An explanation of the welding coefficient of 0.85 – for educational purposes
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It has always been believed that the welding coefficient is selected during design calculations, and the flaw detection level and ratio are determined based on this coefficient. But recently I heard a statement that I had never encountered before; I would like to ask the experts: For pressure vessels at normal pressure, the welding coefficient is 0.85. According to standard 47003.1, double-sided welding or a fully penetrated butt joint equivalent to double-sided welding should be used, and with local non-destructive testing, the value of 0.85 is applicable. Recently I heard a serious claim that full penetration welding can be used without performing non-destructive testing, and in such cases the welding coefficient can still be 0.85. The proportion of testing has no direct relation to the welding coefficient; as long as the customer agrees to this welding coefficient, that’s sufficient. I also worked in design for 2 years before; I only had a basic understanding of it. But hearing this statement really shocked me, and I hope everyone can discuss it more
It seems there’s something similar in ASME, but one cannot deliberately reduce the coefficients in order to avoid NDT; it requires self-discipline – one shouldn’t just try to find loopholes. So I guess such a rule wouldn’t exist in China, as it might lead to distortions: lol:lol
This statement is incorrect. The weld joint factor should be determined based on the weld pattern of the butt joint and the proportion of non-destructive testing.
There is a requirement in the Code for Fixed Vessels, Article 3.15(2) on page P15: It is not allowed to reduce the weld joint coefficient in order to exempt pressure vessel products from non-destructive testing. Since the weld joint coefficient is set at 0.85, testing must be carried out as specified; there is no option of skipping non-destructive testing.
The current view is that it applies to vessels at atmospheric pressure; if they are indeed at atmospheric pressure, I wonder whether this practice exists in the industry
You had better take a close look at the standards for atmospheric pressure vessels. However, for flammable media, as well as those that pose moderate, high, or extreme hazards, it is best to conduct tests in accordance with the standard requirements; otherwise, the consequences of any leakage can be disastrous.
Non-destructive testing is used to determine whether there are any defects in a weld. Even if a weld is fully penetrated, without non-destructive testing, how can we be sure that its strength meets 85% of that of the base material?
This must be carried out strictly in accordance with standards; there must be a basis for it, it can’t just be done because someone says so.
Coefficients are determined by proportions and levels; proportions and levels cannot be inferred from coefficients. Atmospheric pressure vessels explain the welding joint coefficient very clearly. If you don’t want to perform flaw detection, then use 0.6; this has nothing to do with whether full penetration has been achieved or not. As someone mentioned above, the welding joint coefficient should not be artificially reduced in order to avoid flaw detection.