While the FSA makes every reasonable attempt to ensure that the information contained in this document is accurate and current, the FSA, its officers, directors, volunteers, and authorized agents are not responsible for any errors or omissions contained therein nor are they responsible for any results obtained from the use of or reliance upon its content. All information is provided “AS IS,” with no guarantee of completeness, accuracy, timeliness or of the results obtained, and without warranty of any kind, express or implied. In no event shall FSA or its officers, directors, volunteers, or authorized agents be liable to you or anyone else for any decision made or action taken in reliance on the information con tained herein or for any for any consequential, indirect, special, or similar damages, even if advised of the possibility of such damages. The informa tion contained in this document is for informational purposes only and does not constitute professional advice. It also includes references to certa in standards that may change over time and should be interpreted only in light of particular circumstances. It is your sole responsibility to confi rm the current state of any referred to standards. FSA reserves the right to modify or update the document content and to modify this Disclaimer at any t ime, effective upon posting of an updated version of this Disclaimer.
This Fluid Sealing Association Knowledge Series training presentation introduces API Piping API Plan 53A. A description is provided on:
▪ What is an API Plan 53A?
▪ How an API Plan 53A Works
▪ What does an API Plan 53A do?
▪ What an API Plan 53A cannot do
▪ Optional Features for an API Plan 53A
▪ Cost to Operate an API Plan 53A
▪ How to Size an API Plan 53A
▪ How to Install an API Plan 53A
▪ General API Plan 53A Commissioning Guidelines
▪ How to Operate an API Plan 53A
▪ General Troubleshooting of an API Plan 53A
▪ Alternatives to an API Plan 53A
What are Piping Plans?
▪ Piping plans collectively are different piping arrangements of fluid used to improve the conditions the mechanical seal operates in with the objective of improving the mechanical seal’s life.
▪ The American Petroleum Institute adopted numbers and created definitions for each piping plan configuration, thereby allowing a common language across the industry to simply describe a particular configuration.
▪ The American Petroleum Institute standard API-682 is where the definition of each piping plan can be found and where they may periodically be updated.
What is an API Plan 53A?
API Plan 53A is one of a series of piping plans that provide a pressurized liquid barrier fluid to a dual liquid lubricated mechanical seal.
An API Plan 53A provides:
▪ Zero emissions of the pumped fluid to the environment
▪ A method to pressurize the barrier fluid
▪ A reservoir of barrier fluid to replace fluid consumed by the mechanical seals
▪ A heat exchanger to dissipate heat generated by the mechanical seal and absorbed from the pump
▪ Instrumentation to monitor seal performance and detect early onset of seal performance deterioration
▪ Containment of pumped fluid in the event of seal or support system failure
What is an API Plan 53A?
API Plan 53A consists of the following components:
Pressurized Gas Supply
Mechanical Seal
Pressure Transmitter
Barrier Fluid Refill
Level Transmitter
Reservoir with Optional
Cooling Coils
Drain
How an API Plan 53A Works
Dual liquid lubricated mechanical seals contain a pumping device within the mechanical seal that circulates barrier fluid in a loop from the mechanical seal, through a reservoir, and returning to the mechanical seal. An API Plan 53A uses gas directly in contact with the barrier fluid in the reservoir to pressurize the barrier fluid circulation loop. The reservoir supplies a volume of barrier fluid to replace fluid consumed by the mechanical seal through normal leakage.
How an API Plan 53A Works
To move the barrier fluid through the circulating loop, a pumping ring is incorporated into the mechanical seal design. There are various styles and shapes of pumping rings, however they are all driven by the rotating shaft of the equipment. With higher shaft speeds, the pressure and flow generated by the pumping ring will increase.
How an API Plan 53A Works
Pressure is generated in an API Plan 53A within a reservoir, where a pressurized gas blanket acts directly on the barrier fluid. The pressure of the barrier fluid will typically be constant and equal to that of the gas supply.
For hot process fluids, the reservoir may contain a cooling coil to remove heat absorbed into the system.
How an API Plan 53A Works
During operation of a liquid dual pressurized mechanical seal, barrier fluid is consumed as a result of normal leakage. Stored liquid volume in the reservoir will exit the reservoir to the barrier loop to replace the lost fluid.
