be checked for dimensional accuracy be-fore welding. Surfaces to be welded shall be free from millscale, slag, rust, grease, paint etc. Edges are to have a smoothand uniform surface. No welding shall be performed when thesurfaces are damp. Suitable protection shall be arranged whenwelding is performed during inclement weather conditions.The groove shall be dry at the time of welding and at a temper-ature of at least + 5C.110 Preheating shall preferably be performed with electricheating elements. Gas burners may be used under controlled

111 A WPS shall be established for welds in special areas,primary structural elements and butt welds in secondary struc-tural elements.112 Welding procedures are qualified for fabrication if satis-factory compliance with requirements is established by one ofthe following methods:

performing of welding procedure tests and subsequent re-view of the welding procedure qualification records

review of previously qualified welding procedure tests review of WPS review and verification of documentation showing suc-

cessful application of welding procedures over a pro-longed period of time.

113 Qualified welding procedures (see 112) are required forall production welding of:

special areas primary structural elements.

114 Tack welding incorporated in the production weldingshall be qualified. Independent of structural importance weld-ing procedures shall be qualified for:

new welding methods high heat input welding methods (e.g. electrogas, electro-

slag, triple tandem submerged arc) on steels with impacttoughness requirements

large thicknesses or high structural restraint.

115 All fabrication welding shall be performed within thelimits of essential variables of the qualified welding procedure.This also includes tack welding, seal welding, welding of lift-ing lugs and attachment welds as well as repair welding.116 When resuming welding on partially filled joints in spe-cial areas, preheating shall be performed and the temperaturewithin the specified tolerances, shall if not otherwise agreed,be equal to the interpass temperature for the welding pass inquestion.117 Grooves produced by gouging shall be in accordancewith the groove profile dimensions given in the welding proce-dure specification.118 Welding consumables shall be classified with respect tostrength, application area and hydrogen level according to rec-ognised classification schemes. Except for solid wires, suchconsumables shall for welding in special areas and on primarystructural elements be extra low hydrogen i.e. a maximum dif-fusible hydrogen content of 5 ml/100 g weld metal. For selfshielded flux cored wire 8 ml/100 g weld metal may be accept-ed subject to agreement.Hydrogen testing shall be according to ISO 3690 or equivalent.119 Consumables that have been contaminated by moisture,rust, oil, grease, dirt or other deleterious matter, shall be dis-carded unless properly reconditioned.Storage and handling of welding consumables shall be in ac-cordance with the manufacturer's recommendations, and in ac-cordance with procedures giving details regarding conditionsin storage rooms, temperature in storage ovens and quivers,length of exposure and conditions, as applicable.Recycling of fluxes for submerged-arc welding shall be per-formed in a manner that ensures a mixture of new and used fluxwith continually homogenous properties.120 Welds shall be terminated in a manner that will ensuresound welds without end-craters. Extension bars and run-offplates shall be removed upon completion and cooling of theweld. The end of the weld shall be made smooth and flush withthe edges of abutting parts.121 Grinding of welds with the intention of increasing the fa-DET NORSKE VERITAS

conditions. Cutting torches should not be used. tigue life and/or reducing the probability of brittle fracture

Offshore Standard DNV-OS-C401, January 2001Page 30 Ch. 2 Sec.2shall be carried out according to agreed specifications.122 Welding production tests shall be made during fabrica-tion of welds in special areas and in primary structural ele-ments to verify that the produced welds are of acceptablequality. Minimum one test coupon is required from each ap-plied welding process.The welding parameters for the WPT shall be as for the actualweld and the environmental conditions shall be kept as realisticas possible. The requirements for a WPT are in general thesame as for the relevant welding procedure test.123 If one or more production tests fail to give satisfactoryresults, two more shall be made, both of which shall give ac-ceptable results.Should one or both of the additional tests fail, the total produc-tion welding performed with the welding procedure in ques-tion shall be evaluated based on testing of welds and basematerial cut-out from the actual structure fabricated.124 In all cases the failure of a production test shall lead to areview of the welding performed to establish the reason for thefailure, and appropriate corrective action shall be carried out.125 Shop primers applied over areas, which will subsequent-ly be welded, shall be of a suitable quality demonstrated tohave acceptably low detrimental effect on the finished weld.

