What is the experimental scientific basis for the weld spacing in pipeline welding?
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◆The distance between welds during pipeline welding, as specified in clause 6.0.2 of GB50235-2010: The distance between the center planes of two butt welds on a straight pipe shall not be less than 150 mm when the nominal diameter of the pipe is 150 mm or greater. When the nominal diameter is less than 100 mm, it shall not be less than the outer diameter of the pipe and shall not be less than 100 mm. In addition to using fixed elbows, the distance between the pipe weld and the starting point of the elbow must be at least equal to the outer diameter of the pipe, and also at least 100 mm. The distance from the pipe weld to the edge of the opening in the branch pipe fitting or half-pipe joint must be no less than 50 mm, and it must also be no less than the outer diameter of the opening. The clear distance between the circumferential weld of the pipe and the support or hanger shall not be less than 50 mm. The clear distance between the weld that requires heat treatment and the support or hanger must be not less than 5 times the width of the weld, and must also be not less than 100 mm. Other standards are similar and will not be listed here. The explanatory notes to this standard interpret these requirements as follows: to avoid excessive concentration of welds that could lead to stress buildup, thereby preventing potential failure of the welded joint. Also consider how the location affects the welder’s work and the progress of heat treatment. ◆Since our domestic standards set such clear requirements, why don’t international advanced standards such as ASME31.3 include similar provisions? Mr. Yue Jincai, one of the most influential experts in the field of pressure pipelines in China, raised doubts about such provisions in standards such as GB50235 and SH3501 in his book \"Pressure Pipeline Technology\": The requirement regarding the distance between welds and supports can be attributed to the fact that welds are weak areas, and therefore they can be placed at a greater distance from areas subject to concentrated loads such as supports. As for the other provisions, they lack a theoretical basis. The size range of the heat-affected zone of welds is approximately 22 mm for gas welding, and no more than 6 mm for arc welding; the spacing requirements specified in the aforementioned standards are far higher than these values. If ease of weld heat treatment is a consideration, then keeping the distance between the two welds small allows them to be heat-treated together. Regarding the distance between the weld and the starting point of the elbow, in the case of non-standard elbows such as bent elbows, their stress concentration factor is lower than that of standard elbows, while their flexibility factor is higher; therefore, there is even less need for such a specification. So, the question is: what is the basis for such standards? I don’t know. Anyway, ASME B31.3 does not require this. What do you all think?
Why isn’t anyone answering? Please reply; I really want to know too – what is the basis for this decision?
In fact, some of the provisions in the standards have no theoretical basis; they are purely decisions made arbitrarily. Regarding these size limitations you mentioned, if a reason is needed, it can be said that although the heat-affected zone of a weld is quite narrow, it is safer to keep a distance from this zone; as to what exactly that distance should be, these values were established to ensure consistency. :lol
These are all forms of experience – including experience with materials, design, and construction – and it’s certainly not necessary to test every type of pipe
If there are no distance requirements, and the weld needs to be inspected using RT radiography, how should the test patches be applied? What is the width of a film strip? The clear distance between the circumferential weld of the pipe and the supports or hangers must be no less than 50 mm. If this distance is smaller than the specified value, it will be impossible to apply the inspection tags after welding – how can inspection then be carried out? If the diameter is large and the thickness is high, how should it be polished? What width is required for ultrasonic polishing? In my opinion, the technical specifications for installation are reasonable; even from a testing perspective, the numerical requirements are appropriate, and there are no regulations stating that testing is not necessary in such cases. Construction should not proceed to the next stage until the previous one is completed; otherwise, that next stage cannot be carried out. To give another inappropriate example, there should be no welds in pipes placed within wall sleeves. It’s not that welders are unable to do this, but it relates to how such defects can be detected and repaired later on. One should not walk in such a way as to leave no path for others.
What you said makes sense; the actual situation should be handled flexibly
Our standards are also based on American standards; those standards specify minimum requirements for weld spacing as well. =========================== Information on weld arrangement: https://bbs.hcbbs.com/thread-790569-1-1.html (Source: Haichuan Chemical Industry Forum)