API Plan 53C

API Piping Plan 53C FSA Knowledge Series

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Abstract This Fluid Sealing Association Knowledge Series training presentation introduces API Piping Plan 53C. A description is provided on: ▪ What is an API Plan 53C? ▪ How an API Plan 53C Works ▪ What does an API Plan 53C do?

▪ What an API Plan 53C cannot do ▪ Optional Features for an API Plan 53C ▪ Cost to Operate With An API Plan 53C ▪ How to Size an API Plan 53C ▪ How to Install an API Plan 53C ▪ General API Plan 53C Commissioning Guidelines ▪ How to Operate an API Plan 53C ▪ General Troubleshooting of an API Plan 53C ▪ Alternatives to an API Plan 53C 3

What Are Piping Plans?

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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.

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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.

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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 53C? An API Plan 53C 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 53C provides:

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Zero emissions of the pumped fluid to the environment

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A method to pressurize the barrier fluid

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A barrier pressure that is proportional to the pressure in the pump

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A reservoir of barrier fluid to replace fluid consumed by the mechanicals seal

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A heat exchanger to dissipate heat generated by the mechanical seal and absorbed from the pump

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Containment of pumped fluid in the event of seal or support system failure

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Instrumentation to monitor seal performance and detect early onset of seal performance deterioration

What is an API Plan 53C? API Plan 53C consists of the following components: Differential Pressure Transmitter

High Point Vent Pressure Relief Valve

Level Indicator Level Transmitter

Piston Accumulator

Barrier Fluid Refill

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Reference Pressure Connection Point

Mechanical Seal Drain

Heat Exchanger

How an API Plan 53C Works Although not as widely installed as a traditional API Plan 53A system, it does differentiate itself from all the other methods as API Plan 53C will change the barrier pressure as the pressure inside the pump changes. This pressure tracking ability makes this system ideally suited to high-pressure pumps, or pumps that experience a wide range of operating pressures.

A Plan 53C barrier system consists of 2 main elements:

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1) The barrier fluid circulating loop where barrier fluid is circulated by a pumping device within the mechanical seal, to a heat exchanger where heat absorbed into the barrier fluid is dissipated and then returns back to the mechanical seal.

2) A piston accumulator which stores barrier fluid and amplifies pressure from the pump to pressurize the barrier fluid circulating loop.

How an API Plan 53C Works

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Dual liquid lubricated mechanical seals contain a pumping device within the mechanical seal that circulates barrier fluid in a cooling circulation loop, through a heat exchanger, returning to the mechanical seal. An API Plan 53C is used to pressurize the fluid in this cooling circulation loop and provide a reservoir of fluid to replace fluid consumed by the mechanical seal through normal leakage.​

Stored Barrier Fluid Piston Accumulator

Reference Pressure Source Mechanical Seal Circulating Loop

Heat Exchanger

How an API Plan 53C Works The piston accumulator pressurizes the barrier fluid loop by using a reference pressure line connected to the pump.

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To Circulation Loop

This reference line is used to pressurize one side of the piston which pushes the piston Barrier Fluid against the barrier fluid located on the other Reservoir side. As the piston rod reduces the effective area of the piston face in contact with the barrier fluid, this has the effect of amplifying the barrier fluid pressure. The pressure amplification ratio is simply the ratio of the area of each side of the piston.

Pumped Fluid (Reference Pressure Chamber)

Piston Rod Piston

Reference Pressure Inlet Connection

How an API Plan 53C Works The pressure amplification ratio can be calculated as: 𝑅𝑎𝑡𝑖𝑜 =

𝐴𝑟𝑒𝑎 𝐴1 𝐴𝑟𝑒𝑎 𝐴2

Barrier Fluid to Circulation Loop Barrier Pressure Acting on Area A2 10

Reference Pressure Acting on Area A1

Reference Pressure Inlet Connection

How an API Plan 53C Works

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Increasing the piston rod diameter has the effect of reducing Area A2 and thus increases the pressure amplification ratio. Due to the practicalities of design and function, amplification ratios are typically in the range of 1.05 to 1.30. As pressure ratios increase, Piston piston rods become larger in Diameter diameter (relative to the cylinder) and the cylinder becomes longer to provide sufficient barrier fluid Rod Diameter storage volume.

