Is it acceptable to use a coefficient of φ of 0.9 for Class B butt joints of pressure vessels containing extremely hazardous or highly hazardous media?
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Question 1: Is it acceptable to use a coefficient φ of 0.9 for Class B butt joints of pressure vessels containing extremely hazardous or highly hazardous media? 1. Paragraph (1) of Article 3.2.10.2.2.2 of the Fixed Capacity Regulations stipulates that 100% inspection shall be carried out on the butt joints of pressure vessels A and B containing media with an extremely high or high toxicity hazard level. 2. Article 3.2.2.1 of the Code for Fixed Pressure Vessels stipulates that butt joints of pressure vessels of Classes A and B manufactured by welding shall be fully penetrated across the entire cross-section. 3. Article 4.5.2 of GB/T 150 stipulates that in cases where all non-destructive testing is performed, the welding joint factor can be taken as φ=1.0 or φ=0.9. 4. Figure D.1 (continued) f) in Appendix D of GB/T150: Application range – circumferential welds for which double-sided welding is not possible and full penetration is required. 5. Figure D.1 (continued) g) in Appendix D of GB/T150: Applicable to longitudinal and circumferential welds that cannot be welded on both sides and require full penetration. Note: Figure g) applies to the weld joints in single-sided manual arc welding that use TIG welding or similar welding methods for root pass welding, and generally meets the requirement of full penetration. The existing questions are as follows: 1. Are full penetration and complete penetration the same thing? Are full penetration of the entire cross-section and complete penetration the same thing? 2. For the joint structure shown in Figure D.1 (continued) g) in Appendix D of GB/T150, full penetration is generally achievable; however, (continued) f) does not state that full penetration can be achieved. Does this mean that the joint structure in (continued) f) cannot guarantee full penetration? 3. The Code for Fixed Pressure Vessels requires that butt joints of pressure vessels of Category A and B shall achieve full penetration across the entire cross-section. If a structure such as that shown in Figure D.1 (continued) f) of Appendix D to GB/T 150 cannot ensure full penetration, does this mean that such a joint structure cannot be used in butt joints of pressure vessels of Category B? 4. For Class B butt joints of pressure vessels containing extremely hazardous or highly hazardous media, the structure shown in Figure D.1 (continued) f) of Appendix D to GB/T150 shall be used for 100% inspection; is it acceptable to use a welding joint coefficient of φ = 0.9?
Firstly, the value of 0.9 is favorable… Secondly, for pressure vessels, especially those of extremely great height, a value of 0.9 has not been encountered yet… Thirdly, due to process reasons, the final ring weld with a thickness of less than 800 can be welded using single-sided gas shielded welding, usually TIG welding
I didn’t go through the books to check those welding structures you mentioned, but I really have never seen a weld coefficient of 0.9……
Use 0.9; this means that shims are used in all cases. This method is not generally employed these days, as it is difficult to control both the welding quality and flaw detection, especially at extremely large heights – careful consideration is required
The above statements are purely personal opinions and are for reference only
First, it should be clarified which thickness the diameter formula is used to calculate Is it seam A or seam B? Then, let’s discuss the impact of the weld coefficient for seam B on design calculations.
Thank you! I inquired on the headquarters website and am still waiting for their reply!
There is plenty of margin in the design, so the calculations will pass
This post was last edited by Forgetting = Forgetting on 2021-5-17 09:54. My personal understanding: the appendix provides recommended legends under equal-strength conditions. The selection of the welding joint coefficient is based on the principle of achieving savings while ensuring safety. 1. Appendix D1, continuation of f: When there is a gasket in the structure of the welded joint, the corresponding coefficient is necessarily 0.9; this applies to the case of surfacing processes. Choosing a coefficient of 0.9 means that the base materials on both sides of the welded joint need to be thickened in order to meet the design requirements (e.g., in multi-layer pressure vessels). After shaping, the gasket does not need to be removed. The presence of a gasket inevitably leads to stress concentration and shifts in stress points. At the same time, the welding metallurgy of the entire weld area is also an important consideration, involving factors such as the tensile strength of the metal after welding, differences in impact absorption capacity, the degree of metal dilution in the heat-affected zone, and element loss during welding. The stress strength of weld seam B is lower than that of weld seam A. Therefore, although this structure achieves full penetration, it is only suitable for Type B joints. The inherent characteristic of a structure with full penetration across the entire cross-section is that the tensile strength of the weld is not lower than the minimum value of that of the base material; moreover, issues such as stress have been thoroughly considered during the design of the welded joint structure, and their effectiveness has been verified over many years of actual use.