F 200 Post weld heat treatment (PWHT)201 For units that shall stay at one location longer than 5years, PWHT shall be applied for joints in C-Mn steels in spe-cial areas when the material thickness at the welds exceeds50 mm (see Fig.3 for guidance on material thickness). If, how-ever, satisfactory performance in the as-welded condition canbe documented by a fitness-for-purpose assessment applying,for example, fracture mechanics testing and analysis, PWHTmay be omitted.

Figure 3Guidance on material thickness for PWHT

202 Heat treatment shall be performed in accordance with aprocedure specification including:

heating and cooling rates temperature gradients soaking temperature range and minimum holding time heating facilities insulation control devices recording equipment configuration of structure to be post-weld heat treated or

Heat treatment records shall be kept throughout the heat treat-ment process.203 Heat treatment shall be performed at a soaking tempera-ture in the range 580 to 620C, for a time of at least 2 minutesper mm thickness. Soaking temperature and time shall be se-lected considering recommendations for the welding consum-ables and steel grade in question. Soaking temperature forquenched and tempered steels shall be decided in each case.204 The temperature difference between the outside and theinside surface during soaking shall not exceed 30C within theheated area. Double-sided heating shall be applied as far aspossible.205 Heating, soaking and cooling shall be carried out in acontrolled manner that prevents cracking or distortions outsidethe dimensional tolerances. The temperature difference alonglines or planes of symmetry shall normally not exceed 30Cwhen the material temperature is above 300C.206 The heat-treatment cycle and the actual metal tempera-ture shall be recorded using thermocouples equally spaced ex-ternally, and whenever possible internally, throughout theheated region.207 Heat treatment, wherever possible, shall be carried outin an enclosing furnace according to written procedures agreedupon. The temperature distribution throughout heating furnac-es shall be controlled within 15C.Where it is impractical to heat-treat the whole item in a closedfurnace, local heat treatment may be adopted.208 Only welding consumables recommended for PWHT bythe manufacturer shall be used for joints to be post weld heattreated.

F 300 Repairs301 Repairs shall be carried out in accordance with qualifiedrepair procedures subject to agreement.302 Guidance to repair work may be found in IACS Ship-building and repair Quality Standard, Part A Sec.9 and Part B.303 Members distorted by welding may be straightened bymechanical means or by carefully supervised application of alimited amount of localised heat. The application of heat ormechanical force shall be in accordance with a written proce-dure.304 Defects in welds may be rectified by grinding, machin-ing or welding. Welds of insufficient strength, ductility ornotch toughness shall be completely removed prior to repair.The mechanical properties of repair weld shall satisfy the min-imum specified properties of the steel in question.305 Repair welding in the same area may be carried outtwice. Further repairs shall be evaluated in each individualcase.

306 The use of arc-air gouging shall be followed by grind-ing, removing the affected material.307 Whenever a defect is removed, the gouged and groundarea shall be examined by magnetic particle testing or othersuitable methods to verify complete removal.308 Repair welding shall be performed using extra low hy-drogen welding consumables, applying an appropriate preheat-ing and working or interpass temperature. The preheating andworking temperature when making shallow and local repairs inspecial areas and primary structural elements shall be raised50C above the level used for production welding and be atleast 100C unless otherwise agreed. The working temperatureshall be maintained until the repair has been completed. To en-sure sound repair welds, the single repair length shall not beshorter than approximately 50 mm.309 Repair of welded joints shall be carried out by removingDET NORSKE VERITAS

details if local PWHT shall be carried out. the unacceptable portion of the weld without substantial re-

Offshore Standard DNV-OS-C401, January 2001Ch. 2 Sec.2 Page 31moval of base material. For planar defects the repair length oneither side of the defect shall be 50 mm longer than the size ofthe defect as confirmed by NDT. Long defects may be requiredrepaired in several steps to avoid overloading or cracking.Each repair step shall be controlled so as not to cause plasticdeformation of the remaining material when removing the de-fect.310 Repair welding of post-weld heat-treated joints shall un-less otherwise agreed initiate a new heat treatment.

