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Who or What Is API Standard 682?

API is the American Petroleum Institute, a national trade association that represents all aspects of America’s oil and natural gas industry. Due to the wide acceptance of the standards, other heavy industries have adopted API standards, including pipeline standards, hazard management practices, and so on.

 API has developed more than 800 standards governing operational safety, environmental protection, and sustainability in the oil, gas, and petrochemical industries.

API 682 Flush Piping Plan 52

The performance and reliability of mechanical seals are directly affected by the configuration of the piping that integrates them into the systems they serve. In Appendix G of the 682 Standard, API lays out requirements and recommendations for designing effective piping support systems for dozens of the oil and gas industry’s most common mechanical seal applications. 

In Appendix G, Standard 682 includes a number of flush piping plans that feature tandem arrangement seals consisting of two mechanical sealing elements  to provide enhanced protection for operators and the environment. These dual seals are further classified as either be pressurized, like Plans 53A and 53B, or unpressurized, like Plan 52. 

Used primarily in oil and gas applications, and, to a lesser degree, in chemical processing and power generation, Plan 52 is often the best choice for operations involving light hydrocarbons and other liquids with high vapor pressure. Here is why: 

Plan 52 Specifics

In Plan 52, a clean, unpressurized buffer fluid is held in an external reservoir (pot) and circulated by a pumping ring between the internal and external seals, forming a buffer between the process fluid and the surrounding environment. The buffer fluid supplied to the secondary seal provides lubrication to the sealing elements and provides an outlet in the event of a process upset or seal failure.   

The buffer fluid must be maintained at a pressure lower than seal chamber pressure, and under 0.28 MPa (2.8 bar) (40 psi). Buffer liquid is circulated to and from the reservoir by means of an internal circulating device.

The configuration and geometry of the piping plan, the material construction of its elements, the type of buffer fluid, and the volume of the reservoir should all be determined by the specifications of the intended application.

Stein Seal Industrial can provide standard API seal buffer plans as well as custom-designed seal buffer pots designed to meet system requirements.

Considerations and Particulars

Plan 52 is among the most effective flushing plans for dual mechanical (Arrangement 2) seals in many applications, and has near zero emissions. Here are some things to keep in mind with Plan 52:  

  • Confirm that the system is properly ventilated before startup.
  • Buffer fluid pressure must be kept close to atmospheric pressure at all times.
  • Reservoir should be vented at all times to keep pressure close to atmospheric pressure and to vent vapors to flare.
  • Should higher vapor pressure liquids leak into the buffer system, they will flash in the reservoir, releasing vapor which can be captured.
  • Pressure switch should be set above minimum flare-back pressure to avoid false alarms.
  • Buffer fluid must be maintained above minimum level at all times.
  • Check for temperature differential between inlet and outlet lines to confirm circulation.
  • Plan 52 is for clean, non-polymerizing, pure products with vapor pressure above that of the buffer system.
  • Because some leakage of process fluid into the reservoir can be expected, buffer fluid must be compatible with process fluid.
  • Plan 52 can incorporate a water-fed cooling coil underneath the reservoir to help suppress the buffer fluid temperature while in operation.
  • Instrumentation can include transmitters for monitoring level, pressure and buffer fluid temperature inside the seal.

Plan 52 from Stein Seal Industrial

Stein Seal Industrial builds API Standard 682 seals and piping plans, including Plan 52, for applications in oil & gas, chemical and petrochemical, power generation, waste water processing, pulp and paper processing, and others.

All Stein Standard 682 manufacturing and testing facilities are certified by a third-party international certification organization.