ENGINEERING COMPANY STANDARD
Documento riservato di proprietà di Eni S.p.A. Divisione Agip. Esso non sarà mostrato a Terzi né utilizzato per scopi diversi da quelli per i quali è stato inviato. This document is property of Eni S.p.A. Divisione Agip. It shall neither be shown to Third Parties not used for purposes other than those for which it has been sent.
GENERAL SPECIFICATION
OFFSHORE PLATFORMS
OFFSHORE STRUCTURES CONSTRUCTION
08833.STR.MET.SPC
Rev. 5 December 2001PREFAZIONE Rev. 0 December 1992 Total pages n. 107 Issue Rev.1 February 1993 Modify sheets 37, 38, 44, 45, 79, 91, 101 Rev.2 September 1993 Total pages n. 107 Modify sheets 6, 7, 10, 11, 12, 13, 14, 15, 16, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 36, 37, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 51, 52, 54, 56, 57, 58, 60, 61, 62, 63, 64, 66, 67, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 81 Rev.3 December 1993 Total pages n. 120
RINA comments are included. General revision. Rev.4 October 1995 Total pages n. 120 General revision. Rev.5 December 2001 Total pages n. 89
Steels with yield strength of 460MPa and steels fabricated with thermomechanical rolling process are considered, check of congruence with specification 08832 STR-MME-SPC Rev.7 has been carried out, extension has been done for offshore welds and sea fastening, standard AWS D1.1/2000 has been considered, a dedicated section for impact test has been included in order to take into account recommendations of draft committee for revision of ISO 13819-2, reference has been done to European standards EN462 and EN970, PWHT applicability criteria has been review, specification has been review and simplify where possible.
CONTENTS
1 GENERAL 5
1.1 SCOPE OF THE WORK 5
1.2 APPLICABLE DOCUMENTS 5
1.3 TERMS AND DEFINITIONS 6
1.4 REPORTING 7
1.5 STRUCTURAL CLASSES AND TYPICAL ELEMENTS 7
1.6 MATERIALS 7 2 WELDING 8 2.1 GENERAL 8 2.2 DEFINITIONS 8 2.3 WELD CLASS 8 2.4 WELDING PROCESSES 9 2.5 CONSUMABLES 10
2.6 STORAGE AND HANDLING OF CONSUMABLES 11
2.7 INITIAL DOCUMENTATION 13
2.8 WELDING BOOK 14
3 WELDING PROCEDURES 16
3.1 GENERAL 16
3.2 WELDING PROCEDURE SPECIFICATIONS 17
3.3 QUALIFICATION OF WELDING PROCEDURES (WPAR) 18
3.4 QUALIFIED PRINCIPAL POSITIONS 18
3.5 VALIDITY OF WELDING PROCEDURES (ESSENTIAL VARIABLES) 18
3.6 TESTING 21
3.7 SPECIAL TESTS 24
4 WELDERS AND WELDING OPERATORS 26
4.1 GENERAL 26 4.2 QUALIFICATIONS 27 4.3 RETESTS 28 5 PRODUCTION WELDS 29 5.1 GENERAL 29 5.2 WELDING SEQUENCES 33 5.3 TEMPERATURE 33 5.4 REPAIRS 34 5.5 CLOSURE WELDS 36
5.6 STRESS RELIEVING POST WELD HEAT TREATMENT 37
5.7 PRODUCTION TESTING COUPONS 39
5.8 WELDING PARAMETER CHECKING 40
6 FABRICATION 42
6.1 GENERAL 42
6.2 FORMING 42
6.3 WELDED ATTACHMENTS 45
6.4 SITE ASSEMBLY ACTIVITIES 45
6.5 MANUFACTURED AND MISCELLANEOUS ITEMS 46
6.6 FINISHING OF SURFACES 46
6.7 RAT HOLES 46
6.8 BOLTED CONNECTIONS 47
7 PREFABRICATED ITEMS TOLERANCES 48
7.1 FABRICATED TUBULARS, NODES AND CONES 48
7.2 ROLLED OR FABRICATED BEAM 50
7.3 STIFFENED PLATE PANELS 51
8 FINAL FABRICATION TOLERANCES 53
8.1 POSITION OF NODES 53
8.2 JACKET LEGS HORIZONTAL AND DIAGONAL MEMBERS STRAIGHTNESS 53
8.3 JACKET CENTERING GUIDE TUBES 53
8.4 JACKET SLEEVES AND SHEAR PLATES 53
8.5 DECK PLANS 54
8.6 PILES 55
8.7 BUOYANCY TANKS 55
8.8 CONDUCTORS 56
8.9 J TUBES 56
8.10 SUPPORTS CAISSON / RISER / J-TUBES 57
8.11 ANODES 57
8.12 HANDRAILS 57
8.13 WALKWAYS, LANDINGS AND STAIRWAYS 57
8.14 TEMPLATE DOCKING PILES CENTRING SYSTEM 58
9 INSPECTION OF WELDMENTS 59 9.1 GENERAL 59 9.2 DEFINITIONS 59 9.3 REFERENCE STANDARDS 59 9.4 METHODS OF NDT 60 9.5 EXTENT OF NDT 61 9.6 EDGE INSPECTION 62 9.7 QUALIFICATION OF NDT PROCEDURES 62 9.8 QUALIFICATION OF NDT PERSONNEL 64
9.9 VISUAL INSPECTION EXECUTION 65
9.10 RADIOGRAPHIC TESTING EXECUTION 65
9.11 ULTRASONIC TESTING EXECUTION 65
9.12 MAGNETIC PARTICLE INSPECTION EXECUTION 67
9.13 STANDARDS OF ACCEPTABILITY 68
9.14 REPORTS 70
10 TESTING OF FIELD INSTALLED COMPONENTS 72
10.1 PREASSEMBLY TESTING 72
10.2 RISER PNEUMATIC TESTING 72
10.3 PNEUMATIC TESTING OF BUOYANCY TANKS AND JACKET LEGS 72
10.4 TESTING OF BALLASTING AND GROUTING SYSTEMS 72
10.5 TESTING OF PACKERS SYSTEM 72
11 APPENDIX 1: STRUCTURAL CLASSES 74
1 GENERAL
1.1 SCOPE OF THE WORK
This specification covers the minimum requirements for fabrication and construction of jackets, decks and modules of the offshore platforms of ENI Division AGIP spa.
This specification contains general requirements: construction drawings shall prevail over this specification.
1.2 APPLICABLE DOCUMENTS
1.2.1 Referred Codes
For items not specially covered by this specification, the latest editions (at the time of contract award) of the following codes in the order shown below shall be used:
American Welding Society (A.W.S.), Structural Welding Code D1.1 / 2000.
API RP 2A "Recommended Practice for Planning, Designing and Constructing Fixed Offshore Platforms".
EEMUA 158 "Construction specification for fixed offshore structures".
American Institute for Steel Construction (AISC), Manual of Steel Construction.
American Welding Society (A.W.S.), Specification for electrodes, wires and fluxes.
RINA "Guide for design, construction and installation of steel fixed off-shore platform".
RINA "List of products approved by RINA according to sections G and H to the rules".
Consumable Classification from Institutes members of the IACS International Association Classification.
