Weld coefficient for 100% RT of longitudinal seams without lining in ring girth linings
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I saw on the internet that someone asked whether, for a device with a DN500 size, where there are linings in the circumferential seams but no linings in the longitudinal seams, and which meets the 100% RT Class II standards, the weld coefficient for this device can be set at 1.0 Some people say to use 1.0, as the welding joint coefficient for the equipment is determined by the longitudinal seams; others suggest using 0.9 based on the circumferential seams. What are everyone’s opinions?
I think it should be like this: for ordinary equipment – air storage tanks with a pressure of 1.0 MPa – first of all, the weld coefficient depends only on weld A; it should be determined based on weld A. Moreover, many drawings indicate weld B, but it seems to have little meaning as it isn’t taken into account in the calculations. The inspection of weld B should be carried out based on weld A. Second, attention should be paid to the final weld of devices with a diameter of less than or equal to DN800, as specified in 10.3.4 of GB150.4. Third, when there are no inspection holes, 100% RT testing must be carried out.
I have encountered similar problems before as well; I researched the topic and took notes. Li Shiyu and others believe that although the stress levels experienced vary, under normal circumstances, the quality requirements for the longitudinal and circumferential welds of a container should be the same, meaning that the same welding joint coefficient should be used. However, in strength calculations, when the wall thickness is controlled by circumferential stress, the weld joint coefficient for longitudinal seams should be used. Ding Bomin (see \"Analysis of ASME VIII Pressure Vessel Code\", P52) and others argue that in GB150, even if a value of 1.0 is adopted for welded joints, since Class B joints are not subjected to the maximum principal stress, it is sufficient to inspect all Class A joints, while it is not necessary to inspect all Class B joints. However, there is no disagreement that the value of the weld joint coefficient should be based on the longitudinal seam subjected to the maximum principal stress.
The company has no old-fashioned elements, and new ideas can also take root.
This discussion is good; there are quite a few disputes in production
In China, Ding Bomin was among the first to study the ASME code system and has a deep understanding of it. Regarding the welding joint factor, it is primarily taken into account that the longitudinal seam is subjected to the maximum principal stress; due to the rolling direction of the sheet metal and the coiling process, the longitudinal seam is more critical than the circumferential seam. When designing containers, the most hazardous operating conditions must be considered, hence the welding joint factor is set at Class A, 1.0. As for the proportion of Type B tests, according to the standard requirements, it is indeed \"possible\" not to conduct all of them.
I’ve learned it.* Personally, I think 1.0 would work.
These days, ordinary devices are designed in a way that tries to circumvent regulations – aiming to make things thicker when they should be thinner, and more complex when they should be simpler. It’s unclear how many hidden problems this creates; some devices start leaking within one or two years. The costs associated with repairs or sending them back for refurbishment result in significant losses, making it a case of losing more than one gains. I still recommend that B-seam inspection be equivalent to A-seam, except when there is no requirement for 100% inspection of the tube used in the shell.
The joint factor specified in the drawings is set at 1.0 since the design calculations take longitudinal joints into account; however, as the safety of the equipment is considered as a whole, the proportion of non-destructive testing remains the same for both longitudinal and circumferential joints.
For longitudinal circumferential seams, different welding joint coefficients can be used, and various inspection and testing requirements may apply. The weld structure varies as well; there is no standard that prohibits this, nor does it affect the quality of the equipment – so what’s the problem?
To avoid ambiguity, it is advisable to indicate them separately: longitudinal seam: 1.0, circumferential seam: 0.9. Furthermore, the circumferential weld joint factor is not useless; for example, in containers subjected to external loads such as wind and earthquakes that cause axial stress, this factor still needs to be taken into account when calculating the allowable stress of the material.