1.05 ratio

1.15 ratio

1.30 ratio

How an API Plan 53C Works As the pressure changes in the reference line, the pressure produced by the piston accumulator and delivered to the barrier fluid circulating loop will change proportionally to the amplification ratio: 𝐵𝑎𝑟𝑟𝑖𝑒𝑟 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 = (𝑅𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒) · (𝐴𝑚𝑝𝑙𝑖𝑓𝑖𝑐𝑎𝑡𝑖𝑜𝑛 𝑅𝑎𝑡𝑖𝑜)

Example: Reference Pressure = 10 barg [145 psig], Amplification ratio: 1.15 Barrier pressure = 10 barg [145 psig] · 1.15 = 11.5 barg [167 psig] 12

This ability to track the barrier pressure with respect to the reference pressure is what makes an API Plan 53C truly unique and differentiates it from all the other dual seal barrier systems. Since the barrier pressure is generated by amplifying the reference pressure from the pump, the piston accumulator requires no external utilities to function, which further simplifies the installation and operation of a Plan 53C system.

How an API Plan 53C Works During operation, barrier fluid is consumed due to normal leakage of the mechanical seal. Barrier fluid stored in the piston accumulator moves into the barrier fluid circulation loop to replace the consumed barrier fluid, resulting in the piston and piston rod slowly moving upwards. The extension of the piston rod from the top of the accumulator provides a direct indication of the volume of barrier fluid remaining in the accumulator.

Empty Full 13

Barrier Fluid Chamber Full Reference Pressure Chamber Empty

Barrier Fluid Chamber Empty Reference Pressure Chamber Full

How an API Plan 53C Works To move the barrier fluid through the circulating loop, a pumping ring can be 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.

Radial flow pumping ring

With higher shaft speeds, the pressure and flow generated by the pumping ring will increase.

Axial flow pumping ring Barrier fluid Process fluid

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Atmosphere side

How an API Plan 53C 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 piston accumulator will exit the accumulator into the cooling loop to replace the consumed fluid. This will result in movement of the piston to compensate for the lost barrier fluid.

When the liquid volume in the accumulator reaches a minimum, an alarm is triggered for the operator to refill the accumulator with fresh barrier fluid.

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How an API Plan 53C Works Piston Rod Protection

A cover is typically installed over the piston rod extension from the accumulator body to protect the piston rod and rod seals from damage and degradation from the environment.

Piston Rod Cover

Piston Rod

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What does an API Plan 53C do?

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An API Plan 53C provides a source of pressurized barrier fluid without the need for external utilities (e.g. live pressure source).

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The piston accumulator design does not utilize any gas source thereby eliminating gas dissolving into the barrier fluid.

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It can be used for high pressure applications (no gas solubility issues).

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The design allows for the selection of a wide variety of heat exchangers that can accommodate higher heat loads.

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The system has a small footprint; the piston accumulator does not need to be immediately adjacent to the cooling loop.

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The barrier pressure will automatically track the reference pressure when process conditions change.

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The only flow within the accumulator is to replace fluid consumed by normal leakage from the mechanical seal and to refill the accumulator.

What an API Plan 53C cannot do An API Plan 53C cannot:

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Guarantee any pumped fluid will not reach the environment

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Predict when a mechanical seal will fail

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Provide a constant barrier pressure

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Provide a simple and easy sizing and selection process without support from your mechanical seal vendor

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Provide continuous operation without periodic refilling of the accumulator

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Operate for extended periods of time in a failure mode

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Provide an extended barrier fluid life when compared to alternative pressurized systems due to higher thermal cycling of the barrier fluid

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Be used with a single seal

What an API Plan 53C cannot do Pumped Fluid Limitations The pumped media is used as the source of pressure in the piston accumulator; thus, the properties of this pumped fluid must be considered when selecting a Plan 53C system. The following pumped fluids should be avoided to ensure reliable operation of the barrier system: ▪ Pumped fluids that solidify at ambient conditions. As there is effectively very little flow of fluid in the reference line, the fluid in this line will, over time, cool down to ambient temperatures. Fluids that will solidify as they cool can plug the reference line preventing the pump pressure from acting against the piston in the accumulator and resulting in loss of barrier pressure.

▪ Pumped fluids that contain suspended solids. The suspended solids can migrate into the piston accumulator and interfere with the function of the piston seal, causing wear and damage to the internal surfaces of the cylinder resulting in leakage past the piston seal and loss of barrier pressure and barrier fluid.

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What an API Plan 53C cannot do Pumped Fluid Limitations ▪

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Pumped fluids at elevated temperatures. As the pumped fluid is introduced into the piston accumulator during commissioning, thermal damage to the piston seal can occur if it is exposed to temperatures above the limits of piston seal material(s).

Pumped fluids that are corrosive. The compatibility of the materials of construction of the piston accumulator with the pumped fluid should be reviewed to ensure no corrosive damage occurs to the internal walls of the accumulator and to the piston seals.

