api mechanical seal factory

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

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.

Pumping processes involving toxic or hazardous fluids that can’t risk leakage because of stringent environmental regulations require a double mechanical seal. Compared to a single mechanical seal, a double seal gives you significantly greater protection against leaks. With a double mechanical seal, you have an arrangement of two mechanical seals (a primary or inboard seal and a secondary or outboard seal) in series—back-to-back, tandem, or face-to-face. Each seal has a rotating (R) surface and a stationary (S) seal surface. These seals can be arranged in one of three patterns.

In a back-to-back arrangement, the stationary seal faces are positioned back-to-back with the rotating seal faces on the outside. The back-to-back arrangement is easy to install and used for many general pumping applications.

The tandem arrangement has the two pairs of seals mounted with the same orientation. This arrangement is preferred for toxic or hazardous applications because the outboard seal provides full pressure back-up, allowing the outboard seal to back up in the event of an inboard seal failure.

In the face-to-face arrangement, the rotating seal faces share a common stationary seal face. This arrangement is useful when equipment space is too constrained to permit back-to-back or tandem seal arrangements.

The American Petroleum Institute (API) Standard 682 classifies double mechanical seals into two configurations—pressurized and unpressurized. The pressurized arrangement has a barrier fluid delivered to the double mechanical seal by a seal support system. The barrier fluid is delivered at a higher pressure than the process fluid and must be chemically compatible with the process fluid as it will lubricate the inboard seal faces and mix with the process fluid. The unpressurized arrangement has a buffer fluid delivered to the double mechanical seal by a seal support system. The buffer fluid is delivered at a lower pressure than the process fluid.

The barrier and buffer fluids you use can be liquid or gas. They provide lubrication and help maintain the required operating temperature of the seal faces. The typical choices are water and water/glycol mixtures, low-viscosity petroleum or synthetic oils, kerosene, diesel, and nitrogen.

To gain a better understanding of the differences between the uses of barrier and buffer fluids, let’s look at two common API plans for double mechanical seals—API Plan 52 Buffer Fluid Seal Pot and API Plan 53A Barrier Fluid Seal Pot Pressurized by Nitrogen.

API Plan 52 takes buffer (unpressurized) fluid from a reservoir (seal pot), delivers it to the seal chamber, circulates it between the inboard and outboard seals using a pumping ring located driven by shaft rotation, then returns the fluid to the reservoir. In the event of an inboard seal failure, process fluid leaks into the seal chamber. When that occurs an increase in buffer fluid pressure and/or level alerts operators to the problem. The outboard seal, however, contains leakage until maintenance can replace the damaged seal.

This plan can include cooling coils in the reservoir to maintain the required buffer fluid temperature, visual or mechanical fluid level indicators, pressure and level transmitters, and connection to a collection system and buffer fluid replenishment source.

The overall design of this API plan for a double mechanical seal is relatively simple in comparison to other plans. Design decisions involving tubing size, length, geometry, type (carbon vs stainless steel), buffer fluid type, and volume of the buffer fluid reservoir are critical in maintaining the proper operating environment for the double seal. If you don’t have this expertise in-house, work with an experienced, local seal support system vendor to ensure the API Plan 52 is designed to meet your specific pumping requirements.

API Plan 53A is conceptually similar to API Plan 52 with the difference that the fluid being circulated between the double mechanical seals is under pressure. A pumping ring is used to circulate the fluid. The reservoir that contains the barrier fluid is pressurized by plant nitrogen. Reservoir pressure should be set a minimum of 20 to 25 psi (1.4 to 1.73 bar) above the maximum seal chamber pressure, allowing the barrier fluid to leak (and lubricate) across the inboard seal faces into the process fluid. For this reason, the barrier fluid must be chemically compatible with the process fluid.

Because barrier fluid is depleted as it moves across the inboard seal faces, it needs to be replenished. This can be done manually or automatically by way of a system that serves multiple pumps. API Plan 53A design options include reservoir type and volume, cooling coils, fluid level and pressure indicators, and transmitters to alert to level or pressure changes that indicate seal failure.