1.2.2 Referred Norms
The following norms are referred to in this specification:
BSI 709 "Methods of destructive testing fusion welded pressure vessel" welding procedures (Para. 3)
BSI 5500 "Specification for unfired fusion welded pressure vessel" local out roundness (Para. 7)
BSI 6072 "Method for magnetic particle flaw detection" NDT (Para. 9)
EN 287 "Approval testing of welders-Fusion welding-Part1" (Para 5), 288 "Specification and approval of welding procedures for metallic material" (Para. 3), 473 "General principles for qualification and certification of NDT personnel", (Para. 9), 10025 "Hot rolled products of non-alloy structural steels and their technical delivery conditions" production weld (Para. 5), 462 "Non-Desstructive testing - Image quality of radiograph -Image quality indicators", 970 "Non-Destructive examination of fusion welds -Visual
examination", 10163 "Delivery requirements for surface condition of hot rolled steel plates and sections"
EN 10045 "Charpy impact test on metallic materials", Charpy-V Specimen (Para. 3)
API RP2X "Reccomended practice for ultrasonic examination of offshore structural fabrication and guidelines for qualification of ultrasonic technicians", Standard 1104 NDT (Para. 9)
Materials which shall be certified by Certifying Authority shall be in accordance with the relevant codes of the Certifying Authority.
1.2.3 Associated Specifications
AGIP 08832-STR-MME-SPC "Purchase of offshore structural steel" Rev. 7.
1.3 TERMS AND DEFINITIONS
The following definitions are given for terms contained in this specification.
1.3.1 Parties Involved
CLIENT: ENI Division AGIP or its Authorised Representative.
CONTRACTOR The Company responsible for the fabrication and construction who has awarded the contract from Client.
Sub-CONTRACTOR: The Company Sub-Contractor to Contractor, approved by Client.
SUPPLIER: The Company who receives the purchase order for supplying of materials or equipment.
EXAMINER or APPROVED BODY:
Person or Society, accepted by the Client, committed to certify:
- procedures, materials and welding operators, - procedures, equipment and NDT personnel.
1.3.2 Definitions and abbreviations
Shall/Is to be: is used where a provision is mandatory.
Should: is used where a provision is advisory but preferred. May: is used where a provision is completely discretionary.
Construction Drawings: drawings issued by Client and developed to a detail level that may change from project to project, depending on Contractor scope of work. Construction drawings together with other specifications define the necessary Contractor information for fabrication drawings built up and relevant engineering detail.
Fabrication Drawings: drawings issued by Contractor that contain all the necessary information required to fabricate items at shop and yard level. Assembly sequence drawings and temporary support drawings are considered fabrication drawings
As built Drawings: fabrication drawings, issued by Contractor, on which are reported all the information on how the construction has been actually built.
Assembly sequence drawings and temporary support drawings need no to be issued in "as-built" version, except that all attachments left onto the structure shall be reported on as built drawings.
Structural Element Class: level of importance of each structural element due to its loading condition and with respect to the overall integrity of the platform. Fabrication: built-up of single item, generally executed in a shop.
Construction: assembly of several items carried out at yard. na: not applicable.
nr: not required.
Ry: minimum specified yield strength. Rm: tensile strength.
t: thikness
NDT: Non Destructive Test.
Closure weld: welds on tubulars with inside diameter of 600 mm or greater without back gouging; generally they are welds made on diagonal tubulars after row roll-up.
Insert: structural element part with the same diagonal dimension section in which it is fitted.
1.4 REPORTING
Reports required throughout this specification shall conform to the applicable Contractor guarantee quality formats which shall contain, at least, the information listed in the relevant paragraphs of this specification.
1.5 STRUCTURAL CLASSES AND TYPICAL ELEMENTS
For the scope of this document the structural elements of the off-shore installations are subdivided in classes.
The definition of the structural classes is reported in Appendix 1 with the definition of structural element class for typical jackets, decks and modules structural elements. Construction drawings may indicate specific informations about structural element class. Ambiguous cases relevant to structural element class shall be cleared by Client.
This classification does not consider structural elements that are removed after platform installation (platform for lifting lugs, temporary ladders, ecc), but includes those items, although removed, they are fundamental (buoyancy tanks, lifting aids, sea fatening etc.).
1.6 MATERIALS
All building steel to be used shall comply with ENI Division AGIP 08832-STR-MME-SPC rev.7 requirements.
Materials substitution and handling shall be in accordance with sections 3.4 and 6.5 of standard EEMUA 158.
2 WELDING
2.1 GENERAL
All structural welding shall be in accordance with the requirements of this specification.
Steel backing strips, out of closure welds, may be used upon Client's approval only, and in accordance with paragraph 3.7.4.
2.2 DEFINITIONS
The following definitions are used:
SMAW: shielded metal arc welding (using manual equipment); SAW: submerged arc welding (using automatic equipment); GTAW: gas tungsten arc welding (using manual equipment); GMAW: gas metal arc welding;
GSFCAW: gas shielding flux cored arc welding; SSFCAW: self shielding flux cored arc welding; WPS: welding procedure specification; WPQR: welding procedure qualification record; HAZ: heat affected zone;
WM: weld metal; FL: fusion line;
KCV set in HAZ:Charpy V test set, consisting of three (3) groups of three (3) specimens each from the following lines: fusion line (FL= 50% WM and 50% HAZ), FL plus 2mm, FL plus 5mm, for a total of 9 specimens;
KCV set in WM: Charpy V test set, consisting of three (3) specimens in weld centreline; TM: thermomechanically controlled rolled (base material): thermomechanical
rolling process carried out with a rigid control of both plate temperature and rolling grade;
Q&T: quenched and tempered (base material).
2.3 WELD CLASS
The welds to be executed are grouped in classes, corresponding to the structural element classes, of which they maintain the same name.
Different requirements on applicable welding processes, mechanical characteristics, NDT type and percentage, defects acceptability combinations are defined for each weld class.
In welded joints between elements of different structural classes the higher structural element class shall govern.
2.4 WELDING PROCESSES
2.4.1 Acceptable Welding Processes
The approval is to be obtained prior the use of the process in production begins.
All welding fabrication of structures shall be accomplished with low hydrogen processes.
Welding processes for structural classes of components are listed in table 2.1.
Other welding processes could be employed under Client approval.
TABLE 2.1: JOINT TYPE AND WELD CLASS
Structural element class = Weld class
a b c d e Butt SAW SMAW GS/SSFCAW (1) 1st run GS/SSFCAW (1)
GTAW SMAW SAW
T butt SAW SMAW GSFCAW (1) SAW SMAW GS/SSFCAW (1) SMAW
1st run GTAW SMAW GS/SSFCAW
Fillet SAW SMAW GSFCAW SAW SMAW GS/SSFCAW GMAW GMAW Closure SMAW GSFCAW SMAW GS/SSFCAW
1st run na GTAW SMAW
Seal SMAW GS/SSFCAW GMAW
Note 1: not applicable for steels with minimum specify yield strength of 460MPa.
The use of GTAW shall be limited to the first passes where second side is not accessible. GTAW shall be utilized only with direct current, straight polarity.
First run on principal tubulars longitudinal double side welds may be carried out by GMAW process providing it is completed removed prior to back passes are executed.
The use of "narrow gap" welding processes are permitted only upon Client's approval. In this case full details about the process, the consumables, the NDT techniques, the relevant applications and the previous experience are to be documented.
2.4.2 Restrictions of Welding Processes
The following procedures require the following positions:
SMAW: all positions, except vertical down;
SAW: flat position in general, horizontal position for fillet weld only;
GMAW: flat position in general, horizontal position for fillet weld only and with "spray arc" technique;
GS/SSFCAW: all positions (except the vertical down for class "e" structures only), under Client's approval only, after a documented experience is furnished to Client's satisfaction.
