Feature 2 | METHODS AND MATERIALS The test is to simulate, as far as
practicable, the welding techniques and practices to be encountered during production welding. The test assembly should be designed to test the skill of the welder and have the shape and dimensions appropriate to the range of approval required. Each completed test weld is to be examined and tested in accordance with the standard used. Examples of the sorts of tests specified are shown in Table 3 for butt and fillet welds. The qualification of welders is to be
documented by the manufacturer and, in the same way as both the welding procedure specification and the welding procedure qualification record, is to be documented by the shipyard. All such records are to be available for review by the surveyor. The welder qualification test, if
• welding process • back gouging
successfully carried out, will qualify the welder to a number of essential variables arising from test weld carried out. These include:
• parent material type • thickness and diameter • joint type
• welding position • welding consumable type
• shielding gas. Te welder is considered to be approved
for an initial period of two years. The welder may retain this qualification for a further two years provided that the shipyard confirms that the welder has used the welding process with acceptable performance in the preceding six months. Where there is any reason to question the welder’s ability, or there is a lack of continuity in the use of the welding process, or insufficient recorded evidence of acceptable weld performance, the welder is required to perform a new qualification test.
Weld inspection during construction Inspection of the welded fabrication is carried out by non-destructive examination techniques (NDE). These include:
46 • visual examination
• surface magnetic particle (MT) or dye penetrant (PT) examination
• volumetric radiographic (RT) or ultrasonic (UT) examination.
In the same way that welding
procedures and individual welders need qual i f icat ions, the use of procedures and the qualification of NDE operators are probably even more important. For each inspection method, operators should be qualified according to a nationally recognised scheme with a grade equivalent to Level II qualification of ISO 9712, SNT-TC-1A, EN 473 or ASNT Central Cer t i f icat ion Program (ACCP) . Operators qualified to Level I may be engaged in the tests under the supervision of personnel qualified to level II or III. In the same way, personnel
responsible for the preparation and approval of NDT procedures should be qualified according to a nationally recognised scheme with a grade equivalent to Level III qualification of ISO 9712, SNT-TC-1A, EN 473 or ASNT Central Certification Program (ACCP). All personnel qualifications should
be verified by certification to prove they are up-to-date and appropriate to the test methods being carried out. The extent of NDE should be in
accordance with the appropriate classification society rules; these identify a minimum number of inspection points dependent on vessel type and size. A typical capesize bulk carrier would require over 3000 checkpoints. In all cases, the extent of applied NDE may be increased at the request of the surveyor where there is reason to question the quality of workmanship of the shipyard. Classification society rules are a
minimum requirement and shipyard quality control departments normally have their own inspection procedures that far exceed the requirements of the classification society. Non-destructive testing should be
conducted after welds have cooled to an ambient temperature and after
Test
Visual Surface crack detection Radiography Bend tests Fracture tests Macro-section
Butt welds
100% -
100% 4
N/R N/R
Fillet welds
100% 100% N/R N/R 1 1
Table 3: Welder qualification test requirements.
post-weld heat treatment where applicable. For steels with specified minimum yield stress of 420 N/ mm2
and above, non-destructive
testing should not be carried out before 48 hours after completion of welding. Where post-weld heat treatment (PWHT) is carried out, the requirement for testing after 48 hours may be relaxed. NA
References
1. IACS, ‘Unified Requirements W11 Normal and higher strength hull structural steels’, February 2009.
2. Lloyd’s Register, ‘Rules for the Manufacture, Testing and Certification of Materials’, July 2009.
3. Gerritsen CHJ, Howarth DJ, ‘A Review of the Development and Application of Laser and Laser-Arc Hybrid Welding in European Shipbuilding’, 11th CF/ DRDC International Meeting on Naval Applications of Materials Technology, Dartmouth, Nova Scotia, June 2005. (Re-published in the publication “Recent Lloyd’s Register Technical Papers”, February 2009).
4. IACS, ‘Unified Requirements W28 Welding procedure qualification tests of steels for hull construction and marine structures’, November 2006.
5 . I n t e r n a t i o n a l S t a n d a r d s Organisation, ‘ISO 15614-1:2004 Specification and qualification of welding procedures for metallic materials - Welding procedure test - Part 1: Arc and gas welding of steels and arc welding of nickel and nickel alloys’.
The Naval Architect July/August 2010
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