Dual Contacting Seals & API Flushing Plan 52 53A 53B

1. Purpose

This procedure describes the Schedule A requirements for Dual Contacting Seals/API Flush Plan 52, 53A and 53B.

2. Auxiliary Seal Flush Plan Arrangements

Incorporate the following guidelines into the requirements for specifying API Flushing Plan 52, 53A or 53B seal support systems (Auxiliary Flush Plan):

• Provide one API Plan 52, 53A or 53B support system for each seal.

• Provide two complete systems (two seal pots or accumulator systems) if a pump has two sets of seals (multi-stage, between bearings).

• Provide both the operating and spare pumps with their own seal support system(s)

3. API Flush Plan 52, Unpressurized Dual Seals

3 .1 Description

An API Flush Plan 52 is an unpressurized dual seal support system consisting of a dual cartridge seal (inboard and outboard), a circulating buffer fluid and a seal pot with an internal cooling water coil. If cooling water is not available, an external air cooled heat exchanger can be installed adjacent to the seal pot. The system is designed to maintain the proper sealing environment for the outboard seal and provide a quench to the inboard, process lubricated seal. Buffer fluid circulation is accomplished through the use of a pumping ring, mounted between the dual seals. Because the sealing system is unpressurized, and process fluid leaks across the inboard seal faces, the buffer fluid will get contaminated and/or diluted over time. The customer is expected to setup the appropriate Preventive Maintenance (PM) schedule to periodically replace the buffer fluid. The seal support system is outfitted with instrumentation designed to help monitor the system’s performance. See “Seal Details” section below for more information.

3.2 501 Equipment Spec

When an Auxiliary Flush Plan API PLAN 52 is specified in the 501 Centrifugal Pumps and Drivers Specification, ensure the following items are addressed and included:

• Name of Buffer Fluid is shown on spec (Selected by rotating equipment specialist)

• Appropriate Instrumentation is shown in spec
• Pressure Transmitter with High Alarm
• Level Transmitter with High and Low Alarm
• Pressure Gauge (can be local readout from pressure transmitter)
• Level Gauge (can be local readout from level transmitter)
• Cooling Plan M (or K if required by the ) is shown on spec.

3.3 Seal Details, P&ID (See Figure 1)

Ensure that the appropriate seal detail is shown on the P&ID for the pump. The following seal details represent API PLAN 52, Unpressurized Dual Contacting seals with slight piping variations.

• TA – Seal Pot connected to closed aromatics drain header and relief header
• TH - Seal Pot connected to H2S drain header and relief header
• TL – Seal Pot connected to relief header (for light, flashing hydrocarbons)

The process fluid being pumped/sealed determines the appropriate seal detail to use. The equipment supplied by the vendor for the API PLAN 52 seal support system is the same, regardless of the seal detail shown on the P&ID.

Contractor Connections shown on Seal Details (See Figure 1)

• Drain – If required

Used to drain contaminated buffer fluid to safe location for maintenance (PM, seal failure, etc)

• Relief Header

Vents hazardous fluids (vapor or liquid) to flare system, allows seal pot to “breath” as temperature changes within seal pot.

• Cooling Water – for cooling coil built into seal pot

Needed to remove heat generated by the seal faces (inboard and outboard) and conducted from the process liquid.

• Alarms (from Transmitters provided by vendor)
• Pressure Alarm High (PAH)

Alarms on high pressure caused by excessive seal leakage of light, flashing hydrocarbons

• Level Alarm Low (LAL)

Alarms on an outboard seal leak of buffer fluid to atmosphere

• Level Alarm High (LAH)

Alarms on inboard seal leak of process liquid to the seal pot

All alarms should be connected to a common trouble alarm as shown on the P&ID. If desired by the customer, each transmitter could be routed back to the DCS for monitoring by operations. This option is more expensive due to the additional wiring and setup at the DCS but allows for continuous monitoring and trending the seal pot levels and pressures which will provide better data for the RCFA after a seal failure.

Figure 1 – Example Seal Detail: "TH"

4. API Flush Plan 53A, Pressurized Dual Seals

4.1 Description

An API Flush Plan 53A is a pressurized dual seal support system consisting of a dual cartridge seal (inboard and outboard), a circulating barrier fluid and a seal pot with an internal cooling water coil (an air cooler option is available) and a pressurized nitrogen blanket. This system can be used when the pump’s normal suction pressure is 280 psig or less. System pressure is set 25-40 psig over seal chamber pressure. The system is designed to maintain the proper sealing environment for both the inboard and outboard seal faces. Barrier fluid circulation is accomplished through the use of a pumping ring, mounted between the dual seals. Because the seal pot is pressurized, and barrier fluid leaks across the inboard seal faces into the process, the barrier fluid must be compatible with the process fluid. During normal operation the amount of leakage is negligible (1-2 cc/hr) but during a seal failure the entire contents of the seal pot (5 gallons) leak across the seal faces and into the process fluid. The customer is expected to monitor the level of barrier fluid in the seal pot and as the level drops, add fresh barrier fluid to the system periodically. The seal support system is outfitted with instrumentation designed to help monitor the system’s performance. See “Seal Details” section below for more information.

4.2 501 Equipment Spec

When an Auxiliary Flush Plan API PLAN 53A is specified in the 501 Centrifugal Pumps and Drivers Specification, ensure the following items are addressed and included:

• Name of Barrier Fluid is shown on spec (Selected by rotating equipment specialist with input from a Process Technology Specialist)
• Appropriate Instrumentation is shown in spec
• Pressure Transmitter with Low Alarm
• Level Transmitter with Low Alarm
• Pressure Gauge (can be local readout from pressure transmitter)
• Level Gauge (can be local readout from level transmitter)
• Cooling Plan M (or K if pump’s liquid is over 500F) is shown on spec.