When you choose an API plan for a double mechanical seal, your primary decision is between a buffer or barrier plan. I’ve highlighted two of the API plans for double mechanical seals above to show the basic differences. There are multiple API plans for double mechanical seals to choose from—pressurization from bladder or piston accumulators, plant nitrogen delivered directly to the seal chamber, and custom-engineered external systems. Your choice will be determined by the process fluid and pumping conditions and the type of double mechanical seal your vendor recommends.

With this information in hand, it’s best to work with an experienced local seal support system vendor. They’ll be able to meet with you on-site to review the specifications for the pumping process, the pump, and the double mechanical seal. They’ll evaluate your existing infrastructure and its influence on seal support system design. Based on this information, they’ll then design the seal support system to meet the specific pumping requirements.

If you work with a global vendor like Swagelok, based on the design, we can quickly assemble and thoroughly test the API plan at our local facilities prior to delivery. We’re also conveniently available for follow-up consultations, on-site, remotely, or by way of a quick phone call.

For well over 50 years, Swagelok has worked closely with Northern California process industries to confidently choose the right API plans for pumping needs. Our locally based Field Engineers and certified technicians provide field verification of your seal support requirements, designs based on best practices gained from global experience.

To find out more about howSwagelok Northern California can help you choose the right API plan for double mechanical seals, as well as process and atmospheric side seals,contact our team today by calling

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).

The Stein Seal® Company has developed API1 STANDARD 682 seals for the oil and gas industry. Stein Seal® has designed, manufactured and tested the seals according to the rigorous API Standard 682 test protocols. In general, these are balanced seals with cartridge construction. These seals are classified in to Types, Category, Arrangements and Configurations. The seals are designed and tested to operate continuously for 25,000 hours without need for replacements.

Type A seal is a balanced, internally-mounted, cartridge design, pusher seal with multiple springs. Secondary sealing elements are elastomeric O-rings.

Category 1 are intended for use in non API 610 pump seal chambers, meeting the dimensional requirements of ASME B 73.1 and ASME B73.2 seal chamber dimensions and their application is limited to seal chamber temperatures from -40°F to 500°F (-40°C ~ 260°C) and gauge pressures up to 300 psi (2 MPa / 20 bar).

Category 2 are intended for use in API 610 pump seal chambers dimensional requirements. Their application is limited to seal chamber temperatures from -40°F to 750°F (-40°C ~ 400°C) and gauge pressures up to 600 psi (4 MPa / 40 bar).

Category 3 provides the most rigorously tested and documented seal design. They meet the seal chamber envelope requirements of API 610 (or equal). Their application is limited to seal chamber temperatures from -40°F to 750°F (-40°C ~ 400°C) and gauge pressures up to 600 psi (4 MPa / 40 bar).

Arrangement 2 seals having two seals per cartridge assembly, utilizing the externally supplied buffer fluid at a pressure less than the seal chamber pressure.

Arrangement 3 seals having two seals per cartridge assembly, utilizing the externally supplied barrier fluid at a pressure higher than the seal chamber pressure.

Face-to-back configuration – These seal are Arrangement 2 or 3 seals.  In which one stationary face is mounted between two flexible rotary unit or one flexible rotary unit between two stationary face. The inner seal is OD pressurized by process fluid and barrier or buffer fluid is on the ID of the inner seal.  The outer seal OD pressurized by barrier or buffer fluid.

Back-to-back configuration – These seal are Arrangement 2 or 3 seals.  In which both the rotary faces are mounted between two stationary flexible units. The pumping fluid is on the ID of the inner seal, and the barrier (pressurized) or buffer (un pressurized) fluid is on the OD of the inner and outer seal.

Face-to-face configuration – These seal are Arrangement 2 or 3 seals.  In which both the rotary faces are mounted between two flexible stationary units. The pumping fluid is on the ID of the inner seal, and the barrier (pressurized) or buffer (un pressurized) fluid is on the OD of the inner and outer seal.

