1. GENERAL
This specification defines minimum quality
and technical standards governing qualification of weld procedures and welders,
and for field production welding procedures for offshore pipelines and piping
components. This specification is to be
used in conjunction with the following documents:
•
Basis of Design
84506-60-00-2L-060
•
General Specification
84506-60-00-2L-000 - Definitions and Specification Directory
•
General Specification
84506-60-00-2L-010 - Quality Assurance / Quality Control
•
General Specification
84506-60-00-2L020 - General Offshore Specification
•
DNV-OS-F101 Submarine Pipeline Systems,
2000
2. WELDING REQUIREMENTS
2.1 Welding and weld inspection shall meet the
requirements of Articles A700 A800 and A900 of Section 9 and Appendix C of the
DNV-OS-F101 with exceptions, additions and clarifications noted herein.
2.2 All production welding of linepipe or
piping components shall be performed in accordance with welding procedures
submitted by CONTRACTOR and approved by COMPANY prior to installation.
2.3 Approved Welding Procedure Specifications
(WPS), together with welder qualification tests results, shall be on file at
the SITE and shall be made available at all times to welders, COMPANY and
CONTRACTOR inspectors. Any welds not
performed by qualified welders and in accordance with approved welding
procedures shall be rejected.
3. WELDING EQUIPMENT
CONTRACTOR shall furnish all
welding equipment, accessories and supplies.
Arc welding machines, ammeters, voltmeters, cable, electrode holders,
wire brushes, and other accessories shall be of a type, quality, and condition
satisfactory to COMPANY. All welding
equipment used for the WORK shall be identical to that used to qualify welding
procedures. Welders and welder helpers shall wear CONTRACTOR/ COMPANY approved
safety equipment during welding work in accordance with CONTRACTORS Safety
Policy / Procedure and the requirements of DNV-OS-F101.
4. WELDING CONSUMABLES SPECIFICATIONS
4.1 CONTRACTOR shall submit to COMPANY for approval manufacturer’s
data for all welding consumables, including manufacturer’s recommended welding
parameters, storage and handling procedures.
4.2 All welding consumables shall conform to DNV-OS-F101, Appendix
C, Article C, and shall be suitable for the intended application.
4.3
CONTRACTOR shall provide manufacturer’s test
certificates for each production batch or lot of welding consumables used in
production.
5. STORAGE AND HANDLING OF WELDING CONSUMABLES
5.1 Welding consumables are to be treated with care to avoid
contamination, deterioration or moisture pick-up. All consumables are to be stored according to
manufacturer’s recommended conditions prior to use and in accordance with
DNV-OS-F101 C500.
5.2 All coated manual welding electrodes received in hermetically
sealed containers shall be stored and handled in accordance with the
manufacturer's recommendations.
Electrodes that have become wet
have cracked or spalled coatings, or show any sign of damage or deterioration,
in COMPANY opinion, shall not be used and shall be promptly removed
from the SITE.
6. WELDING PROCEDURE QUALIFICATION
6.2 Weld procedure qualification(s) are to be carried out with
identical equipment as that to be used during installation. Tests shall be performed in a place
designated by CONTRACTOR and agreed by COMPANY and shall be conducted under
typical installation conditions.
6.3 All welding procedures shall be qualified according to
Appendix C, Article D and E of the DNV-OS-F101 and the additional requirements
of this specification.
6.4 Test welds for the proposed welding qualification procedures
shall be witnessed by COMPANY.
6.5 Qualification tests shall be made prior to mobilization
offshore to ensure that tests, and re-tests if required, are satisfactorily
completed without impacting the project schedule.
6.6 When
manual welding is to be used, one complete test joint shall be made. For automatic welding equipment, three
consecutive complete test joints shall be made.
Each test joint shall be subject to and must pass visual examination and
non-destructive examination. One shall
be selected for mechanical tests.
6.7 Charpy
impact tests shall be carried out according to DNV-OS-F101, Appendix C, Table
C-4 and Section F309. The min design temperature shall consider the potential
effects of blowdown, gas filling or upset conditions.
6.8
Two transverse macro-cross sections shall be
taken, to examine the weld and adjacent parent metal, and to perform Vickers
(HV10) hardness tests according to DNV-OS-F101, Appendix C, Section F311 to
313. The maximum hardness shall be 270 HV10
6.9
Crack Tip Opening Displacement Tests (CTOD)
shall be conducted for each qualified welding procedure. Four sets of three samples each shall be removed
from qualification weld and tested according to BS 7448, part 1, at the minimum
design temperature Sample size shall be BX2B.