Optional Features for an API Plan 53C Piston Rod Position (level) Indicator Since the volume of barrier fluid remaining in the accumulator is inversely proportional to the extension of the piston rod from the accumulator, a variety of position indicating methods can be utilized.

Local position (level) indicator ▪ Linear scale with pointer attached to the end of the piston rod ▪

Colored coded linear scale cylinder that is covered with a larger cylinder that moves with the piston rod, covering and uncovering colored bands with movement of the piston rod

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Magnetic scale which is activated with a magnet moving with the piston rod

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Optional Features for an API Plan 53C Analog position (level) indicator ▪

Proximity switches located at alarm positions. Provides remote indication that the piston rod is or is not at the location of the proximity switch.

Digital position (level) indicator ▪

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Linear digital transmitter that can provide precise remote indication of the position of the piston rod.

Optional Features for an API Plan 53C

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In pumping applications where the reference pressure source and the piston accumulator amplification ratio do not meet the minimum differential pressure, a spring can be added to increase the force acting on Area A2 thereby increasing the barrier pressure. The spring can be located in the reference pressure chamber (in the process fluid) or on the atmospheric side of the piston rod.

Coil Spring Barrier Pressure Acting on Area A2

Spring Force Acting on Area A2

Reference Pressure Acting on Area A1

Optional Features for an API Plan 53C Valve and Instrumentation options:

DPIT

LI

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Temperature measurement – Addition of thermowells and local temperature indicators to measure barrier fluid temperature in and out of the mechanical seal

LT

Temperature Indicators TI

TI

Typical temperature indicator and thermowell

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Optional Features for an API Plan 53C Valve and Instrumentation options:

DPIT

LI

▪ Pressure measurement – Addition of a pressure gauge or pressure transmitter to provide measurement of the barrier pressure

LT

Pressure Transmitter with Local Readout

PIT PI

Pressure Gauge 25

Optional Features for an API Plan 53C Barrier fluid circulation: Internal to the mechanical seal ▪

Radial flow pumping ring

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Axial flow pumping ring

Radial flow pumping ring 26

Axial flow pumping ring

Optional Features for an API Plan 53C Heat Exchanger style: API Plan 53C allows the selection of a variety of different style heat exchangers.

Shell and tube heat exchanger

Tube-in-tube heat exchanger Natural convection heat exchanger 27

Forced convection heat exchanger

Optional Features for an API Plan 53C Accumulator Design Features

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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

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Materials of construction ▪ Pressure vessel material choices and piston and rod seal materials for pumped fluid compatibility and/or environment compatibility

Optional Features for an API Plan 53C Barrier Fluid Refilling Options ▪

Portable wheeled cart with reservoir and pump (hand or pneumatic)

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Local reservoir with pump (hand or pneumatic)

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Central reservoir with pump refilling multiple API Plan 53C accumulators

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Reservoir with automated refill control system (digital or pneumatically actuated)

Portable Wheeled Cart with Hand Pump

Local Reservoir with Pneumatic Pump 29

Cost to Operate With an API Plan 53C 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 A method to remove heat absorbed into the barrier fluid requires utilities either in the form of cooling water (for a water-cooled heat exchanger) or electricity (for a forced convection heat exchanger). Natural convection heat exchangers do not require any utilities.

Cost of energy balance Heat is removed from the process via the API plan 53C system. This energy needs to be replaced within the pumping system and there is an associated cost for the energy to achieve this.

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Cost to Operate With an API Plan 53C 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 drive needs to overcome. There is a cost for the energy needed to overcome this frictional drag

Labor costs An API plan 53C system requires routine maintenance to: 1) Monitor the performance of the API Plan 53C system and mechanical seal 2) Periodically replenish the consumed barrier fluid

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Cost to Operate With an API Plan 53C Typically, the initial investment for an API plan 53C system is high, however the ongoing operational costs are low after the system is installed.

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Energy to operate

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Carbon footprint

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$

$$$$

Initial investment

$

$$$$

Cost of operation

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$$$$

Refer to the Fluid Sealing Association’s Lifecycle Cost Calculator (LCC) for a more detailed analysis.

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How to Size an API Plan 53C Accumulator size The stored liquid volume (working volume) in the piston accumulator is selected based on the consumption rate of barrier fluid by the mechanical seal and the desired refill interval. Typically, a refill interval of 28 days is selected.

