Why is the welding joint coefficient at the opening taken to be the same as the inherent coefficient of the cylinder?
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Dear teachers, I have a question. Regardless of whether there are welds around the opening, or whether the opening is located on a weld and is to be inspected 100% within the 2Dop range, if the welding joint coefficient for the shell itself is 0.85, should the welding joint coefficient for the shell with an opening also be set at 0.85? The reason is as follows: The weld joint coefficient at the opening in the shell is used to determine how much area remains after deducting the calculated thickness from the effective thickness, and this remaining area is then allocated as the reinforcement area A1. When the weld joint coefficient for the shell itself is 0.85, the allowable stress applied to the calculated thickness of the shell is set at 85% of the stress value of the base material; accordingly, the calculated thickness is determined, and thus the effective thickness – that is, the reinforcement area A1 resulting from the calculated thickness – is also determined. Therefore, whether there are welds around the opening or not, or whether a 100% inspection is carried out within the 2Dop area surrounding the opening, it has no impact on the allowable stress, which remains at 0.85[σ]t. As a result, the calculated thickness stays the same, and so does the reinforcement area A1. However, if the weld joint coefficient at the opening is set to 1, based on the condition that there are no welds around the opening or that a 100% inspection is performed in the 2Dop area surrounding it, this means that the allowable stress for the shell becomes [σ]t. This artificially reduces the calculated thickness of the shell and increases the reinforcement area A1. In effect, this approach involves using part of the calculated thickness for reinforcement, leading to an insufficient calculated thickness. Therefore, in order to ensure consistency in the calculated thickness of the cylinder, the welding joint coefficient at the openings in the shell should always be the same as that of the shell itself. Is this the correct understanding?
The manufacturing section of GB150-2011 does not require 100% RT testing of the reinforcement areas at the nozzles, as was the case in GB/T150-1998. Therefore, in terms of design, when conducting partial inspections of the equipment, a weld coefficient of 0.85 should be applied to the welds in the reinforcement areas of the nozzles; whereas for full inspections of the equipment, a weld coefficient of 1 should be used. This is just my personal opinion.
This post was last edited by wanlirn on 2022-11-9 at 16:31. Should the weld joint coefficient for the perforated housing be set to 0.85? Under those conditions you mentioned, it’s not 0.85 that is used, but rather 1. GB150 was issued in 2011, and it has remained the same all these years; the Standardization Committee has provided explanations for this. . Based on the principle of equal-area reinforcement through openings, when there are butt welded joints within the reinforcement area (that is, in the area affected by secondary stresses), the requirements related to the primary stresses of the equipment still apply. However, when there are no butt joints within the reinforcement area, then the entire thickness of the material can be utilized; therefore, it makes no sense to use a value of 0.85 in such cases. On the other hand, what about pipes? For example, if you use a 273*10 seamless pipe, it is also subject to the same quality requirements as the equipment – so should you still use a value of 0.85? ? ? Definitely not
Personal understanding: Whether the welding joint coefficient for the equipment itself is 0.85 or 1 depends on the established testing criteria. The 150 formula is based on structural design and corresponding calculations aimed at achieving equal strength; the welding joint coefficient at the openings should also be consistent with that of the cylinder system
1: GB 150-1998 10.8.2.2 states that “all areas at and below the weld intersections shall be inspected.” 2: GB/T 150.4-2011 10.3.2 specifies that “for items a) to e) listed below, the weld intersections shall be inspected 100%.” (Note: Commas are used here to indicate a list of items.) In summary, both versions convey the same meaning: weld intersections must be inspected 100%. 3: GB/T 150.3-2011 6.1.4 outlines the scope of non-destructive testing, stating that “when an opening passes through or is adjacent to a welded joint in a container, it is necessary to ensure that there are no defects exceeding acceptable limits within a radius of 2dop from the center of the opening.” Combining 1, 2, and 3, all weld joints within a 2dop range around the hole center shall undergo non-destructive testing. 4: In accordance with the provisions of GB/T 150.1-2011 4.5.2.2, for steel vessels, when double-sided welded butt joints or fully penetrated butt joints equivalent to double-sided welding are used and all non-destructive testing is carried out, the welding joint factor is set at 1.0 ； When a single-sided welded butt joint is used (with gussets in close contact with the base metal along the entire length of the weld root) and full non-destructive testing is carried out, the welding joint coefficient is taken as 0.9. 5. The welding joint coefficients for other metal materials are determined in accordance with the relevant referenced standards.
Combining 1, 2, and 3, all weld joints within a 2dop range around the hole center shall undergo non-destructive testing. However, the qualified grade remains the same as that of the cylinder; in this case, 100% does not correspond to a grade of 100% Class II when determining the joint quality. Therefore, it is also not possible to set the welding joint coefficient at 1.
The weld coefficient is only related to the non-destructive testing ratio and the type of weld; it has nothing to do with the acceptable grade of the weld.
This post was last edited by wanlirn on 2022-11-15 08:41. All the requirements regarding non-destructive testing specified in GB150 for pressure vessels must also be met; those in Table 6 for the manufacturing process apply as well. It’s not the case that just by using non-destructive testing on the joints, the welding joint factor can be set to 1. I would like to remind you to carefully understand that the requirements outlined in points a) to e) of 10.3.2 regarding 100% testing for local inspection are different from those concerning the qualification level of butt joints, which involves full testing of all welded joints. In other words, for a single weld, you achieve 100% compliance; however, the required qualification level is grade III, so the welding joint coefficient remains 0.85.
“\"Weld joint coefficient at the opening in the shell\" – Is there any butt weld joint in the shell at the opening? How to remove it without a joint, and how to do it when there is a welded joint? With such a question, the issue becomes clear.
1: GB/T 150.1-2011 4.5.2.1 only states that the welding joint coefficient should be determined based on the type of weld in butt joints and the proportion of length subject to non-destructive testing; it does not mention the acceptable level. Where is then the information regarding the acceptable level mentioned? 2: In my understanding, if all welds at the openings are subject to non-destructive testing, then the acceptance standard for those welds should also be based on the standards applicable to full non-destructive testing, regardless of the proportion of non-destructive testing carried out on the cylinder body or its acceptance criteria.
The weld joint factor applies to AB welds. Under normal circumstances, the openings are avoided in areas with Class A and B welds, so there is no need to introduce a 0.85 coefficient. Even if there are Class A and B welds within the scope of the opening reinforcement calculations, such welds are required to undergo 100% flaw detection, and the welding joint factor should still be set at 1.