os-c401
OFFSHORE STANDARD
D ET N ORSK
E V
ERITAS
DNV-OS-C401
FABRICATION AND TESTING OF
OFFSHORE STRUCTURES
APRIL 2004
Since issued in print (April 2004), this booklet has been amended, latest in April 2005.
See the reference to “Amendments and Corrections” on the next page.
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FOREWORD
DET 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 consultancy services relating to quality of ships, offshore units and installations, and onshore industries worldwide, and carries out research in 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 Methodology B)Materials Technology C)Structures D)Systems
E)Special Facilities F)Pipelines and Risers G)Asset Operation H)Marine Operations J)Wind Turbines
Amendments and Corrections
This document is valid until superseded by a new revision. Minor amendments and corrections will be published in a separate document normally updated twice per year (April and October).
For a complete listing of the changes, see the “Amendments and Corrections” document located at: https://www.sodocs.net/doc/1a10231468.html,/global/, under category “Offshore Codes”.
The electronic web-versions of the DNV Offshore Codes will be regularly updated to include these amendments and corrections.
Amended April 2005Offshore Standard DNV-OS-C401, April 2004 see note on front cover Changes – Page 3
Main changes
?General
The present edition supersedes the January 2001 edition.?Main changes
—Improving definitions of welding procedure particulars, clarifying how to adhere to the term “welding proce-dures”.
—Introducing enhanced flexibility in selecting method for qualification of WPS by referring to the DNV ship rules.
It is an industrial desire to have a reference with basis in line with IACS requirements for steels up to and including grade NV40 F.
—Overall conditions for fracture mechanics (FM) and post weld heat treatment (PWHT) application transferred into relevant design standards; i.e. DNV-OS-C101 and DNV-OS-C201. Related questions to fracture mechanics are directly linked to the design assumptions laid down for the
unit, and thus the relevant requirements must naturally be handled at the design stage.
—Requirements related to fracture mechanics (placed in DNV-OS-C101 and DNV-OS-C201) adjusted to reflect latest pertinent research work results.
—Application of welding consumables are linked to cate-gory areas of the structure as well as welding consumables adjusted to the material grade/strength group parameter.—‘Fabrication and tolerances’ has been reworked to be more comprehensive.
—For tank testing, text has been reworked to make it clearer for the users.
Corrections and Clarifications
In addition to the above mentioned rule changes, a number of corrections and clarifications have been made to the existing rule text.
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Offshore Standard DNV-OS-C401, April 2004Amended April 2005 Page 4 – Changes see note on front cover
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Amended April 2005Offshore Standard DNV-OS-C401, April 2004 see note on front cover Contents – Page 5
CONTENTS
CH. 1INTRODUCTION (7)
Sec. 1Introduction (9)
A.General (9)
A100Introduction (9)
A200Objective (9)
A300Organisation of contents (9)
B.Normative References (9)
B100General (9)
B200Offshore service specifications and rules (9)
B300Offshore Standards (9)
B400Other references (9)
https://www.sodocs.net/doc/1a10231468.html,rmative References (9)
C100General (9)
D.Definitions (10)
D100Verbal forms (10)
D200Terms (10)
D300Abbreviations (10)
D400Latin symbols (11)
D500Greek symbols (11)
CH. 2TECHNICAL PROVISIONS (13)
Sec. 1Welding Procedures and Qualification of
Welders (15)
A.General (15)
A100Scope (15)
A200Welding processes (15)
B.Welding Procedures (15)
B100General (15)
B200Preliminary welding procedure specification, pWPS (15)
B300Welding Procedure qualification test (WPQT) (15)
B400Welding procedure qualification record (WPQR) (15)
B500Welding procedure specifications (WPS) (15)
C.Welding Procedure Tests, C-Mn Steel and
Low Alloy Steel (15)
C100Butt welds on plates (15)
C200Butt welds in pipes (17)
C300Full penetration T-, Y-, and K- joints (18)
C400Tubular joints (18)
C500Fillet welds (19)
C600Re-testing (19)
C700Validity of a WPS (19)
