High Pressure Noncontacting Mechanical Seal For API Applications

Abstract

Since the introduction of noncontacting, gas lubricated, dual pressurized mechanical seals for process pumps over five years ago, and they have primarily been applied to ANSI pumps and other applications where the barrier pressure was below 300 psig. This pressure limit was not due to a limitation in material strength or face pattern technology as noncontacting seals have been applied in compressors at pressures well above this. The challenge came in fitting a dual pressurized cartridge seal into the limited size seal cavity available in most process pumps. The radial and axial dimensions of a pump seal chamber limit the size and shape of the seal faces as well as the supporting hardware needed to make a convenient cartridge seal design. A pressure responsive primary sealing ring geometry has been developed to allow a dual pressurized sealing arrangement to routinely handle pressures up to 600 psig. This pressure capability enables the dual pressurized gas seal to be utilized in applications generally found in the API market where contacting liquid lubricated seals are commonly used options. Discussed herein are the design, theoretical results obtained through the use of finite element analysis modelling and test results. Also discussed are the results of a modified API 682 qualification test and details of field installations.