api mechanical seal plans for sale

To keep mechanical seal systems functioning as long as possible, we recommend using standardized seal piping plans. Detailed API seal piping plans ensure minimal seal face wear by maintaining the optimal seal chamber environment.

Since they were first formulated, seal piping plans have been maintained and remodeled by the American Petroleum Institute (API). Current plans are based on API 682 and are sorted numerically. In some cases, designated letters are also used to differentiate between plans.

Please contact AESSEAL Systems Division for further details. Tel: +44 (0)28 9266 9966 Email: systems@aesseal.com For more information, and a video demonstrating the piping plan in operation, select a plan below

The API plans presented in this section are developed in accordance with the API 682, 3 revision / API 610, 10 revision standard. This is the standard scheme of the drilling pipes, which are widely used in industry. It is possible to customize these plans to meet the needs of customers.

The flushing of the seal from the outlet to the seal chamber via the aperture and flushing the seals from the seal chamber to the inlet through the diaphragm

Diagram of the system for ensuring the operation of a single seal with an impeller that creates fluid circulation through the stuffing box along an Autonomous circuit.

If the pressure in the oil seal chamber of the pump is less than the design pressure of the tank (4mpa), the installation of a safety valve on the tank pipelines is not required.

"Tandem" type mechanical seals can be used both with a refrigerator at the pump"s working medium temperature up to 400 °C, and without it at the working medium temperature up to 150 °C.

Diagram of the system for ensuring the operability of a double seal with a tank. The system operates at constant maintenance of the pressure of the shut-off fluid (pressure in the tank) within:

At pump working medium temperatures up to 150°C seals are used without a refrigerator, at the temperature of the pumped medium 150...400°C-with a refrigerator.

For servicing seals of a group of pumps that perform the same task and are located close to each other, it is possible to use the system diagram shown below.

The most commonly used scheme is a system with the supply of shut-off fluid from a separate pipeline with an overpressure m through the seal of the threads.

At pump working medium temperatures up to 150°C seals are used without a refrigerator, at the temperature of the pumped medium 150...400°C-with a refrigerator.

For condensate pumps, where dry operation of the mechanical seals is not excluded, the guaranteed supply of the shut-off fluid can be carried out according to the following scheme.

At pump working medium temperatures up to 150°C seals are used without a refrigerator, at the temperature of the pumped medium 150...400°C-with a refrigerator.

API plan 65 allows you to determine the volume of leaks through the mechanical seal. If the friction pair breaks through, the external strapping tank is equipped with an upper-level alarm that will trigger as soon as the liquid level in the tank increases.

The mechanical seal is the most likely part of the pump to fail.  Approximately 70% of the pumps removed from service for maintenance are victims of mechanical seal failure.  Mechanical seal parts are highly engineered with very close tolerances and any upset in the pump or associated system can cause seal failure, including:

Mechanical seals are based on positioning two very flat and smooth discs called seal faces, one rotating on the shaft and one stationary in the pump, against each other.  The discs are flat and smooth enough to ALMOST prevent the pumped fluid from leaking out between them.  However, the faces do rely on a very thin film of fluid between the faces to lubricate that rubbing fit.  Without this film of fluid, the seals will overheat and fail.  Lack of lubrication is the PRIMARY cause of seal failure.  If the fluid is very hot, it can flash to a vapor as the fluid moves across the faces, again resulting in lack of lubrication.  Note that gas seals use a gas film between the faces to minimize face contact and heat buildup.

Seal flush plans are intended to keep the area around the seal in the most seal friendly environment practical, usually meaning clean and cool.  Dual seal plans also provide backup and leak detection for safety.

Note that seal flush plans use pressure differences at the pump to drive the flush fluids.  The pump suction is low pressure, the seal chamber is a medium pressure, and the pump discharge is at high pressure.

As the seal faces faces rub together (with their thin film of lubricating fluid), they generate heat.  The heat can build up in the seal chamber and push the fluid towards its boiling point, resulting in premature flashing, lack of lubrication, and failure.  This first set of seal plans is intended to create circulation through the seal chamber to dissipate the heat out of the seal chamber and back into the pumped fluid.