One set shall be notched through
the weld metal center. The other three
sets shall be notched in the weld heat affected zone in three locations: at the
intersection of the fusion line at 1/4t, the fusion line at mid-wall and the
fusion line at 3/4t. Figure C-1 of DNV-OS-F101 shows these notch
locations. CTOD values shall be reported
on the procedure qualification record.
7. WELDER QUALIFICATION
7.1 Before starting production welding, all welders shall be
qualified in accordance with approved welding procedures, for the process,
position, and welding direction to be used.
Welders shall make a test weld and satisfy applicable requirements of
the DNV-OS-F101, Appendix C, Article B.
7.2
Qualification tests shall be carried out with
identical equipment to that used during production welding, and normally where
production welding is to take place, i.e. work shop, yard, vessel. Test welds are to be carried out by two
welders per joint in accordance with the qualified weld procedure(s). Welders shall be qualified based on test
results from their respective weld sections, and at CONTRACTOR expense. Testing
shall be in accordance with DNV-OS-F101, Appendix C Article B
7.3
Should CONTRACTOR employ welder(s) who have
qualified to any COMPANY approved existing welding procedure(s) (see Section
2.2 above), within the previous six months, CONTRACTOR may submit such welder
qualification(s) for COMPANY review. COMPANY, at its sole discretion, may
accept some or all such existing welder qualification(s) in place of requiring
new welder qualification(S).
7.4 Welder qualification reports for each procedure a welder
qualifies to shall include all data shown in the DNV-OS-F101, plus procedure
identification. These reports shall be submitted for COMPANY approval.
8. PREPARATION FOR PRODUCTION WELDING
8.1 Internal
line-up clamps shall be used to ensure accurate alignment and spacing, and shall
not be removed until one hundred percent (100%) of the first pass is
completed. An external line-up clamp may
be used where it is impractical to use an internal clamp, subject to prior
COMPANY approval. External line-up
clamps shall not be removed until a minimum fifty percent (50%) of the first
pass has been completed, evenly distributed around the pipe circumference or as
required by the approved procedure.
8.2 When tack welds are necessary for
alignment, these shall be made in the weld groove, using a qualified welding
procedure. Defective tack welds are to
be completely removed.
8.3 Welding repairs shall not be allowed on
the pipe end bevel. If the defect cannot
be ground out within the limits specified, a new bevel shall be cut.
8.4 Pipe ends shall be cleaned by power
driven wire brushes and / or grinders to the base metal, for a minimum 25mm
from the prepared edge, on both the pipe inside and outside.
8.5
Whenever ultrasonic testing is used for
examination of girth welds, the cut pipe ends shall have a minimum 50mm wide
band 100% inspected for laminations. Any laminations that would interfere with
the UT inspection of the weld shall be removed by cutting back the end of the
pipe to remove the lamination and pipe ends re-inspected in accordance with the
original requirements.
9. GROUNDING AND STRAY ARCS
9.1
Grounding methods and equipment shall be used in
a manner to prevent arc burns to pipe surfaces outside the weld bevel. Electrode holders shall be fully insulated
types, to minimize risks of accidental stray arcs. Arcs shall only be struck on
the weld fusion faces.
9.2 Arc burns outside the fusion faces caused by carelessness,
poor workmanship, poor ground connections and faulty equipment shall be cut out
by CONTRACTOR. CONTRACTOR shall remove
the entire pipe cylinder affected by an arc burn, prepare two new bevels, and
make a new weld to join unaffected pipe sections.
9.3 COMPANY may under certain circumstances, and without setting a
precedent, allow CONTRACTOR to repair an arc burn, should all the following
conditions be met:
•
CONTRACTOR shall completely
remove the arc burn by grinding, and smoothly transition the ground area to
adjoining unaffected pipe wall, leaving no stress risers. CONTRACTOR shall check arc burn removal by
etching with a twenty percent (20%) solution of ammonium persulfate.
•
CONTRACTOR shall prove, to
COMPANY satisfaction, the absence of surface cracking or defects, using
COMPANY-approved Magnetic Particle Inspection (MPI). MPI shall be applied in accordance with the
manufacturer's procedures. Any further
surface cracking or defects found shall be removed by grinding and checked by
MPI, until there are no surface cracks or defects.
