Gas leakage from reciprocating compressors can be more than a loss of product. Leakage of gas to the atmosphere can be a concern from an environmental, health and safety, and area classification perspective. Despite the reason, minimizing or eliminating gas leakage is a goal of all manufacturers, operators and owners of reciprocating compressors. There are several static and dynamic seals where leakage can occur.
This report will discuss the areas of potential leakage and the steps that have been taken to eliminate or reduce leakage at these points from a design perspective. The focus is to offer an understanding of the steps the natural gas industry has already taken to reduce or control gas leakage. The topics discussed include gas piping connections, compressor cylinder valve caps, compressor cylinder heads, unloading devices, piston rod pressure packing and collection for recovery or disposal.
Gas Piping Connection
The type of connections and sealing elements vary in both size and pressure rating. For the most common operating pressures in the natural gas industry, American National Standards Institute (ANSI)-type flanges are applied. Spiral-wound metallic gaskets replaced flat-face, paper-style gaskets long ago.
The sealing capability of spiral-wound gaskets will depend upon the proper flange-to-flange alignment. Once piping is installed properly, leakage at these flanged joints can be eliminated. Higher-pressure piping joints may have ring- or lens-type joint connections. Some smaller lines may be tubing with compression-style fittings. Regardless of the type or size of the connection, good fit-up practices must be followed.
Connections must be properly aligned, avoiding undue force to draw the two mating surfaces together. Gas leak detection methods can be used to confirm positive sealing at piping connections. Analysis and allowance for piping growth from thermal changes will greatly help reduce forces and alignment concerns at the piping connections. . . .
By Dan Hannon
Read the full story in the November issue of COMPRESSORTech2.