API Standard Pumps—Shaft Sealing Systems for Centrifugal and Rotary. Pumps. FOURTH EDITION | MAY | PAGES | $ | PRODUCT NO. API - pdf - Download as PDF File .pdf), Text File .txt) or read online. API - Ebook download as PDF File .pdf) or read book online. API Mechanical Seal.
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EagleBurgmann range of balanced pusher and metal bellows mechanical seals acc. to API 4th ed. EagleBurgmann SPB6 seal supply system Plan 53B. API PIPING PLANS API 4th Edition “To check out mechanical seal flushing arrangements and piping plans, I have consistently found this to be the most. and the API seal selection software on CD. Find your nearest contact at www mmoonneeyy.info Important Note. Operating manuals and plant.
The testing cycle was designed to simulate start-ups and shut-downs as well as variations in operating conditions that mat be typical for a mechanical seal in a real application. Category 3 seals are for heavy duty services requiring all of the features necessary for severe applications. Always precharge bladder to 0. Plan C1A1B11 designates a seal that be a Category 1. Orifice nipples may be provided at the pump discharge if specified.
Becomes a self-venting plan for horizontal pumps. Default API Plan for most single seals. In general, applications with clean non-polymerizing fluids with moderate temperatures. Calculation of recirculation flow rate, heat removal and orifice size are required. Check the margin between discharge pressure and seal chamber pressure to ensure proper flow of fluid. Do not use with media containing solids and abrasives.
Can handle dirty liquids to some extent. In general used in slightly dirty and non-polymerizing fluids. Always ensure that orifice is placed after the Y strainer. This plan is normally discouraged due to unreliability of Y strainer. Calculation of recirculation is required. Provides continuous vent for vertical pumps. Wherever Plan 11 is not usable due to low-pressure margin between discharge and seal chamber pressure.
Used in vertical pumps. Check margin between seal chamber pressure and suction pressure. Ensures product recirculation as well as venting. Increase cooling of seal chamber. Combination of plan 11 and plan Used in light hydrocarbon services. Check for pressure margin between discharge to seal chamber pressure and seal chamber to suction pressure. Improves pressure margin over vapour pressure.
Improves temperature margin to meet secondary sealing element limits, to reduce coking or polymerizing and to improve lubricity. Self venting plan. Provides sufficient pressure difference to allow proper flow rate. For high temperature applications e. In hot non-polymerizing fluids. Always ensure that cooler is placed after the orifice. Check pressure difference between discharge and seal chamber. Cooler duty is high leading to fouling on waterside.
Potential plugging on process side if fluid viscosity rises quickly. For high temperature applications with slightly dirty liquid. This plan is normally discouraged due to non-reliability of Y strainer. Circulation is maintained by pumping ring. In idle condition heat transfer is maintained by thermosyphon effect and in running condition by a pumping ring. Lower product stabilization temperature is achieved. Establishes required margin between fluid vapour pressure and seal chamber pressure.
In hot and clean services e. Maintain maximum 0. Vent valve required at highest point of piping system. Ensure that pump has a close clearance throat bush. Ensure that the seal outlet connection is in the top half of the gland. Ensure that the cooler is mounted above the pump centre line. Vent the system fully before start up. Removes entrained solids from the process fluid. Particles from cyclone separator are returned to suction.
Used in media with suspended solids. Pump throat bushing is recommended. Ensure use for services containing solids with specific gravity twice or more than that of process fluid. Efficiency of a cyclone separator is proportional to the diameter. A larger cyclone diameter leads to less efficient separation, a smaller cyclone diameter provides more efficient separation. Reduces flashing or air intrusion across seal faces by providing a positive flush.
Maintains vapour pressure margin. Always provided at a pressure greater than seal chamber pressure. If maintained properly the best of all single seal plans subject to acceptance of contamination. Dirty or contaminated fluids. High temperature applications. Polymerizing and oxidizing fluids. Media with poor lubrication properties. External source should be continuous and reliable at all times, even during start up and shut down. Flush fluid must be compatible with process fluid due to product contamination.
Product degradation can occur. Ensure use with close clearance throat bushing to maintain pressure in stuffing box and control the rate of contamination of pumped media. Careful selection of flush fluid required to ensure that it does not vapourised on entering the seal chamber. Fluid expenditure of Plan 32 may be as expensive as one or more seals per year. Improves pressure margin to vapour pressure. In hot services containing suspended solids.