•
CONTRACTOR shall determine
minimum remaining pipe wall in the repaired area, using Ultrasonic Testing (UT)
techniques in accordance with the manufactures procedures, and following
equipment calibration with a calibration plate of appropriate thickness. The
repair can be accepted if the remaining wall thickness is within the specified
pipe wall tolerance
10. MARKING OF PRODUCTION WELDS
10.1 Each root
bead welder shall place his unique identification number on the upper half of
the anti-corrosion or weight coating, immediately adjacent to his weld. All other welders shall write their
identification unique numbers beneath those markings with a weatherproof
crayon, or other COMPANY approved material which shall not be detrimental to
the coating or the pipe.
10.2 No welder
shall change his unique identification number under any circumstances, for the
entire construction period. Should a
welder be terminated from the Work, no other welder shall use his
identification number.
11. PRODUCTION WELDING
11.1 Production
welding shall be in accordance with Article G of Appendix C of the DNV-OS-F101
and the following requirements. No
welding shall be performed when surfaces are wet, when rain is falling on
surfaces to be welded or during high winds, unless the welders and the work are
properly protected. Unacceptable weather
conditions shall be determined at COMPANY discretion.
11.2
Where pre- or post-weld heat treatment is
required for approved welding procedures, no production welds shall be accepted
unless both temperature level and heat treatment duration is maintained within
procedure qualification test parameters.
Pre- or post-weld heat treatment shall be monitored by thermocouples,
"Tempilsticks", or other COMPANY approved devices.
11.3
Tack welds incorporated in the final weld shall
be thoroughly cleaned of scale and prepared by grinding each end to ensure
complete root continuity. All tack welds
shall be made in accordance with approved welding procedure. Minimum tack weld
length shall be 75 mm.
11.4 For any SMAW welding, hot passes shall be started within 5
minutes of root bead completion. Should
CONTRACTOR fail to start the hot pass within 5 minutes of completing the root
bead, the weld shall be cut out.
11.5 Each weld
pass shall be cleaned to remove any remaining slag or flux, using power brushes
and grinders where feasible, before a further pass is applied.
11.6 While making a weld, visible welding defects, such as cracks and
cavities, shall be completely removed, with particular attention paid to
cleanliness of the junctions between weld metal and fusion faces, before
deposition of further weld metal.
11.7 Surface porosity clusters, stops, starts and high points shall be
removed by grinding as allowed by applicable standards.
11.8 Completed welds shall meet requirements of the DNV-OS-F101,
except that the weld reinforcement height shall not be less than 0.8 mm nor
more than 1.6 mm above the pipe surface, and shall tie-in at least 1.6 mm of
parent metal on each side of the bevel.
11.9 If the
pipeline must be laid down on the sea floor during offshore pipelay, all weld
passes including the capping pass shall be completed. Should welding be stopped without abandoning
the pipeline, weld passes shall be added to all welds that have been started
until fifty percent (50%) of the weld has been completed.
11.10 Prior to
restarting after interruptions, all incomplete welds shall be subjected to MPI
and preheated to the minimum preheat temperature specified in the approved WPS.
Welds that do not meet the above criteria shall be cut out.
11.11
Shielding shall be provided as required to
prevent damage to pipe coating from
weld spatter
12.
VISUAL INSPECTION OF WELDS
12.1 All
completed production welds shall be thoroughly cleaned by power wire
brushes or grinders, prior to visual
weld examination and shall meet the requirements of the DNV Rules, Article A800 of Section 9 and Appendix
D.
13. N.D.T.
OF COMPLETED WELDS
13.1 Non-Destructive Testing (NDT) applied to
complete pipeline welds shall comply with Project Specification for Pipeline
NDT (84506-60-30-2L-340).
14. REPAIR OR REMOVAL OF WELDING DEFECTS
14.1 CONTRACTOR
shall quality weld repair procedures for COMPANY approval prior to
construction. No weld shall be repaired without prior COMPANY approval, and
then only as directed by COMPANY and in
accordance with COMPANY approved weld repair procedures.
14.2
Only low hydrogen welding processes shall be
used for repairs.
14.3 Weld repair
procedures are to be prepared and shall contain the following information in
addition to the requirements of the DNV-OS-F101, Appendix C, Article G.
•
Defect removal method
•
Preparation of repair area
•
Details of low hydrogen
electrodes proposed
•
Non-Destructive Testing (to
confirm defect removal)
•
Permissible minimum and
maximum weld repair sizes (repair cavity shall be in accordance with
DNV-OS-F101, Appendix C, Article G300)
•
Back welding shall be
considered a repair and procedures for back welding shall be submitted to
COMPANY as approved and qualified before use.