C800Fracture mechanic (FM) testing (22)
D.Welding Procedure Tests, Aluminium (23)
D100General (23)
D200Butt welds (23)
D300Fillet welds (24)
D400Re-testing (24)
E.Welding Procedure Tests, Stainless Steel (25)
E100General (25)
E200Supplementary requirements for
austenitic stainless steel (25)
E300Supplementary requirements for ferritic-austenitic
stainless steel (25)
F.Qualification of Welders (26)
F100General (26)
F200Standards for qualification testing (26)
G.Testing (26)
G100General (26)
G200Tensile testing at ambient temperature (26)
G300Bend testing....................................................................26Sec. 2Fabrication and Tolerances. (28)
A.General (28)
A100Objective and scope (28)
B.Fabrication Planning (28)
B100General (28)
B200Quality system and workmanship (28)
C.Inspection (28)
C100General (28)
D.Material Identification, Cutting and Forming (28)
D100Material identification (28)
D200Cutting and forming (28)
E.Tolerances (29)
E100Tolerances for alignment and straightness (29)
F.Assembly, Welding, Heat Treatment and Repairs (32)
F100Assembly and welding (32)
F200Post weld heat treatment (PWHT) (33)
F300Repairs (33)
Sec. 3Non-Destructive Testing (35)
A.General (35)
A100Scope (35)
B.Non-Destructive Testing (NDT) (35)
B100General (35)
B200NDT procedures (35)
B300Personnel qualification (35)
B400Extent of NDT (35)
B500Acceptance criteria for NDT (37)
Sec. 4Other Tests (39)
A.General (39)
A100Scope (39)
B.Testing of Tightness (39)
B100General (39)
C.Structural Tests (39)
C100General (39)
Sec. 5Corrosion Protection Systems (40)
A.General (40)
A100Scope (40)
A200General (40)
A300Application of coating (40)
A400Fabrication and installation of sacrificial anodes (40)
A500Fabrication and installation of
impressed current systems (40)
Sec. 6Miscellaneous (41)
https://www.sodocs.net/doc/1a10231468.html,e General (41)
A100Scope (41)
B.Bolts (41)
B100Bolts and nuts (41)
C.Mechanical Fastening (41)
C100Contact surfaces in slip resistant connections (41)
CH. 3CERTIFICATION AND CLASSIFICATION 43 Sec. 1General (45)
A.Introduction (45)
A100Scope (45)
B.Specific Certification and Classification Requirements (45)
B100General (45)
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Offshore Standard DNV-OS-C401, April 2004Amended April 2005 Page 6 – Contents see note on front cover
B200Basic requirements (45)
B300Welding shops and -contractors (45)
B400Welding consumables (45)
B500Welding procedures and qualification of welders...........45B600Corrosion protection systems (45)
C.Records and Documentation (45)
C100General (45)
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Veritasveien 1, NO-1322 H?vik, Norway Tel.: +47 67 57 99 00 Fax: +47 67 57 99 11
OFFSHORE STANDARD
DNV-OS-C401
FABRICATION AND TESTING OF
OFFSHORE STRUCTURES
CHAPTER 1
INTRODUCTION
CONTENTS
PAGE Sec.1Introduction (9)
Amended April 2005Offshore Standard DNV-OS-C401, April 2004 see note on front cover Ch.1 Sec.1 – Page 9
SECTION 1
INTRODUCTION
A. General
A 100Introduction
101 This standard contains requirements for fabrication and testing of offshore structures.
A 200Objective
201 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 contractual matters 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 300Organisation of contents
301 Ch.2 Sec.1 to Ch.2 Sec.6 give common requirements that are considered applicable to all types of offshore units and installations.
B. Normative References
B 100General
101 The references given in Table B1, Table B2 and Table B3 include provisions, which through reference in this text constitute provisions for this standard.
B 200Offshore service specifications and rules
201 The offshore service specifications and rules given in Table B1 are referred to in this standard.
B 300Offshore Standards
301 The offshore standards given in Table B2 are referred to in this standard.B 400Other references
401 The other references given in Table B3 are referred to in this standard.
C. Informative References
C 100General
101 The documents listed in Table C1 include acceptable methods for fulfilling the requirements in the standard and may be used as a source of supplementary information. Other rec-ognised documents as listed below may be used provided it is shown that they meet or exceed the level of safety of the actual standards.