Welding procedures shall not exceed the following limits:
SMAW: for heat input exceeding 3 kJ/mm; bead width exceeding 16mm or 4 times the core wire diameter;
SAW: for heat input exceeding 5 kJ/mm;
GTAW: when adequate environmental shielding is not provided;
GSFCAW: for heat input exceeding 3 KJ/mm; when adequate environmental shielding is not provided;
SSFCAW: for heat inputs exceeding 1.5 kJ/mm; with weave beads; vertical up; without the voltage and wire-feed speed are set and locked;
ALL: welding on materials less than 30mm thickness with a heat input exceeding 3 kJ/mm; heat input greater than 3 kJ/mm for steels with minimum specify yield strength of 460Mpa; square edge butt welds greater than 8mm thickness; welding on second side of a joint without back gouging except for SAW procedures using the punch-through technique; single-pass fillet welds (other than by submerged arc) with a leg length greater than 7mm; use of ceramic inserts.
2.5 CONSUMABLES
The use of consumables is subject to meeting the welding procedure qualification requirements.
Consumables to be used shall have chemical composition similar to and have a yield strength not lower than the base material.
Consumables to be used for welded joints between steels having different yield strength shall be those applicable to the higher strength steel.
The use of filler metals giving a low diffusible hydrogen deposit (less than 5 cm³ per 100g of weld deposit, carried out with mercury measurement method, or humidity equal to 0.2% of the weld metal weight, according to AWS D1.1.) is compulsory when one of the following conditions is fulfilled:
welds in classes "a, b, c";
weld thickness greater than 10mm;
Specified Minimum Yield Strength of one of the parts to be joined equal to or greater than 275MPa.
Electrodes in sealed boxes shall have the hydrogen level certified.
Electrodes classification shall conform to AWS. Electrodes classified conform to other specifications or codes are accepted provided correspondence and in that case the WPQ has in the name anessential variable All electrodes, according to the reference code or specification, shall be marked.
2.5.1 SMAW
Electrodes for SMAW shall conform to AWS specification A5.5 classification E7015-A1, or E7016-A1, E7018-A1, E8016-C3, E8018-C3, E9018-M and AWS A5.1 classification E7015, E7016, E7018 ed E7028 (the last one for fillet weld only).
2.5.2 SAW
Wires and fluxes for SAW shall conform to AWS specification A5.17 classification F6XX-EXXX or F6XX-EXXX or F6XX-F6XX-EXXX or AWS specification A5.23 classification F7XX-EXXX-A1 or F8XX-F7XX-EXXX-A1.
2.5.3 GTAW
Rods for GTAW shall conform to AWS specification A5.18 and electrodes shall conform to AWS specification A5.12.
2.5.4 GMAW
GMAW consumables shall be in accordance with AWS specification A5.18 (classes ER 70S2, ER 70S3, ER 70S6, ER 70S7). Processes with 100% CO2 are not allowed; gas
mixtures with 80% Ar and 20% CO2 are acceptable.
2.5.5 GSFCAW and SSFCAW
Consumables shall be in accordance with AWS specification A5.20 (classes E70/71-T6 E70/71-T8) and AWS A 5.29 (class E81T1-Ni1-Ni2). Gas mixture normally used is that with 80% Ar and 20% CO2. Other type of gas mixture may be applied after Client approval.
2.5.6 Gases
CO2 is to have a purity grade not lower than 99.8% and a dew point not higher than 45°C
below zero.
Argon and Helium are to have a purity grade not lower than 99.99% and a dew point not higher than 45°C below zero.
Gases are to be supplied in bottles where type is to be clearly indicated. Fixed distribution networks are to be clearly identified in their content. Heaters for CO2 are to be used.
2.6 STORAGE AND HANDLING OF CONSUMABLES
All consumables shall be supplied in sealed moisture proof containers capable of maintaining the consumables free from moisture for at least six months.
Unopened containers shall be stored in a dry location where the temperature shall not be less than 20°C and the relative humidity shall not exceed 50%.
Electrodes, fluxes and wires that have been contaminated by water, oil, grease, or all other deemed unsuitable, or unmarked consumables shall not be employed in the work and shall be removed from the worksites.
Client may require an additional monthly test (or two months in shop) and whenever he considers that the consumable baking and maintaining procedure are applied in wrong way.
On any electrode batch and on any flux lot, a moisture test in accordance with AWS specification A5.5, may be carried out at Client's discretion. Samples shall be taken from ovens where electrodes and fluxes are stored, ready for production use. The maximum moisture content by weight for low hydrogen consumables shall be 0.2% for electrodes and 0.1% for fluxes.
Client reserves the right to verify the consumables chemical and mechanical characteristics by destructive testing.
2.6.1 Electrodes
Low hydrogen electrodes shall be baked for 2 hours at 350/450°C, unless otherwise recommended by the supplier. Thermocouple, which shall be previously calibrated shall be placed at midheight owen. Initial drying may be omitted in case the electrodes are supplied in fully sealed packs with a guaranteed hydrogen level content.
After withdrawing from ovens for use, electrodes shall be contained in heated portable quivers at a temperature not lower than 70°C and shall be used within 4 hours.
Electrodes not used within above time limit may be rebaked, provided they are in good conditions. Redrying is generally acceptable to a maximum of 2 times.
Electrodes that shall not immediatly applied may be stored in ovens at a temperature not lower than 100°C after baking.
In alternative electrodes characterized by a low hydrogen level maintainment after box opening may be used. Those electrodes are commercially available in packages equal to a workday or half workday. Anyway Client may require a test to verify the characteristical performance of those electrodes.
If these electrode types are used, those unemployed, at the day end, shall not be employed again.
2.6.2 Fluxes
Low hydrogen fluxes storage, usage and rebaking requirements shall be as for electrodes.
The maximum amount of recycled flux used for welding shall not exceed 30% of the total (70% minimum new flux). Fluxes may be recycled aspirating from welding and filtered to eliminate impurity before mixing with new one.
The Contractor shall provide a handling and recycling procedure including details of baking, use of heated hoppers, recovery system and circumstances in which flux is deemed unsuitable and scrapped.
2.6.3 Wires
Wires storage, usage and re baking shall be the same as for electrodes.
To avoid porosity, gas holes, hot cracking and low electrical contact, wires shall be free from grease and moisture.
Current swing avoidance during welding shall be avoided through a regular coil speed.
At the workday end all the automatic welding coil winders shall be emptied as to avoid wire moisture contamination.
2.7 INITIAL DOCUMENTATION
Prior to begin fabrication and for all welding processes Contractor shall submit to Client's approval:
A. storage and consumables handling procedure; B. welding procedure specifications list;
C. welding procedure qualifications list; D. welder/operator qualification list;
E. welding machine calibration certification; F. fabrication procedures and erection sequences; G. list of proposed welding consumables and Supplier; H. procedures for heat treatment;
I. procedures for NDT testing and inspection and associated personnel qualification; J. cold forming and straightening procedures;
K. identification and control procedures for materials;
L. procedures for dimensional control, control of tolerances during fabrication.
M. fabrication drawings including plate seam arrangement drawings and plate cutting drawings;
N. drawings and calculations of temporary works; inclusive of support points, jacking points and sling points;
O. certificates of supply materials;
P. key plans showing member identification and weld marking scheme.
For particular cases Contractor may require derogation for the points M, N, O, P above listed
All the documents listed above shall be in accordance with the provisions given in following sections.
2.8 WELDING BOOK
Before the beginning of the works, the Contractor shall prepare a welding book covering all the welding operations to be performed. This book shall be permanently available to the Client on the site where the welding is to be carried out.
It shall comprise:
identification sketches or a list of welded joints per type;
a summary of the accepted welding procedures with their qualifications;
all welding procedure specifications which shall be applied;
destructive and non destructive testing, specifying the technique used for the latter. WPQ and WPS that shall be carried out during fabrication shall be added to the welding book.