A seal piping plan is designed, manufactured and supplied to improve the environment around the mechanical seal and therefore increase the performance and reliability of the seal. Piping plans range from very simple systems such as fluid recirculation into the seal chamber to complex systems which provide pressurization, cooling and circulation for support fluids and gases. The basic operation of the piping plan and also the requirements for instrumentation are followed as per API Standard 682 guidelines. Major piping plans supplied by Stein Seal® are Plan-21, Plan-23, Plan-32, Plan-52, Plan-53A, Plan-53B & Plan-53C.

Our API 682 seal design features, manufacturing capabilities and test facilities are witnessed and certified by a third party international certification organization. API 682 product offerings and capabilities can be found on our website www.steinseal.in

API Standard 682, titled "Pumps - Shaft Sealing Systems for Centrifugal and Rotary Pumps," is the American Petroleum Institute (API) standard for end-face mechanical seals.centrifugal pumps. It is based on the combined knowledge and experience of seal manufacturers, engineering companies, and end users. API 682 is primarily intended for use in the petroleum, natural gas and chemical industries, but is often referenced for other types of equipment and industries.

By the late 1980s, mechanical seals had been accepted as the preferred method for sealing rotating pumps for many years. However, mechanical seal standards were generally buried in other standards such as DIN 24960, ANSI B73, and API 610. All of these standards were primarily pump standards and any references to seals were directed at how mechanical seals would interact with pumps.

API 610 is the API standard about centrifugal pumps and is primarily intended for use in the petroleum, natural gas and chemical industries. Although the 1st through 7th Editions of API 610 included specifications for mechanical seals, beginning with the 8th Edition, API 610 defers to API 682 for seal specifications.

In the late 1980s a group of refinery equipment engineers and managers began to compare sealing solutions in refinery applications. This group, led by V. R. Dodd of Chevron, came up with a general plan and the American Petroleum Institute (API) agreed to establish a standard for mechanical seals: API 682. A Task Force was formed in 1990 and the first meeting was held in January 1991. This Task Force was composed of fourteen members from various refineries, seal and pump manufacturers. API 682, First Edition, was published in October 1994.

One interesting aspect of API 682 is that it includes a strong set of defaults. That is, unless the user indicates otherwise, API 682 makes default choices for specifics such as:

Some statements within API 682 are normative, that is, required, whereas others are informative, that is, descriptive but not required. In particular, many of the illustrations are informative. This distinction has not always been apparent to the reader.

The first edition of API 682 was entirely new although parts of it were extracted from the pump standard API 610 and existing API standard paragraphs.

Although this mission statement no longer appears in the standard, it remains the basic principle driving the work of the API 682 Task Force and its relevance remains the same for the 4th Edition as it did for the 1st.

In addition to providing requirements for mechanical seals, the 1st Edition of API 682 also provided a guide on how to select the correct seal for a number of common refinery applications. In order to provide this seal selection guide, it was necessary to categorize applications into a number of services:

Prior to API 682, 1st Edition, multiple seals were designated as being either “tandem” or “double” seals; however, advances in seal design had rendered these classic terms obsolete. As a result, there was some confusion on how multiple seals were designated. The task force decided to use a more descriptive designation and chose to define dual seal arrangements. A dual seal would be two sets of sealing faces used in the same seal chamber. The fluid between these two sets of sealing faces could be either pressurized or unpressurized. Three standard arrangements were defined:

After having defined the services, seal types, and seal arrangements, a series of flowcharts were created to help in selecting a seal type, special materials or design requirements, and supporting piping plans.

API 682 seals were to have a high probability of three years of reliable service. In order to prove this, seal performance testing on process fluids under representative pressures and temperatures was required. These performance tests are called “Qualification Tests”.

