Steel pipe imperfection and Steel pipe defect concepts

What are steel pipe imperfections and steel pipe defects?

- Steel pipe imperfection (English word imperfection) refers to the discontinuities or irregularities on the product that are detected according to the method given by the applicable standard.

- Steel pipe defect (English word defect) refers to a defect of sufficient size that becomes the basis for product rejection by applicable standards.

Yes, steel pipe defect is more serious than steel pipe imperfection, just like the difference between illegality and crime. They all mean something is wrong, but to varying degrees.

Common pipe body or pipe end imperfections include pits, cracks, folds, bulges, bruises, gouges, delaminations, hair lines, etc. Manual methods can be used if the depth does not exceed 12.5% of the specified wall thickness of the pipe. It should be completely removed by grinding, but the remaining wall thickness should be within the specified limits, and the area should be smoothly transitioned from the outline of the pipe body during grinding or machining. If the measured remaining wall thickness of the pipe body exceeds 87.5% of the entire pipe body wall thickness, it is a qualified product, otherwise, it is determined to be a non-conforming product. At the same time, it should be noted that imperfection does not allow repair welding. Imperfections or defects found at the pipe end should be marked the cause identified, and mechanically removed as required. Common steel pipe defects include:

(1) Any quenching cracks and arc burns;

(2) Any surface cracking imperfection that reduces the net effective wall thickness to less than 87.5%;

(3) Any surface cracking imperfection with an area greater than 260mm2 detected by non-destructive testing (except appearance inspection) specified in the standard or order;

(4) Any non-surface cracking imperfection within 1.6mm on both sides of the weld that reduces the net effective wall thickness to less than 87.5%;

(5) Any linear imperfection on the inner and outer surfaces in any direction and depth greater than the values shown in Table 1. Therefore, when imperfections or defects appear on steel pipes, they should be dealt with as soon as possible.

There are three main methods of processing:

(1) Grinding or machining of any quenching cracks on the pipe body is not allowed; if the remaining wall thickness is within the specified limit and there are other defects, the defect should be removed by grinding or machining, and the defect should be removed by grinding or machining. There should be a large enough fillet radius to prevent sudden changes in wall thickness; if the grinding depth exceeds 10% of the specified wall thickness, the affected area should be re-inspected to ensure that the defect has been eliminated. The re-inspection should be: a. Use the same method as the original Test the same test equipment with the same sensitivity, or; b Use other NDE methods and prove that they have equal or higher sensitivity than the original method.

(2) Cut off (make sure the remaining length is within the required range)

(3) Rejection