Determination of the welding joint coefficient for the head seam of local flaw detection equipment
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For equipment used in local flaw detection of pressure vessels, the weld coefficient for the cylinder shell is taken as 0.85. When the head has seams, full penetration welding is required, along with 100% flaw detection. At this point, should the weld coefficient for the head be 1.0? In this way, regardless of whether the equipment has undergone 100% flaw detection or not, the head weld coefficient should be 1.0. I’m not sure how everyone determines the head weld coefficient; I would appreciate any guidance you can provide!
100% RT MT or PT
It’s not like that. Although the end caps increase the flaw detection rate to 100%, the acceptable quality level still depends on that of the entire equipment. If the cylinder meets the standard of >=20%, it is considered grade III compliant; the head, on the other hand, must meet the 100%-III standard, but the welding joint coefficient remains 0.85
Now, a 100% inspection is required to ensure that the standard is not lower than level II, in accordance with the new fixed capacity regulations
100% testing, grade II compliance; the joint coefficient is set at 1.0； 100% inspection, grade III qualified; the joint coefficient is set at 0.85.
Should the end cap manufactured as a single piece also use a value of 0.85, in line with the cylinder using that coefficient? Should the welding coefficient for cylinders with openings in non-welded areas also be set at 0.85, just like for those cylinders? There’s no need for that; it’s better to look at things from two perspectives ； Wherever there are requirements for a welding coefficient of 1.0 on that end cap, it’s not necessary to use the same value as that of the cylinder ； Moreover, achieving a value of 0.85 will invisibly increase the thickness of the head, and devices that can produce welds must necessarily be of larger diameter.
You have the wrong understanding. GB150 Q&A – This question has been answered. The end cap only increases the inspection rate to 100%; the qualified level depends on the equipment. The tolerance specifications you provided are applicable to the equipment.
Why follow the cylinder? If a 100% inspection can achieve grade II compliance, why then reduce the welding factor? The welding coefficient is not determined by the cylinder; it is based on the inspection ratio and groove type.
I think it should still follow the cylinder standard, with 100% flaw detection, and the acceptance level should be the same as that of the cylinder. I asked the company’s audit officer specifically, and he said that the weld coefficient for the cylinder walls applies mainly to longitudinal welds; for cylinders made of tubes, the weld coefficient is 1, while it is 0.85 for circumferential welds. When there are no seams on the end caps, the value is 1. Therefore, the drawing must indicate whether the weld coefficient applies to longitudinal welds or circumferential welds. I’m not quite in agreement with his statement; having worked on pressure vessel design for so many years, the weld coefficients are always specified based on the cylinder and head.
This post was last edited by zjq1962 on 2018-11-3 at 08:21. There is no basis for requiring that the joint coefficient on the head must be identical to that of the cylinder; conversely, if the required quality standard is increased and the joint coefficient is set to 1.0, the extra thickness required for reinforcing the openings in the pipes connected to the head will be greater. 100% testing has been completed; increasing the joint coefficient is beneficial for cost efficiency.
As I understand it, the head is subject to 100% inspection; if the equipment is rated at level III, then the head can also be rated at level III, and there is no rule prohibiting an upgrade in the rating level.