Circulation is maintained by using pumping ring in running condition and by thermosyphon effect in stand still condition. No process contamination. No direct process leakage to atmosphere. No need to maintain pressure system as in Plan 53A. For media where product dilution is not allowed but leakage to atmosphere in diluted form may be allowed. Preferred for clean, non-polymerizing media with vapour pressure higher than buffer fluid pressure Is also used for lower vapour pressure media.
Keep the sealant vessel vent continuously open, which is necessary to maintain buffer fluid pressure close to atmospheric pressure and vent the vapors to flare. Should not be used in dirty or polymerizing products. A restriction orifice is necessary in vent line to maintain back pressure in pot and facilitate quick release of vapors to flare. Pressure switch setting should be done above minimum flare back pressure in order to avoid false alarms.
Never run the system with level in the sealant vessel being at low level as marked on the level gauge. Check for temperature difference in inlet and outlet lines to ensure that circulation is on. Vent the system properly before start up. Circulation is maintained by using pumping ring in running condition and with thermosyphon effect in stand still condition.
In no case will media leak to atmosphere Provided the seal support system pressure is not lost. Clean fluid film formation between the inboard seal faces gives better seal life.
Works as a Plan 52 arrangement if barrier fluid pressure is lost. Applications where no leakage to atmosphere can be tolerated e. For dirty, abrasive or polymerizing products where media is unsuitable as a lubricant for inboard seal faces.
There will always be some leakage of barrier fluid into the product. Check compatibility of barrier fluid with product. Always ensure that the pressure source maintains higher pressure at the seal support system so that process does not dilute the barrier fluid.
In certain cases the inert gas can dissolve in the barrier media. Product quality can deteriorate due to barrier fluid contamination. The pressure is maintained in the seal circuit by a bladder accumulator. Keeps barrier fluid and pressurised gas inert gas separate by using a bladder.
Heat is removed from the circulation system by an air-cooled or water-cooled heat exchanger. Being a stand-alone system does not rely upon a central pressure source.
Hence much more reliable than a Plan 53A. In no case will media leak to atmosphere. Low volume of barrier fluid in system, hence heat dissipation is totally dependent on cooler efficiency. Always precharge bladder to 0. The pressure is maintained and fluctuations are compensated in the seal circuit by a piston type accumulator.
Vent system properly before start up. In no case will the media leak to the atmosphere. This allows successful operation of dual seals lacking reverse balance feature at inboard seal, when having highly variable seal chamber pressure.
Where pump pressure varies during operation needing an auto setting of barrier fluid pressure, thus maintaining the same differential throughout. Always connect reference pressure line from seal chamber to accumulator and keep it open.
Pressurised external barrier fluid circulation from a central pressure source or by a stand alone pumping unit e. Ensures higher flow rate, better heat dissipation and positive circulation of barrier fluid. Can also be given as a stand alone unit per pump. Increases cooler efficiency due to higher flow rate to the heat exchanger. For dirty, abrasives or polymerizing products where media is unsuitable as a lubricant for inboard seal faces.
Carefully consider the reliability of barrier fluid source, if a central source is used. Circulating system must be pressurised at least 1. Product contamination does occur. Barrier fluid selected should be compatible with the process fluid. Loss of pressure in system can lead to entire barrier liquid contamination. Unpressurised external barrier fluid circulation from a central pressure source or by a stand alone pumping unit Features: Ensures higher flow rate, better heat dissipation and positive circulation of buffer fluid.
Can also be given as a stand-alone unit per pump. No direct leakage to atmosphere. For media where product dilution is not allowed but leakage to atmosphere in diluted form maybe allowed 2. Preferred for clean, non-polymerizing media that may solidify in contact with atmosphere.
Wherever Plan 52 circulation is insufficient to dissipate heat. Carefully consider the reliability of buffer fluid source, if a central source is used. Circulating system pressure must be less than seal chamber pressure and less than 28bar 3.
Not suitable for polymerizing media. Ensure suitable flow is maintained at all times. GBI port can be piped to use as in Plan For future provisions for API Plans 72, 75 and Always keep the ports plugged.
Used for: Features 1 Can be used with Plan 72 with buffer gas or with Plan 71 without buffer gas systems. Collection can be redirected to process fluid by using separate pumping device. Can be used in single containment seal also. Duties with condensing leakages. Most importantly to API. In doing so. The Second Edition continued with the same requirements and adds additional design details for the new seal types.
The First Edition introduced a structured selection process where the user followed a series of tables and flowcharts to arrive at a seal selection. API seals are designed to meet a minimum of three years of uninterrupted service.
API defines three basic seal types that are used in this standard. The Second Edition expanded this greatly due to the addition of new seal types. Key Concepts One of the challenges the First Edition Task Force had was to standardize a number of concepts in the sealing industry.