Table B1 DNV Offshore Service Specifications and rules Reference Title
DNV-OSS-101Rules for Classification of Offshore Drilling and
Support Units
DNV-OSS-102Rules for Classification of Floating Production
and Storage Units
Rules for Classification of Ships
Table B2 DNV Offshore Standards
Reference Title
DNV-OS-B101Metallic Materials
DNV-OS-C101Design of Offshore Steel Structures, General
(LRFD method)
DNV-OS-C201Structural Design of Offshore Units (WSD
method)Table B3 Other references
Reference Title
ANSI/AWS
D1.1
Structural Welding Code - Steel
ASME Section IX, Welding and Brazing Qualifications
Non-Interfiled (Boiler and Pressure Vessel
Codes)
ASTM G48Standard Test Methods for Pitting and Crevice
Corrosion Resistance of Stainless Steels and
Related Alloys by Use of Ferric Chloride Solu-
tion
ASTM E562Standard Test Method for Determining Volume
Fraction by Systematic Manual Point Count
BS 7448-2Fracture mechanics toughness tests. Method for
determination of KIc, critical CTOD and critical
J values of welds in metallic materials
EN 287Approval testing of welders - Fusion welding EN 1418Welding personnel – Approval testing of welding
operators for fusion welding and resistance weld
setters for fully mechanized and automatic weld-
ing of metallic materials
IACS Shipbuilding and Repair Quality Standard, Part
A - Shipbuilding and repair Quality Standard for
New Construction and Part B - Repair Quality
Standard for Existing Ships
ISO 148Steel - Charpy impact test (V-notch)
ISO 898Mechanical properties of fasteners made of car-
bon and alloy steel
ISO 6507-1Metallic materials - Vickers hardness test - Part
1: Test method
ISO 8501-1Preparation of steel substrates before application
of paints and related products -- Visual assess-
ment of surface cleanliness - Part 1: Rust grades
and preparation grades of uncoated steel sub-
strates and of steel substrates after overall
removal of previous coatings
ISO 9001:2000Quality management systems - Requirements ISO 9606Approval testing of welders - Fusion welding ISO 10042Arc-welded joints in aluminium and its weldable
alloys - Guidance on quality levels for imperfec-
tions
NACE MR0175Sulphide Stress Cracking Resistant Metallic
Materials for Oilfield Equipment - Item No.
21302
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Offshore Standard DNV-OS-C401, April 2004Amended April 2005 Page 10 – Ch.1 Sec.1see note on front cover
D. Definitions
D 100Verbal forms
101 Shall: Indicates a mandatory requirement to be followed for 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 certain course of action is preferred or particularly suitable. Alterna-tive courses of action are allowable under the standard where agreed between contracting parties but shall be justified and documented.
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 a possibility to the user of the standard.
105 Agreement, or by agreement: Unless otherwise indi-cated, agreed in writing between contractor and purchaser.
D 200Terms
201 Purchaser: The owner or another party acting on his behalf, who is responsible for procuring materials, components or 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 be followed in making a weld, including reference to materials, welding consumables, preparation, preheating (if necessary), method and control of welding and post-weld heat treatment (if relevant), and necessary equipment to be used.
204 Preliminary welding procedure specification (pWPS): A tentative welding procedure specification providing required welding variables, which is assumed to be adequate by the contractor, but which has not been qualified by the pur-chaser.
205 Welding procedure specification (WPS): A welding pro-cedure specification, which has been qualified by the pur-chaser to conform with an agreed qualification scheme.
206 Welding procedure qualification test (WPQT): The process of accomplishing welding and testing of a standardised test piece, as indicated in the pWPS.
207 Welding procedure qualification record (WPQR):A record comprising a summary of necessary data needed for the issue of a pWPS.
208 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.
209 Structural testing is a hydrostatic test, carried out in order to demonstrate the tightness of the tanks and the struc-tural adequacy of the design. Where hydrostatic testing is not practically feasible, hydropneumatic testing may be carried out instead under provision that the test is simulating, as far as practicable, the actual loading of the tank.
210 Leak testing is an air or other medium test, carried out in order to demonstrate the tightness of the structure.
211 Hydropneumatic testing is a combination of hydrostatic and air testing, carried out in order to demonstrate the tightness of the tanks and the structural adequacy of the design.
212 Hose testing is a water test carried out to demonstrate tightness of structural items.
213 Shop primer is a thin coating applied after surface prep-aration and prior to fabrication as a protection against corro-sion during fabrication.
214 Protective coating is a final coating protecting the struc-ture from corrosion
215 Watertight means capable of preventing the passage of water through the structure under a head of water for which the surrounding structure is designed.