The general idea of the qualification test was to prove that the design was sound. The goal of the qualification test was to simulate a long-term steady state run followed by a process upset. The simulated process upset consisted of pressure changes, temperature changes and included loss of flush. The results of these tests were made available to the purchaser for evaluation. There was no acceptance criteria presented in API 682 1st Edition.

In addition to the qualification test of the design, every API 682 seal, whether new or repaired, is to be pressure tested with air before being shipped to the end user.

One of the major criticisms of API 682 1st Edition was that all the seals were “heavy duty” and therefore expensive with no alternatives for easy services. To some degree, this was intentional and was done in order to reduce inventory, promote familiarity with a limited number of seal types and to increase reliability. Another criticism of API 682 1st Edition was that it considered only API 610 pumps and only refinery applications. The chemical and petrochemical industries routinely use ASME pumps in addition to API 610 pumps. Broadening the scope of pumps covered by API 682 would allow standardized seals to be applied in a greater number of industries.

In 2nd Edition, the organization of API 682 was changed to conform to ISO standards: This reorganization means that there is no simple cross reference guide between 1st edition and 2nd edition paragraph numbers.

The 2nd Edition introduced the concept of seal categories. A seal category describes the type of pump into which the seal will be installed, the operating window, the design features, and the testing and documentation requirements. There are three categories designated as Category 1, 2, or 3.

Category 1 seals are intended for non-API-610 pumps. This category is applicable for temperatures between –40°F and 500°F (-40°C and 260°C) and pressures to 315 PSI (22 bar).

Category 2 seal are intended for API-610 This category is applicable for temperatures between –40°F and 750°F (-40°C and 400°C) and pressures to 615 PSI (42 bar).

Category 3 seals are essentially the original seals of 1st Edition and are also intended for API-610 pumps. Category 3 seals are intended for the most demanding applications. This category is applicable for temperatures between –40°F and 750°F (-40°C and 400°C) and pressures to 615 PSI (42 bar). Design features include a distributed flush and floating throttle bushing for single seals. Additional documentation must be also provided.

Containment seals are the outer seal of Arrangement 2. In the 2nd Edition, containment seals can be used with a liquid buffer fluid, a gas buffer fluid or without a buffer fluid. In the case of a dry running containment seal, the containment seal will be exposed primarily to buffer gas or vaporized process fluid. Such containment seals must therefore be designed for continuous dry running while meeting the reliability goals of the standard. Dry running containment seals may be either contacting or non-contacting.

Non-contacting inner seals are also introduced for Arrangement 2. One of the primary targets for non-contacting inner seals is in flashing hydrocarbon services. In some of these services, it is impossible to obtain adequate vapor margins to prevent flashing of the fluid in the seal chamber. This seal will be used with a dry running containment seal and the leakage past the inner seal will be piped to a vapor recovery system.

The other new seal type introduced in 2nd Edition was the dry running gas seal used in Arrangement 3. This seal is designed to run on a gas barrier fluid such as nitrogen.

Several new piping plans were introduced in the 2nd Edition. These included additional options for dual pressurized liquid seals as well as new piping plans to support containment seals and dual pressurized gas seals.

One of the strengths of the 1st Edition was to provide qualification tests in which seal vendors would be required to prove the suitability of their seals for a given service. The 2nd Edition expanded on these requirements by adding new tests for containment seals and dual gas seals as well as defining acceptance criteria for all tests.

For all practical purposes, API 682 3rd Edition is the same as 2nd Edition. The completed 2nd Edition was submitted to the ISO Organization for approval as their ISO 21049. At the time, API and ISO had an agreement to jointly issue standards. The ISO Organization made slight editorial changes to 2nd Edition, including correcting typographical errors and unit conversions. Therefore, API had to re-issue a corrected 2nd edition but choose to label it as 3rd edition. API 682 3rd Edition was published in September 2004.

API and ISO no longer have the agreement to jointly issue standards. The 2004 issue of ISO 21049 is the only issue and plans to update it are unknown.