Earlier we learned that is designed to default to a single solution but that. The First Edition allowed only three basic seal arrangements. This included defining the test medium. It became a standard. Up to this point. While the First Edition did not cover the design of the component parts of a mechanical seal. The Second Edition expanded this concept with additional details to cover the new seal types and piping plans.
This standard does not apply to seals designed to fit into the small stuffing boxes designed for packing. The answer was to qualify all seals in a well defined test program that.
We will briefly cover some of these concepts now and they will be covered in more detail later in the training program. A seal category is a sub-specification that defines the seal.
The question the Task Force faced was how the standard would give the end user the confidence level that these seals can achieve this goal. API was the first document to address many of these key concepts. Where an alternate selection is available. Footer7 Experience in Motion Page 7. Seal arrangements define the number of seals. There are literally hundreds of different seals in use today.
These definitions include design details as well as materials of construction. One of the most important aspects of seal applications is initially selecting the correct type of seal and piping plan.
Seal categories was a new concept introduced in the Second Edition.
Historically people used terms like spring pusher. This was an inefficient means of referencing a specific seal. Footer8 Experience in Motion Page 8.
The default spring material is Alloy C A Seal Types is a basic description of the seal. One of the challenges for the API Task Force was to create standard seal types that would define the basic seal design. The figure on the left shows the default configuration where the springs are rotating with the shaft. A throttle bushing in the gland is required for all single seals.
There are also additional design details which will be defined under the seal category. The figure on the right shows an alternate arrangement where the springs are stationary with the seal gland. This stationary design may be required in higher speed applications.
The default face materials for the Type A seal are Silicon Carbide versus premium grade blister resistant carbon.
There are some German standards that define interface between component seals and pumps as well as some ANSI. In these and the following figures. Type B. There is an option where a SS single coil spring can be used. Note that the seal type does not designate the number of seals.
This will help you quickly see which components are rotating and which are stationary. There are three basic Seal Types designated as Type A. The other metal parts such as the sleeve. They would also add other design features such as high balance. Then to define the materials. The concept of Seal Type captures all of these details.
This will be defined under the seal arrangement. The applies only to the diaphragms of the bellows and not the adapter or face flange materials. The metal bellows acts as both the spring element and the dynamic gasket. The default configuration is shown on the left with the bellows mounted onto the sleeve and rotating with the shaft. All other metal parts including the sleeve and gland are SS. The default bellows material is Alloy C The figure on the right shows an alternate arrangement where the bellows are stationary with the seal gland.
The default face materials for the Type B seal are Silicon Carbide versus premium grade blister resistant carbon. Seal Arrangements and Configuration Codes Now that we have defined the basic seal types. When should you choose one over the other? These are referred to as contacting wet seals. This seal is designed to run under full operating conditions for a minimum of Like the Type B seal.
API states that a stationary flexible element must be used. The Second Edition introduced two new options: The face flange is generally a low expansion alloy to maintain the shrink fit to the seal face at elevated temperatures. The default Type C seal has a stationary flexible element but can be provided with a rotating flexible element as an alternate.
In a good running seal. The default configuration is shown on the left. This directs the seal quench which is generally steam towards the seal faces to exclude air and minimize coking.
In applications requiring a distributed flush. Rotating vs Stationary Flexible Element Seals The default Type A and Type B seals have a rotating flexible element but can be provided with a stationary flexible element as an alternate. This liquid provides lubrication and hydrostatic support of the fluid faces. The faces are generally flat and do not have any face features so this design does not intentionally create hydrodynamic forces to separate the faces.
This seal is designed to run on a liquid fluid film. The user should generally stay with the default selection unless there is a technical reason to change to the alternate. Footer10 Experience in Motion Page The default face materials for the Type C seal are Silicon Carbide versus premium grade blister resistant carbon. The rotating configuration. Because this design requires liquid across the faces. The First Edition was limited to only liquid mechanical seal.
This is a stationary bellows with the bellows assembly attached to the gland. The standard secondary gasket materials is a flexible graphite. We need to examine these options before we can discuss seal arrangements. The seal arrangement defines the number of seals. A bronze anti-coke device is also required. The default bellows material is Alloy Footer11 Experience in Motion Page These seals are also designed to run for a minimum of This seal can be used as a dual pressurized gas seal or as a inner seal of a dual non-pressurized seal arrangement running on process fluids.
Here the seals operate on a barrier gas provided from an outside source through a control panel. The Containment Seal is designed to run for the life of the primary seal or at least This will allow for an orderly shutdown of the equipment. It will normally be exposed to only buffer gas or vaporized process fluid. It was not the intention of the standard that this seal can be run indefinitely with a failed inner seal.