216 Weathertight means that in any sea conditions water will not penetrate into the ship.
D 300Abbreviations
301 The abbreviations given in Table D1 are used in this standard.
Table C1 DNV Recommended Practices and Classification
Notes
Reference Title
DNV-RP-C203Fatigue Strength Analysis of Offshore Steel
Structures
Classification
Note 30.1
Buckling Strength Analysis
Table D1 Abbreviations
Abbreviation In full
AC Alternating current
ANSI American National Standards Institute
ASME American Society of Mechanical Engineers
ASTM American Society for Testing of Materials
AWS American Welding Society
BM Base material
BS British Standard (issued by British Standard Institu-
tion)
CE Carbon equivalent
C-Mn Carbon manganese
CTOD Crack tip opening displacement
DAC Distance amplitude curve
DC Direct current
DNV Det Norske Veritas
ECA Engineering critical assessment
EN European de Normalisation
FM Fracture mechanics
HAZ Heat affected zone
IACS International Association of Classification Socie-
ties
ISO International Organisation for Standardisation
MAG Metal active gas (welding)
MIG Metal inert gas (welding)
NACE National Association of Corrosion Engineers
NDT Non-destructive testing
PWHT Post weld heat treatment
pWPS Preliminary welding procedure specification
RP Recommended practice
SMAW Shielded metal arc welding
SMYS Specified minimum yield stress
TIG Tungsten inert gas (welding)
WM Weld metal or Deposit
WPQR Welding procedure qualification record
WPS Welding procedure specification
WPT Welding production test
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Amended April 2005
Offshore Standard DNV-OS-C401, April 2004see note on front cover Ch.1 Sec.1 – Page 11
D 400Latin symbols
401 The following Latin symbols are used:
D 500Greek symbols 501 The following Greek symbols are used:a
=size of test specimen b
=size of test specimen d
=diameter of round tensile test specimen d f
=distance from the plane of the fatigue pre-crack to the fusion line e
=plastic deformation h T
=test pressure height h op1
=vertical distance from the load point to the posi-tion of maximum filling height h s3
=vertical distance from the load point to the top of the tank h p0
=height corresponding to valve opening pressure when exceeding the general value h op2=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 the extreme operational draught (T E ), h op2 is not normally to be taken as being less than T E
h D2=pressure head due to flow through pipes
l e =equivalent parameter for conical shells
l min =breadth of test assembly plates
l r =length of template or rod
r =nominal radius of the shell
r a =actual distance from the centre of the sphere to the shell wall
r e =equivalent parameter for conical shells
r a =actual distance from the cylinder axis to the shell wall
s =distance between stiffeners or girders t =thickness t1=wall thickness of the greater tube (can)t2=wall thickness of the smaller tube (brace)A =diameter used in wrap around bending test C =diameter of roller in bend test D =outside diameter D1=outside diameter of the greater tube (can)D2= outside diameter of the smaller tube (brace)KV =impact energy requirement L o =length of test area in test specimens L min =length of test assembly plates N =number of R =radius R c =forming radius T =thickness of plate in bend test W =width of weld α=tubular joint angle δ=measure of deformation compared to theoretical geometry λi =length of area with acceptable location of the fatigue pre-crack ν=Poisson's ratio σ1=largest compressive principal membrane stress σ2=principal membrane stress normal to σ1ψ=ratio between principal stresses.
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Veritasveien 1, NO-1322 H?vik, Norway Tel.: +47 67 57 99 00 Fax: +47 67 57 99 11
OFFSHORE STANDARD
DNV-OS-C401
FABRICATION AND TESTING OF
OFFSHORE STRUCTURES
CHAPTER 2
TECHNICAL PROVISIONS
CONTENTS
PAGE Sec.1Welding Procedures and Qualification of Welders..................................................................15Sec.2Fabrication and Tolerances......................................................................................................28Sec.3Non-Destructive Testing..........................................................................................................35Sec.4Other Tests...............................................................................................................................39Sec.5Corrosion Protection Systems..................................................................................................40Sec.6Miscellaneous (41)
Amended April 2005Offshore Standard DNV-OS-C401, April 2004 see note on front cover Ch.2 Sec.1 – Page 15
SECTION 1
WELDING PROCEDURES AND QUALIFICATION OF WELDERS
A. General
A 100Scope
101 This section specifies requirements for welding proce-dures and welding procedure tests for C-Mn steel and low alloy steel, aluminium, austenitic stainless steels and ferritic-auste-nitic (duplex) stainless steels as well as qualification of weld-ers.
A 200Welding processes
201 Welding may be performed with the following processes unless otherwise specified:
—manual metal arc welding (metal arc welding with covered electrode)
—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 Procedures
B 100General
101 A welding procedure specification shall as a minimum contain the following information as relevant for the welding operation:
—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, polar-ity
—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 200Preliminary welding procedure specification, pWPS
201 A pWPS shall be prepared for acceptance by the pur-chaser prior to starting up the agreed welding procedure qual-ification test (WPQT).
B 300Welding Procedure qualification test (WPQT) 301 When a welding procedure specification (WPS) is required to be qualified by a WPQT, the welding process shall be performed based on the accepted pWPS. (See Sec.2 F112).
B 400Welding procedure qualification record (WPQR) 401 A WPQR can be basis for the purchaser’s acceptance of a WPS. Prior to starting up production the WPQR shall be sub-mitted to the purchaser for review including any corrosion test results, as applicable.
