Purge packing refers to a packing case modified to accept an external purge pressure 15 to 20 psi above the primary packing vent/drain pressure with no more than 5 psi external system back pressure. The purge gas must be sweet natural gas or an inert gas, such as nitrogen. The purpose of purge gas is to block and contain hazardous, toxic, flammable or corrosive gases, and to prevent such from entering the compressor frame where damage to the running gear, or personnel safety hazards can occur.
Packing case materials are cast iron and steel. When steel is used, it is heat treated to be in compliance with NACE. Garter springs are 316 stainless steel, for both sweet and sour applications (acceptable for sour service based upon acceptable field experience).
