3.4 High Pressure, High Temperature

As metal bellows seals are limited to typically 20 bar if it is required to seal a high temperature above this pressure it is necessary to use a pusher seal design. With the use of high temperature elastomers it may be possible to use the seals up to 250 C, depending on the characteristics of the process fluid, including the atmospheric boiling point, potential for solidification, etc. Depending on the specific fluid characteristics and safety requirements the usual options are to provide either a single seal with special coolant circuit, such as that described for API Plan 23, or a dual seal with a coolant buffer system as described in section 3.4.6.7.

At high rotational speeds, such as in excess of a surface speed of 30 m/s, or approximately 6000 rev/min on a 100 mm shaft, the design of the seal to cater for the speed becomes important. It is necessary for the rotating mass of the seal to be dynamically balanced and be as compact as feasible to minimize centrifugal forces. It is also necessary to provide a stable lubricating film in the seal face with minimal friction to provide stable seal operation with minimum heat generation.

A conventional rotating floating component will create high out-of-balance and potential instability. High speed seals are therefore designed with a stationary floating component with the rotor clamped directly to the shaft. This may be a one piece ring, Figure 3.116(a), or a specialist designed rotating component with a...