B 500Welding procedure specifications (WPS)
501 A WPS shall be accepted by the purchaser upon con-formity with the requirements of an agreed qualification scheme.
502 A WPS shall be valid under the provision that produc-tion welding is carried out with the same type of welding equipment on which the WPS has been established.
503 The conditions on which the WPS has been established shall be representative of the working environment for the work shop or site where the production welding will be per-formed. (See C700).
C. Welding Procedure Tests, C-Mn Steel and
Low Alloy Steel
C 100Butt welds on plates
101 The test assembly may consist of two plates welded together. As far as possible the plates shall have a size that can simulate the heat transfer during the production welding. For manual or semiautomatic welding, a test assembly according to 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 the correct gap for the edge preparation used. 50 mm at each end of the test piece shall be discarded.
l min=300 mm
L min=350 mm
l min=400 mm
L min=1000 mm
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Offshore Standard DNV-OS-C401, April 2004Amended April 2005 Page 16 – Ch.2 Sec.1see note on front cover
Figure 1
Test 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 extent of 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 requirements given in Sec.3 B.
103 The following mechanical tests are required from each assembly (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 accordance with G, type B.
The tensile strength shall not be below the specified minimum tensile strength for the steel grade in question. Figure 2
Sampling of test specimens in 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 test specimens may replace transverse bend test specimens.
The test specimens shall be bent on a mandrel with diameter 4t, where t is the thickness of the specimen, except for extra high strength steel grades NV 550, NV 620 and NV 690 where the diameter shall be 5 t.
The bending angle shall be at least 120°. After bending, the test specimens shall not reveal any open defects in any direc-tion greater than 3 mm. Defects appearing at the corners of a test 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 one side to clearly reveal the fusion line and the HAZ. Cracks and lack of fusion are not accepted.
The welded joints shall have a regular profile with smooth transitions to the base materials and without significant or excessive reinforcement.
107 The Charpy V-notch specimens shall be machined in accordance with the requirements given in DNV-OS-B101. Four sets of three specimens each shall be sampled 2 mm below the surface of the parent material and transverse to the weld. 12 Charpy V-notch specimens shall be localised in the welded joint as follows:
— 3 specimens with the notch along the weld metal cen-treline
—
3 specimens with the notch in the fusion line
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— 3 specimens with the notch in the HAZ, 2 mm from the fusion line
— 3 specimens with the notch in the HAZ, 5 mm from the fusion line.
The V-notch shall be perpendicular to the plate surface.
For plate thickness t > 50 mm two additional sets of specimens shall be taken from the root area: one with the notch in centre of weld and one with the notch in the fusion line.
For dissimilar metal joints and/or joints between cast or forged and rolled materials, impact tests shall be carried out on test specimens with notch in fusion line, 2 mm from fusion line and 5 mm from fusion line in each parent material.
The Charpy V-notch test temperature and the average value for absorbed energy (KV) in weld metal, fusion line and HAZ shall be the same as required for the base material in transverse direction (see DNV-OS-B101).
The requirements given by the DNV Rules for Classification of Ships Pt.2 Ch.3 Sec.2 B308 can be applied as an alternative. For grades of improved weldability (see DNV-OS-B101), the Charpy V-notch test temperature and the average value for absorbed energy in weld metal, fusion line and HAZ shall be the same as required for the base material of the comparable normal weldability grade in transverse direction.
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 for each notch location, but one single value of three values from specimens from the same notch location may be below the average requirements, but not below 70% of minimum aver-age.
110 Where the results from a set of three impact test speci-mens do not comply with the requirements, an additional set of three impact test specimens may be taken.
The results obtained shall be combined with the original results to form a new average, which, for acceptance, shall be not less than the required value. Additionally, for these combined results not more than two individual values shall be less than the required average value, and of these, not more than one shall be less than 70% of the average required value.
When the result of any test, other than impact test, fails to meet the requirements, two further tests may be made from the same welded joint. If both these additional tests are satisfactory, the test is acceptable.
111 The hardness testing shall be in accordance with ISO 6507-1 or equivalent. The Vickers method (HV10) shall be used.
Indentations shall be made along traverses in the weld, HAZ and the parent metal approximately 1 mm below the surface. For each traverse a minimum of 3 indentations shall be made in the weld, HAZ (both sides) and parent metal (both sides). For HAZ the first indentation shall be placed as close to the fusion line as possible. For double sided welds, for fillet and T-butt welds one additional row of indentations shall be made through the root area.
For material grades up to and including NV 460, a maximum hardness limit of 350 HV10 shall be met for welds in sub-merged structures exposed to cathodic protection. Hardness limits for higher grades shall be subject to agreement.
Guidance note:
For NV 500, NV 550, NV 620 and NV 690 grades a maximum hardness 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 mate-rial grades, the test temperature and achieved impact energy shall comply with the minimum specified requirements for the lower steel grade.