Seal Configuration refers to the orientation of the seal components in an assembly. In previous editions, orientations were defined as face-to-back, back-to-back, and face-to-face and these terms are carried over into the 4th Edition. In 4th Edition, any orientation (face to back, back to back, face to face) can be used in a dual seal provided that the design features are appropriate to the functionality of that particular arrangement.

Fourth Edition added additional specifications for clearances, placed these requirements in the form of tables and noted that seal components are not to be considered as “shaft catchers” to restrict shaft movement. The minimum clearances specified apply only to equipment within the scope of the standard. Equipment outside that scope, such as non-cartridge seals, older pumps, non-API 610 pumps and certain severe services, might benefit from larger clearances.

Before API 682, API 610 (the pump standard) used a simple seal code to specify seals. API 682 attempted to use a more comprehensive seal code; however, that code changed with every edition of API 682. The 4th Edition code, described in Annex D, is probably the best to date and includes some concepts and codes from the historical API 610 seal code.

API standards are reviewed every five years and re-issued every ten years. A new Taskforce for API 682 was formed in 2017 and preparations for 5th Edition are underway.

Buck, G. S., Huebner, M. B, Thorp, J. M., and Fernandez, C. L. “Advances in Mechanical Sealing – An Introduction to API-682 Second Edition”, Texas A&M Turbomachinery Symposium, 2003.

API Standard 682, Second Edition, 2001, “Pumps – Shaft Sealing Systems for Centrifugal and Rotary Pumps,” American Petroleum Institute, Washington, D.C.

API Standard 682, Third Edition, 2004, “Pumps – Shaft Sealing Systems for Centrifugal and Rotary Pumps,” American Petroleum Institute, Washington, D.C.

API Standard 682, Fourth Edition, 2014, “Pumps – Shaft Sealing Systems for Centrifugal and Rotary Pumps,” American Petroleum Institute, Washington, D.C.

Thomas Böhm, Head of Standardization – Division Mechanical Seals & API Task Force member and Markus Fries, Product Manager, EagleBurgmann GmbH & Co. KG, Wolfratshausen/Germany

The American Petroleum Institute (API) founded in 1919 has been occupying itself with technical standards since 1924. To this day, API has adopted roughly 500 standards that address the most diverse processes and components and which ensure a maximum of operating and process reliability. Individual standards - including the API 682 regulations for mechanical seals and seal supply systems - have become so popular in the meantime that they have been referenced in outside industry applications. The authors of the new edition point out that this had never been intended and clarify what API 682 is actually about: it concerns the seal systems in pumps of the oil & gas and (petro)chemical industries.

Initial information about mechanical seals was originally provided in the API 610 pump standard. During the 90s, API 682 then developed into a separate, more comprehensive standard for mechanical seals and supply systems. A typical quality of the API 682 standard is that is permanently updated by practical people. A further quality of the API 682 is that it does not normatively permit only a single technical solution. In addition to proven and tested standard solutions (defaults), the regulations also deliberately list alternatives (options) - and even allow customized solutions (engineered solutions).

The objective of API 682 is a continuous operation of the seal system for at least three years (25,000 operating hours subject to the legally stipulated emission values, or for max. "Screening Value" of 1000 ppm vol, EPA method 21), increased operational reliability, and simplified maintenance.

The 4th Edition includes the revised product coding system. The proven classification parameters "Category," "Arrangement," and "Type" will be continued. These are now listed first. Details regarding the supply system - specified as "Plan" - are also in the old and in the new code. The addition of precise information to material selection and shaft diameter is new. This gives more meaning to the Code and guarantees a clear specification of the mechanical seal and its operation.

The selection process of an API seal system is a complicated affair. Several flow charts and tables on more than 10 pages are dedicated to this topic in the new edition. In order to determine the seal arrangement more precisely, a scheme pursuant to the "Risk & Hazard Code" has been introduced in the 4th Edition for the first time. The starting point here is the pumped medium whose real hazard potential is accurately recorded and described by "Risk & Hazard Codes" in the "Material Safety Data Sheets." The selection scheme enables the quick and secure recognition of whether a single seal (Arrangement 1) is sufficient or if a double seal with barrier pressure system is required.

