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by Morgan Zealear, on 6/11/21 9:00 AM
For newer engineers, it is crucial to understand the different mechanical seals and their associated support systems they are likely to encounter in Northern California refineries, as centrifugal pumps are abundant in refinery operations.
Nearly 40% of pump failures are attributed to mechanical seal failure and can cause significant downtime for refineries or potential sanctions from regulatory agencies such as BAAQMD or Cal/OSHA. Thus, comprehensive knowledge of mechanical seal types and support systems is vital for maximizing uptime and maintaining safe and reliable pumping operations. There are three pump seal types that are most common in Northern California refineries: 1) process side, 2) dual (between-seals), and 3) atmospheric side. Depending on specific process conditions and mechanical seal type, a seal support system should be implemented accordingly.
Summary of Pump Seal Types and Support Systems in Northern California Refineries
Seal support systems supply either a gas or liquid to a mechanical seal to regulate the environment in which it operates and to protect rotating equipment from damage by:
- Providing lubrication to seal faces
- Controlling temperature and pressure in the seal chamber and seal
- Flushing contaminants and/or residue build-up from the seal
- Preventing process fluid leakage into the atmosphere
Let’s take a look at seal types and appropriate seal plans for each.
Process Side
Single, process side mechanical seals are implemented when the pumped fluid does not pose an environmental threat, as the process fluid has the potential to vaporize as it crosses the seal faces and may dissipate into the atmosphere.
Support systems for process side seals provide cooling and lubrication to single mechanical seals to prevent seal abrasion by circulating process fluid either:
- from seal chamber to the pump suction,
- pump discharge to seal chamber, or
- from pump discharge to seal chamber to pump suction.
Alternatively, a flush fluid from an external source can be used to provide lubrication and cooling (API Plan 32).
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Categorization: ⬤ Process Fluid Flush ⬤ Cooled Flush ⬤ Cyclone Separator ⬤ External Flush |
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API Plan |
Description |
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Plan 11 |
API Plan 11 recirculates flow from high-pressure suction of the pump (discharge piping) through a flow control orifice to the seal. |
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Plan 12 |
API Plan 12 recirculates flow from high-pressure suction of the pump (discharge piping) through a strainer then through a flow control orifice to the seal. |
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Plan 13 |
API Plan 13 recirculates flow from the seal chamber to the suction side of the pump and is common for vertical pumps. |
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Plan 14 |
API Plan 14 combines Plans 11 and 13 to recirculate flow from the pump discharge into the seal chamber and from the seal chamber to the pump suction. |
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Plan 21 |
API Plan 21 utilizes Plan 11 while adding a cooler. Flow is directed from the discharge side of the pump through an orifice and a cooler before being directed back to the seal chamber. |
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Plan 22 |
API Plan 22 utilizes plan 21 while adding a strainer. Flow is directed from the discharge side of the pump, through a strainer, orifice, and cooler before being directed back to the seal chamber. |
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Plan 23 |
API Plan 23 employs a circulation device (pumping ring) to direct the fluid from the seal chamber through a cooler before returning the cooled fluid to the seal chamber. A throat bushing isolates the cooled fluid from hot process fluid. |
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Plan 31 |
API Plan 31 directs process fluid flow from the discharge side of the pump through a cyclone separator. Clean flush fluid is sent from the separator to the seal chamber, while sending fluid with solids into the suction side of the pump. |
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Plan 41 |
API Plan 41 utilizes Plan 31 while implementing a cooler for the clean flush fluid leaving the separator to be routed through before being directed back to the seal chamber. |
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Plan 32 |
API Plan 32, typically used with a close-clearance throat bushing, delivers a clean flush fluid from an external source to the seal chamber to ensure higher seal chamber pressure. |
Dual/Between Seals
Dual mechanical seals provide superior leak prevention out of all pump seal types, consisting of an inboard (primary) seal and an outboard (secondary) seal. Inboard seals keep process fluid within the pump housing, whereas outboard seals prevent buffer/barrier fluid leakage to the atmosphere. Support systems deliver a buffer (unpressurized) or barrier (pressurized) fluid to the seal chamber to lubricate seal faces and remove heat from the seal chamber.