It is always the outer seal in a dual nonpressurized seal arrangement. The most common use for this design is in dual gas seals.
The Containment Seal will operate under relatively low-duty conditions for the life of the seal. When the inner seal fails. Normal emissions past the primary seal are prevented from reaching atmosphere by the Containment Seal.
This seal can be either a non-contacting lift-off design or a contacting design. Containment Seal A Containment Seal is designed as a dry running backup seal. Since these faces are separated by a greater distance than liquid seals. This hydrodynamic lift is created by the use of shallow waves.
Since the containment seal chamber is normally connected to the flare or a vapor recovery system. A Non-Contacting seal is designed to create hydrodynamic forces to separate the faces under all operating conditions.
The use of a Non-Contacting seal as a primary seal can be traced back to applications where the fluid on the primary seal may be impossible to keep in a liquid state.
The Second Edition has grown to eleven options due to the expansion of the scope and addition of new seal types. Footer12 Experience in Motion Page It is important to understand these Arrangements and Configurations and their relationships to each other. Under Arrangement 3. The first column is for Arrangement 1 seals or single seals.
Please take a moment to review this chart. The third column is for Arrangement 3 seals. These are two seals in series with a containment seal chamber pressure less than seal chamber pressure. These are also called dual pressurized seals. There are three configurations available for this arrangement depending upon the state of the barrier fluid and the design of the primary seal. The First Edition allowed only three options.
The configurations shown in each column describe the orientation of the two seals. The second column is for Arrangement 2 seals.
These are also called a dual unpressurized seals. These seals are operated with a barrier maintained at a pressure above the seal chamber pressure. We will cover each configuration in more detail on the following slides. In other cases. Footer13 Experience in Motion Page The first digit. The Containment Seal may be either a contacting or non-contacting design.
This is the same seal that was designated as the Arrangement 2 seal from the First Edition. Some of the features shown may or may not be required depending upon other parts of the standard. The design features on the illustration is only meant to show the basic seal and orientation. This seal is an Arrangement 2 the first digit with the inner seal as a Contacting Wet seal the next two digits and the outer seal as a Contacting Wet seal the last two digits.
This is the most common seal arrangement. Since the vaporized process is not externally supplied. There is only one seal per cartridge. For Arrangement 1. The next two digits. This would be a good point to look at the configuration nomenclature.
Just some trivia for you. This is the traditional liquid inner seal with a dry running backup seal. This configuration requires a little more background. All leakage past the inner seal is prevented from going to atmosphere by the Containment Seal. The inner seal is designed to be non-contacting and can operate on either a liquid.
In most cases this can be achieved with the proper piping plan. The outer seal is a Containment Seal. To insure that it stays a liquid. In some cases though. This may be required for specific applications or pump designs. The reason the face-to-back orientation has been selected as the default has to do with the failure mode of the seal.
The Containment Seal chamber is vented to a vapor recover system. If the outer seal fails and there is a loss of barrier fluid and pressure. When there is mixed phase or full liquid phase in the seal chamber.
This configuration has seen only limited applications in the field. This is also the Arrangement 3 configuration described in the First Edition. Footer14 Experience in Motion Page There are two major subdivision under this arrangement — those with a liquid barrier and those with a gas barrier. Other orientations are available in Arrangement 3 liquid seals. For these applications a Non-Contacting inner seal can be designed to operates on the vapor phase process fluids.
This is also called a dual pressurized liquid seal. This means that it is the preferred orientation of the seals. This is especially true in service with very light hydrocarbons. The face-to-back configuration is the default configuration for the standard. Because the seal is designed to run on a liquid. In most cases. Until the release of the Second Edition.
These are also called dual gas seals. This has been the most widely used orientation for these seals. If the extra features improved seal performance.
Footer15 Experience in Motion Page With the inclusion of more pump types with smaller seal chambers many of the required features may not physically fit in the smaller installation envelope.
If the extra features were not required. This defeated some of the benefits of having a standard. And last but not least. While this addressed many of the needs of a refinery. This is an Arrangement 3 Non-Contacting seal in a back-to-back orientation.
As with the liquid seals. The end users and Task Force recognized that different applications may require different levels of seal sophistication.
Other orientations are also recognized by the standard. These have seen widespread use throughout the refinery and chemical industries since the introduction of the First Edition.
The Second Edition and beyond defines three seal Categories: Category 1 seals are designed for general duty services.
This is because these seals will likely be exposed to more corrosive environments in chemical pumps. Footer16 Experience in Motion Page Category 3 seals are for heavy duty services requiring all of the features necessary for severe applications.