Example:

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Leakage rate of outer seal: Leakage rate of inner seal: Total barrier fluid consumption: Safety Factor 2 x 2 mL/hr: Leakage per day = 24 x 4: Leakage in 28 days = 28 x 96: Minimum working volume:

1.5 mL /hr 0.5 mL/hr 2 mL/hr 4 mL/hr 96 mL 2688 mL 2.7 liters (0.7 Gal)

How to Size an API Plan 53C Pressure Amplification Ratio The recommended minimum differential pressure between the barrier fluid pressure and minimum seal chamber pressure is the greater of 1.4 Bar (20 psi) or 10% of seal chamber pressure.

Example using the seal chamber pressure as the reference pressure:

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Seal Chamber Pressure

Amplification Ratio

Barrier Pressure

Barrier Pressure Differential

Bar (psi)

(-)

Bar (psi)

Bar (psi)

9.2 (133)

1.15

10.6 (153)

1.4 (20)

4.6 (67)

1.30

6.0 (87)

1.4 (20)

How to Size an API Plan 53C Pressure Amplification Ratio In pumping applications where the reference pressure source and the piston accumulator amplification ratio do not meet the minimum differential pressure, a spring assisted design needs to be selected.

The spring assisted design adds additional force to the reference pressure forces to increase the barrier fluid pressure.

Piston

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Spring

Piston Rod

How to Size an API Plan 53C Reference Pressure Source Selecting the right amplification ratio and reference pressure point on the pump pressure casing is key to meeting the minimum differential barrier pressure.

Additionally, the range of pressure at the reference point must also be factored into the selection process.

For high pressure pumps, the seal chamber can be used as a reference pressure and meet the minimum differential pressure requirements. A simple connection in the seal chamber or mechanical seal gland plate can be used to plumb a reference line to the piston accumulator. However, for low pressure pumps, a pressure higher than the seal chamber must be used to meet the minimum differential pressure requirements. Depending on the pump design, this can be the pump’s final discharge pressure or the discharge of an intermediate stage (if the pump is a multi-stage design).

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How to Size an API Plan 53C Alarm Set Points Alarms are established to notify the operator that actions are required.

There are a few critical set points: Low Low Liquid Level (LLLL) / Shutdown Alarm (Optional) ▪ This alarm notifies the operator that the accumulator is approaching running out of barrier fluid

Low Liquid Level (LLL) / Refill Alarm ▪ This alarm notifies the operator to add barrier fluid to the accumulator Normal Liquid Level (NLL) / Fill Set Point ▪ This notifies the operator to stop adding barrier fluid to the accumulator 37

How to Size an API Plan 53C Barrier fluid circulation The barrier fluid flow produced by the mechanical seal pumping ring (or external pump) needs to be sufficient to enable transfer of the heat absorbed into the barrier fluid (a combination of energy from seal heat generation and heat soak from the equipment) to the heat exchanger.

Natural Convection Heat Loss

Seal Face Heat Generation Seal Heat Soak from Equipment 38

Barrier Fluid Circulation

Heat Dissipated by Heat Exchanger

How to Size an API Plan 53C An insufficient barrier fluid 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 result in a number of problems affecting the performance and reliability of the mechanical seal.

Mechanical seals with internal pumping devices (pumping rings) have a strong correlation to shaft speed. Flow can dramatically reduce when shaft speeds are low and may require the use of an external circulation pump.

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How to Size an API Plan 53C Heat Exchanger One of the main advantages of an API Plan 53C is the flexibility offered in the choice of heat exchanger style and capacity. With the absence of physical restrictions of traditional API Plan 53A systems, larger cooling capacity heat exchangers can be selected.

When matching the heat exchanger cooling capacity to the heat load placed on the barrier fluid, consideration needs to be made to the effect of increases in the resistance to barrier fluid flow commonly associated with larger heat exchangers.

Undersized heat exchangers will result in excessive barrier fluid temperature which creates a rapid decrease in mechanical seal reliability.

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How to Install an API Plan 53C Heat Exchanger location The position of the heat exchanger 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).

Piston Accumulator location The piston accumulator can be mounted a substantial distance away from the barrier fluid circulating loop without any impact to the system’s performance. However, many installations will mount the heat exchanger and accumulator together on the same stand.

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How to Install an API Plan 53C Interconnection pipe/tubing Tube or piping connecting the mechanical seal to the heat exchanger 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” per foot)

Low point drains should be provided to remove barrier fluid when decommissioning the equipment.

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General API Plan 53C Commissioning Guidelines Commissioning must occur with the pump depressurized!​ Filling the Accumulator Filling the barrier fluid circulation loop is a multi step process that is repeated to ensure the barrier system is free of trapped air.

