welding coated steel pipes

[miyo]

I have a project of a water line made of steel pipes coated inside with cement-alumina.
Looking for information aout the right way to weld them without harming the coating.

 

[onrush]

Dear miyo,

Coupling is needed to joint two plain end coated pipes.
Welding should be done outside of coated pipe between coupling.

 

[BRIS]

I agree with onrush but assume you mean without damaging the internal lining not the coating. The caoting can be made good after welding. If pipes are 800mm diameter or more you can repair the lining after welding otherwise you ned to use a bell and spigot type joint or coupling with fillet welding onm the outside not butt welding.