Flange Flatness Helps Prevent Leaks

Having a hard time sealing certain bolted flange connections? Your flange faces may not be flat enough!

Yes, the flange seating face flatness tolerances may be buried inside of a Nonmandatory PCC-1 Appendix, but that does not mean that they are not important. In fact, maintaining these tolerances may help prevent the gasket from “walking” out of the flange for hard-to-seal bolted flange connections.

I find the tolerances in ASME PCC-1 Table D-2-1 to be most useful for in-service bolted flange connections that have begun to leak over time. This table includes acceptable tolerances for both the circumferential flange seating surface flatness and the radial flange seating surface flatness. Machining the flange face back to these acceptable flatness tolerances may be your best bet for solving difficult leaks.