When the liquid volume in the reservoir reaches a minimum, an alarm is triggered for the operator to refill the reservoir with fresh barrier fluid. The refill alarm can be simply based on a minimum liquid level in the reservoir.
What does an API Plan 53A do?
▪ Provides a large recirculating volume of barrier fluid
▪ Maintains a constant barrier fluid pressure equal to that of the gas supply
▪ Barrier pressure is not affected by environmental temperature changes, if the pressure control valve is self-relieving
▪ Provides a visible liquid level of barrier fluid
▪ Can aid in monitoring the health of the mechanical seal
▪ Has a small installed footprint
▪ Provides a method to remove heat soak and seal generated heat
▪ Isolates the process fluid from the atmosphere
▪ In the event of catastrophic seal failure, can provide contingent sealing
What an API Plan 53A cannot do
An API Plan 53A cannot:
▪ Guarantee any pumped fluid will not reach the environment
▪ Predict when a mechanical seal will fail
▪ Provide continuous process containment with loss of pressurized gas supply
▪ Support high pressure applications
▪ Operate for extended periods of time after a seal failure
▪ Support more than one seal installation at a time
▪ Be used with a single seal
Optional Features for an API Plan 53A
Valves and Instrumentation:
Transmitter
▪ Options to monitor barrier fluid level in the reservoir
▪ Level Transmitter (recommended)
▪ Level Switch
▪ Sight Glass
▪ Options to monitor barrier fluid pressure
▪ Pressure Transmitter (recommended)
▪ Pressure Switch
▪ Pressure Gauge
▪ Valves to allow isolation of reservoir from the mechanical seal for maintenance and barrier fluid refilling/draining.
Optional Features for an API Plan 53A
Valves and Instrumentation:
▪ Temperature measurement – Addition of thermowells and local temperature indicators to measure barrier fluid temperature in and out of the mechanical seal
Temperature indicator
Thermowell
Eccentric Reducers
Optional Features for an API Plan 53A
Barrier fluid circulation:
Internal to the mechanical seal
▪ Radial flow pumping ring
▪ Axial flow pumping ring
Radial flow pumping ring
Axial flow pumping ring
Optional Features for an API Plan 53A
Reservoir Cooling Coils
API Plan 53A allows the selection of a variety of different size reservoirs. While reservoirs with internal cooling coils are typically used, natural convection or forced convection heat exchangers external of the reservoir may also be used.
Natural convection heat exchanger
Forced convection heat exchanger
Reservoir with internal cooling coils
Optional Features for an API Plan 53A
Reservoir Design Features
▪ Pressure vessel code and certification
▪ ASTM (American Society for Testing and Materials)
▪ PED (Pressure Equipment Directive)
▪ GOST (Gosudarstvennyy Standard)
▪ UL (Underwriters Laboratory)
▪ CR (Canadian Registration)
▪ Region-specific design regulations
▪ Materials of construction
▪ Reservoir material choices for barrier fluid compatibility and/or environment compatibility
▪ Customer-specific surface coatings and colors
Optional Features for an API Plan 53A
Barrier Fluid Refilling Options
▪ Portable wheeled cart with reservoir and pump (hand or pneumatic)
▪ Local reservoir with pump (hand or pneumatic)
▪ Central reservoir with pump refilling multiple API
Plan 53A reservoirs
▪ Reservoir with automated refill control system (digital or pneumatically actuated)
Portable Wheeled Cart with Hand Pump
Local Reservoir with Pneumatic Pump
Cost to Operate with an API Plan 53A
Cost of barrier fluid
Barrier fluid is consumed during the normal operation of the mechanical seal. Consumption rate will vary with mechanical seal design, shaft speed, pressure, and barrier fluid.
Cost of utilities
Utilities are required to maintain a constant supply of pressurized gas during normal operation of the mechanical seal, typically nitrogen or compressed air. The method of capturing or generating the gas supply will require utilities as well.
A method to remove heat soak absorbed into the barrier fluid requires utilities either in the form of cooling water (for a water-cooled reservoir) or electricity (for a forced convection heat exchanger). Natural convection heat exchangers do not require any utilities.
