In general, the pipes that produced in solid form with smooth outside and inside layer is called Single-wall pipe. It must be mention that, single-wall pipes has not any profile between the layers. The main purposes of using this pipe are when the fluid inside has pressure or for the conditions when the pipe diameter which is required in project is small which is not available in double-wall pipes.
Raw materials for production of this pipe are HDPE100 and HDPE80 (in our country). Previously HDPE63 was, also, in this group which do not use anymore for this purpose. Using HDPE100 instead of HDPE80 for the same diameter and thickness of the pipe result to increase the resistance of the pipe against inside pressure. So, for reaching to the same tolerability of inside pressure for the specific diameter in single-wall pipes by using HDPE100, in comparison with HDPE80, the thickness of the wall will decrease. So, HDPE100 is more common to use in single-wall pipes unless there is a need to have more thickness in wall because there are some small amount of outside pressure or for packing condition.
In double-wall pipes inside diameter of the pipe is considered where as in single-wall pipes the outside diameter is considered. By increasing the tolerability of inside pressure of a pipe the thickness of the pipe will increase. As a result, the area which fluid can transported through will decrease. For this reason, there is need to be more accurate for calculating the pressure resistance amount with consideration of confidence coefficient which is required.
Butt Welding is one of the most usable type of connection is single-layer pipes. In this kind of connection, after melting the two end side of the pipes, by forcing and putting the pressure in both pipes to each other the connecting process will happen and after cooling down they remove the pressure.