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Categorization: ⬤ Buffer Fluids (Unpressurized) ⬤ Barrier Fluids (Pressurized) |
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API Plan |
Description |
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Plan 52 |
API Plan 52 utilizes a reservoir and circulates unpressurized buffer fluid between the inboard and outboard seals using a pumping ring to provide positive circulation through the support system and into the seal. Process fluid and buffer fluid must be compatible. |
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Plan 55 |
API Plan 55 is a custom engineered system that circulates unpressurized buffer fluid to and from the seal chamber via a pump on an external reservoir. This plan can contain additional components, such as coolers and filters, depending on application parameters. |
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Plan 72 |
API Plan 72 delivers buffer gas, typically an external nitrogen source, between the inboard and outboard seals and utilizes a coalescing filter to remove moisture and particulate from the gas supply. A pressure regulator on the panel regulates the nitrogen before entering the seal chamber and should be no more than 10 psi. |
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Plan 53A |
API Plan 53A circulates pressurized barrier fluid, typically from a reservoir pressurized by nitrogen, between the inboard and outboard seals. |
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Plan 53B |
API Plan 53B circulates pressurized barrier fluid between the inboard and outboard seals, where pressurization is achieved through a bladder accumulator. |
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Plan 53C |
API Plan 53C circulates pressurized barrier fluid between the inboard and outboard seals, where pressurization is achieved through a piston accumulator. |
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Plan 54 |
API Plan 54 is a custom engineered system that circulates pressurized barrier fluid to and from the seal chamber via a pump located on an external reservoir. This plan can contain additional components, such as coolers and filters, depending on application parameters. |
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Plan 74 |
API Plan 74 circulates pressurized barrier gas, typically an external nitrogen source, between inboard and outboard seals and utilizes a coalescing filter to remove moisture and particulate from the gas supply. A pressure regulator on the panel regulates the nitrogen to at least 25 psi above the seal chamber. |
Atmospheric Seals
When a single mechanical seal can’t operate without the assistance of quench to the atmospheric side, API Plan 51 or 62 may be incorporated to prevent icing or coking. Atmospheric side support systems deliver an unpressurized quench fluid to the atmospheric side of a mechanical seal.
API Plan 51 may be employed to prevent icing on the atmospheric side of seals, typically on vertical pumps. API Plan 62 uses low-pressure steam, water, or nitrogen to quench the atmospheric side of seals to prevent coking.
Look to Local Seal Support Experts
Due to the wide variety of seal support plans, it can be difficult to know which plan is best suited for refinery pumping applications and which additional components should be implemented. Seal support selection requires careful consideration of pump seal types, process fluid, and process conditions to provide optimal mechanical seal support for reliable pumping operations in Northern California refineries.
Whether you are looking to upgrade a seal support system or are struggling with mechanical seal reliability, local seal support experts at Swagelok Northern California have over 50 years of experience with pumping applications in local refineries. Our highly experienced Field Engineers can provide an onsite evaluation to make recommendations with regards to plan selection, system design, instrumentation, and components to enhance pump reliability.
To find out more about how Swagelok Northern California can help you optimize mechanical seal reliability through seal support systems for pump seal types in Northern California Refineries, contact our team today by calling 510-933-6200.
Morgan Zealear | Product Engineer – Assembly Services
Morgan holds a B.S. in Mechanical Engineering from the University of California at Santa Barbara. He is certified in Section IX, Grab Sample Panel Configuration, and Mechanical Efficiency Program Specification (API 682). He is also well-versed in B31.3 Process Piping Code. Before joining Swagelok Northern California, he was a Manufacturing Engineer at Sierra Instruments, primarily focused on capillary thermal meters for the semiconductor industry (ASML).