For each welding procedure qualification (WPAR) shall be indicated:
the references(s) of the qualification certificate(s) specifying the range of thicknesses and covered diameters together with maximum CEV and Pcm qualified for steels with Re > 275MPa;
the welding procedure qualification records, with the testing record certificates and inspection, during fabrication, certificates of the base and filler metals;
the chemical composition and the carbon equivalent CEV / Pcm of the test pieces (for steels with a minimum specified yield strength higher than or equal to 275MPa only).
For each welding procedure specification (WPS) shall be indicated:
base material grade (when the grade actually used is be different from that initially foreseen on the drawings, this shall be indicated);
the joint configuration before and after welding (size and tolerance); passes number; if a temporary or permanent backing is used; the grade of the backing material, the precision of the backing fit, the method of removal (if foreseen);
conditions and special measurements, e.g. preheating and postheating temperature (soaking time), maximum interpass temperature;
if stress relieving treatment is foreseen: the procedure, the temperature, the hold time, the heating and cooling rates, and the tolerances for each of these parameters.
For each pass the following indications shall be given:
the welding process specifying, if necessary, whether it is a manual, a semi-automatic or an automatic process;
the welding position;
welding parameters with tolerances (voltage, speed of travel, current, heat input, flow rate and type of gas);
welding technique detailing polarity and nature of current; welding direction; type of protection (gas); weave bead or stringer bead; whether or not back welding is carried out after gouging and/or grinding.
3 WELDING PROCEDURES
3.1 GENERAL
Welding of weld classes "a, b, c" shall be carried out in accordance with approved and qualified welding procedures only.
All welding procedures applied shall be qualified unless Contractor procedures have already been qualified or Contractor qualifications have been in use in the preceding 12 month. Welding procedure qualified before this period may be applied providing a test coupon is carried out as production welding begins.
Welding of weld class "d" may be executed with procedure previously qualified by Contractor, without the need of new qualification.
Welding of weld class "e" may be carried out with pre-qualify processes without new qualifications (see section 3.3).
Prior to beginning work, the Contractor shall qualify all the required welding procedures for the various materials and welded seams of the structures to be fabricated.
The Approved Body committed to certify the welding procedures shall be accepted by the Client.
The information indicated on each WPS shall be consistent and shall not leave the welder to choose within different combinations of parameters.
3.1.1 Preheating and Interpass
Tacking and welding shall be carried out with preheating temperatures ranges stated in table 3.1. Carbon Equivalent formula is (IIW):
CEV = C+Mn/6+(Mo+Cr+V)/5+(Ni+Cu)/15
TABLE 3.1: MINIMUM PREHEATING TEMPERATURES (°C) Weld thickness (t) CEV (check analisys) t < 20mm t < 30mm t > 30mm < 0.39 20 20 50 (20) < 0.41 20 20 75 (50) < 0.43 20 50 (20) 100 (75) < 0.45 50 (20) 100 (75) 125 (100)
Note: values in brackets refer to SAW only.
Arc air gouging and oxicutting may be carried out without preheating.
Preheating temperature is to be measured on bevels and at 50mm minimum from bevels at both sides.
Working interpass temperature shall not be lower than preheating one, nor higher than 250°C.
Preheating and interpass values differing from the above stated may be used provided measured during the execution of welding procedure qualification.
3.1.2 Heat input
Welding heat input shall be calculated with one of the following formulas:
HI = 0.006 VA / s HI = 0.001 VAT / (ROL)
where:HI= heat input in KJ/mm; V = arc voltage in Volts; A = arc current in Ampere; s = welding speed in cm/min; T = arc time in second; ROL = electrode run-out-length in mm.
Heat input value for filling passes and for any process on TM steel may be higher than those considered in paragraph 2.4.2, provided adequate welding procedure qualification demonstrates it is not detrimental to the mechanical characteristics of welded joint.
3.2 WELDING PROCEDURE SPECIFICATIONS
Welding procedure specifications (WPS) shall specify the EN 288 requirements in addition to the following information (as recorded on relevant Procedure Qualification Record):
company name and unique WPS number;
welding process, or processes when more than one is used in making a complete joint;
steel type, and whether it is normalised or TM, thickness, length, width and pipe diameter (when applicable) used for procedure qualification;
sketch of joint showing plate edge preparation (specifying if oxygen cutting or machining) and joint fit-up tolerances;
thickness and diameter ranges qualified;
welding position and welding direction (for vertical position);
the make, trade name, classification and size of welding consumable and fluxes. Any pretreatment of electrode/consumable;
name, type and flow rate for gas shielding, and backing if applicable;
sketch showing number of beads, welding sequence and relevant consumables and welding parameters for each joint zone;
for each run: the current type, polarity, arc current and voltage, welding speed, or electrode run-out length and relevant burning time;
treatment to second side;
actual preheat and maximum interpass temperature used in the qualification test weld, and those to be used in production; method of temperature measurement;
for semi-automatic processes: torch position, wire protrusion, frequency and waving amplitude;
post weld heat treatments (for avoiding hydrogen cracking and for stress relieving) if applicable;
any deposition augmentation system used;
tack welding procedure;
removal methods for weld defects.
3.3 QUALIFICATION OF WELDING PROCEDURES (WPAR)
Qualification of welding procedures shall comply with AWS D1.1 or EN 288 or RINA and as specified in the following.
The welding procedures shall be certified by an Approved Body accepted by the Client.
Prequalified joints foreseen by AWS D1.1 apply only to weld class "e".
The qualification of the welding procedures performed may be used for any other workshop or worksite within the same organization.
The execution of procedure qualifications for SAW shall be done using the maximum value of the allowable recycled flux percentage (paragraph 2.6.2).
Where tack welds in production will remain in final joint and are done by a different process to that used for weld body, the procedure test plate shall be similarly tack welded and one macro section taken through a tack location.
3.4 QUALIFIED PRINCIPAL POSITIONS
Qualified principal positions shall be in accordance with table 4.1, page 109, AWS D1.1-2000.
3.5 VALIDITY OF WELDING PROCEDURES (ESSENTIAL VARIABLES)
A qualified welding procedure is to be used within the limitation of essential variables as stated below. The changes described below are to be considered essential and are to initiate a new procedure qualification test.
When a combination of welding processes is used, the essential variables applicable to each process shall be applied.
WPQ carried out on base material of quality not "Z" may be applied to other similar steels, including quality "Z", or lower grade.
3.5.1 Material
Base Material: change of grade of steel, change of steel quality. Increase in product CEV above 0.02% (for Re > 300MPa only), and Pcm above 0.01% of maximum nominal value of steel in comparison with the value of WPS. Change in supply condition (as rolled, normalised, TM, Q&T). The qualification obtained for a normalised materials is accepted also for TM materials, and not viceversa. Change of microalloy elements or manufacturing procedure for steels with minimum specify yield strength of 460MPa.
Groove preparation: presence of bevels protective coat. Oxycutting without grinding to sound metal.
3.5.2 Weld Geometry and Position
Groove angle: change of included angle greater than +10° or -5°.
Components angle : where acute angles in the stub to node can welds are below 45° weld processes are to be qualified by the test of TKY joints. The bevel angle in this test is to be the smallest used in fabrication.
Root face and root gap: changes of root face and root gap shall be in accordance with AWS D1.1-2000, either for double side weldings and for single side weldings.
Groove design: change from double side welding to single side welding and vice versa; change in groove weld preparation shape (V groove, U groove, etc. except that a single half V bevel qualifies a single V, K qualifies X, and 2:1 and 1:1 preparations qualify each other and all intermediate geometries).
Thickness: outside the qualified range listed in EN 288 -3.
Misalignment: values exceeding the lesser of 5mm or 10%t on double sided joints, 3mm or 10%t on single sided joints. Misalignment of 2mm is permitted, regardless of other parameters.
Diameter: outside the qualified range listed in EN 288 -3.
