Page 425 - Centrifugal Pumps 2E

Mechanical Seals 389

Mechanical Seals for Refinery Service

Refinery services can be broken down into two primary classes based
on temperature:

• Applications below 350°F
• Applications above 350°F

For applications below 350°F elastomeric seals should be used. These
applications may also involve the sealing of high pressure as well. A typi-
cal package seal for this class of service is shown in Figure 17-26.
For applications above 350°F, a metal bellows seal should be used.
Pressure on most high temperature applications will be low and would
not present a problem for most metal bellows available to industry. A
typical package seal for this class of service is shown in Figure 17-27.
Both seals illustrated in Figures 17-26 and 17-27 meet the requirements
of American Petroleum Institute's (API) 610 Standard. This standard
does not cover the design of individual seal components. That is the re-
sponsibility of the seal manufacturer. The standard does cover the mini-
mum requirements of equipment for use in refinery services. These re-
quirements would include:

• Seal chamber and shaft sleeve considerations.
• Hardness of seal materials to be used on a pump shaft.
• Preferred use of balanced seals unless otherwise specified.
• Containment of seal face leakage by one of the following arrange-
ments:
Single seal with an auxiliary sealing device such as a floating close
clearance bushing or other suitable device.
Tandem seal arrangement with a barrier fluid maintained at a pres-
sure lower than seal chamber pressure.
Double seal arrangement with a barrier fluid maintained at a pres-
sure greater than seal chamber pressure.
• Gland plate design including register fit to the seal chamber and con-
finement of static seals.

Materials of construction are identified as well as piping plans for seal
installations. Piping plans for seal installations are so important that they
are shown in Figures 17-28A and B for easy reference. API Specification
610 represents the collective knowledge and experience of end users,
pump and seal manufacturers. This specification is updated periodically,
and anyone involved in refinery equipment should have an updated copy
of the specification from the American Petroleum Institute.