The "lived" standard of API 682 is also demonstrated in the new edition in that the two silicon carbide (SiC) variants "Reaction Bonded Silicon Carbide" and "Self-Sintered Silicon Carbide" can be used equally as "default" materials for sliding surfaces. Until now, sintered SiC was set for chemical applications due to its superior chemical stability, whereas the reaction bonded variant established itself in the refinery sector. This allocation was canceled due to practical application examples that were brought to the attention of the Task Force - and which called for a course correction.

Plan 53 with a pressurized barrier fluid belongs to the more complicated supply systems. In detail, three types are possible: Plan 53A is the solution with the constructively least amount of effort. The pressure on the barrier medium here is generated directly by the gas pressurization - normally with nitrogen - in the tank. However, the application has limits because higher barrier pressures could cause a dissolution of the nitrogen in the barrier medium. The consequence would be the risk of inadequate lubrication in the sealing gap of the mechanical seal. Higher barrier pressures are therefore the pursuit of Plans 53B and 53C.

Whereas Plan 53C works with a piston accumulator, putting it among the more sophisticated seal supply systems, Plan 53B uses an especially clever solution: Pressurization occurs via an elastomer bladder in the reservoir that separates the nitrogen from the barrier fluid. Pressure monitoring with consideration of the temperature in the bladder accumulator records the values and transfers them to the control room. The fill level with consideration of any temperature impacts is calculated there and the correct time for refilling the barrier fluid is determined.

A new prescribed refilling interval of at least 28 days has also been included in the 4th Edition. Consequently, the fluid reservoir must be large enough to reliably supply the seal with barrier fluid during this entire period. To obtain as compact reservoirs as possible, the seal manufacturers are required to find optimized system solutions with minimal leakage values.

The Task Force also addressed the topic of heat resistance of fittings for supply systems in an extremely pragmatic and practically oriented manner. In the past there were frequent debates about whether supply systems for high temperature applications – e.g. a 400°C-approved pump – has to be equipped with special instrumentation for the high temperature. Now the temperature specification for the instrumentation has been limited to a commonsensical 100°C. If instruments with higher temperature limits are required in the future the customer has to inform the seal vendor accordingly.

The essential improvements - in addition to all the technical supplements and updates - are the clear structures of the latest API regulation. The body of text was tightened and restructured, while technical details and background information were placed in the Annexes.

A special detail of the 4th Edition is the new red plugs that are inserted into the supply connections of the seal gland when the unit is delivered. These plastic closures prevent the ingress of dirt in the seal. During operation, the connections are either assigned to pipelines, or the plastic plugs are replaced with enclosed metal plugs. A nice side effect: 4th Edition API seals are quickly identified by the red plugs.

The EagleBurgmann API specialists Markus Fries and Thomas Böhm (from left to right) with a new developed API mechanical seal and the corresponding seal supply system according to API Plan 53B.

EagleBurgmann is one of the leading international providers of industrial seal technology that is used in diverse industries (oil & gas, power, refinery, chemical, energy, food, paper, water, and mining, among others). The company employs roughly 6,000 employees worldwide. 60 subsidiaries and 250 locations stand for global presence - and the associated proximity to the customer. The comprehensive product portfolio includes everything from well-engineered serial seals to application-related individual constructions.

API conform mechanical seals and supply systems take an important place in the EagleBurgmann range. For more than 20 years, the company has been consequently providing its know-how in further developing API specifications for the design of seal systems for the oil & gas and (petro) chemistry sectors - and is active in the API 682 Task Force. Worldwide there are more than 21,000 EagleBurgmann API seal systems in use.

Many users do not like the strong handed approach used by API 682. However, with a little study of API 682, the user can easily learn to specify his preferences in detail using the seal data sheet.

