Understanding How the API Plan 52 Seal System Works For Canadian Operations

Pumping processes involving hazardous or toxic fluids often utilize dual mechanical seals to ensure operator safety and compliance with environmental regulations. The American Petroleum Institute (API) Standard 682 classifies dual mechanical seals into two categories— pressured and unpressured. For unpressurized configurations, a seal flush system, such as API Plan 52, is required for the seal to operate. A buffer fluid is circulated between the inboard and outboard seals to form a “buffer” between the process fluid and environment.

API Plan 52 seal systems are the most commonly used pressurized dual mechanical seal flush systems in Canadian operations. Plan 52 is widely used in oil and gas operations, but can also be used in chemical and petrochemical refining and power generation applications. Let’s take a look into how the API Plan 52 seal system works for centrifugal pumps and applications in oil and gas, chemical and petrochemical refinement, and power generation.

API Plan 52 Seal System Explained

API Plan 52 seal systems employ a seal pot (reservoir) to deliver an unpressurized buffer fluid to the seal chamber and circulate the fluid between the inboard and outboard mechanical seals. A pumping ring is utilized to provide positive circulation through the seal flush system and into the seal. This plan is commonly used with light hydrocarbons or fluids with a high vapour pressure.

In the event of an inboard seal failure, process fluid will leak into the seal chamber, mixing with the buffer fluid. Thus, the selected buffer fluid must be compatible with the process fluid. One challenge with this plan is frictional losses in the buffer fluid inlet and outlet lines. Frictional losses may be minimized through properly selecting tube size, using large radius and/or 45-degree bends, and reducing the length of tubing in the design. 

Practical Considerations for API Plan 52

Tubing configuration and geometry, materials of construction, buffer fluid type, and seal pot volume can be determined and configured based on specific pumping and mechanical seal requirements. API Plan 52 seal systems can include cooling coils within the reservoir to maintain the temperature of buffer fluid being delivered to the seal chamber. This plan can also include instrumentation, such as pressure transmitters, level transmitters, and thermometers depending on the given application. Fluid systems vendors should be consulted to determine configuration specifics such as those listed above.

Depending on the application of dual mechanical seal flush systems, there may be benefits in the higher standards of an ASME stamped seal pot as opposed to a seal pot that meets a lower piping standard. ASME stamped vessels can be more easily tracked and maintained through their Canadian Registration Number (CRN). 

When utilizing API Plan 52 for dual mechanical seals in any application, it is important to:

• Avoid running the system when the seal pot level is low, as indicated by a level gauge.
• Vent the system properly before startup.
• Verify the seal pot vent remains open at all times to ensure the buffer fluid pressure is maintained near atmospheric pressure.
• Ensure the vent line always remains open and is connected to the flare.
• Periodically verify buffer fluid quality and replace when necessary.

Applications of API Plan 52 Seal System

While plan 52 is beneficial and often necessary for applications including light hydrocarbons and high vapour pressure fluids, it may also be used for non-flashing services. This plan is favourable for applications where the process fluid or product should not be contaminated by a buffer fluid.

In oil and gas operations, including steam-assisted gravity drainage (SAGD), API plan 52 can be used for dual mechanical seals for centrifugal pumps in upstream, midstream, and downstream operations with either high vapour pressure or lower vapour pressure fluids. In chemical plants and petrochemical refineries, dual mechanical seals may be used for high vapour pressure fluid applications. For chemical plants where chemicals are extremely hazardous, a more robust sealing system may be implemented. For power generation, API Plan 52 may be used for water pumping applications, such as boiler feedwater pumps and water treatment pumps.

Local Expertise Backed by Global Experience

Whether you are looking to implement a new custom-configured API Plan 52 seal system—or you are looking to upgrade your current plan—Field Advisors at Edmonton Valve & Fitting can provide expert consultations to determine how to increase pumping reliability and efficiency. We are well-versed in local pumping applications for industries including oil and gas, chemical and petrochemical refining, and power generation. We also offer ASME stamped seal pots for customers who would like to ensure proper testing and maintenance tracking with a CRN.