API Mechanical Seal Flushing Plan

API MECHANICAL SEAL FLUSHING PLAN

In mechanical seal heat is generated between the rotating and stationary seal face. If more amount of heat is generated between the faces cause the mechanical seal failure. In order to avoid the seal failure flushing fluid is injected between the seal face. There are different types of flushing plans used depend upon the conditions. These are following condition for selecting suitable mechanical seal flushing plan for both the supplier and vendor. 

Nature of working fluid (pumping fluid)such as toxic, corrosiveness, hazards chemicals.

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Suspended solid particles in the pumping fluid.

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Temperature of pumping fluid

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Vapour pressure of pumping fluid

API Plans: Plans: They are various types of flushing plans used in most of the industrial pumps. Now we see the API standard plans in detail.

API PLAN 02

In this mechanical seal plan the dead-ended seal chamber with no flush line arrangement. In which the pumping fluid pass through the back of impeller and fill the seal chamber. There by the seal faces were cooled. The pressure in the seal chamber is controlled by the expeller at the back of the impeller. In the case of moderate temperature services large bore open throat seal chamber is used. On the other hand for high temperature services cooling jacket seal chamber is used. Process fluid must have adequate boiling point margin to avoid vaporization between the seal faces. Often used in combination with steam quench Plan 62.

API Flushing Plan 02

Advantages: Advantages: 

Simple no environmental controls

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Economic design of pump Disadvantages:

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The plan only used for clean fluids

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Pump back clearance is very important because change in back clearance cause change in seal chamber pressure.

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Increase in throttle bush clearance also cause change in seal chamber pressure.

API PLAN 11

Seal flush is taken from the pump discharge through an orifice. The function of orifice is to regulate the flow rate of flushing fluid to the seal chamber. In this plan use an orifice with a minimum 3 mm diameter based on the calculate flow rates to size orifice to adequate seal chamber flow. The flush fluid is injected directly over the seal faces with piping at 12 O clock position. In multistage pumps we get the flushing from the most convenient pump area.


Advantages: 

Flushing fluid taken from the discharge, hence increase seal chamber pressure and allow the fluid with less vapour margin Disadvantage:

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Used for clean fluid

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Typical failure mode is a clogged orifice – check temperatures at pipe ends

API PLAN 13

In this mechanical seal plan the flushing fluid enter the seal chamber from the back of the impeller. In which the seal chamber pressure is normally 1 to 1.5 times greater than the suction pressure. Hence it is re-circulating the flushing back to the pump suction. This type of flushing plan is mostly used in vertical pumps and continuous seal chamber venting is also provided. There by seal chamber heat is removal. In the case of moderate temperature fluids with moderate solids vent piping loop prior to starting vertical pumps. The size of orifice is determined by calculating the flow rates of fluid to the seal chamber normally the size of an orifice with a minimum 3 mm diameter is used in most of the industrial pumps.


If the seal chamber pressure is very high then it indicates that to select the proper orifice and throat bushing sizing. Typical failure mode is a clogged orifice – check temperatures at pipe ends Advantages: 

Used for fluid which contain moderate solid particles Disadvantage:

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Due to the presence of solid particles, orifice clogging is takes place this leads to seal failure.

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Only used for vertical pumps

API PLAN 14

In this mechanical seal flushing plan the fluid from discharge and recirculation back to the pump suction with orifices. This type of flushing plan is the combination of Plan 11 and 13 there by the seal chamber heat is removed. Increase seal chamber pressure and fluid flow rate is determined by the seal chamber inlet and outlet orifice. This type of seal plan is used on vertical pumps and Clean fluids at moderate temperatures. Increase boiling point margin of flushing fluid with proper orifice and throat bushing sizing. Flush should be directed over seal faces, Vent piping loop prior to starting vertical pumps


API PLAN 21

This type of mechanical seal plan is used for the flushing fluid with high temperature. This plan is similar to API plan 02 but it consisting of circulation ring for circulates the flushing fluid to the heat exchanger to reduce the temperature of the flushing before it reach the seal face. This type of flushing plan is used for high temperature service typically less than 177 oC. If reduce fluid temperature to increase vapour margin.


If the flushing fluid is over 80 oC, Seal cooler and piping must have air vents at highest elevation. Venting the seal chamber before starting the pump is very important because to avoid the dry run of mechanical seal. Calculate the flow rates to size an orifice for adequate seal chamber flow Increase boiling point margin with proper orifice and throat bushing sizing. Regularly monitor device inlet and outlet temperatures for signs of clogging or fouling

API PLAN 23 This mechanical Seal flush plan is similar to API plan 11 the only difference is the fluid from the pump discharge is cooled by a cooler before the seal chamber as shown in the figure. This is the standard flush plan for hot water services such as used in boiler feed water pump. Efficient seal cooling with low cooler duty increase fluid vapour margin. This plan is used for high temperature service, hot hydrocarbons and Boiler feed water and hot water over 80 oC.


Seal cooler and piping must have air vents at highest elevation. The piping arrangement is shown below.

Piping System of Plan 23

Seal chamber requires close clearance throat bushing to isolate hot process fluid from the cold seal chamber flushing fluid. Regularly monitor cooler inlet and outlet temperatures for signs of plugging or fouling.

API PLAN 31

In this type mechanical seal flush plan is used for the pumping fluid consisting of solid particles. The flushing fluid from pump discharge is passing through a cyclone separator for separating the suspended solids from the pumping fluid. Centrifuged solid particles are returned to pump suction from the cyclone separator. Seal chamber heat is flushed by the fluid from the cyclone separator. This type of flushing plan is used for dirty or contaminated fluids, water with sand or pipe slug etc.., Cyclone separator works best on solids with a specific gravity twice the process fluid. Seal chamber pressure must be nearly equal to suction pressure for proper flows. The piping should not include an orifice and is not expected to vent the seal chamber.


