How to measure the thickness of elbow?

Ha ha, that's for sure. If you measure a seamless elbow in this question, then the thin part must be placed on the inner arc when pushing (the seamless pipe has a partial wall), and this question you said is normal. But no matter which part or point is measured, as long as the thickness of any part of the elbow is not less than 87.5% of the required wall thickness when you order, as long as it is lower than this thickness, both the inner arc and the outer arc are unqualified. 87.5% is stipulated in the standard. On the contrary, the positive and negative deviation of elbow wall thickness is 12.5%, with the thickest not higher than 1 12.5% and the thinnest not lower than 87.5%, but generally only the thinnest is required, not the thickest. A little thicker is fine. But if it is a power pipe fitting, negative deviation is not allowed. That is to say, if it is * 10 thick, the thickness of any part of the elbow shall not be less than 10 thick.