Some statements within API 682 are normative, that is, required, whereas others are informative, that is, descriptive but not required.  In particular, many of the illustrations are informative.  This distinction has not always been apparent to the reader.

In spite of its strong handed approach, API 682 encourages innovative or developing technology. However, non-standard alternatives should be carefully discussed between the purchaser and seal company.

It is important to realize that API 682 is a users’ standard; it was written by and for the end users of mechanical seals and these users wanted to force changes.  The result was an entirely new standard written around a limited set of seal types, arrangements and materials that were favored by the end users in refineries.  These new seals were also required to be proven through a series of rigidly prescribed tests.  Although everyone agreed that API 682 seals were robust and well suited to the best practices of the refining industry, cost quickly became a limiting factor to the specification.  Consequently, API 682 1stEdition was not applied as extensively as had been anticipated. Subsequent editions have had an increase in the scope and also are more flexible with respect to defaults and options.

It is important to know the background and development of API 682 in order to fully understand and apply the standard. The story of API 682 begins in the late 1980’s.

By the late 1980’s, mechanical seals had been accepted as the preferred method for sealing rotating pumps for many years. However, prior to API 682, mechanical seal standards were generally buried in other standards such as DIN 24960, ANSI B73 and API 610. All of these standards were primarily pump standards and any references to seals were directed at how mechanical seals would interact with pumps.

In the late 1980’s a group of refinery equipment engineers and managers began to compare sealing solutions in refinery applications. This group, led by V. R. Dodd of Chevron, came up with a general plan and the American Petroleum Institute (API) agreed to establish a standard for mechanical seals: API 682.   A Task Force was formed in 1990 and the first meeting was held in January 1991.  This Task Force was comprised of fourteen members from various refineries, seal and pump manufacturers.   API 682, First Edition, was published in October 1994.

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.

An actual pump reliability improvement issue might serve as a model for tackling sealing issues in modern refineries. You really don’t have to become a mechanical seal expert, but you will have to avail yourself of the right Internet Information Tools, interrogate your in-plant data, and ask the right questions of more than one mechanical seal manufacturer.

This example relates to Crude Vacuum Bottoms (“CVB”) Pumps and explains a North American refinery’s troubled history with seal systems for its 4x6x13 overhung top suction/top discharge pumps. The operating characteristics are somewhat typical for such pumping services: Flowrate between 750 and 800 U.S. gallons per minute, about 650 feet of head, 750 degrees Fahrenheit (399 degrees Celsius), about 5 psia suction pressure, S.G. = 0.77, and 3,560 rpm.

The pumps were installed in 1972 when the refinery was commissioned; in 2014 they used a dual seal configuration with an API Plan 54 barrier fluid circulation arrangement. You can view or download all (close to 100) API Flush Piping Plans from www.aesseal.com/en/resources/api-plans and similar web pages. Figures 1 and 2 are helpful in this regard; they allow us to visualize modern seals in an API Plan 54 and (figure 2) show an up-to-date pump-around unit close-up.

The circulator system was put together back in the late 1980’s with little or no design engineering input. To paraphrase the equipment owners, they have in the past and continue to have, numerous failures on this seal system. A majority of the company’s serious seal failure incidents were attributed to stoppages of barrier fluid flow due to line blockage and the ensuing overheating of the inner seal. The refinery also reported instances where the pumps were started without the circulator units running, or where the pressure regulating valves were adjusted incorrectly, resulting in over-pressuring of the inner seal bellows.

The refinery quite accurately labeled these pumps their “worst bad actors” for mechanical seal life. While convinced that the seals themselves were good for the service, they recognized that there were issues with unreliable seal support systems. They now had to deal with two different proposals from manufacturers No.1 and No. 2. Manufacturer No.1 was suggesting installation of a new Plan 54 circulator system designed for the refinery’s application and fitted with short high-pressure hydraulic tubing runs, per the guidelines of API 682. However, manufacturer No.2 recommended installation of a Plan 53A system with a new seal, complete with a pumping ring and seal oil pot pressurized with nitrogen.

