17.02 Should pipe in buildings be threaded or welded?

Aboveground piping may be threaded or welded. We highly recommend welded pipe joints for aboveground piping to minimize the risk of leaks. Either butt weld or socket weld fittings are appropriate.

There are locations where welded joints are not practical and threaded joints are allowed: connection to tanks and equipment, connections to existing fuel system piping, and connection to threaded valves and accessories.

Threaded pipe fittings are commonly malleable iron – not cast iron, and are typically Class 150 or Class 300 rated. Many contractors use forged fittings for unions, because of their superior sealing characteristics, or replace unions with flange connections.