API Plan 21

Description;

API Plan 21 is a cooled mechanical seal flush arrangement for single seals, where process fluid is taken from the pump discharge, passed through a restriction orifice, cooled through a heat exchanger, and then introduced into the seal chamber. The cooled process flush lubricates the seal faces without diluting the process stream, while reducing seal chamber temperature and improving vapor margin in hot or volatile services.

 

This plan is suited for clean, non-polymerizing fluids where controlled cooling is required before the flush enters the seal chamber. The arrangement is commonly applied in chemical plants, petrochemical units, refineries, oil & gas facilities, and power plant pump systems. For very high heat-load applications, the selection should be reviewed against alternative cooled circulation plans such as API Plan 23.

 

Key Features;

· Improves lubricity and reduces vaporization risk at the seal faces.

· Cooled flush supply from pump discharge for hot process services.

· Suitable for clean, non-polymerizing, high-temperature process fluids.

· Heat exchanger lowers flush temperature before entry into the seal chamber.

· Restriction orifice helps control flush flow and reduce pressure before cooling.

· Dismantlable heat exchanger design supports cleaning of the cooling-water side.

· Maintains process-fluid lubrication without external dilution of the product stream.

 

Service Overview;

Parameter Value

Equipment Centrifugal process pumps with single mechanical seals

Fluid Clean, hot, volatile, non-polymerizing process fluids

Service Nature High-temperature seal chamber cooling and vapor-margin improvement

Operating Mode Pump-discharge flush through the orifice and heat exchanger to seal chamber

 

Specifications;

Item Min Max Typical / Notes

Size On Request On Request Connection and heat-exchanger size selected by pump flow, seal chamber pressure, and heat load

Pressure — 62 bar (899 psi) Plan 21 package pressure rating as supplied data

Temp. Ambient / service dependent +180°C (+356°F) Maximum stated service temperature

Speed — Seal dependent Not a piping-plan limit; governed by pump speed and mechanical seal design

Cooling

Capacity — 10.5 kW (14.1 hp) Heat exchanger duty; final performance depends on cooling-water temperature and flow

 

Materials;

Component Standard Material Optional Material Comment

Cooling Coil / Tube Side SS 316 SS 316L, Duplex SS, Hastelloy Process-contact material selected for corrosion compatibility

Shell / Vessel Carbon Steel / Stainless Steel SS 316, coated CS, alloy shell Based on cooling-water quality and site specification

Orifice Plate /

Restriction Orifice SS 316 Duplex SS, Hastelloy Sized to control flush flow and pressure drop

Piping / Fittings SS 316 SS 304, SS 316L, alloy materials Depends on process fluid and plant piping class

Seals / Gaskets FKM / PTFE-based options Graphite, spiral-wound gasket options Selected according to temperature and chemical compatibility

 

Applications;

· Oil and gas process units with volatile fluids.

· Refinery process pumps in hot hydrocarbon duties.

· High-temperature single mechanical seal installations.

· Power plant technology and auxiliary process systems.

· Petrochemical pump services requiring cooled seal flush.

· Chemical industry process pumps handling hot clean fluids.

· Services where cooling is required but process dilution is not acceptable.

 

Operating Limits;

Parameter Value

Pressure Up to 62 bar (899 psi)

Temp. Up to +180°C (+356°F)

Speed Seal / pump dependent

Size Range On Request

Cooling Capacity Up to 10.5 kW (14.1 hp)

Parameter Value

Standard MOC SS 316 coil, CS / SS shell

 

Selection note;

Connection size, orifice bore, cooling-water requirement, and heat-exchanger area should be verified against actual seal heat load, pump differential pressure, process vapor pressure, and cooling-water availability before release for manufacture.