The refinery currently has a Preferred Supplier Agreement with Manufacturer No.1. Fortunately, it was not an exclusive agreement; hence, they also dealt with Manufacturer No. 2 for some applications. “We have some people here in our maintenance organization in favor of the No.2 proposal simply because we have never been able to get our existing system operating reliably and they blame No.1. There are others more in favor of No.1’s proposal because we don’t fault their seal but rather the fact that we’ve tried to make an inherently unreliable support system work with little success, and also because the concern that No.1 raises regarding nitrogen absorption seems appropriate.”

“To get to the point,” notes the originator of the request, “I am interested in what you could advise with respect to reliable seal systems for pumps in CVB service such as ours. We are also looking for a system that is not operator-intensive—simply because many of our failures have been attributed to incorrectly operating the circulator units. An unbiased opinion from someone knowledgeable would go a long way towards helping us reach an agreement on how we should proceed.”

Perhaps we can answer your questions in a manner that’s either not offending any seal manufacturer or, alternatively, offends all involved parties in equal measure. That way, there is reduced suspicion of bias, although we well know it’s not possible to please everyone.

First off, you deserve credit for including lots of relevant data with your questions. Moreover, we commend your company for already working with more than one seal manufacturer, although, for comparison purposes, we have always included a third one. Since you have involved the two largest manufacturers of refinery pump seals, consider adding the third and fourth largest to your data bank. Speak with their Engineering Managers. Chances are these managers have considerable experience in exactly the application you are dealing with. They will have no reluctance to give you suitable client references.

Elaborating on this point and as a matter of recommended standard practice, be sure to ask all four companies to disclose to you where they have supplied seals of the type they recommend for use at your refinery. Of course, these seals must be in successful use in the same medium and at the same temperatures, pressures and –very important–at equal or higher PV (pressure-times-velocity) values. Do not let a seal manufacturer claim this to be proprietary information; it really is not. Incidentally, the various seals involved here are OK. We certainly have no hesitation to accept No.1’s model ABC / XYZ seal face combination as being quite suitable for your high temperature vacuum service.

Realize that API Plan 54 is certainly used elsewhere and is correct here, too. You may be dealing with the proverbial “straw that breaks the camel’s back” by not having the piping or hydraulic tubing runs comply with API 682. But more than the piping is involved here. A 25-year old barrier fluid circulator unit (of the proprietary type mentioned by the refinery) is not current technology. Let Numbers 3 and 4 advise you on their thoroughly engineered, fully packaged and thoughtfully instrumented seal support systems. Bring your support system into compliance with best-in-class practices and consider it money well spent.

The underlying point in this story deals with drawing the right conclusions from your own data and realizing that component upgrading is often needed in situations involving old seal support systems. Don’t invest in seal replacement efforts if these same seals are in verified successful use elsewhere. Study the seal support systems available from manufacturers Number 3 and 4 and involve both their Engineering Department and one or two lubricant suppliers. And do not hesitate to consult the right Internet sources—no salesperson will call.

The website of the world’s fourth-largest mechanical seal manufacturer (www.aesseal.com) gave a welcome endorsement by way of a simple four-point summary. It started by listing the application parameters of API Flush Plan 54:

Keep in mind also that a competent pump rebuild shop (CPRS) has the ability to combine pump repairs with substantial pump upgrading. While probably not needed in connection with this particular CVB pump, there are instances where modifications to the seal environment make economic sense.

We asked the refinery to refer to Subject Category 21 in reference 1. We also re-emphasized that we do not have to be seal experts to select good mechanical seals. All we need to do is ask the right questions, carefully examine vendor-supplied reference data and tabulate the responses. Never let a vendor make you the test location for cheaper substitutes. Vendors 1 through 4 know each other’s products. You, the buyer, are entitled to see full disclosure of all prior experience.

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