Non-standard steel pipe is a special-shaped steel pipe compared with national standard seamless steel pipe except national standard. In the production of seamless steel pipe, it is classified according to the national conventional requirements for external diameter and wall size and thickness, and some errors are allowed, which is within the national standard. In actual use, the national standards often have some limitations, which corresponds to the emergence of non-standard seamless steel pipe, non-standard steel pipe specifications, in order to supplement the GB standard seamless steel pipe production rather than the national standards for seamless steel pipe quality ratio.


In the production of non-standard steel pipes, some national seamless steel pipes or round steel pipes are produced as pipes. Because of small sales volume, the price is often higher than that of common national seamless steel pipes. However, non-standard seamless steel pipes also have drawbacks, because there is no fixed standard requirements, some manufacturers use two seamless steel pipes or defective pipes, so the price is much cheaper. Therefore, the price of non-standard seamless steel tube is often unstable, and the quality of products is uneven.