Flush fluid flows from high pressure at pump discharge to the medium pressure seal chamber and back into the main flow to remove heat from seal chamber

Can be used to increase seal chamber pressure.  Increased chamber pressure may be required to keep chamber fluid from flashing to vapor or to provide enough pressure to push the fluid between the faces for lubrication. (Seal chamber must be 5 psi minimum above external atmospheric pressure).

These seal plans are intended to provide the seal with the friendliest environment possible by cooling and/or cleaning the fluid in the seal chamber.  The throat that separates the seal chamber from the main pumped fluid can be further restricted by adding a close clearance bushing in the bottom of the seal chamber, better isolating the cool, clean seal chamber fluid from the hot, abrasive fluid in the pump.

Rather than a Plan 21 single pass system, a Plan 23 is a multi-pass system.  Fluid comes FROM THE SEAL CHAMBER instead of the pump discharge, is cooled, and directed back to the seal chamber.

Fluid is driven out of the chamber and through the cooler by “pumping ring” or other “pumping feature” built into the seal.  These features provide very little differential pressure.  Connecting tubing must have long, sweeping bends, well vented high points, and low point blowouts to ensure fluid flows.

Quench piping does NOT change conditions inside the seal chamber, at the wet side of the seal faces.  Rather, it affects or monitors the environment on the ATMOSHPERIC side of the seal faces.

Pumps that leak when they are filled, even before they are started, often have a flush line intended for a Plan 11 or 13 connected to the QUENCH port, leading to the atmospheric side of the seal.  There should be a “Q” or the work “QUENCH” stamped in the gland at this port.

For flush plans Plan 65A, 65B, 66A, and 66B, facility owners may want to know if their seals are leaking excessively without going to the expense of dual seals.  These seal plans direct excessive leakage on the outside of the seal to an alarm instrument.  Remember that seals leak a little bit.  They need to in order to lubricate the faces and function correctly.  The plans below handle the nuisance leakage in different ways.

Used in salting services like sodium hydroxide.  The leakage across the seal faces will turn to salt when it reaches atmosphere.  The salt crystals can wear the faces or build up in the seal, preventing the movement necessary to keep the seal faces in contact.  The salt on the outboard of the seal can be washed away with a water quench through the quench and drain ports.  Usually a close clearance bushing is installed at the extreme outboard end to the seal assembly to help keep the quench fluid moving from the quench to the drain port (or vice versa) and not just run out along the shaft.  Also used for slurry services.

Grease can be introduced into the quench port.  This external grease can provide temporary lubrication to the seal in case the pump sees large air or vapor pockets which would normally rob the seal faces of the required lubricating fluid film.

Quench can also be gas.  In hot hydrocarbon services, the fluid will turn to solid coke when it reaches the atmospheric side of the seal.  The fluid would remain a liquid if the area outside the seal faces is robbed of oxygen with a flood of nitrogen or steam.

An alarm does NOT necessarily mean a failed seal.  The collection vessel might be full from years of nuisance leakage.  Try emptying the vessel and observing how fast the vessel fills.

Two throttle bushings are used to ensure that the vapor (or fluid) leakage is limited along the shaft and out of the drain.  A pressure switch picks up a rise on pressure above nuisance levels on the outboard side of the seal.

Dual seals provide a backup seal in case the primary seal fails.  They prevent hazardous fluids from leaking to the surrounding area, desirable for both environmental protection and the safety of nearby personnel.  Dual seals also capture and control any leakage of pumpage across the primary seal. The backup seal is kept lubricated by introducing a buffer/barrier fluid (often a mineral or synthetic oil, a water/glycol mix, or diesel) into the space between the primary (inboard) and secondary (outboard or backup) seals.  The buffer/barrier fluid is contained in a tank (5 gallons is most common) adjacent to the pump.  Instrumentation on the tank indicates what is happening with the seals.