The default for Categories 1 and 2 is a single point injection unless the users specifies a distributed flush or there in inadequate vapor pressure margin in the application. All seals require the gland to make metal-to-metal contact with the seal chamber face.
This is essentially the same seal that was defined in the First Edition. These are heavy duty refinery seals used in API pumps. Category 2 seals are similar to the seals defined in API 7th edition. Here is a chart showing a comparison of some of the features of the three seal Categories. They are to be installed into the smaller chemical duty pumps in lower pressure and temperature applications.
These would describe seals for different levels of severity. In a Category 1 seal. The default face materials for Category 1 seals are direct sintered SiC vs Carbon. Distributed flush is required for Category 3 seals. This is taken from Annex A of the Second Edition. The criteria to determine this is in the standard.
Categories 2 and 3 require contact both inside and outside the stud circle. The Category 2 and 3 seals are for API pumps. These have been designated as seal Categories.
The default material for Categories 2 and 3 is reaction bonded SiC vs Carbon. Category 3 require extensive documentation from both the user and the seal OEM.
For now. In practice. The use of metric units through the standard as well as the entire formatting of the document was directed towards its release as an ISO For this reason.
The Category 2 seal requires a fixed non-sparking metal bushing with a floating Carbon bushing as an option. This document has focused on the use of SI units. Pumping ring HQ curves are required for Category 3 seals. Category 2 and 3 seals are designed for the 10mm shaft size increments used in API A floating bushing is optional.
A Category 3 seal requires a floating Carbon bushing. The remainder of the differences apply to the level of documentation required for each seal. Category 1 and 2 seals can be designed from components that have been previous qualified in different tests.
Category 1 single seals require a fixed Carbon throttle bushing in the gland. While the concept of Categories introduces a level of complexity to the standard. We will be discussing seal qualification testing in a later module. Categories 1 and 2 require minimal documentation to help reduce the cost to both the user and the OEM. For the standard to truly be accepted as an international standard this is necessary. This includes all data. One of the ways of achieving this is by specifying design requirements for the seals.
To fully comply. The Second Edition and beyond follow the same path and contains even more specifications on seal design. The requirements in this standard are an attempt to capture design features that have proven to be successful in the field. Hook sleeves with a snap ring pseudo-cartridges are not allowed.
Some OEMs will likely provide user interface fasteners such as drive collar set screws in the units requested while the internal fasteners on the seal remain as originally designed.
The selection of stress levels. Component seals are not allowed. The default configuration for Type A and B seals are with a rotating flexible element. Task Force members from the major seal OEMs were present and provided guidance and buy-in to these requirements. We will cover the design requirements in the same order that they are listed in the Second Edition.
Cartridge seals slide onto the shaft as a complete assembly and do not rely on the position of the shaft to set the seals. If specified. During the development of all of these standards. The default Type C seal has a stationary flexible element. Hardware issues such as fasteners will be more difficult to address. Footer18 Experience in Motion Page The standard does this in three sections general design requirements which apply to all seals.
The Task Force did. In either case. Design Requirements One of the primary goals of the standard is to specify seals that have proven to be successful. This will make it easier for you to follow along if you have the standard. All mechanical seals will be cartridge seals. Hook sleeves are not allowed. For most items such as drawings or data sheets. Footer19 Experience in Motion Page Throttle and throat bushing may also be tighter depending upon design. This includes using cooling.
This can also be seen in vertical pumps or other designs that rely on motor bearings for axial shaft positioning. All O-ring grooves must be sized to allow for the expansion of perfluoroelastomers. The connection ports on the seal gland must be permanently marked e. Unless specified. For static gaskets. There are several exceptions to this. The size requirements of the connections have also changed and are now a function of the seal category and shaft size.
For vacuum services. Seal chamber conditions must prevent the flashing of process fluids. There is still a differentiation between the size of connections intended for process fluids and connections to the atmospheric side of the seal. Pumping rings and containment seal bushing may have a minimum clearance of 1. The standard also outlines remedies if these conditions can not be met. The chart is divided to columns showing the applicable seal configuration.
For dynamic gaskets such as balance shoulders. The sealing surfaces around O-rings are required to have minimum surface finishes.
Seal glands must be designed for the MAWP of the pump. There is a recognition that some multistage pumps that experience shaft sag under static conditions may not be able to meet this requirement.
Under these conditions. Under any circumstances. Seal OEMs must design the seals to be tolerant of a perpendicularity between the shaft and seal chamber face of 0.