Disadvantage: 

The solid particles density must at least twice the pumping fluid density.

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Very close throttle bush clearance to be maintained.

API PLAN 32

Normally this type of mechanical seal flushing plan is used for the fluid contain more amount of suspended solid materials and low vapour pressure fluids. In this mechanical seal flushing plan, the flushing fluid is pumped in to the seal chamber from an external clean source. Seal chamber heat removal Process and solids removal from seal chamber Increase seal chamber pressure and fluid vapour margin. The injection fluid must be compatible with process fluid. In which the pump manufacture use throat bushing sized to hold pressure or maintain flow velocity of the flushing fluid. To restrict dirty process fluid enter in to the seal chamber, injection flow rate is maintained 1.5 ksc or 1.5 psi greater than the pump discharge pressure in the case of single stage pump. Where in the case of multistage pump the injection pressure will be vary with the pressure developed by the end impeller (that is after that impeller mechanical seal is mounted).

API Flushing Plan 32 Advantages: 

Used on dirty or contaminated fluids, paper pulp etc..,

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High temperature service

Disadvantages: 

Regularly monitor control system for closed valves or signs of plugging

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By using of external pump system for injecting flushing fluid, thereby we spend additional energy for the whole system.

API PLAN 41

This mechanical seal flushing plan is the combination of Plan 21 and 31. In this type of seal flushing, the flushing fluid from pump discharge through cyclone separator and cooler. Solids removal in the cyclone separator and pass through the cooler to flush seal faces in the seal chamber. This type of flushing plan is used for high temperature service typically less than 177oC.

API Flushing Plan 41 The seal cooler and piping must have air vents at highest elevation for vent before starting the pump. Advantages: 

This plan is used for dirty or contaminated fluids water with sand or pipe slug

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When using API 682 seal cooler pipe with series flow to maximize heat transfer Disadvantages:

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Cyclone separator works best on solids with a specific gravity twice the process fluid

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Seal chamber pressure must be nearly equal to suction pressure for proper flows

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Typical failure mode is clogged separator or pipes – check temperatures at pipe ends

API PLAN 52

In this type of mechanical seal flushing plan is used in dual seal arrangement. In which it consist of an unpressurized buffer fluid is circulation through a reservoir. The buffer fluid is used to flushing the secondary seal and the fluid is circulated by a pumping ring (similar as API plan 23) in the dual seal assembly. Outboard seal acts as a safety backup to the primary seal for zero to very low process emissions to the atmosphere. The inner seal is flushed by process liquid as shown in the figure.

API Flushing Plan 52 Piping loop must self vent to vapour recovery flare system near atmospheric pressure. Generally the process vapour pressure is greater than reservoir pressure. In which the Primary seal leakage is indicated by increased in vent pressure. Reservoir level gauge indicated outboard seal leakage. This type of seal plan use Methanol as buffer fluid. Advantages: 

Used for toxic fluid and maintain zero leak to the atmosphere.

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Used for high vapour pressure fluids light hydrocarbons

Disadvantages: 

Buffer fluid must be compatible with process leakage.

API PLAN 53A

When compare with API Plan 52, the buffer fluid is pressurized by by an external source. The pressurized barrier fluid circulation through reservoir by a pumping ring in the dual seal assembly. The buffer fluid isolate process fluid to the atmosphere if there is primary seal leak. Thereby zero process emissions.

API Flushing Plan 53 A The piping system of API flushing plan 53 A is shown below. As API 628 the minimum distance between the mechanical seal center line to the center line of the buffer receiver. (Horizontal and Vertical distance)

Piping System Of API Flushing Plan 53 A Advantages: 

High vapour pressure fluids, light hydrocarbons etc..,

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Hazardous toxic fluids

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Dirty abrasive fluids Mixers/agitators and vacuum service Disadvantages:

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This system is more complicated piping arrangement when compare with other API flushing plans.

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The seal chamber pressure depend upon the external pressure source. Hence the same is to be monitor continuously.

API PLAN 53 B

This plan is similar to API plan 53 the major difference in this type of flushing plan, in which it consisting of a finned pipe and accumulator bladder without buffer receiver. The finned pipe is used to cool the buffer fluid which pick up the heat from the secondary seal faces. The accumulator is act as a buffer receiver and maintains the pressure act on the seal faces. This is used to overcome the disadvantage of API Plan 53A. The accumulator bladder is usually filled with nitrogen or a suitable gas it does not affect the process fluid in case of bladder leak.

API Flushing Plan 53 B

Advantages: 

High vapour pressure fluids, light hydrocarbons

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Dirty/abrasive fluids Disadvantages:

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Accumulator must be pressurized at all times usually by gas charge Barrier fluid must be compatible with process

API PLAN 54

In this type seal plan the barrier fluid is injected by an external circulating system for isolate process fluid leak to the atmosphere. Thereby Zero process emissions . Here the circulation can be established by pressure of the injecting fluid. The circulating pressure of the pumping fluid is normally greater than the pumping pressure. Piping loop must be fully vented before starting the pump.

API Flushing Plan 54 Advantages: 

Used with dual pressurized seals (double)

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High vapour pressure fluids light hydrocarbons

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Dirty abrasive fluids Disadvantages:

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Circulating system must be pressurized and energized at all times

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Barrier fluid must be compatible with process

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API Mechanical Seal Flushing Plan

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