Welder Qualification Range on a Thickness Change
A welder qualified with a 10 mm test coupon in the 6G position using GTAW root and SMAW fill is assigned to weld a 20 mm thick pipe in the 6G position using the same process combination. The qualification record shows the test passed RT and bend tests. The WPS for the production joint covers 15-25 mm thickness and requires a 150 C preheat. The welder has not welded 20 mm pipe before. The supervisor argues the 6G position is the hardest, so a 10 mm 6G test covers anything thicker in the same position.
1. Does the 10 mm qualification cover the 20 mm production joint? Explain the thickness range rules.
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Position and thickness are separate essential variables. Qualifying in 6G covers the positions within that test's range, but thickness coverage is governed by the thickness rules of the qualification standard, not by position difficulty. Under common rules, a test coupon of 10 mm thickness qualifies a range that is typically bounded above by a multiple of the test thickness, often 2T, so 10 mm would cover up to about 20 mm only if the standard's multiplier and any minimum apply. The answer must be checked against the specific code in force: some standards limit the upper qualified thickness to 2T for the test, others use different factors, and pipe diameter also has its own range. The supervisor's 'hardest position' argument is not a thickness rule and cannot substitute. The inspector should verify the qualified thickness range on the record and, if 20 mm is outside it, require a new qualification or a qualified welder.
2. What else must be verified before this welder starts the production joint?
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The welder must be qualified for the process combination, the position, the thickness, and the pipe diameter range. The WPS must be qualified and must cover 15-25 mm and the 150 C preheat. The welder must be briefed on the WPS, and preheat must be applied and measured before welding. Consumables must be controlled: GTAW filler and SMAW electrodes must be stored and issued correctly, and low-hydrogen electrodes must be held in a holding oven. The welder's continuity of qualification should be current. The inspector should also confirm the joint fit-up and that the welder has demonstrated the technique on the actual thickness, for example by a first-article weld with RT or by a supervised start. Records of all of this should be retained in the quality file.