Most of the connection symbols and locations are the same as the First Edition. This is seen primarily as a concern in between bearing. The chart from the standard has been broken into three slides to show the required details of the connections. One of the differences is found in dual seals. Corners or steps must be chamferred or radiused to prevent O-ring damage during installation. Since there has been an increase in the number of configurations and the function of the seals.
The containment seal vent CSV is located at the top of the containment seal chamber and will allow vapor phase process to be piped off to flare or a vapor recovery system. Footer20 Experience in Motion Page The containment seal drain CSD is intended to allow for liquid phase or mixed phase process fluids to drain from the bottom of the containment seal chamber.
The gas buffer inlet GBI is used to provide a inert gas sweep of the containment seal cavity and to help isolate the containment seal faces from process leakage.
The location designates where the connection though-hole breaks into the ID of the seal gland. Barrier fluid connections designate whether the connection is for liquid or gas. Fixed throttle bushing shall have a diametrical clearance no more than 0. At first. The connections are often required at these locations to allow for venting or to promote thermosyphoning of the fluid. In practice most dual gas seals are run dead-ended and the GBO port will be plugged. The actual location of the port on the OD of the gland may be angled to provide a tangential outlet or to avoid pump obstructions.
Clearances for floating throttle bushings are based on sleeve diameter and are shown in the chart. Additional design requirements include the need to plug all connections in the gland. This is intended to prevent a user from inadvertently leaving a connection opened during commissioning of the seal.
Plugs must be solid plugs made out of the same material as the gland and in accordance with ASME B Footer21 Experience in Motion Page 21 Floating carbon bushing requirements for diametrical clearance. This is not the intention of the standard.
The standard also gives requirements for both fixed and floating throttle bushings. For larger sizes. This may be into the seal chamber. It is important to note the angular location of the connections given in these charts. Since the glands and connecting piping are considered to be pressure containing parts of the sealing system. Seal faces shall be carbon versus silicon carbide or silicon carbide versus silicon carbide.
The Second Edition attempts to improve this situation by setting sleeve clearances based on shaft diameter. This created some problems with seal installation and removal of seals in the field. Drive collars set screws should not pass through the piloted area of the sleeve since deformation of the shaft under these screws would make removal of the seal more difficult.
There are alternative material stated for many components. Designs proposed with a greater number of screws requires customer approval. Footer22 Experience in Motion Page To help prevent unnecessary seal run out. Areas of the sleeves that are exposed to radial loads generated by set screws may require a thicker sleeve under the screws. The standard defines default materials for all major seal components.
All seal sleeves shall have a shoulder that will positively locate seal components that are mounted onto the sleeve during assembly. The minimum sleeve thickness shall be 2. Standard drive collars should have less than nine set screws. The First Edition issued requirements that the clearance between the sleeve bore and shaft OD shall not be more than 0. Sleeves that rely on mechanical compressed flexible graphite gaskets shall be sealed at the bearing end of the sleeve and the gasket shall be captured between the sleeve and shaft.
For some services. Most metal components other than bellows diaphragms and springs are stainless steel or its equivalent. Sleeves with O-rings shall be sealed at the impeller end of the sleeve. Other design requirements such as the use of single springs on Type A seals and the exclusion of lapped joints for sealing seal faces are included in the standard.
The sleeves shall be piloted near both ends with the center of the bore relieved. These requirements are based on the shaft diameter and shown in the chart. Drive collars set screws shall be sufficiently hard to embed into the shaft. The next section contains design requirements specific for different seal arrangements and configurations. Category 3 Category 3 seals share the same requirements as Category 2 with the exception that a distributed flush is required on all Arrangement 1 seals with rotating flexible elements.
All seals must also have a throttle bushing. This requirement minimizes the potential to distort the gland during tightening of the gland nuts. On Arrangement 1 and Arrangement 2 seals with rotating flexible elements. In the First Edition. Auxiliary sleeves are often used to aid in the assembly of the seals or to allow common seal sizes to be used for the inner and outer seal.
Arrangement 2. Gland gaskets must be confined. Where possible. Designs that utilize an auxiliary sleeve or adapter sleeve on the inboard are acceptable. Upon installation. Footer23 Experience in Motion Page This requirement eliminates the use of full face flat gaskets.
General Arrangement 2 seals are designed with two seals in a face-to-back orientation and with a buffer fluid cavity maintained at a pressure less than seal chamber pressure. In addition. Category 2 The standard seal flush for a Category 2 seal is also a single point injection.