Cost to Operate with an API Plan 53A
Cost of energy balance
Heat is removed from the process via heat soak into the API Plan 53A system. This energy needs to be replaced within the pumping system and there is an associated cost for the energy to achieve this.
Friction losses
The operation of a dual mechanical seal results in friction being generated by the seal faces. This friction creates a drag on the rotation of the shaft which the driver needs to overcome. There is a cost for the energy needed to overcome this frictional drag
Labor costs
An API Plan 53A system requires routine maintenance to:
1) Monitor the performance of the API Plan 53A system and mechanical seal
2) Periodically replenish the consumed barrier fluid
Cost to Operate with an API Plan 53A
Typically, the initial investment for an API Plan 53A system is high, however the ongoing operational costs are low after the system is installed. ▪ Energy to operate
Carbon footprint
Initial investment
Cost of operation
Refer to the Fluid Sealing Association’s Lifecycle Cost Calculator (LCC) for a more detailed analysis.
How to Size an API Plan 53A
Reservoir size
▪ Typical sizes: 11.3 or 18.9 liters (3 or 5 gallon) total volume with a working volume equal to 20-30% of the total reservoir volume.
▪ API 682 reservoir sizing guidelines:
▪ Shaft diameter < 60 mm = 3 Gallon reservoir
▪ Shaft diameter > 60 mm = 5 Gallon reservoir
Example: Leakage rate of outer seal: 1.5 mL /hr
Leakage rate of inner seal: 0.5 mL/hr
Total barrier fluid consumption: 2 mL/hr
Safety Factor 2 x 2 mL/hr: 4 mL/hr
Leakage per day = 24 x 4: 96 mL
Leakage in 28 days = 28 x 96: 2688 mL
Min. Working volume: 2.7 liters (0.7 Gal)
Total Reservoir volume : 9 to 13.5 liters (2.4 to 3.6 gallons)
How to Size an API Plan 53A
Alarm Set Points
Alarms are established to notify the operator that actions are required.
There are a few critical set points:
Low Liquid Level (LLL) / Refill Alarm
This alarm notifies the operator to add barrier fluid to the reservoir
Normal Liquid Level (NLL) / Fill Set Point
This notifies the operator to stop adding barrier fluid to the reservoir
High Liquid Level (HLL) / Over Fill Alarm
This alarm notifies the operator that the reservoir is overfilled
How to Size an API Plan 53A
Barrier fluid circulation
The barrier fluid flow produced by the mechanical seal pumping needs to be sufficient to enable transfer of the heat absorbed into the barrier fluid to the cooling coils in the reservoir (or heat exchanger). The energy absorbed into the barrier fluid is a combination of seal generated heat and heat soak from the equipment.
How to Size an API Plan 53A
▪ For barrier pressures up to 10 barg (150 psig)
▪ Pressure limit is to prevent gas absorption into barrier fluid
▪ Typically not used for pumping temperatures above 176.6˚C (350˚F) due to heat dissipation capacity
▪ Mechanical seal must have an integrated pumping device. Sometimes, an external circulating pump is used (then considered as an API Plan 54.)
How to Size an API Plan 53A
▪ An insufficient flow rate will result in large differential temperatures between the barrier fluid in and out connections at the mechanical seal and an increase in the overall temperature of the barrier fluid.
▪ Excessive barrier fluid temperatures affect the performance and reliability of the mechanical seal and the life of the barrier fluid.
▪ Mechanical seals with internal pumping devices (pumping rings) have a strong correlation to shaft speed. Flow can dramatically reduce when shaft speeds are low.
▪ The reservoir cooling capacity should be matched to the heat load placed on the barrier fluid.
How to Install an API Plan 53A
Reservoir location
The position of the reservoir relative to the mechanical seal is important. It should be located as close as possible and a short distance above the mechanical seal centerline (without obscuring access for pump maintenance activities).
How to Install an API Plan 53A
Interconnection piping/tubing
▪ Pipes or tubes connecting the mechanical seal to the reservoir should be selected to produce minimal resistance to barrier flow. Large diameter bores, smooth radius bends, short distances, minimal ancillary equipment added into the circulating loop all help lower the resistance to barrier fluid flow.