Remember that a lubricating fluid film will flow from high pressure to low pressure.  If the pump seal chamber pressure is higher than the pressure on the other side of the seal, the pumpage will be the lubricating film.  If the pump’s seal chamber pressure is lower than the external pressure, the external atmosphere will migrate into the pump.  Pumps under vacuum cannot use an ordinary single seal, since air from the atmosphere would be drawn between the faces, causing them to run dry and fail. Using a dual seal allows a fluid to be present at the outside of the seal.  In a pump under vacuum, the buffer fluid would be pulled into the pump between the seal faces, keeping the inboard seal well lubricated.

If the pump seal chamber pressure is higher than the BUFFER fluid between the primary and backup seal faces, then the pumped fluid will flow from the high seal chamber pressure into the low pressure buffer fluid.  This is called a DUAL UNPRESSURIZEDseal (formerly called a tandem seal), and the fluid is called a BUFFER fluid.

If the pump seal chamber pressure is lower than the BARRIER fluid between the primary and backup seal faces, then the barrier fluid will flow across the primary seal from the space between the primary and backup seals into the pump.  This is called a DUAL PRESSURIZEDseal (formerly called a double seal), and the fluid is called a BARRIER fluid.

Buffer fluid circulates from the buffer fluid reservoir, through the space between the primary and backup seal, and back to the reservoir.  Fluid is circulated by a weak pumping action built into the seal.

It the fluid flashes to vapor at low pressure, the vapor is piped to a flare or vapor recovery system, through an orifice at the top of the tank.  If the primary seal is allowing too much leakage, the vapor will build pressure in the reservoir against the orifice and a pressure instrument can alert the operator.

If the fluid remains as a liquid under low pressure, any leakage will cause the fluid level in the buffer tank to rise, where a high level alarm can be tripped.  Just because the high level alarm is tripped does not mean that the primary seal is failing; it is the rate of leakage filling the tank which matters.  The high level may have been reached after collecting years of nuisance leakage.  Often, an oil change to the original level is all that is required.  Be sure the fluid is disposed of properly.

Seal face friction or hot pumpage can add heat to the buffer fluid.  A cooling water coil is often installed in the reservoir to cool the buffer fluid.

Dual pressurized system (seal barrier fluid is at a higher pressure than the pump seal chamber).  Pressurized systems are used to ensure that very dangerous fluids remain in the pump.  The difference between 53A, 53B, and 53C is the method of pressurizing the barrier fluid.  Pressure in the barrier fluid should be at least 10 psi over the pressure in the pump seal chamber.

Barrier fluid circulates from the barrier fluid reservoir, through the space between the primary and backup seal, and back to the reservoir.  Fluid is circulated by a weak pumping action built into the seal.

A low level alarm in the reservoir alerts the operator that a seal may be failing, allowing the barrier fluid to enter the pump through the primary seal or the atmosphere through the backup seal.

Seal faces can be designed to maintain a gas film between them rather than a fluid film.  These piping plans are intended to work with theses gas film (dry running) seals.  Plan 72 and 74 bring the buffer or barrier gas into the seal; plans 75 and 76 are for the gas exiting the seal.

Secondary seal is ordinarily running with a gas film between the faces.  When the primary seal fails, the pumped fluid will fill the space between the primary and backup seal.  The backup seal is now working as a liquid seal rather than a gas seal and is designed to run for about 8 hours, allowing the operators time for an orderly pump shutdown.

Plan 72 buffer gas flow keeps the gas in the seal from becoming concentrated from nuisance leakage over time so that any leakage from the gas backup seal is mostly inert flush gas and not toxic pump vapors.

Seal support systems are vital to the reliable functioning of the thousands of pumps that keep a refinery running around the clock. When they are properly designed, installed, and maintained, the seal support systems help ensure pump reliability and maximize the pump life by maintaining the optimum seal chamber conditions. In Northern California, pump reliability takes on an added dimension—environmental compliance. Any leakage of hydrocarbons could result in sanctions from the California Division of Occupational Safety and Health (Cal/OSHA) or Bay Area Air Quality Management District (BAAQMD).

If you’re new to API plans, you’ll quickly realize that the range of options available in API seal flush plans reflects the range and complexity of the various pumping processes and conditions across a refinery. Choosing the right API seal flush plan is a critical step in ensuring pump reliability. In my years of experience in working with process engineers and maintenance teams at Northern California refineries, we’ve always achieved better outcomes when I have the opportunity for on-site analysis of pumping processes and can advise them on the latest advancements and configuration options available.

