API Plan 62

Overview:

In API Plan 62 a non-hazardous external fluid or inert gas is injected into the atmospheric side of the mechanical seal to prevent fouling. Common options for plan 62 mediums include low pressure steam, nitrogen, or clean water. The flow of fluid across the atmospheric side of the seal mitigates the accumulation of crystallized process fluid (e.g. coking in hydrocarbon applications) and prevents seal hang up. Additionally, plan 62 can help heat or cool the seal, depending on the application. This plan is also referred to as a “seal quench”. 

Advantages:

Increased reliability – Plan 62 prevents seal o-ring or face hang up by ensuring the atmospheric side of the seal remains free of particulates.

Best For:

Fluids subject to crystallization at atmospheric pressure. This can be either hot applications, such as hydrocarbons, or cold applications, such as ethylene that is subject to icing or freezing at atmospheric pressure.

Best Practices:

• The plan 62 pressure should be set relatively low – approximately 5 psi or less. The goal is to create positive fluid flow through the atmospheric side of the seal to prevent the accumulation of crystallized solids. If the plan 62 pressure is set too high, there may be a risk of reverse pressurization of the seal faces, leading to premature failure. 
• If steam is used as the quench medium, ensure the steam is dry prior to injection into the seal. This can be achieved by the use of a steam trap and proper sloping of steam piping. Also, caution the use of steam as the quench medium in vertical pump applications. Depending on the seal design, condensate from the steam can become trapped on the atmospheric side of the seal, resulting in decreased seal reliability.
• The seal should be properly designed for a plan 62 flush arrangement. This includes the presence of a bushing, quench port, and drain port – all located on the atmospheric side of the seal. A segmented carbon bushing will limit the amount of quench leakage out of the front of the seal gland, however, a fixed carbon or bronze bushing is acceptable.
• If a liquid is used for the quench medium (e.g. water), consider the implementation of a lip seal in lieu of a bushing in the seal gland. This will limit the leakage of quench fluid from the front of the seal gland. The liquid quench setting should be based on flowrate, rather than pressure. Typical flowrates are less than 1 gallon per minute (gpm) and often measured in gallons per hour; at this flowrate there will be adequate prevention of fouling and heat transfer at the seal faces (given there is a temperature difference between the seal and quench fluid). 
• Routine Maintenance:
  • Ensure the quench pressure (for inert gases and steam) is set at no more than 5 psi by reading the local pressure indication. Additionally, ensure there is positive flow of the quench fluid out of the drain port or piping and that it is not obstructed. This will also allow condensate to drain from the seal. The plan 62 quench should be active at all times, regardless of pump status (operating or standby). 
  • Ensure the quench flowrate (for non-hazardous fluids) is set such that there is positive flow out of the drain port or piping. If the quench is only to be used for the prevention of fouling of crystallized solids, the flowrate can be very low. This will lead to potential savings by reducing the amount of quench fluid used. If the quench fluid is to be used to additionally cool the seal, maintain a flowrate of approximately 3 gallons per hour (0.05 gpm). Ensure the pressure does not exceed 5 psi to avoid reverse pressurization of the seal faces.