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 |
| 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) |
| Standard MOC | SS 316 coil, CS / SS shell |
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