4.3 Seal Details, P&ID (See Figure 2)

Ensure that the appropriate seal detail is shown in the P&ID for the pump. Seal detail “FA” represents API PLAN 53A, Pressurized Dual Contacting seals.

Contractor Connections for Seal Detail FA (See Figure 2)

• Nitrogen Source

Supplies pressurized nitrogen blanket to seal pot. Source can be plant N2 header if the pressure is high enough or a common N2 bottle rack setup in the process unit.

• Cooling Water – for cooling coil built into seal pot

Needed to remove heat generated by the seal faces (inboard and outboard) and conducted from the process liquid.

• Alarms (Instrumentation)
• Pressure Alarm Low (PAL)

Alarms on loss of N2 pressure, typically set at a differential pressure of 15 psi over seal chamber pressure.

• Level Alarm Low (LAL)

Alarms on an inboard or outboard seal leak (fast leakage rate over a few days). This alarm will also indicate when the seal pot needs to be refilled due to normal leakage across the seal faces (slow leakage rate over weeks/months)

All alarms should be connected to a common trouble alarm as shown on the P&ID. If desired by the customer, each transmitter could be routed back to the DCS for monitoring by operations. This option is more expensive due to the additional wiring and setup at the DCS but allows for continuous monitoring and trending the seal pot levels and pressures which will provide better data for the RCFA after a seal failure.

Figure 2 – Seal Detail "FA"

5. API Flush Plan 53B, Pressurized Dual Seals

5.1 Description

An API Flush Plan 53B is a pressurized dual seal support system consisting of a dual cartridge seal (inboard and outboard), a circulating barrier fluid, a seal cooler (water or air) and a bladder accumulator pre-charged with nitrogen. API Flush Plan 53B is used when nitrogen entrainment of the barrier fluid is a concern due to direct contact between the barrier fluid and the nitrogen blanket at high pressures. Use this seal support system when the pump’s normal suction pressure is greater than 280 psig. This system is set to 25-40 psig over seal chamber pressure. The system is designed to maintain the proper sealing environment for both the inboard and outboard seal faces. Barrier fluid circulation is accomplished through the use of a pumping ring, built into the dual seal. Because the seal system is pressurized, and barrier fluid leaks across the inboard seal faces, the barrier fluid must be compatible with the process fluid. During normal operation the amount of leakage is negligible (10-20 cc/hr) but during a seal failure the entire volume within the seal support system (5 gallons) leaks across the seal faces and into the process fluid. The customer is expected to monitor the volume of barrier fluid in the seal support system and as the amount of barrier fluid decreases in the system, add fresh barrier fluid periodically. The seal support system is outfitted with instrumentation designed to help monitor the system’s performance. See “Seal Details” section below for more information.

5.2 501 Equipment Spec

When an Auxiliary Flush Plan API PLAN 53B is specified in the 501 Centrifugal Pumps and Drivers Specification, ensure the following items are addressed and included:

• Name of Barrier Fluid is shown on spec (Selected by rotating equipment specialist)
• Appropriate Instrumentation is shown in spec
• Pressure Transmitter with Low Alarm
• Pressure Gauge (can be local readout from pressure transmitter)
• Temperature Gauge (on the outlet side of the seal cooler)
• Cooling Plan M (or, if needed K) is shown on spec, with note for sight flow indicators.

5.3 Seal Details, P&ID

Ensure that the appropriate seal detail is shown in the P&ID for the pump. Seal detail “FB” represents API PLAN 53B, Pressurized Dual Contacting seals.

Contractor Connections for Seal Detail FB (See Figure 3):

• Cooling Water – for cooling coil built into seal cooler

Required to remove heat generated by the seal faces (inboard and outboard) and conducted from the process liquid.

• Alarms (Instrumentation)
• Pressure Alarm Low (PAL)

Indirectly monitors barrier fluid volume. As the barrier fluid leaks across the seal, the pressure will decrease.

Will also alarm on loss of N2 pressure due to bladder or seal leak

Figure 3 - Seal Detail "FB"

6. Additional Information

6.1 Buffer/Barrier Fluids

Barrier Fluid differs from the Buffer Fluid used in an API Flush Plan 52 in pressure only. A Buffer Fluid operated at a pressure greater than the seal chamber pressure shall be called a Barrier Fluid. Unlike a Buffer fluid which provides quench to the inboard seal and only lubricates the outboard seal face, a Barrier Fluid lubricates both the inboard and outboard seal faces.

Inflection Point Engineering specifies Synthetic Barrier Fluid whenever possible. This will ensure that the best fluid is used to lubricate the seal faces, increasing seal reliability. See for more details regarding barrier fluids.

6.2 Appendix – GA and Installation Guidelines

Figure 4 - Example General Arrangement

Figure 5 - Installation Guidelines

Installation Guidelines/Best Practices

• Minimize piping line loses
• Use ¾” piping/tubing to reduce pressure drop (½” acceptable where flow is produced by pump differential pressure, ie. API Plan 21/22)
• Use large radius bends for tubing
• avoid 90 elbow fittings
• Slope horizontal runs upward to be self-venting – ½” per ft
• Install drain at lowest point
• Place seal pot or cooler on the side of the pump that coincides with the shaft rotation and optimized fluid flow. (see Figure 5, above)
• Always vent system prior to start-up (API Plan 23)

* Disregard elbows, shown in above picture, shown for illustrative purposes only.