Iron and steel pipes were the first kinds of pipes of plumbing used to conduct fluid between hydraulic system components. At present, pipe is the least expensive way to go when assembling hydraulic systems.

Seamless steel pipe is recommended for use in hydraulic systems with the pipe free of rust, scale and dirt

Early classifications of pipe wall thicknesses were: standard, extra heavy and double extra heavy. Today, pipes are classified by schedule number as specified by the American National Services Institute (ANSI). The schedule numbers vary from 10 through to 160. The larger the number, the heavier the wall thickness. The outer pipe diameter stays the same for a given pipe size, while the inside opening becomes smaller as schedule number increases.  

A comparison of early classifications versus the ANSI classification is as follows: Standard – Schedule 40, Extra Heavy – Schedule 80. The double extra heavy classification does not compare with a schedule number. However, the inside diameter of a double extra heavy pipe is approximately one half that of a schedule 160 pipe.     

In many cases, flanges are welded to the pipe ends and gaskets or “O” rings are used to seal the hydraulic connections. Various pipe fittings are used to route the piping to and from each of the hydraulic components in the system

These fittings can be threaded or welded in place as the need arises. Threaded connections are used in low hydraulic pressure applications and welded connections are used if high hydraulic pressure, high temperature or a severe mechanical load exists.    

All piping should be secured with clamps to prevent vibration and excessive stress due to the weight of the fluid. Do not weld the clamps to the pipe as it may weaken the pipe and cause a stress crack.