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1)

The piston needs to be moved so that the piston rod is at its maximum extension out of the accumulator. Low pressure compressed air connected to the reference pressure port can be used to move the piston.

2)

Barrier fluid is added to the barrier fill connection or low point drain with the high vent valve open. Fluid is added until flow out of the vent valve is observed.

General API Plan 53C Commissioning Guidelines

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3)

Close the vent valve and continue adding barrier fluid. As barrier fluid is added, the end of the piston rod will move into the piston accumulator. Stop adding barrier fluid once the full indicating signal is activated.

4)

Caution – do not overfill the accumulator. This will cause the piston to bottom out and no longer be free to slide and maintain the correct pressure. If the temperature of the barrier fluid increases, the thermal expansion of the barrier fluid will create a runaway pressure increase which can result in seal failure, damage to the piston accumulator, or rupture of the system.

5)

Open the vent valve and using low pressure compressed air connected to the reference pressure port, push the piston so that the piston rod is at its maximum extension out of the accumulator.

General API Plan 53C Commissioning Guidelines 6) Repeat steps 5) and 3) until no visible gas is entrained in the fluid exiting from the vent valve.

7) Reconnect the reference port to port in the pump casing.

8) The final step is to repeat step 3) so that the barrier system contains its maximum volume of barrier fluid.

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General API Plan 53C Commissioning Guidelines Alarm Set Point Verification During the fill and vent cycles, the changes in piston position 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 fittings for visible leakage. Tighten any fittings if leakage is found.

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General API Plan 53C Commissioning Guidelines Heat Exchanger Commissioning Depending on the style of heat exchanger in use, any required utilities, such as cooling water or electrical fan, should be activated and verified that cooling water or air is flowing.

External Barrier Fluid Circulating Pump When present, any external barrier fluid circulating pump should be switched on to start barrier fluid circulation.

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General API Plan 53C Commissioning Guidelines Pump Commissioning The pump is now ready to be flooded, and the equipment operators standard commissioning procedures followed.

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How to Operate an API Plan 53C Periodic Barrier Fluid Refilling Barrier fluid is consumed during the normal operation of the mechanical seal. This will require periodic replenishment of barrier fluid into the accumulator to make up for the fluid consumed. Barrier fluid is added to the accumulator until the Full set point piston position has been reached.

Caution – do not overfill the accumulator. This will cause the piston to bottom out and will no longer be free to slide and maintain the correct pressure. If the temperature of the barrier fluid increases, the thermal expansion of the barrier fluid will create a runaway pressure increase which can result in seal failure, damage to the piston accumulator, or rupture of the system.

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.

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How to Operate an API Plan 53C Periodic Inspection of Utilities Periodic measurement of the barrier fluid temperature into and out of the 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 exchanger heat transfer surfaces.

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General Troubleshooting of an API Plan 53C Symptom

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Potential causes

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Decreasing refill interval

Increasing mechanical seal leakage Leaking fittings Damage to piston or piston rod seals

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Elevated temperature

Insufficient barrier fluid circulation Heat exchanger fouling Insufficient heat exchanger cooling flow Undersized heat exchanger Inadequate venting Increase in process temperature Increase in process pressure

General Troubleshooting of an API Plan 53C Symptom

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Potential causes

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Rapid decrease in pressure

Major mechanical seal failure Delayed maintenance refilling of the accumulator Failure of piston or piston rod seals Blocked reference pressure line Jammed piston

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Decreasing barrier differential pressure

Delayed maintenance refilling of the accumulator Damage or failure of the piston seal

General Troubleshooting of an API Plan 53C

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Symptom

Potential causes

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▪ Major mechanical seal failure ▪ Delayed maintenance refilling of the accumulator ▪ Damage or failure of the piston rod seal ▪ Increase in the process (reference line) pressure

Increasing barrier differential pressure

Alternatives to an API Plan 53C Alternative piping plans that are similar:

API Plan 53A Gas pressurized vessel

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API Plan 53B Pressurized bladder accumulator system

Alternatives to an API Plan 53C Alternative piping plans that are similar:

PIT

API Plan 54 Fluid from an external system

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FIT

API Plan 74 Dual pressurized non-contacting gas seal

API Plan 53C Summary API Plan 53C pressurized seal systems offer a unique ability to automatically adjust the barrier pressure as the pressure in the pump changes making this a simple, safe and reliable solution in a range of pumping applications. The correct sizing of the piston accumulator, heat exchanger and barrier fluid flow rate together with best installation and operational practices are the key to years of reliable performance from an API Plan 53C system.

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THANKS!

www.fluidsealing.com

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