The tables below provide an overview of the three standard categories of API seal flush plans—process side, between seals, and atmospheric. It’s not a comprehensive list of all API plans, but I hope they provide enough information to help you understand the range of options available in each category and take the first steps in matching plans with your specific pumping processes.

Description: Process side API seal flush plans use a single mechanical seal to prevent pump (process) fluid from leaking. In this arrangement, the process fluid is the lubricant. It provides a thin film between the seal faces to reduce friction and absorb heat. In doing this, the pressurized process fluid “leaks” across the seal faces and returns to the process flow.

Recirculates process fluid from pump discharge through a cooler, then to the seal chamber; Preferred for viscous process fluids that could clog seal flush cooler

Recirculates process fluid from the seal chamber through a cooler, then back into the seal chamber using a pumping ring; By continually recirculating seal chamber fluid through the seal flush cooler, it provides greater cooling capacity compared to Plan 21

Recirculates process fluid from pump discharge through a cyclone separator, sending clean process fluid to the seal chamber and particulates back to pump suction; For optimum performance, particulates should have a specific gravity twice the process fluid

Delivers clean or cool flush fluid to the seal chamber from an external source; Employs a close-clearance throat bushing to ensure seal chamber higher pressure; Because flush fluid will migrate past the bushing it must be chemically compatible with process fluid

Recirculates process fluid from pump discharge through a cyclone separator, sending clean process fluid to the seal chamber and particulates back to pump suction; Particulates should have a specific gravity twice the process fluid

Each of these API seal flush plans has options to help tailor the plan to the requirements of the specific pumping process. Instrumentation such as temperature, pressure, and flow gauges help monitor system performance. If you’re not using process fluid to lubricate the mechanical seal, flush fluids can be water, water/glycol, or mineral- or synthetic-based hydraulic and lubricating oils. Cooling capacity needs to be carefully calculated based on process fluid temperature, pressure, and mechanical seal type. When you’re faced with choosing among these options, the guidance of an experienced, local seal support system vendor is critical. Well-informed design decisions are the foundation for long-term reliability.

Description: The majority of refinery processes deal with hydrocarbons. In comparison to process side API seal flush plans, between seal plans provide a higher degree of protection against leakage. As a result, between seal plans (or dual mechanical seals) are used in the majority of refinery pumping applications.

These API seal flush plans deliver a barrier (pressurized) or buffer (unpressurized) fluid delivered from an external source to the space between the inboard and outboard seals. Barrier fluids can be a water/glycol mix, or mineral- or synthetic-based hydraulic and lubricating oils.

Uses a pressurized bladder accumulator to isolate pressurized gas from barrier fluid and delivers clean barrier fluid between the inboard and outboard seals at a pressure higher than the process fluid pressure; An internal pumping ring circulates the nitrogen barrier fluid; Bladder prohibits gas absorption into the barrier fluid and facilitates higher operating pressures than Plan 53A

Preferred for applications where the seal chamber pressure varies during pump operation; Uses a sensing line from the seal chamber into the piston accumulator to deliver barrier fluid from a reservoir at a constant, but higher pressure than the process fluid pressure; An internal pumping ring circulates the barrier fluid

Delivers buffer gas (typically plant nitrogen) from an external source to the seal chamber at a lower pressure than the process pressure; Uses a coalescing filter to remove any moisture and particulate present in the plant nitrogen supply; Any process fluid vaporizing across the inboard seal is then swept into a closed collection system

Delivers barrier gas (typically plant nitrogen) from an external source to the seal chamber at a higher pressure than the process pressure; Uses a coalescing filter to remove any moisture and particulate present in the plant nitrogen supply; Allows a small amount of nitrogen to leak into the process fluid

These plans also can also have a significant number of design options. Plans 54 and 55 lend themselves to a high degree of customization regarding reservoir volume, pump, filters, coolers, and instrumentations. These plans can also be configured to support multiple pumps with similar pumping characteristics. Plan 72 has the option of adding a condensing or non-condensing leakage collection system. For each of these, determining the proper pressure is one of the most critical factors regarding system performance.

