Terminology explanation of deviation and tolerance of steel pipe

　　deviation: in the production process, because the actual size of the STM 304 Carbon Steel Seamless Fluid Pipe is difficult to meet the nominal size requirements, that is, it is often larger or smaller than the nominal size, so the standard specifies that there is a difference between the actual size and the nominal size. If the difference is positive, it is called positive deviation; if the difference is negative, it is called negative deviation.

　　tolerance: the sum of the absolute values of the positive and negative deviation values specified in the standard is called tolerance, or "tolerance zone". Deviation has directionality, that is to say, "positive" or "negative"; tolerance has no directionality, so it is wrong to call deviation value "positive tolerance" or "negative tolerance".