In the same way, the tensile strength to be obtained on the welded assembly shall be in agreement with the requirements relating to the plate steel having the lower strength.
As an example the test temperature, impact energy and tensile strength for the butt welded joints given in Fig.3 are those required for the plate of grade D in the left assembly and for the plate of grade E in the right assembly.
Figure 3
Butt welded plate joints of different grades
C 200Butt welds in pipes
201 The test assembly shall be in accordance with Fig.4.
Figure 4
Test assembly for butt welds in pipes
202 NDT shall be carried out in accordance with the specifi-cation given for the production welding in question. The extent of the testing shall be as follows:
—100% visual inspection
Table C1 Impact energy requirement for sub-size specimens
Dimensions of Charpy V-notch test specimen Impact energy
10 x 10 mm KV
10 x 7.5 mm5/6 KV
10 x 5 mm2/3 KV
a=minimum value 150 mm
D=outside diameter
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—100% radiographic or ultrasonic testing
—100% surface crack detection (dye penetrant or magnetic
particle testing).The soundness of the weld shall comply with requirements given in Sec.3 B.
203 The following mechanical tests are required from each assembly (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 5
Sampling of test specimens in pipes
204 The results of mechanical testing shall comply with the relevant requirements given in C100.
C 300Full penetration T-, Y-, and K- joints
301 WPQT's for full penetration groove welds between plates at right angles or inclined, i.e. T- or Y- and K- configu-rations, shall cover a weld length of minimum 350 mm (see Fig.6).
302 NDT shall be carried out in accordance with the specifi-cation given for the production welding in question. The extent of 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 requirements given in Sec.3 B.
Figure 6
Test assembly for full penetration T-joints
303 The following mechanical tests are required from each assembly (see Fig.7):
— 4 (6) sets of Charpy V-notch tests with the notch location
as given in 107
— 1 macrosection test (metallographic examination + hard-ness measurements).The results of mechanical testing shall comply with the rele-vant requirements given in C100.
Figure 7
Sampling of test specimens on full penetration T-joints
C 400Tubular joints
401 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 extent of 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 requirements
a = 3 t, minimum value 150 mm
b =
6 t, minimum value 350 mm
given in Sec.3 B.
Figure 8
Test assembly for tubular joints
403 The following mechanical tests are required from each assembly (see Fig.9):
—12 Charpy V-notch tests sampled at 9 o'clock and with the notch location as given in 107
— 2 macro section tests (metallographic examination + hard-ness measurements) at 12 and 6 o'clock.
404 The results of mechanical testing shall comply with the relevant requirements given in C100.
405 Restrictions and testing for joint configuration involving acute angles (less than 15°) should be specified. AWS D1.1 is a good reference for structural welds.
C 500Fillet welds
501 The two plates are assembled and positioned edgewise so as to constitute a tee-assembly with no clearance. As far as possible 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
Test assembly for fillet welds For manual and semi-automatic welding the length of the test piece 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 position shall be included in the test length and shall be clearly marked for subsequent examination.
The ends of the specimen are exempted from examination over a length of 50 mm.
502 NDT shall be carried out in accordance with the specifi-cation given for the production welding in question. The extent of 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 requirements given in Sec.3 B.
If the stop and restart spot is included in the test length, special attention shall be paid to this position with respect to profile, proper fusion and absence of crater defects.
503 The following tests shall be performed:
— 2 macro section tests (metallographic examination, hard-ness measurements).
One of the macrosections shall be taken at the marked position of the stop and restart (for more details see 106).
For hardness testing, see 111.
C 600Re-testing
601 If the welding procedure test fails to comply with any of the requirements for NDT one extra test shall be welded and subjected to the same testing. If this additional test does not meet the relevant requirements, the actual pWPS shall be con-sidered as not qualified and a re-specification of the pWPS shall be made prior to a new welding procedure test.
C 700Validity of a WPS
701 The validity of a WPS shall be restricted to the work-shop performing the qualification. Workshops, work site or workshop branches under the same technical management and working in accordance with the same QA-program and – pro-cedures are considered as one workshop or site work.
702 Qualification of a welding procedure remains valid pro-vided the parameters are kept within the qualified ranges of essential variable during production welding. The essential variables and qualified ranges are given in 703. When varia-tions outside the qualification ranges of essential variables occur, the welding procedure qualification shall be considered invalid, and the WPS shall therefore be re-specified and re-qualified.