If you’re making an investment in a new or upgraded seal support system, it’s well worth the time to work with an experienced Field Engineer who understands the importance of configuring the options for the specific pumping process.

Description: In comparison to the range of options in the above API seal flush plan categories, atmospheric side plans are much simpler. Their purpose is to provide a non-pressurized cooling flush to a mechanical seal"s faces on the atmosphere side to prevent or remove solid formations—crystallization, icing, and coking. Water, steam, and nitrogen are the typical flush fluids.

A quench improves atmospheric seal performance by absorbing or removing any process fluid leakage, preventing process fluid from being exposed to the atmosphere, and cooling or heating (relative to the process fluid temperature) to prevent the formation of solids proximate to the mechanical seal.

Delivers clean flush fluid from an external reservoir to the atmospheric side of a single seal preventing icing at ambient temperatures on the atmospheric side; Used for vertical pump applications

Delivers a low rate (2 to 4 PSI) of quench fluid (nitrogen, water, steam) from an external source to the atmosphere side of the seal. Typically uses a throttle bushing for containment.

Each of the atmospheric side plans has an option to collect condensing process fluid leakage into a reservoir. In the event of excessive leakage, a level transmitter on the reservoir triggers an alarm.

The proper design of your flush plan is the biggest factor in ensuring long-term performance and reliability. You may have the in-house expertise to determine the appropriate API flush plans for the various pumps in a new installation or upgrades of existing pumps, but your outcomes will improve if you engage the service of an experienced, local partner. In working with process engineers for over the years, I can tell you first-hand that you’ll:

An experienced API seal flush plan partner has Field Engineers to evaluate each process and pumping conditions, fluid compatibility issues, and infrastructure considerations (on-site or virtually) to help determine plan requirements.

Swagelok has decades of expertise in helping refineries determine the proper API seal flush plans. We can design, fabricate, and thoroughly test the API seal plans prior to delivery. For over 50 years, Swagelok has been meeting the seal support needs of refineries in Northern California. We offer a complete range of API seal flush plans, available as kits or assemblies.

To learn howSwagelok Northen Californiacan assist you in choosing API seal flush plans that are right for your process needs by providing expert consultation, design, and fabrication,contact our teamtoday by calling

API Plan 62 delivers an external quench fluid to the atmospheric side of the seal. A typical application in a refinery is the prevention of coking on seal faces in hot hydrocarbon service by employing a steam quench. Nitrogen or clean water may also be used to quench or cool and clean the atmospheric side of the seal.

See page 77 of the Mechanical Seal Support Systems Application Guide for additional details and ordering information. Contact your authorized Swagelok sales and service center for information on optional components.

After more than five years of planning, the American Petroleum Institute (API) is preparing to release the 4th edition of API Standard 682 (ISO 21049:2011). The API 682 standard, which dates back to 1994 and is formally known as Shaft Sealing Systems for Centrifugal and Rotary Pumps, offers specifications and best practices for mechanical seals and systems to pump end users.

The standard’s latest edition began to take shape in 2006, when API formed a 4th edition task force to respond to end users’ questions and comments about previous editions. The task force soon realized that major changes, including reorganization and editing, would be necessary. While addressing every aspect of the resulting 4th edition (which is more than 250 pages long) would be impossible, this article summarizes the standard’s main points.

Those who use API 682 should understand the standard’s scope and remember that the standard does not include specifications for equipment outside that scope, such as engineered seals or mixers. Another important but often misunderstood point is that API 682’s figures are illustrative and not normative in their entirety.

For example, one of API 682’s figures shows a fixed throttle bushing combined with a rotating Type A seal, but seal manufacturers do not always have to combine these two components. The standard provides normative details in clauses and tables to help purchasers distinguish between requirements and suggestions.

The 4th edition continues to divide seals into three categories, three types and three arrangements. For all practical purposes, seal manufacturers can combine a seal’s component parts into nearly any orientation or configuration. Each orientation and configuration has advantages and disadvantages with respect to certain applications, performance and system disturbances.

