API Plan 62 is an API 682 piping plan that feeds a quench from an outside source, usually low-pressure steam, nitrogen or water, into the atmospheric side of a seal between the seal faces and a throttle bushing, then drains it away. The quench washes out process fluid that leaks across the faces before it can form coke or crystals, and keeps atmospheric humidity from freezing into ice there; any of these would stop the seal from moving freely.

In the 4th edition of API 682, Plan 62 is clause G.24 of Annex G, the standard’s normative annex of piping plans.

How Plan 62 Works

The quench enters through the quench port in the seal gland, sweeps the cavity between the seal faces and the throttle bushing, and leaves through the drain port in the same gland, carrying with it any process fluid that has leaked across the faces.

The quench does not lubricate the faces, and the cooling it gives a hot seal is small.

The Throttle Bushing and Drain

The throttle bushing closes off the outboard end of the quench cavity, so that quench fluid and process leakage leave through the drain port rather than spraying out of the end of the gland. The drain port is left open, and the mixture flows out of it by gravity.

In a Plan 62 the bushing is typically a floating or segmented design, to limit quench leakage to atmosphere. On a single seal, the bushing is also the only thing containing process leakage that gets past the faces.

On coking service, make the drain as accessible as possible and drill it through as large as the gland allows.

Where a steam or water quench is used, fit an oil condition bottle to the bearing housing to monitor the bearing oil for water.

When Plan 62 Is Used

Plan 62 is used where process fluid leaking to the atmospheric side of the seal would form solids there, or where atmospheric humidity would freeze there. Three kinds of service make up most Plan 62 duties:

  • Hot hydrocarbons: the leakage cokes. A steam quench is the general guideline for hydrocarbon service when the pumping temperature is above 350 °F (about 177 °C).
  • Fluids with solids in solution: the leakage crystallizes on contact with the atmosphere.
  • Cold and cryogenic services: atmospheric humidity freezes into ice on the atmospheric side of the seal.

A hot oil pump whose seal runs on a non-circulating Plan 02 normally needs a Plan 62 as well.

Plan 62 is most commonly fitted to single seals. Where the pumped fluid is flammable or toxic, many countries require a dual seal.

Which Quench Medium to Use

The quench medium is chosen by what would otherwise form on the atmospheric side of the seal, whether coke or crystals from the leaked product or ice from atmospheric humidity, and in practice it is one of three: steam, water or nitrogen.

Steam

A steam quench stops coking by washing the leakage away from the atmospheric side of the faces and by keeping the quench space below the temperature at which the leaked product decomposes into coke.

The steam flow has to be large enough to do both.

Water

A water quench prevents crystallization: it keeps fluids that carry solids in solution, or that crystallize on exposure to the atmosphere, from building up crystals under the seal faces.

Nitrogen

A nitrogen quench prevents coke on hot hydrocarbon seals and ice on cold or cryogenic seals. On hot seals, nitrogen quenches are generally observed to be less effective than steam.

The Parts of a Plan 62 Line

A Plan 62 line is made up of a block valve, a flow restriction, a pressure gauge, a condensate trap on steam service, and the quench and drain connections on the seal gland. The supply runs from a plant utility header to the gland’s quench connection, and a second line runs from the drain connection to a collection point:

  • Block valve: isolates the quench supply for seal maintenance.
  • Flow restriction: a pressure regulator, needle valve or orifice that holds the quench at the low pressure the seal needs.
  • Pressure gauge: fitted downstream of the restriction, it shows the pressure actually reaching the gland.
  • Condensate trap: on a steam quench only, it drains condensate from the supply line ahead of the seal.
  • Quench and drain connections: the gland ports marked Q and D, with the drain piped open to the collection system.

Quench Supply Pressure

A Plan 62 quench is supplied at low pressure: whatever the medium, the quench pressure is commonly less than 5 psig, with many applications between 1 and 3 psig.

A steam quench is regulated to about 3 to 5 psi.

The steam has to be superheated (dry).