Q. Alignment of piping flanges?

Alignment of piping flanges shall be in accordance with ASME B16.5. This code specifies that:

• Flange centerline misalignment must be within 1/8 in (3 mm) maximum offset.

• Flange planar misalignment must be parallel within 1/16 in per foot (5 mm per meter) of diameter.

• Flange torsional misalignment must be within 1/8 in (3 mm) maximum rotational offset.

Install the gasket on the gasket seating surface and bring the mating flange in contact with the gasket.

Care shall be taken to insure the proper seating and centering of the gasket. Note that spiral wound and double jacketed gaskets are designed for one-time installation and shall not be reused.

Holding gaskets in place often presents a problem, and pipe fitters tend to use greases, pastes, or other substances to stick them to the flange face. This practice should be avoided if at all possible, since it tends to cause serious in-service leaks. If absolutely necessary to use something to hold the gasket in place, thin adhesive tapes may be used, but only along the outside edges of the gasket. Extensive care must be taken to ensure that it does not infringe on the seating surfaces. Tape on the seating surfaces will deform the gasket when made-up; it will then burn or melt out in operation and leakage will occur.