The default inner seal for all Arrangement 2 seal is a contacting wet CW seal. In inner seal must be designed to withstand a reverse pressure differential of 2. Category 1 The standard seal flush for a Category 1 seal is a single point injection. All Category 3 seals will be provided with a floating carbon throttle bushing. For Category 1 seals. Arrangement 1 For single seals. In the Second Edition. For Category 2 seals. Gland gaskets must be fully confined in a groove. Since the buffer fluid cavity is almost always connected to a flare or vapor recovery system.
If specified due to process conditions and if axial space is available. The barrier fluid may be a liquid or a gas. If the seal uses a Plan General Arrangement 3 seals are dual seals where the barrier fluid is maintained at a pressure higher than the seal chamber pressure.
Like Arrangement 2 seals. If it is recommended by the seal OEM and approved by the user. The containment seal bushing shall be designed so that the minimum radial clearance between the bushing and rotating seal components is 1. Other piping details such as connection size. The differential temperature is a function of many things such as barrier fluid properties. Arrangement 3. To help isolate the containment seal from this leakage. The default design requires that the seal consist of two seal rings and two mating rings.
Leakage is then directed to exit the containment seal cavity through the vent or drain. In 3CW-FB configuration. For Category 3 seals. This may be required to provide an external flush to isolate the seal chamber. Arrangement 3 seal sleeves shall be designed as one piece where possible. The inner seal in all Arrangement 3 configurations must be designed so that the inner seal will withstand reverse pressure without opening.
For Category 1 and 2 seals. Footer24 Experience in Motion Page API removed almost all of the seal references. These remain since the are applicable to all pumps including the newly incorporated ASME and ISO pumps and they greatly affect the performance of the mechanical seal. This can be a great number of different components. The standard specifically covers the accessories listed below: Auxiliary piping systems Cyclone separators Orifices Seal coolers Reservoirs Pumping rings Condensate collection reservoirs Gas supply panels Auxiliary Piping Systems Auxiliary piping systems address the requirements for piping.
Group III cover cooling water systems to support any other accessory. Concentricity between the pump shaft and the seal chamber pilot diameter must be less than 0. The only pump requirements that remain in API Second Edition and beyond pertain to interfaces between the seal and the pump seal chamber.
This is measured by attaching a dial indicator to the shaft and measuring the total indicator reading through one complete revolution of the shaft.
This is measured by attaching a dial indicator to the shaft and reading the total indicator reading through one complete revolution. Group II covers piping requirements for steam injections. Footer25 Experience in Motion Page It also includes cooling water piping to reservoirs and seal coolers.
Perpendicularity between the pump shaft and the face of the seal chamber must have a TIR less than 0. Example of the include piping used to connect the seal to a barrier fluid reservoir or seal cooler. To achieve this. The standard divides up piping systems into three groups.
API removed almost all pump references. Accessories Accessories are any components in the seal system other than the seal that are required to create an acceptable sealing environment.
The default material for cyclone separators austenitic stainless steels. The standard recommends that the contaminants have at least twice the density of the fluid. Plan 23 systems must include a permanent stainless steel tag which describes the importance of completely venting the system.
The number and size of orifices is to be determined the vendor supplying the auxiliary piping system. Orifice unions are not allowed. Some of the highlights include: The purpose of a cyclone separator is to remove solid contaminants from the seal flush and provide a better environment for the seal. Many of the requirements are included in a table which covers specific descriptions or specifications for various piping components.
They are also subdivided into the hazardous nature of the product. In additionally. A flow orifice should only be used if the differential across the cyclone separator is too high.
The standard contains many more requirements and it should be read in its entirety before specifying auxiliary piping systems. For between bearings pumps. Piping systems shall be designed so that air pockets are eliminated by manually venting at high points or by designing the system to be self venting. The requirements in this table are specific for the piping group Group I.
This can be a pumping device integral with the mechanical seal or an external circulation pump. Systems that rely solely on thremosyphoning are not allowed. Designs that rely on internal pumping rings should be designed so that the inlet into the seal gland is at the bottom of the gland and the outlet at the top of the gland.
The minimum diameter for an orifice is 3mm 0. If multiple orifices are required. Footer26 Experience in Motion Page Flow Control Devices Orifices are used to control the flow of fluid in seal flush systems. Orifice nipples may be provided at the pump discharge if specified.
Barrier and buffer fluid systems require some means of forced circulation. Since separation of the contaminants take place by centrifugal force. Cyclone Separators The first accessory covered in the standard is the cyclone separator.
Whenever possible. Cyclone separators are used in piping plans 31 and This table includes specifications for tubing.