Before the 4th edition, API 682 did not specify a minimum clearance between the inside diameter of a stationary seal part and the outside diameter of a rotating seal part. The 4th edition specifies this minimum clearance—typically the clearance between the sleeve and the mating ring. The specified clearances are representative of standard clearances that end users have used for decades. End users should not consider seal components to be “shaft catchers” to restrict shaft movement. The minimum clearance specified in API 682 also applies only to equipment within the standard’s scope. Equipment outside that scope, such as non-cartridge seals, older pumps, non-API 610 pumps and certain severe services, might benefit from larger clearances.

The new standard also updates the default bushings for the gland plate for the three seal categories. Fixed throttle bushings are now the default for Category 1 only, while floating bushings are the default for Categories 2 and 3.

While the 4th edition features the recommended seal selection procedure from the standard’s first three editions, it adds an alternative selection method in Annex A. Proposed by task force member Michael Goodrich, this alternative method recommends using material data sheet information to select a sealing arrangement.

Plans 66A and 66B are new to the standard, although end users have used them previously in pipeline applications. These plans detect and restrict excessive leakage rates in case of an Arrangement 1 seal failure.

The 4th edition now requires Plan 52, 53A, 53B and 53C systems to have a sufficient working volume of buffer or barrier fluid for at least 28 days of operation without refilling. As a point of reference, the default reservoir for Plans 52 and 53A has a three-gallon capacity, or pot, for pump shafts smaller than 2.5 inches and a five-gallon pot for larger shaft sizes. Plan 53C must have the same working volume of fluid as Plan 53A. For Plan 53B, the default bladder and accumulator sizes are five gallons and nine gallons, respectively. The design of Plan 53B systems can be complex, especially when ambient temperatures vary widely, and purchasers should become familiar with the calculations and procedures in the 4th edition’s Annex F tutorial. The new edition also discusses the option of adding a pressure gauge and isolation valve to check the accumulator or bladder’s integrity in a Plan 53B system.

The 4th edition has revised the data sheets in Annex C extensively to make them the same for all seal categories. Only two data sheets are included in the 4th edition—one in metric units and one in U.S. customary units. The new edition also folds Annex J into Annex E.

Previous editions of API 682 required metal plugs and anaerobic sealants when shipping new or repaired cartridges. After much debate, the task force decided that threaded connection points should be protected with plastic plugs for shipment. These plastic plugs should be red and have center tabs that operators can pull easily to distinguish the plugs from metal plugs. Shippers should also attach yellow warning tags to the plugs to indicate that end users need to remove the plugs before operation.

Although tutorial notes are scattered throughout API 682, this edition expands the tutorial section, Annex F, from seven pages to 42 pages. The expanded annex includes illustrative calculations. In particular, users interested in systems such as Plan 53B will find Annex F to be useful.

The 4th edition of API 682 is the product of more than 20 years of discussion, debate, usage and peer review. It includes a strong set of defaults and is by far the best and most logical starting point for mechanical seal and systems use. Equipment operators should take the time to familiarize themselves with API 682 to get the most out of this comprehensive standard.

In LIDERING we have an extensive range of mechanical seals for all types of pumps: from seals for domestic pumps to seals for process pumps, specific in complex applications in the chemical and petrochemical industry. In addition, we offer a wide range of spare parts compatible with the originals of the main manufacturers of pumps (RMS). Our catalog also includes cartridge seals for more demanding industrial processes, and our extensive range of products is ever-growing in order to adapt to the requirements of our customers.

In Part 3 of our series on Double/Dual Mechanical Seals we take a look at the best piping plans/support systems to put in place to increase seal/equipment reliability and reduce energy/water costs.

More importantly, to extend the life of a double/dual seal, you want to control the fluid film that comes into contact with the primary seal faces to establish the ideal lubrication, temperature and pressure within the seal. Across all types of mechanical seal failures, inadequate/incorrect seal support systemsare the second highest cause of seal failures (Figure 1).

Standard environmental control plans (also called piping plans) have been developed for double/dual seals and choosing the right environmental control plan is critical to your seal performance and reliability.