14.4
If the repair station is aft of lay vessel
tensioners, CONTRACTOR shall define by fracture analysis, the maximum cut-out
lengths permissible in accordance with DNV-os-F101, at all positions around the
pipe for depth of 25%, 50%, 75% and 100% wall thickness.
14.5
Repair test welds are to be made in the overhead
through vertical position, using sections of pipe chosen at random from the
purchased linepipe
14.6
Test specimens removed from repair qualification
welds shall be tested in accordance with the DNV-OS-F101. The tests shall
include one tensile, one nick break, two side bends, one set of CVN impact
tests (taken through the weld deposit), and one macro section with HV-10
hardness test. The tests shall comply with the requirements specified for the
original welds.
14.7
Repair welds shall be made by welder(s)
qualified to approved weld repair procedures.
14.8 Defects shall be removed by grinding or arc-air gouging a
gradually tapered cut from below the defect to the weld metal surface at both
the ends and sides. Cut width and
profile shall allow adequate access for welding electrodes. Before starting repair welds, COMPANY shall
be satisfied the defect is removed and the gouge shape is acceptable.
14.9 Grinding
shall be performed after any arc air gouging to remove any carbon pick-up.
14.10 CONTRACTOR shall inspect the repair groove by
approved non-destructive testing methods after defect removal, to ensure
defect(s) are completely removed.
14.11 COMPANY
shall allow only one repair of each defect, and repaired welds shall be subject
to the same testing, inspection and acceptance criteria as original welds. Weld repairs shall be re inspected using the
same methods (as a minimum) by CONTRACTOR, covering the repaired area and an
additional 50 mm length at each end of the repair area.
14.12 Second repairs of root flaws (repair of a failed
repair) are not permitted, and CONTRACTOR shall cut out the weld. However, should the second radiograph clearly
show an unchanged defect that was missed completely during the repair attempt,
COMPANY may allow a second repair attempt on that defect, at COMPANY sole
discretion, and without setting a precedent.
14.13 Since
radiographic examination methods shows defects in only two (2) dimensions, COMPANY may reject welds if in
the opinion of COMPANY, the defect depth affects the weld strength, regardless
of the fact that these welds meet the standards of inspection.
14.14 Should two or more welders make a defective weld,
CONTRACTOR welding foremen and COMPANY shall decide which welder is responsible
for the defective work. CONTRACTOR shall
remove from the job any welder, who, in COMPANY judgment, is responsible for an
excessive number of defective welds, even though the welder has satisfactorily
passed the qualifying tests.
14.15 Preheat temperature for repair welding shall be
specified (min 50*C above normal production welding) by the CONTRACTOR
in the proposed welding procedures.
14.16 All
repairs shall be fully monitored at each stage by QC and recorded on
comprehensive welding inspection check sheets.
14.17 A
complete repair matrix shall be prepared by the CONTRACTOR with all weld repair
information, including but not limited to Barge lay tensions, defect size and
defect orientation.
15.
PIPE END DEFECTS AND REPAIRS
15.1 Pipe end
defects shall be repaired in accordance with Project Specification for Seamless
Linepipe (84506-60-30-2L-210).
16. QUALITY
CONTROL
16.1 Quality Control
System
The CONTRACTOR shall have a
quality control system and quality control manual covering all construction
activities. Controlled copies of the
quality control manual shall be available for COMPANY approval and for monitoring
of all construction activities.
16.2 Material and NDT Traceability
The CONTRACTOR shall establish a
procedure to document and provide complete traceability of all primary
materials to their original mill certifications. The procedure shall identify methods for
maintaining the identity of material from manufacturing stages through
transport, receipt, storage, and final component fabrication. A system shall be employed for linking unique
inspection records, weld numbers, and welder identification.
16.3 Quality Control
Procedures
The CONTRACTOR shall establish
detailed procedures for control of welding quality. The procedures shall be submitted for review
and approved by the COMPANY before starting fabrication:
a)
Welding and weld repair
b)
Storage, control, and identification of welding
consumables
c)
Welder qualification records
d)
Inspection / NDT
e)
Post weld heat treatment, if required
f)
Monitoring the progress and quality of welding including
repairs
g)
Material and NDT traceability
17. RECORDS
17.1 Records of
non-destructive testing, including X-ray film, shall be filed to comply with
sequential weld completion, and shall be available for COMPANY review upon
request during construction. Upon Work completion, CONTRACTOR shall submit
all records to COMPANY for permanent retention, as specified in the Contract
Documents. All records shall be clearly
identified and traceable to the physical weld.
All data records shall be
supplied in a hard copy and electronic format.