Can we make a hole for an attachment in a "TEE"? 2

[gvn]

We have a Class 1500# piping system designed to ASME B31.3. Piping is Duplex SS (UNS S31803), 4"NB, 80S. We would like to have a 1" hole drilled radially on the Tee & weldolet type branch welded for Chemical Injection. Is this permitted by B31.3 Code? Also, is it permissble to cut the TEE say 10 to 15mm for welding (fitting to fitting adjustment)? Any guidance will be of great help and appreciated.

 

[JohnBreen]

Hello,

You are describing what would be termed (by B31) an "unlisted component". Sooooo, you would have to either do proof testing or a rigorous analysis (e.g., FEA) to qualify the fitting to the Code requirements for pressure design. Read B31.3 paragraph 304.7.2 carefully.

Consider this, a B16.9 Tee does not meet the Code requirements for "area replacement" for the "hole" at the branch. They work (under pressure loading) because of the smooth grain continuity and the gradual thickness variations. The B16.9 requirement is based upon proof testing. If the fitting is welded to pipe and pressure tested to destruction, the pipe must fail before the fitting fails. There are generally no restrictions on geometry (or wall thickness except at the weld lines) except end-to-end dimensions and "squareness" tolerances. So various manufacturers shape them differently. Some have quite "round or spherical cheeks" others are "barrel shaped" and others quite cylindrical. Some have more generous crotch radii than others. But they are all B16.9 Tees; i.e. they have been shown to be able to survive the proof tests.

When you alter a Standard fitting, you no longer have a proven component and so you must qualify it according to B31.3 paragraph 304.7.2

Good luck with your design.

Best regards, John.