The pipes made by casting molten iron above No. 18 and adding a nodularizing agent through high-speed centrifugal casting of a centrifugal ductile iron machine are called "ductile iron pipes", referred to as ball pipes, ductile iron pipes, and ductile iron pipes for short. Compared with carbon steel seamless pipes, ductile iron pipes are more suitable for the transportation of tap water, and are ideal materials for tap water pipes.

The manufacture of welded steel pipes generally undergoes major processes such as uncoiling, straightening, trimming, forming, and welding, as well as a series of auxiliary processes such as flaw detection, flattening, and pressure testing.

Steel sheet piles and soil retaining structures are less rigid than underground diaphragm walls and mixing piles. If the design and construction are not taken seriously, the foundation pit (trough) will become unstable, seepage and leakage of slurry and mud will cause the surrounding foundation soil to settle, and cause damage to surrounding buildings and pipelines.

Steel pipes (seamless steel pipes, welded steel pipes, etc.) can be divided into three types of damage during shipping: rust damage, physical damage, and corrosion

Stress relief annealing is a process of heating steel pipes (seamless pipes, welded steel pipes) to an appropriate temperature, and gradually cooling down after holding for a certain period of time. Its purpose is to remove the residual stress of the steel pipe due to machining, deformation processing, casting, forging, heat treatment and welding.

Among the standards for seamless steel pipes and welded steel pipes, Brinell hardness is the most widely used, and the indentation diameter is often used to express the hardness of the material, which is intuitive and convenient. But it is not suitable for steel pipes of harder or thinner steel.