This plan is used when working with hazardous process fluids in which no leakage into the product can be tolerated. It provides a backup seal in case of inboard seal failure.

If an inner seal leak is not detected early enough, the higher pressure process fluid will displace the buffer fluid. This can result in the process fluid completely filling the barrier fluid chamber between the inboard and outboard primary seals. Should the outer seal leak, product will be released into the atmosphere.

Uses a pressurized external reservoir or barrier fluid tank to provide a clean, pressurized barrier fluid to both the inboard and outboard primary seals of a pressurized double/dual seal.

The tank pressure must be maintained at the proper level.  If the barrier fluid tank pressure drops, the system will begin to operate like a Plan 52, or unpressurized dual seal, which does not provide the same level of sealing integrity.  Specifically, the inner seal leakage direction will be reversed and the barrier fluid will, over time, become contaminated with the process fluid.

Directs a clean compatible fluid into and out of the dual mechanical seal barrier/buffer fluid ports. The purpose of this fluid is to prevent the pumped fluid from damaging the inboard seal faces, to remove heat from the seal, and to lubricate the outboard seal faces.

Careful consideration should be given to the reliability of the barrier fluid source. When the source is interrupted or contaminated, the resulting seal failures can be very costly.

The higher the differential pressure, the more transfer/migration into the product. The control should never be used where the barrier fluid pressure is likely to fall below seal chamber pressure. If this were to happen, the failure of one inboard seal from any mechanical seal in the system could contaminate the entire barrier fluid system with product and cause additional seal failures.

Once the inboard seal wears out or fails, the amount of barrier fluid that entered the product system is virtually unlimited unless it is shut down quickly.  Alerting instruments should be put in place to avoid this.

Using appropriate monitoring devices, alarms, switches, etc. will provide a means to monitor the health of your double/dual seal to identify potential issues in advance avoiding costly unplanned outages. A basic Plan 52 buffer system will have a sight glass to monitor the buffer fluid level, a pressure gauge and connections to and from the mechanical seal, as well as a vent and drain valve. Cooling coils and level switches are typically available as optional items.

For assistance with using the best seal support system for your specific challenge, ask your local Chesterton office or contact our Ask the Expert service.

Mechanical seals are a great cause of concern and failures in many operating plants. This is especially true of systems that are pumping or compressing dirty fluids. Some examples include bottoms pumps, sulfur pumps, or equipment that is handling abrasive or challenging process media. Mechanical seals are often redesigned, replaced and repaired simply because of the challenging conditions these seals face during operation. This has continually led to excessive costs in terms of repair or redesign, not to mention production loss and cost associated on a critical unspared asset.

While seals have to be properly selected and designed for the application during the project’s engineering stages, it is equally critical to select the right and most cost-effective seal plan to help support the seal’s operating environment. The seal flush plan is as equally critical and perhaps more so to help establish a reliable operating mechanical seal. API Standard 682 from the American Petroleum Institute provides various seal plan configurations, their advantages and disadvantages and a good description of each of the plans. To gain an in-depth understanding of the various types of applications and plans available for selection, refer to API 682. In addition, a lot of seal vendors publish handy booklets that contain good, brief and quick references and explanations of the different API seal plans.

This particular article looks at API Plan 53B and how paying careful attention to some aspects of this plan can ensure a proper and reliable running seal in many applications. Of course, the mechanical seal should be correctly and most optimally designed for the particular application at hand.

Figure 1 shows a basic overview of what a 53B seal flush plan looks like. It is a pressurized flush plan that gets used with a dual seal (i.e., two seals) configuration. The accumulator contains a bladder that is pre-charged at a certain calculated bladder pre-charge pressure value through the bladder charge connection shown in Figure 1. Next, the barrier fluid, which can be royal purple or another process compatible based media, is injected into the system at a certain calculated hydraulic charge pressure through the make-up barrier fill or a similar port provided on the piping setup. The idea is that when the seal fails (leaks are more than expected since all seals leak to some extent), then the barrier fluid, being at a higher pressure, will push the leakage back into the process rather than letting the process media leak outside into the ambient. This helps prevent environmental release and avoids wastage of costly process media to the atmosphere. It is quite clear based on this that such plans are best suited for applications that are toxic and hazardous and where negligible leakage is allowed into the atmosphere due to such concerns. Consider reading ample literature available from various sources to gain a deeper understanding of this particular plan.

