Why " pre-stressing" ?

The steel of plastic jacket pipes is expanding while heating up from a low pipe laying temperature up to a high temperature in operation.

But the earth covering of the pipe system limits the extension of the steel. This results in exceeding the stress limits of the composite pipe system (steel / plastic jacket and foam).

Therefore, the pipe is pre-stressed to a middle temperature and the trench is refilled in heated condition.

This is where RESITHERM starts to go.