There are many requirements stated in this section. For shaft diameters over 60mm 2. All connecting piping must be continually sloping upward to the reservoir and use smooth. As a minimum. One of the changes introduced in the Second Edition was the addition of a new reservoir size. The First Edition required that all reservoirs have a minimum 20 l 5 gallons fluid capacity at the normal liquid level.
For small seal sizes under 60mm or 2. The 20 l 5 gallon reservoir is constructed for 8 inch schedule 40 pipe. Seal coolers shall be designed so that both the tube and shell side can be completely vented and drained.
A low level alarm switch is also required. For shaft diameters 60mm 2. The 12 l 3 gallon reservoir is constructed from 6 inch schedule 40 pipe. A high level alarm switch is optional. Examples of these include: A separate reservoir is required for each seal. The standard contains many specific requirements for features. The reservoirs are considered to be part of the pump piping system so they shall be designed. The cooling water or other cooling medium is on the shell side.
All reservoirs shall have a pressure switch and pressure gauge to monitor the pressure above the fluid level in the reservoir. The height of the normal liquid level shall be at least 1m 3 ft above the gland plate of the seal.
The Second Edition allowed the use of smaller fluid capacity for smaller seals. The shell side shall be equipped with a service valve on at the low point to allow flushing of the cooling water. In the Second Edition and beyond. For shaft sizes over 60mm 2. For between bearing pumps. Seal coolers shall be designed so that seal flush or process fluid is on the tube side of the cooler. The standard design for the reservoir is a fixed head construction.
The reservoir shall be constructed from at least 8 inch schedule 40 carbon steel pipe with a minimum 12 l 3 gallon capacity. Since the customer requirements can be varied on these panels. There shall be no connection. Since leakage from the containment seal cavity will drain to the reservoir.
The reservoir is used specifically in the new Plan If the pump is constructed of a material other than carbon steel. The pressure gauge is mounted as one of the last components so that it more accurately measures the gas pressure to the seal. The reservoir is also used to monitor the performance of the inner seal and provide an alarm for inner seal failure. Permanent marking shall indicate the normal liquid level. Piping schematics of these are shown in the piping plan section.
Footer28 Experience in Motion Page The purpose of the reservoir is to collect the leakage. Condensate Collection Reservoir The condensate collection reservoir is used to collect leakage from a containment seal cavity. The top of the coils shall be below the barrier fluid return connection.
Additional level switch and test connections are optional. The reservoir shall have at least flanged end. The alternate design features a removable head located at the bottom of the reservoir. The Second Edition described only one design of gas control panel as shown in the figure on the right. The default material of construction of the reservoir and any component or fitting directly welded to it shall be L stainless steel.
A high flow switch is optional. The sight glass shall be a reflex. If the leakage solidifies at ambient temperatures. The system must contain the following components as a minimum: It is clearly stated in the standard that the seal will be tested as it will offered for sale to the industry. Inspection of seal components contains all of the provision for various forms of NDT including radiographic.
This includes realistic fluids. This testing is done to qualify a seal design. The users on the Task Force were concerned that these tests should simulate real world conditions. Testing for a specific seal model will only need to be done once. It is not intended as a testing requirement for an actual job seal.
Pump OEM testing covers concerns about seal performance during pump testing. The next three topics will be covered in considerably more detail. It is especially difficult to prove compliance with long life objectives since very long term testing 3 years is unrealistic and prohibitively expensive. Many test programs in the lab are performed under ideal conditions.
In the end. Footer29 Experience in Motion Page Qualification Testing It is very easy to create a performance objective for a piece of equipment. Qualification testing is intended to subject the seal to a set of conditions that that will simulate operation in the field. If any of these are changed. Qualification testing is intended to qualify a seal model. It can be considerably more difficult for an OEM to prove that they have achieved compliance with these objective.
The face materials. The requirements range from inspection at the time of manufacturing through the final shipment to the customer. These inspections are generally applicable only to welding or casting inspections. Qualification testing involves certifying the basic seal design. If the user will be specifying any of these components. These include the components listed below This training module will not go into details of the requirements.
The seals still need to be tested but there is an option. These are divided into three sections: Since there is no industry standard definition of seal size. After selecting the fluid. It was important to demonstrate that seal would work during long term.
They then selected five test fluids that were representative of the application groups. The standard covers a range of shaft diameters from 20mm 0. These are further divided by specific fluids or temperature ranges. Category 1 and 2 seals have a less stringent testing requirement.
The First Edition Task Force started by identifying a number of typical refinery applications categories based of the process fluid. This chart describes the test fluids used for the qualification testing. A small seal with a balance diameter from 50 to 75mm 2 — 3 inches and a large seal with a balance diameter from to mm 4 — 5 inches must be tested.