Welding positions: outside the qualified range listed in table 4.1, page 109, AWS D1.1-2000.
3.5.3 Consumables and Equipment
Welding consumables: change of electrode trade name; electrode and wire type are considered equivalent on condition that they belong to the same certification class and are approved by a Certifying Authority, in that case they do not have to be requalified.
Power: changes are made to pulsed power welding parameters.
Welding parameters: change from AC to DC or vice versa; change in DC polarity.
3.5.4 Procedures
Welding process: any change in welding process.
Preheating/working temperature: for preheating the lower limit of approval is the nominal preheat temperature applied at the start of the welding procedure test, with a tolerance of -10°/+50°C. For interpass the upper limit of approval is the nominal interpass temperature reached in the welding procedure test.
Post weld heat treatment: added or omitted; change beyond specified temperature range; soaking time increased more than 25%; increasing or decreasing speed more than 20%.
Gas shielding: gas type change from active to inert and viceversa; change of 10% or beyond in gas composition; change +27% or -10% in flow rate.
Grinding: if grinding between passes is omitted.
Back-gouging: each reduction in depth of back-gouging in comparison with the qualified one for automatic process; each increase higher than 10mm of qualified depth.
Back welding: if omitted.
Welding direction: change from uphill to downhill, and vice versa.
3.5.4.1 Welding Parameters
Voltage and current: change beyond 10% of mean values.
Bead: if each bead width increase, for any electrode diameter.
Speed: if wire feed speed setting for any pass is changed by more than 5%.
Heat input: change beyond 10% (tolerance applies to mean heats input values measured during qualification in root, fill and weld cap passes) for weld class "a" and nodes of class "b". Welding of all other elements of class "b" and of every other class is considered a change beyond 15%. Where heat inputs in two positions are different, qualification in both positions qualifies all intermediate heat inputs.
3.5.5 Specific for SMAW
Measured current for any electrode diameter is changed by more than 20%.
Run out length for any electrode size is changed by more than 10%; where the runs out lengths in two positions are different, qualification in both positions qualifies all intermediate run out lengths.
Core diameter of an electrode used for capping passes is reduced. All passes in the cap of the qualifying weld shall use the same electrode diameter.
3.5.6 Specific for SAW
Number of wires used for any pass is changed.
Separation of tandem arcs, transverse or longitudinal, is changed by more than 10%.
Feeding direction is changed by more than 5° transverse or 3° longitudinal to the weld.
Use of iron powder.
3.5.7 Specific for GTAW
Root gap exceeding 3mm is to be qualified with separate procedure.
3.5.8 Specific for FCAW (GS and SS)
If the mean voltage for any pass deposited by other automatic or semi-automatic process is changed by more than 10%.
Change of contact tip-to-workpiece distance.
3.6 TESTING
The qualification of welding procedures is based upon visual examination, non-destructive testing and mechanical testing on test samples. Type and number of tests are those specified in table 7.7. of RINA Codes.
If different welding consumables or welding processes are applied for the same joint, impact tests required are to be carried out for the related regions of the weld. If SAW tandem process is used and fills passes have width over 19mm one KCV set is required at depth of 8mm.
Size and shape of specimens and test execution for Charpy-V are to comply with EU10045.
3.6.1 Testing Coupon
The test plates used for procedure qualification (samples location) shall have the rolling direction parallel to the test weld.
CEV shall be not less than 0,02% and Pcm than 0,01% in comparison with the maximum of the specification of the steel to be welded.
For Z quality material beams, samples taken for WPQ shall have welding direction parallel to the rolling direction; for materials of other quality the welding direction can be perpendicular to the rolling direction. (fig. 3.1)
Test conditions shall be a realistic simulation of the actual conditions that will be experienced.
When PWHT of nodes or other sub-assemblies is required, all relevant procedures qualifications shall include PWHT over the full range of material thickness.
The dimensions of the test plates (coupons) shall be in accordance with EN 288-3, paragraph 6. Position and cut of test coupons shall be in accordance with EN 288-3 section 7.2.
When plate thickness to be tested is over 36mm or the power of tensile testing machine is not sufficient, tensile specimens may be cut into a number of approximately equal strips not exceeding 36mm (or the machine strength equivalent thickness whichever is the greater) with a minimum overlap of 2 mm. Test shall be performed on each strip and the results averaged.
3.6.2 Acceptance Criteria
The welding procedure is qualified when the soundness and mechanical properties comply with the requirements hereafter indicated:
Non-destructive tests:
Welded joints soundness is to comply with the prescriptions of section 9.13. NDT shall be carried out not prior than 48 hours from weld completion and in any case after PWHT when applicable. Repairs are not allowed.
The locations of all imperfections exceeding 50% of the reference level shall be marked, and the cutting of tests pieces shall be arranged to avoid these imperfect regions.
Destructive tests:
Transverse tensile tests: the tensile strength of the welded joint is to be in accordance with EN 288-3 paragraph 7.4.1; in case of welding between steels of different grades the tensile strength shall be equal to the lower steel grade.
All weld metal tensile test: specimens shall be taken out from full weld metal, and shall take the form of the "reduced transverse test" piece to BS 709; the tensile strength of the welded joint is to be at least equal to the minimum specified tensile strength.
Bend tests: test conditions and acceptability limits shall be in accordance with EN 288-3 paragraph 7.4.2; bending angle test shall be of 180°.
Toughness tests: the average and minimum Charpy V-notch energy absorption recorded at each specified position in WM and HAZ shall comply with the requirements stated in tables 3.2, 3.3 and 3.4:
TABLE 3.2: IMPACT TEST TEMPERATURE
°Tp > -5 °C t < 12,5 mm 12,5 mm< t < 25,4 mm 25,4 mm < t < 50,8 mm 50,8 mm < t < 70 mm 70 mm < t < 100 mm 100 mm < t < 150mm °Tp > +5 °C t < 15 mm 15 mm < t < 30 mm 30 mm < t < 50,8 mm 50,8 mm < t < 70 mm 70 mm < t < 100 mm 100 mm < t < 150 mm Structural element class Test temperature a -20°C b -20°C -40°C c 0°C 0°C (1) D
E Impact test not required not applicable
TABLE 3.3 ADSORBED ENERGY Nominal yeld strength (Ry) Average adsorbed energy on base material (J) Average adsorbed energy on weld metal and heat affected zone (J) Minimum adsorbed energy on weld metal and heat affected zone
(J)
> 450 Mpa 60 45 32
350<Ry< 450 Mpa 50 36 26
Ry<350 Mpa 40 27 19
Minimum value obtained by a single specimen must be greater than 70% of the average value required
TABLE 3.4 IMPACT TEST LOCATION
Thickness Location Double and single side welding t < 45mm Cap root WM + HAZ none t > 45mm Cap root WM + HAZ WM + HAZ Note: - Cap: 2mm +/- 0.5mm below external weld cap surface.
- Root: in root region of back welding. - WM: weld metal in the centre of weld.
- HAZ: heat affected zone. HAZ means: FL, FL+2mm, FL+5mm.
Macro section: EN 288-3 paragraph 7.4.3, test condition and acceptability shall be applied.
Hardness: the maximum hardness in any part across the welded joint shall not exceed 325 HV10.
3.6.3 Retesting
Retesting shall be in accordance with EN 288-3, paragraph 7.5 with the following amendements.
Tensile: when the failure, on one or both the specimen, occurs for a load value that is less than 95% of the tensile strength, the procedure will be rejected. When the failure, on one or both the specimen, occurs for a load value that is between 95% and 100% of the tensile strength, two additional tests will be carried out for the interested specimen.
Bends: two other specimens of similar type (face, root or side), located as near as possible to the failed specimen, shall meet specification.