One of the key advantages of this particular plan is the cost associated with implementing it in a given plant compared to other similar options (i.e., Plan 54 or others). However, it is imperative to realize that the reliability of a 53B plan and the mechanical seal it supports is highly dependent on the plant operator who maintains this and checks on the system on a regular basis. While a number of seal failures can be attributed to incorrect designs or other issues, equally, if not more, causes can be attributed to how a plan 53B is operated and maintained on a running asset.

Here are a few important points that should be considered while working with any plan 53B in a maintenance and operating organization.It is important to vent a 53B through the appropriate vent points provided to ensure there is no vapor entrapment prior to seal start-up. Attention should be paid to horizontal versus vertical heat exchangers provided on the system. Based on experience, it is easier to vent out vertical heat exchanger configurations versus horizontal systems. However, horizontal systems are provided or should be provided with block valves to help ensure proper venting.

In colder climates where a plan 53B is installed outside, the system should be properly heat traced and winterized. This includes the seal flush piping, the accumulator and the exchangers. The accumulator contains a nitrogen bladder with a pre-charge pressure as previously indicated. Fluctuations in the ambient temperature can have a dramatic effect on system pressure and lead to seal failures and loss of seal system reliability.

Operations should confirm and check with engineering that the right calculated values are provided for the pre-charge pressure for the bladder and also the hydraulic system charge pressures. These are quite critical to ensuring system and seal reliability. Any discrepancies in these calculated values can risk reverse pressurization (i.e., seal reversal) and subsequent failure of the sealing system. It is important to note that some plants consider playing around with the pre-charge and hydraulic charge values to buy more time between system failure and low-level alarm of the barrier fluid so the operator has sufficient time to fill and make up the loss of barrier in the system. However, experience has shown the best way to address this issue is to procure accumulators of higher volumes to provide for this as opposed to modifying pressures to buy more volume in the system. The latter seems to have much smaller effects compared to sizing the accumulator correctly in the first place. Also, if consideration is being given to changing pre-charge and hydraulic pressures, this should be in discussions with the original equipment manufacturer (OEM) seal vendor since excess pressures on a given seal can compromise and affect seal leakage rates, thus reducing the time and volume present in the system.

It is equally important that the operator only charge (i.e., make-up fill with hand-pump) the system when the low-level alarm pressure is initiated. Charging the system at every minor occasion when the barrier pressure and level drops is not warranted. This, on the contrary, will lead to a poor seal system and seal reliability as a result of multiple pressure charging in short intervals.

Operations should keep a log of charging frequencies, depending on the low-level alarm. This, along with visual inspections, can provide a good clue to seal failures and acceptable leakage rates. The question most often asked by an operator is: What is considered an acceptable leakage? While engineering, along with the seal OEM, can provide acceptable leakage rates, to get a very good measure of seal reliability, the operator can keep an eye out for the frequency of fill and also, if correctly done, the volume filled during the initial fill cycle.

Since the pump throat bushing controls the stuffing box environment, it would be beneficial to incorporate the throat bushing on the seal cartridge itself to help with maintenance, as opposed to locating it within the pump. This holds true not just for the 53B seal plan, but for others as well.

Having a temperature gauge located on both the inlet and outlet of the seal helps in establishing a temperature gradient between the seal’s in and out flow. A difference of around 20 to 30 degrees C is acceptable; any more delta T changes can point to possible issues with the seal, cooling water, or other variables. This can help the operator make on-site decisions to engage or escalate the issue to engineering in the event of a potential problem.

While there are many individual experiences connected to running a 53B seal flush plan, these important points most certainly can help the operator make an informed decision to help seal reliability and mean time between failures (MTBF) in a running plant. Engineering should perform a detailed root cause analysis on complex seal issues and provide the appropriate solutions sought to address repeated failures. This will help the plant’s bottom line: Cost and Revenue.