NACE 0175 - PREQUALIFIED MATERIALS

NACE MR 0175 is not concerned with threads or geometry, it is strictly concerned with whether the material can withstand Stress Corrosion Cracking due to exposure to H2S. The materials are qualified by NACE test Procedure TM 0175.

Socketweld connections are typically not allowed because the welding process alters the material, both thermally and chemically.

I am unaware of any restriction on threaded connections.

Strider, the issue with welding is actually a lot more complicated than that depending on the material in question. the problems with welding almost always are due to a HAZ that has gotten HARDER than allowed. But there may be other metallurgical issues as well depending on the particular alloy in question and it's hardening mechanism.

Hard materials crack in H2S when softer ones don't. Think of the crystal atomic bonds of the metal like rubber bands, the tighter you stretch them, the harder it is to move them any further, but the easier it is to break them.