Two types of welded joints can be used: the butt weld and the slip welding joint:
As a rule, pipes with butt weld joints are used for gas and drinking water pipelines; with aggressive aqueous media the slip welding joint can be used as an alternative. The advantage of the latter is a continuous internal protection of the pipe string.
In addition, the use of non-permanent, mechanical connections (coupling and flange connection) is possible in particular for exposed joints. More information can be found here.