Can different grades of PE be connected to each other?

Butt fusion
It is possible to butt fuse pipes and fittings of different grades and SDR (Standard Dimensional Ratio), but this is very rarely undertaken and should only be carried out under controlled conditions and in accordance with the instructions of the pipe and/or fitting suppliers.

Where there are pipes of the same grade, e.g. PE100, but different wall thicknesses, the preferred approach is to machine down the end of the thicker wall pipe or fitting using a lathe or similar machine so that the pipe wall thicknesses on both sides of the joint interface are identical. The reduction of the wall thickness should not be in the form of a step, but in the shape of a cone.

Electrofusion
Electrofusion fittings are more commonly used to join different grades and SDRs of PE pipe. Again this should only be carried out in accordance with the instructions of the pipe and/or fitting suppliers. Special care needs to be taken to avoid collapse of thinner pipes during the fusion period.

Electrofusion fittings may also be of different grade and SDR than the pipes, in which case the lower rating (pipe or fitting) governs the rating of the assembly as a whole.

Mechanical fittings 
Special mechanical fittings are more commonly used to connect different grades and SDRs of PE pipe and even to join PE pipes to metallic pipes etc. Care should be taken to follow the fitting manufacturer’s instructions.

General Note

The use of different grades and SDRs can reduce the maximum operating pressure of a network and this should be taken into account when designing and operating the network.