Macro and hardness: the surveys on two more sections of the coupon have to meet specification.
Toughness: in case one specimen tested gives an energy value below the specified minimum single, or more than one value is lower than the minimum average, one further set shall be tested from the same location. The new set shall meet the specified minimum values and conditions, and in addition the mean value of all the two tested sets (the new and the failed) shall attain the specified minimum average value. In case of any additional failure the welding procedure shall be rejected.
3.7 SPECIAL TESTS
3.7.1 TKY Joints
The joint qualification shall be carried out in accordance with EN 288-3 paragraph 6.2.4. The can shall be positioned with vertical axis and brace acute angle downward (fig. 3.2).
Welding shall be carried out with a qualified T-butt procedure, or with a qualified butt weld procedure. In this case the required mechanicals to qualify the T-butt procedure shall be carried out.
Testing shall be 100% NDT, WM and HAZ thoughness at 12 and 3 o'clock positions, macro and hardnesses at 12, 3 and 6 o'clock positions. Acceptability shall be in accordance with applicable requirements of this specification.
3.7.2 Welding Repair
Special qualification for repair of excavated welds is required in case the repair process differs from the filling used.
The qualification shall be carried out in the worse position, through the utilisation of parameteres which are worse than the expected ones.
HAZ of both parent material and original weld shall be tested.
The Contractor shall issue standard WPQ repair that may be applied in various cases, including the applied methodology, length and maximum excavation depth, cleaning and NDT methods, preheat temperature and weld re shaping, if any. The previous methodology shall be exactly applied.
The requirements of section 5.4 shall apply.
3.7.3 Buttering
Buttering procedure carried out with the same process and parameters as for the filling weld need not to be qualified.
In case buttering is done with a different welding process, or with same process but different parameters, from main weld, the buttered area and HAZ shall be tested as for a different process weld. Both HAZ on base material induced by buttering and HAZ on buttered area induced by main weld shall be KCV tested. In case one KCV set position coincides with another KCV set, one may be superseded.
Welding procedure shall be carried out with maximum allowed root gap conditions.
Buttering thickness shall be 4mm and at least 3mm width on each bevel; normally buttering shall apply only to weldments having thickness 15mm and above. Buttering area shall be MT inspected.
3.7.4 Permanent Backing Strip Welds
Contractor may apply this technique providing a special WPQ including the insertion of steel backing strip into the fit-up joint and its tightening against bevel root, first passes, filling passes and relevant NDT execution.
This procedure is not applied in stub-can joints.
The test is carried out by welding a joint, at scale 1:1, built up by two tubulars pieces with diameter equal to the minus on which the process is intended to be applied (fig.3.3). A macrographic examination shall be executed on the weld root.
Tacking shall be carried out inside the bevel all over the weld root: tacking shall never be done outside bevel.
Air gap between the bevel root and backing strip shall be the minimum, before root welding starts.
A special UT procedure shall be defined and applied to verify the bevel fusion, the absence of tacking between base material and backing strip, and to recognize the root discontinuity caused by backing strip. The actual bevel inclination shall be considered for choosing UT probes. The procedure shall include the execution of an identification mark on base material at 100mm from joint, to verify the root gap dimensions and the centre of backing strip in every point before weld execution.
"Backing strip" welds shall be indicated on "as built" drawings. Maximum root gap variation in backing strip welds shall not exceed 6mm the root gap used during qualification. Backing strip weld is allowed with root gap values higher than 12mm but not exceeding 20mm.
Overall procedure produced by Contractor shall be approved by the Client before its application.
The requirements of section 5.5 shall apply in case of use of permanent backing strip in closure welds.
3.7.5 Grout Beads
Mechanical tests required on grout weld beads shall be two macros, with hardness survey on fusion line and HAZ under bead, one KCV set in HAZ and WM as shown in figure 3.4.
KCV temperature test shall be equal to the test temperature utilised for the parent material and shall conform with the minimum energy requirements for this last one.
4 WELDERS AND WELDING OPERATORS
4.1 GENERAL
All welding on the structures shall be performed by welders or operators qualified by an Approved Body accepted by the Client.
All qualified welder shall have a certification that witnesses the qualification. The certification shall be in accordance with EN 287 code or EN1418 code in case of weld operators.
The purpose of welder performance tests is to verify that the welders may produce welds in accordance with this specification requirements using a qualified welding procedure.
Welder qualification tests shall be carried out to an approved welding procedure specification. Welders having successfully performed the welds of qualification tests of a qualified process are automatically qualified for the same procedure.
All welders shall be qualified with at least one of the qualification tests indicated in table 7 of EN 287-1 1997 "Approval testing of welders - Fusion welding - Part1: Steels"
All welds using SMAW process are to be conducted with low hydrogen electrodes. During qualification at least one stop/start has to be produced in each run.
The welders are generally to be qualified for all positions butt welding. For welding occurring only in one or limited number of positions, performance test may, after agreement with Client, be performed only in this (these) position(s). Welders, to be qualified for GSFCAW/SSFCAW or GMAW fillet, are to be qualified in all positions
The welder can be qualified for mixed welding process by only one test, or by two tests as for EN 287-1 ch. 6.2.
Semi killed or fully killed C-Mn steels are normally to be used for welder qualification tests.
4.1.1 Certification Validity
The certification validity shall be submitted to the Client approval when fabrication starts, and it shall be in accordance with EN 287-1 with the following amendements.
A welder or welding operator may be required to be re qualified if inspection during fabrication reveals that extensive repairs are due to poor performance. This shall be done following a period of supervised retraining. The length of this period shall be at Client discretion but shall be not less than one week. The Contractor shall record details of retraining.
Client may review existing welder qualification meeting the requirements of this specification: existing qualifications may be accepted at his solely discretion.
4.1.2 Categories of qualification and test requirement
The fundamental categories that the Client will recognise are listed in the following paragraphs of this section.
The coupons to be welded are indicated in the same paragraphs. The coupons shall be checked in accordance with table 8 of EN 287-1. NDT acceptability shall be as per more stringent requirements of this specification.
Requalification is necessary if a different welding AWS classification consumable is used. It shall be in compliance with EN 287-1 paragraph 6.5.
4.2 QUALIFICATIONS
All the qualifications listed in EN 287-1 page 11,paragraph 6.3, will be applied.
The extensions of the welders qualifications shall be in compliance with table 3 of EN 287-1
4.2.1 Automatic welding
Welding operators using the submerged automatic arc welding (SAW) process shall be qualified as per AWS D1.1/2000 Chapter 4 Part C (or EN1418) and shall mark their welds for identification purposes.
Qualification with more than one wire qualifies one wire weld according to codes.
4.2.2 Manual double-side welding
WPQ test welds shall be carried out in accordance with EN 287-1, table 7.
4.2.3 Manual single-side welding
WPQ test welds shall be carried out in accordance with EN 287-1, table 7.
4.2.4 Closure Butt Welds
This qualification is required for all welders using the closure butt weld procedure.
The qualification requirements are the same as per manual single side welding, except that the root gap value shall be as per relevant WPQ.
The strong-backs shall be sufficiently strong so that the gap between bevels does not reduce significantly during welding.
The extension of the qualification is ruled by EN 287-1, table 3.
4.2.5 Fillet welds
4.2.6 Carbon arcair gougers
Manual welders are acceptable as Carbon arcair gougers.
Carbon arcair gougers, for structural class "a, b", shall demonstrate their ability to remove metal to a uniform depth in a workmanlike manner.
An up-dated register of approved arc-air gougers shall be keep.
4.2.7 Tackers
Tackers, for structural class "a, b", shall be qualified as per AWS D1.1/2000 section 4 part C unless already qualified for manual welding.