▪ High point vents must be installed to allow removal of air from the system during commissioning. Lines should slop upwards to the vent point with a minimum slope of 40 mm per meter (0.5 inches per foot)
▪ Low point drains should be provided to remove barrier fluid when decommissioning the equipment.
General API Plan 53A Commissioning Guidelines
Commissioning must occur with the pump depressurized!
Filling the Reservoir
Typically, the reservoir is filled from a portable cart containing barrier fluid and a pump. The pump is often a hand pump or a pneumatically driven piston pump. Use clean, fresh barrier fluid to fill the reservoir.
Continue adding barrier fluid until the normal liquid level has been reached.
General API Plan 53A Commissioning Guidelines
Venting the System
When possible, the shaft should be rotated by hand to assist purging the mechanical seal barrier cavity of air.
Bleed all instrument block and bleed valves.
Continue venting until a solid stream of liquid with no bubbles is flowing from the vent valves.
General API Plan 53A Commissioning Guidelines
Alarm Set Point Verification
During the filling cycles, the changes in liquid level can be used to confirm the alarm set points and to validate communication between the instrument, the data acquisition system, and the local readout.
Leak Checks
Check all connections and fitting for visible leakage. Tighten any fittings if leakage is found.
General API Plan 53A Commissioning Guidelines
Reservoir Cooling Commissioning
Depending on the style of reservoir and cooling in use, any required utilities, such as cooling water or electrical fan, should be activated and verified that cooling water or air is flowing.
Barrier Loop Pressurization
Barrier fluid should be pressurized as the final step prior to pump commissioning to avoid reverse pressurization and contamination of the inner seal with process fluid. Open the valve to the pressurized gas supply and check for leaks or drops in pressure or barrier fluid level.
General
Pump Commissioning
The pump is now ready to be flooded with process fluid, and the equipment operator’s standard commissioning procedures should be followed.
How to Operate an API Plan 53A
Periodic Barrier Fluid Refilling
Barrier fluid is consumed as mechanical seal leakage during normal operation. This will require periodic replenishment of barrier fluid into the reservoir to make up for the fluid consumed. Barrier fluid is added to the reservoir until the normal liquid level has been reached.
The barrier fluid consumption rate is a strong indicator of the health of the mechanical seal. A decrease in the refill interval is an early warning of declining mechanical seal performance.
How to Operate an API Plan 53A
Periodic Inspection of Utilities
Periodic measurement of the barrier fluid temperature into and out of the reservoir (or heat exchanger) should be performed to monitor heat exchange efficiency.
An increase in the differential temperature across the heat exchanger inlet and outlet is an indication of a decrease in efficiency that can be caused by insufficient cooling flow or fouling of the heat exchanging heat transfer surfaces.
General Troubleshooting of an API Plan 53A
Symptom Potential causes
▪ Decreasing refill interval
▪ Elevated temperature
Increasing mechanical seal leakage
Leaking fittings
Insufficient barrier fluid circulation
Cooling coil fouling
Insufficient cooling flow
Undersized cooling
Inadequate venting
Change in process pressure or temperature
General Troubleshooting of an API Plan 53A
Symptom Potential causes
▪ Rapid decrease in pressure
Major mechanical seal failure
Delayed maintenance refilling of pressurized gas
canister supply (for non-header gas systems)
▪ Increase in reservoir liquid level
Major inner seal mechanical seal failure
Delayed maintenance refilling of pressurized gas
canister supply (for non-header gas systems)
▪ Rapid decrease in reservoir
Major mechanical seal failure liquid level
Major leak in barrier fluid loop
Alternatives to an API Plan 53A
Alternative piping plans that are similar:
API Plan 53B
Pressurized bladder accumulator system
Plan 53C
Piston accumulator pressurized system
Alternatives to an API Plan 53A
Alternative piping plans that are similar:
Plan 54
Fluid from an external system
Plan 74
Dual pressurized non-contacting gas seal
API Plan 53A Summary
API Plan 53A pressurized seal systems offer a safe and reliable solution for a wide range of applications.
These systems maintain a constant barrier pressure independent of environmental temperature and pressure decay, offering significant advantages over other dual seal systems.
The correct sizing of the reservoir for cooling and the barrier fluid flow rate, together with best installation & operational practices are the keys to years of reliable performance from an API Plan 53A system.