703 A qualified welding procedure shall be used within the ranges of the parameters of essential variables listed below. Base material
The following changes shall lead to a new qualification:
a)In general, significant change of material properties which
will obviously affect the weldability and mechanical prop-erties.
a=minimum value 150 mm
D1=outside diameter of the greater tubular (can) t1=wall thickness of the can
D2=outside diameter of the smaller tube (brace) t2=wall thickness of the brace L min=350 mm L min=1000 mm
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Guidance note:
When qualifying a welding procedure, it is recommended to use specified material with highest carbon equivalent (CE) available in the workshop or work site, especially when the thickness is large.
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b)More specifically, structural steels of both normal and
improved 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 520
N/mm2.
ii)High strength steel, grades A 27, D 27, E 27, A 32, D 32, E 32, F 32, A 36, D 36, E 36, F 36, A 40, D 40, E
40, F 40 or equivalent structural steels with minimum
specified 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 equivalent
structural steels with minimum specified yield
strength 420 to 690 N/mm2.
The qualification on steel grades of higher toughness require-ments will qualify the grades of lower toughness but not vice versa.
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 C2 there 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 welds shall be as given in Table C2.
The requirements for qualified thickness range for single run fillet welds are in addition to the requirements of Table C2, that the throat thickness, t w, shall be in the range 0.75 t w to 1.5 t w. However, a test with a throat thickness ≥ 10 mm shall give qualification 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 pipes and tubular joints
The qualification of a welding procedure test on diameter D shall include qualification for diameters in the following ranges as given in Table C3.
Angle of tubular joints
A welding procedure test carried out on a tubular joint with angle α shall qualify all tubular joint angles in the range of αto 90°.
Welding consumables
The following changes shall lead to a new qualification:—any change in consumable classification
—change of consumable brand when impact testing is required at temperatures below – 20°C
—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 purging gases.
Welding positions
The 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 Table C4.
Figure 10
Plate test positions
Table C2 Qualified thickness range
Thickness t in mm of test piece
Qualification range 1)2)
for single run or single
run from both sides
for multi-run welding
and all fillet welds
t ≤ 120.8 t to 1.1 t 3 mm up to 2 t 12 < t ≤ 1000.8 t to 1.1 t0.5 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
2)For butt welds in plates of thickness > 50 mm, the Charpy V-notch
requirement for the root area, ref. 107, shall be complied with.Table C3 Qualified range for pipes and tubular joints Diameter of the test piece D
(mm) 1) 2)
Qualification range
D < 168.30.5 D to 2 D
D ≥ 168≥ 0.5 D and plates
1) D is the outside diameter of the pipe or outside diameter of the brace
2)Qualification given for plates also covers pipes when the outside diam-
eter is greater than 500 mm
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Figure 11
Pipe test positions
Type of joint
The 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 vice
versa)
—deletion of back gouging
—addition or deletion of ceramic backing
—deletion of backing in cases where the backing material is
equivalent to the base material
—change from T-, Y- or K-joint to butt joint
—change from butt joint in plates to butt joints in pipes with
outside diameter less than 500mm
—any change of groove dimensions specified in the WPS
and agreed with the purchaser, such as change of specified type of groove, root face and gap, which may significantly affect penetration, fusion and dilution of the weld.
Welding condition
The following changes shall lead to a new qualification:—any change of welding process
—change from weaving to stringer bead technique or vice
versa
—stringer to weave ratio outside the tolerances specified in
the agreed WPS
—change from multi-pass welding to one-pass welding —change in welding current from A.C. to D.C., or vice
versa, or change of polarity. If recommended by the con-sumable manufacturer particular exemption may be given for SMAW in change from A.C. to D.C.
—change in metal powder or wire addition beyond ±10%.—change from spray arc to short arc pulse, or vice versa —any change beyond 25°C of the maximum interpass tem-perature
—change in heat input beyond ± 25% for steel up to 420 MPa
in specified yield strength. For material with specified yield strength equal to or above 420 MPa the change shall not be more than ± 10%, unless otherwise qualified —any decrease in preheating temperature
—change of post weld heat treatment parameters except for
holding time, which may be adjusted as a function of thickness.
