API Standard 682, titled "Pumps - Shaft Sealing Systems for Centrifugal and Rotary Pumps," is the American Petroleum Institute (API) standard for end-face mechanical seals.
[1] The purpose of API 682 is to assist in the selection and operation of end face mechanical seals in centrifugal pumps.
It is based on the combined knowledge and experience of seal manufacturers, engineering companies, and end users.
This Task Force was composed of fourteen members from various refineries, seal and pump manufacturers.
[2] One interesting aspect of API 682 is that it includes a strong set of defaults.
The mission statement for the 1st Edition was: "This standard is designed to default to the equipment types most commonly supplied that have a high probability of meeting the objective of at least three years of uninterrupted service while complying with emissions regulations.
The task force decided to use a more descriptive designation and chose to define dual seal arrangements.
API 682 seals were to have a high probability of three years of reliable service.
In order to prove this, seal performance testing on process fluids under representative pressures and temperatures was required.
The goal of the qualification test was to simulate a long-term steady state run followed by a process upset.
[3] One of the major criticisms of API 682 1st Edition was that all the seals were “heavy duty” and therefore expensive with no alternatives for easy services.
To some degree, this was intentional and was done in order to reduce inventory, promote familiarity with a limited number of seal types and to increase reliability.
Broadening the scope of pumps covered by API 682 would allow standardized seals to be applied in a greater number of industries.
Design features include a distributed flush and floating throttle bushing for single seals.
Such containment seals must therefore be designed for continuous dry running while meeting the reliability goals of the standard.
In some of these services, it is impossible to obtain adequate vapor margins to prevent flashing of the fluid in the seal chamber.
The ISO Organization made slight editorial changes to 2nd Edition, including correcting typographical errors and unit conversions.
[6] Fourth Edition added additional specifications for clearances, placed these requirements in the form of tables and noted that seal components are not to be considered as “shaft catchers” to restrict shaft movement.
In particular, the piping plans now default to using transmitters with local indicators as part of the instrumentation.