311 Minor discontinuities may be removed by grinding ormachining, making a smooth transition into the surroundingmaterial. The thickness shall not be reduced to less than 93%of the nominal thickness but in no case by more than 3 mm.The extent of such repair shall be agreed upon.312 All repairs shall be re-inspected with the same NDTmethods to the same or increased extent as necessary.DET NORSKE VERITAS

Offshore Standard DNV-OS-C401, January 2001Page 32 Ch. 2 Sec.3SECTION 3TESTING OF WELDS

A. GeneralA 100 Scope101 This section gives requirements for fracture mechanicstests and non-destructive testing.

B. Destructive TestingB 100 Fracture mechanics (FM) testing101 For units that shall stay at one location longer than 5years, FM testing shall be included in the qualification of weld-ing procedures for joints for which all of the following apply: the design temperature is lower than + 10C the joint is located in a special area where at least one of the adjoining members is fabricated

from steel with a SMYS larger than or equal to 350 MPa.(Testing on steel with SMYS lower than 350 MPa is notrequired.)

102 The test weld shall be made and tested for the actualcombination of steel grade, manufacturer, welding process andwelding consumable (brand) used. FM testing is, however, notrequired for consumables used for root passes only in two-sid-ed welds.103 The FM tests shall be carried out on a full penetrationbutt-weld with K- or single V-preparation. The back of the Kand one of the legs of the single V (on which the FM test shallbe carried out) shall be perpendicular to the plane of the plate.Tests on either of these weld bevel preparations qualify for alltypes of bevel preparations.104 The test weld shall be welded with a heat input repre-senting the maximum heat input used in the fabrication. Thetest weld shall be made on a plate with a thickness not smallerthan 90% of the maximum plate or wall thickness for which thewelding procedure shall apply. The test weld also qualifies forplate thicknesses down to 50% of the test weld plate thickness.105 On each test weld at least three FM test specimens shallbe tested in each of the weld deposit and the heat affected zone(HAZ). (Details regarding the required number of test speci-mens and the location of fatigue pre-cracks are given furtherbelow.)106 Testing of the HAZ or the weld deposit can be omitted iftests with satisfactory results according to the requirements inthis standard have been carried out previously by either thesteel manufacturer or the welding consumable manufacturer.107 The FM tests shall be carried out according to BS 7448Part 2 (with detailed requirements as given below) using 3-point bend specimens. The CTOD-technique with B x 2Bspecimens shall be used. For nominal plate thicknesses of thetest weld equal to or exceeding 80 mm, B x B specimens maybe used.All specimens shall be tested with the fatigue pre-crack placedin the through-thickness direction. For tests of the weld depositthe fatigue pre-crack shall sample the central part of the depos-it. For tests in the HAZ the required location of the fatiguecrack depth is given in 108.An evaluation of the relevant test temperature shall be madefor all joints in question. Unless there is a high probability that

atures the test temperature shall be:

108 Subsequent to the CTOD-test the specimens in the HAZshall be sectioned and examined as described below.A metallographic section according to BS 7448 Part 2 Section11.2 shall be prepared from each HAZ specimen. The metallo-graphic section shall include weld metal and base metal. If nec-essary, in order to determine the exact location of the fatiguepre-crack, sections from both sides of the pre-crack shall beprepared. The faces of the metallographic sections shall not betaken deeper than the deepest point of the fatigue pre-crack andnot more than 3 mm from the deepest point of the fatigue pre-crack.A figure of a cross-section through the weld (of an un-fracturedspecimen) is shown in Fig.1.

Figure 1Cross-section through the weld

Measurements of the distance, df, between the plane of the fa-tigue pre-crack and the fusion line shall be taken. Within t

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