Carbon Steel RF to Carbon Steel FF Flange Connection a Poor Practice? 1

[DGrayPPD]

Although mechanically I know that this is okay, it is my understanding that connecting a raised face flange to flat face flange is a poor piping practice and should be avoided regardless of what material the flanges are.

Am I correct?

 

[moltenmetal]

FF to FF and RF to RF is safe, always, but like all rules of thumb, it is a suboptimization rather than a real solution to a real problem.

FF to RF is permissible, sometimes, without meaningful negative consequences. Permitting FF to RF when both flanges are ductile is NOT bad practice. In some cases is unavoidable, i.e. when one of the flanges isn't in fact raised face, but rather is a LAP JOINT.