4.3 RETESTS
Retest applicability requirements shall be in accordance with EN 287-1 paragraph 9 requirements.
Welders failing tests shall follow a congruous training period before retest. Such a training must be proved by documents.
5 PRODUCTION WELDS
5.1 GENERAL
5.1.1 Technique
The width of individual deposited weld beads in flat, horizontal and overhead position, with GMAW and SMAW process, shall not exceed three times the electrode wire diameter or 16mm, whichever is the less. In vertical position the width shall not exceed 15mm. For SAW tandem process only fill beads may be 24mm. Vertical down welding is an acceptable technique only for GSFCAW and SSFCAW process, for weld class "e".
Run-out tabs for SAW are recommended to have a length greater than 150mm or 200mm, depending if single wire or twin wire technique is used. Such tabs shall be positioned on both sides of each longitudinal weld. The arc shall only be struck on the bevel faces only and not on base material.
Each run of weld metal shall be thoroughly cleaned from flux, spatter and all slag removed, by brush, prior to deposit the next run. For double side buttweld the second side shall be cleaned to sound metal prior to deposit the second side runs.
Should carbon arc air gouging be used, carbon and other residual debris shall be completely removed by grinding or other approved mechanical methods.
The welding procedure for a single side butt weld shall provide 100% fusion of the root and be such that distortion or contraction of the weld metal is minimized.
Peening of welds shall not be permitted.
Preheating temperature shall be raised by 50°C above that qualified, for fillet and T butt welds with root gap exceeding 20mm.
Welding joints shall be fully protected by shelters from the effects of inclement weather (wind, air draughts or chimney effects). Gas metal arc welding (GMAW) shall be permitted in workshop only and special care shall be exercised to protect the weld arc from air draughts.
Two adjacent weld toes distance shall not be lower than 51mm, unless there are geometrical problems. In this last case weld classes "a, b, c, d" shall be ground smooth before NDT execution.
5.1.2 Preparation and Fit-up
Surfaces to be joined by welding and extended adjacent areas shall be thoroughly cleaned to remove all material or substance detrimental to welding.
Whenever practicable, clamps, magnets, holding devices or other setting-up fixtures shall be used in assembling structural members in order to avoid tack welding.
Mechanical grinding and NDT of oxycut surfaces to be welded is required (see also Section 9.6).
Arc gouging to open tight grooves are permitted on double side welding only, provided is followed by grinding to bright metal.
Before welding the stub to node can, the relevant welding area on the can shall be 100% UT to detect for laminations. When beam shall be welded on flange beam, the flange beam area subjected to weld shall be UT tested to verify the laminations absence. A similar control shall be performed on plates in the position of joint between pad-eyes and main beams.
5.1.3 Tack Welding
Otherwise spacers shall be employed prior to tack welding to ensure correct root gap spacing.
Tacking shall be done within the bevels. Tack welding shall be performed by qualified tack welders and an approved qualified welding procedure, including preheating requirements.
Steel bars tacked inside the bevel shall be permitted if their position is clearly marked on base material and that Client may verify their removal. Steel bar material shall be similar to base material type or lower grade.
All tack welds, on structural class "a, b, c", shall have a minimum length of 4 times the weld thickness, with a minimum of 100mm; all other structural classes the minimum length is 2 times the weld thickness or 50mm whichever are the major. Tack welds may be incorporated into double side main butt welds provided they are sound, have been executed by qualified welders (not tack welders), and have their ends grounded and feathered.
Tack welds with a length of 50mm or greater that have shown cracks and when the crack is believed to extend to the bevels, shall be MT on all the interested areas after removal of defective points and before commence welding.
5.1.4 Weld Interruption
Welding shall be a continuous operation as far as practical. For components of class "a, b, c" very constrained and for mud-mats, preheating shall never be discontinued before at least 1/3 of the joint thickness has been welded. When the above limit is reached the weld joint may be allowed to cool down to room temperature: the cooling rate shall be minimized by wrapping the weld areas with dry insulating blankets. After any interruption and before continuation of welding, the weld is to be inspected visually for defects and cracks and, if necessary or required by the Client, tested by MT.
5.1.5 Weld Profiles
As a minimum, weld profiles and weld finish shall comply with A.W.S. D1.1/2000 Para 5.24 and 6.9; in the case of lack of fusion, incomplete penetration or for marginal indentation, the values shown in section 9.13 of this specification shall not be exceeded.
The external and internal weld reinforcement must not exceed 3mm for welding thicknesses up to 25mm, 4mm for thicknesses up to 50mm and 5mm for thicknesses over 50mm. The excess penetration in root welding, with GTAW process, shall not exceed 2mm
Weld profiles shall not interfere with the NDT technique specified: reshaping shall be carried out to this purpose, if necessary. Weld profiles shall not be re shaped by use of a gas torch, or by other unapproved means to change their appearance.
When specified on the Project Drawings the weld toes shall satisfied API RP2A sect.11 requirements. If necessary, the weld toe can be grinded to obtain the required profile. In that
case a rotary burr grinder (no disc grinder) shall be used, as shown figure 5.1. Grinding shall produce a smooth concave profile at the weld toe with the depth of depression penetrating into the plate surface to at least 0.5mm below the bottom of any undercut, but not deeper than 2mm or 5% of the thickness, whatever the bigger, below the surface.
Localized unacceptable undercuts at the weld toe region of any stub to node can welds shall be removed by the technique mentioned above.
5.1.6 Double side welding
Double side welding shall be carried out whenever possible. In particular:
in longitudinal and circumferential joints of tubulars and node cans having diameter 800mm and greater. Limitations to this statement are permitted only in case of non accessibility to back side of the weld;
in T butt welds of nodal joints when construction drawings show the presence of stub. 5.1.7 Welding Grooves
Contractor is to prepare his own standard weld joint groove preparation in accordance with the indications given on the fabrication drawings and WPS qualified.
Where the joint is accessible from both sides, double side groove preparation, X or K type, shall be used to join members with thickness greater than 25mm; one side groove preparation, V or 1/2 K, may be used to join members with thickness 25mm or less. Contractor may choose a desired welding groove provided all full penetration requirements are fulfilled.
Bevel inspection shall be in accordance with paragraph 9.6.
Root back gouging is always required in double side joints.
5.1.8 Mismatch
The butt joint mismatch of welded plate, pipe, or structural shape edges shall not exceed the table 5.1 values:
TABLE 5.1: MISMATCH VALUES
Joint type Mismatch:
the lesser of 0.1t or: Double side Longitudinal
Circumferential
4 mm 3 mm Single side Longitudinal
Circumferential
3 mm 3 mm
When members of unequal size are joined, the larger member shall be prepared with a 1/4 tapered transition. The requirements apply both to thickness and width (e.g. beams flanges) dimensions. Worked taper in double sided joints are not required when thickness difference is 1.15t or less.
5.1.9 Spacing between welds 5.1.9.1 Longitudinal seams
When tubular members are fabricated from two or more welded barrels, the longitudinal seams axes of adjacent sections shall be staggered at least 300mm.
5.1.9.2 Node can welds intersecting stubs
Longitudinal and circumferential chord welds shall be separated from stub to chord welds as indicated in construction drawings, typical node. Otherwise the following requirements are to be fulfilled.
flush grinding of the outside area of chord welds intersecting the stub, extended for 150mm at least on both stub sides;
MT and UT on ground area;
stress relieving of the complete node.
Circumferential node can weld between two stubs is not allowed.
The distance between longitudinal stub seam and any node can seam type measured between weld toe and weld toe shall be in any case not less than 51mm.
5.1.9.3 Node can welds and ring stiffeners
The distance between ring stiffeners welds toe and circumferential chord weld toe is to be at least the chord thickness or 75mm, whichever is greater.