Figure 12
Positions of test plate for fillet welds
Table C4 Qualified principal positions for butt welds and fillet welds, steel Test weld
Joint configuration 1)2)Principal positions Qualified positions 3)
Butt welds
Fillet welds Plates or Pipes Plates Pipes
Butt welds in plates
2G + 3G 1G 2G 3G 4G
All 1G 1G, 2G, 4G
3G 1G, 4G All 1F 1F, 2F, 4F
3F 1F, 4F Butt welds in pipes
2G + 5G = 6G
1G 2G 5G All 1G 1G, 2G, 4G
All
All 1G 1G, 2G 1G, 5G
All 1F 1F, 2F, 4F All Fillet welds
2F + 3F 1F 2F 3F 4F 5F
All 1F 1F, 2F, 4F
3F 1F, 2F, 4F All
1)Pipes with D > 500 mm are considered equivalent to plates (apply only to the can in tubular joints)2)Tubular joints shall be qualified separately
3)
The vertical downwards position shall be qualified separately
C 800Fracture mechanic (FM) testing
801 Requirements to fracture mechanic testing are given in DNV-OS-C101 or DNV-OS-C201.
802 The test weld shall be made and tested for the actual combination of steel grade, manufacturer, welding process and welding consumable (brand) used. FM testing is, however, not required for consumables used for root passes only in two-sided welds.
803 The FM tests shall be carried out on a full penetration butt-weld with K- or single V-preparation. The back of the K and one of the legs of the single V (on which the FM test shall be carried out) shall be perpendicular to the plane of the plate.
Tests on either of these weld bevel preparations qualify for all types of bevel preparations.
804 The test weld shall be welded with a heat input repre-senting the maximum heat input used in the fabrication. The test weld shall be made on a plate with a thickness not smaller than 90% of the maximum plate or wall thickness for which the welding procedure shall apply. The test weld also qualifies for plate thicknesses down to 50% of the test weld plate thickness. 805 On each test weld at least three FM test specimens shall be 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 further below.)
806 Testing of the HAZ or the weld deposit can be omitted if tests with satisfactory results according to the requirements in this standard have been carried out previously by either the steel manufacturer or the welding consumable manufacturer. 807 The FM tests shall be carried out according to BS 7448 Part 2 (with detailed requirements as given below) using 3-point bend specimens. The CTOD-technique with B x 2B specimens shall be used. For nominal plate thicknesses of the test weld equal to or exceeding 80 mm, B x B specimens may be used.
All specimens shall be tested with the fatigue pre-crack placed in the through-thickness direction. For tests of the weld deposit the fatigue pre-crack shall sample the central part of the deposit. For tests in the HAZ the required location of the fatigue crack depth is given in 108.
An evaluation of the relevant test temperature shall be made for all joints in question. Unless there is a high probability that the extreme loads on the joints will concur with lower temper-atures the test temperature shall be:
808 Subsequent to the CTOD-test the specimens in the HAZ shall be sectioned and examined as described below.
A metallographic section according to BS 7448 Part 2 Section
11.2 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 fatigue pre-crack, sections from both sides of the pre-crack shall be prepared. The faces of the metallographic sections shall not be taken deeper than the deepest point of the fatigue pre-crack and not 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-fractured specimen) is shown in Fig.13.Figure 13
Cross-section through the weld
BM=Base material
WM=Weld metal or deposit
d f=distanc
e from the plane o
f the fatigue pre-crack to
the fusion line (varies along the fatigue pre-crack) l i=length (in mm) of area with acceptable location of the fatigue pre-crack (see below)
t=Plate thickness
Measurements of the distance, d f, between the plane of the fatigue pre-crack and the fusion line shall be taken. Within the central 75% of the plate thickness the areas where d f≤ 0.5 mm shall be identified. The length, λi of each of these areas shall be determined. The location of the fatigue pre-crack shall sat-isfy the following criteria:
ΣNλi=≤ 3 mm for t ≤ 20 mm
=0.15 t for 20 < t ≤ 80 mm
=≥ 12 mm for t > 80 mm
N=number of areas with d f≤ 0.5 mm
809 Results from HAZ specimens on which the location of the fatigue pre-crack does not satisfy the requirement above, are not valid. In addition to these requirements given for HAZ specimens, all the requirements specified in BS 7448 Part 2 apply for both HAZ and weld deposit specimens.
Three valid tests for each of weld deposit and HAZ shall be carried out. The critical CTOD for all of the specimens shall be equal to or larger than 0.15 mm.
If (for HAZ or weld deposit) one or more of the three speci-mens has a critical CTOD lower than 0.15 mm additional tests may be carried out. In such a case the characteristic value, as defined in Table C5, shall be equal to or larger than 0.15 mm. 810 If the characteristic value as specified in Table C5 is larger than 0.15 mm an ECA (Engineering critical assessment) may be carried out with the purpose of demonstrating that extra capacity may be available in the structure.
For joints submerged at lowest
waterline:
≤ 0°C
Other joints:≤ design temperature.
Table C5 Characteristic value of CTOD
Number of valid tests 1)Characteristic value
3 to 5Lowest result
6 to 10Second lowest result
11 to 15Third lowest result
1)All valid tests that have been carried out shall be included
in the evaluation. It is not permissible to discard any valid
test result.