5.1.9.4 Cones
Circumferential welds within cone are not allowed, unless approved by Client or specified on the construction drawings. All cones shall be right conic frustum.
5.1.9.5 Pipe and node splices
The minimum distance between two circumferential welds shall be 1m or one diameter, whichever is greater.
Nodes can with length minor or equal than 3m shall be supply in one piece only.
Nodes can with length greater than 3m may be supply made in two pieces. In this case the minimum length of the single piece shall be not less than 1m and the circumferential weld between the two pieces shall comply with the following:
To be not located between two stubs;
Satisfy the requirements reported in the project drawings for the circumferential welds of the nodes
In any case the location of the circumferential weld in the node can shall be submitted to Client for approval.
There shall not be more than 2 splices in any 4m of pipe.
5.1.9.6 Beam splices
In cantilever beams no splice shall be located closer to the point of support than 1/2 of the cantilever length.
In beams with two or more supports there shall not be splices in following positions (fig.5.2):
in the middle 1/4 of the span;
in the 1/8 of the span nearest to any supports;
not closer than 1m to any support or node.
5.2 WELDING SEQUENCES
Contractor shall develop welding sequences to control tolerances within specification and prevent the build-up of excessive residual internal stresses in the structure. No welding shall be carried out between pretensioned parts.
Postheating of 300°C for 2 to 4 hours may be applied to reduce the risk of hydrogen induced cracking in welds of complex items, according to the thickness, if it need or it is required by the Client.
Welding sequences are to be defined, to the Client's approval, for complex items (e.g. nodes with four or more stubs, pile clusters, etc.) including:
WPS to apply;
sequence of items welding and welding direction and way;
number and location of welders at each stage of assembly;
position of preheaters and shelters;
postheating (if applied).
5.3 TEMPERATURE
Welding is not allowed if weldment temperature is lower than 5°C. In these cases preheating is mandatory to the required minimum temperature prior to begin welding. Preheating shall be applied to an area of 100mm minimum from bevel borders.
Definite methods and procedures shall be established for all operations involving preheat and interpass temperature control. Thermic crayons shall be used only outside the weld bevel. Temperature check or measurements shall be done at 50mm minimum from bevel borders and on back side where accessible; temperature reading on weld bead is for interpass temperature measurement only.
5.4 REPAIRS
Contractor shall prepare a written repair weld procedure, for each repair, including details of removal methods, weld area preparation, etc. Repair shall be carried out as per qualified procedures only.
Defects removal for repair shall be carried out by any method foreseen by this specification and shall produce a clean uncontaminated surface for the repair weld execution.
5.4.1 Repair of finished welds
Defects in weld metal may be repaired without Client's approval provided the repair procedure is qualified.
A register shall be kept by Contractor that details the location of all repairs, the defects, the names of the original welders, dates and repair procedures.
Contractor shall have a relevant NDT documentation to identify the exact defect position. Minimum excavation length shall be 100mm. Excavations closer than 100mm shall be linked into a single excavation.
Serious failures, like cracks, will be treated in a proper way. When detected, they will be examined in order to establish the originating reasons; then they will be repaired.
The crack shall be removed by either grinding or arcair gouging plus grinding to sound metal; grinding shall be carried out in a 50mm area from both ends of the crack, which is determinated by MT or PT. The MT shall be extended to base material surface to detect possible propagation. UT shall be used to assure defect removal. All NDT shall be carried out in optimum conditions of accessibility.
Preheating temperature for repairs shall be 50°C higher than the relevant WPS temperature requirement.
Re inspection shall be as per the original inspection technique and shall include all weld metal within 100mm of the repair. The areas interested to the cracks, after the repair, shall be UT detected.
All weld repairs shall be executed prior to any stress relieving heat treatment, when required.
In case that, after repair completion, NDT shows the presence of new unacceptable defects, the reasons are to be cleared up and reported to the Client prior to proceed with the new repair. In any case the excavation for the new repair is to be widened in order to reduce residual stress concentrations. Client reserves the right to ask for PWHT on multiple repaired joints.
Cosmetics grinding for eliminating shape defects on cap layers are permitted only if necessary, but are not considered repairs.
Local grinding may be used to remove notches up to 5mm deep in order to give an even profile. Notches deeper than 5mm shall be ground out and the face buttered according to the applicable requirements of this specification.
5.4.3 Buttering
Buttering shall be applied as a corrective action only. Buttering shall be done using qualified welding procedure.
Following buttering bevel preparations shall be re established by grinding or machining to the acceptable limits. Buttered area of double side welding shall be 100% MT prior the execution of root pass, if applicable.
Buttering on stub to can node welds may be applied to the node can side instead of stub side.
The exact root opening shall allow the closure with a single pass by the qualified procedure.
The requirements of section 3.7.3 shall apply.
5.4.4 Base Metal Repairs
All corrective action shall be in accordance with the approved procedure.
All boundaries of cavities resulting from removal of detrimental defects shall be faired to a slope of at least 4 to 1.
The repair of failures by grinding shall follows the procedures set in EN10163 rules with the following limitations:
the residual thickness after grinding shall be not less than 93% of the nominal thickness;
the maximum depth of the grinded area shall not be greater than 3 mm;
the depressions shall be radiused to the other surfaces;
the maximum extension of the grinded area shall not be greater than 5% for each m² of surface.
To verify the complete removal of discontinuities, the grinded areas shall be MTI tested.
The repair by welding is allowed only if previously authorised by the Client and if executed in conformity with EN10163, with the following limitations:
the repair by welding is carried out by qualified welders and in accordance with qualified procedures. Reference is made to Cap. 3. and 4. for what concerns the qualification of procedures and welders;
the weld is MTI and UT tested. The acceptance criteria of the UT test are as described in paragraph 9.13.3.
5.5 CLOSURE WELDS
Qualified root gap values, including qualified tolerance, may be difficult to be reached during assembly phase. In this case only class "a, b" closure welds shall be carried out in accordance with the following requirements. WPS to apply shall be chosen by the Contractor considering actual situations and bevel mismatch and Client shall be informed on the choice. Special and limit situations shall be approved by Client. Weld process used for class "a, b" closure welds can be used for welds in other structural classes in case of high root gap.
Considered welds are single side only. These welds shall be carried out with a special WPQ considering a greater root gap, or with a different WPQ.
When the root gap exceeds qualified value the following possibilities apply:
3mm buttering on each bevel with root gap values between 4mm and 12mm as maximum (see paragraph 3.7.3.); otherwise GTAW process may be used both for buttering and air closure. In this case only Charpy-V test, in root region, 1mm under surface is required;
permanent backing strip with root gap values higher than 12mm up to 20mm (paragraph3.7.4.)
with root gap higher than 20mm an insert is required, following the tolerance values indicated in paragraph 5.1.9.5 and 5.1.9.6.
The above described conditions are reported in the following table 5.2 in function of the element thickness:
TABLE .5.2: HIGH ROOT GAP
Element thickness (mm)
t < 20 t >20 Actions
Limit root gap values (mm)
4 4 Normal
10 12 Buttering
18 20 Backing strip
> 18 > 20 Insert
Welders qualification for first pass shall be carried out accordingly, following the relevant requirements of this specification.
Contractor shall identify all closure welds on fabrication drawings, indicating the applied procedures.
5.5.1 Normal and buttering actions
The requirements are relevant to joints with root gap between 4mm and 12mm. SMAW and GTAW process may be used to carry out the first two passes.
GTAW root process used both for buttering and filling, follows mixed process requirements including KCV test in WM and HAZ, two macro sections, hardness and bends.
Buttering carried out by SMAW process does not require qualification with thickness up to 6mm.
