rp mech seal

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IndustriesLimited, India

INDEX

TOPIC DESCRIPTION PAGE NO.1.0 Scope 32.0 Definition 43.0 Applicable Standards 44.0 Purpose 45.0 Seal Categories 46.0 Seal Types 57.0 Seal Designs 68.0 Seal Arrangements and Configurations 69.0 Seal Accessories 7

10.0 Seal Piping Plans 911.0 Seal Selection Procedure 1912.0 Seal Maintenance and Best Practices 2013.0 Seal Documentation 2214.0 References 2315.0 Appendix-1 Seal Types Drawings 24

Appendix-2 Seal Piping Plan Flowchart 25


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1.0 SCOPE

This document covers best practices for mechanical seals and sealingsystems installed in centrifugal and rotary pumps with an aim to achieve aminimum of 3 years of seal life.

The scope of the document is to provide guidelines and best practices on sealselection and maintenance.

This document is best used in conjunction with API 682.


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2.0 DEFINITION:

A mechanical seal is a device which prevents leakage of fluids along rotatingshafts. Primary seal function is at right angles to the axis of rotation betweenone stationary ring and one rotating ring. The associated sealing systems areprovided for the principal purpose of cooling and lubricating the seal faces.

3.0 APPLICABLE STANDARDS:The primary standards applicable to seals and sealing systems for pumps are;

API 610 - Centrifugal Pumps for General Refinery Service, 10 th Edition API 682 - Shaft Sealing Systems for Centrifugal and Rotary Pumps, 2 nd

Ed. 2002 ISO 21049:2004 Pumps -- Shaft sealing systems for centrifugal and

rotary pumps

4.0 PURPOSE :

The purpose of this document is to detail best practices with regards to thedesign, selection, operation and maintenance of mechanical seals and sealingsystems for centrifugal and rotary pumps.

The document is intended for;1. Field Maintenance Personnel2. CES (Functional) Engineers3. Project Engineers4. Planning and Materials Engineers

5.0 SEAL CATOGORIES:

A seal category is intended to cover the proposed pump, its operatingwindow, materials of construction, design features and documentationrequirements for the seal. API 682 has listed three categories (see Table 1)and has provided specifications for each category.

The code has standardized on face materials of Silicon carbide (SiC) andf f


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T ABLE 1: S EAL C ATEGORIES API 682 2 ND E DITION

6.0 SEAL TYPES : (REFER APPENDIX -1 FOR IMAGES )

The code has classified the seals in three types.

Type A is a pusher seal with rotating flexible element.Face materials: Silicon Carbide and CarbonMetal Components: SS 316Springs: Hastalloy C-276O-Rings: Fuoroelastomers

Type B is a bellow seal with rotating flexible element.Face materials: Silicon Carbide and CarbonDiaphragms: Hastalloy C-276Metal Components: SS 316O-Rings: Fuoroelastomers / Flexible Graphite *

Note: Fluoroelastomers shall not be used at a temperature beyond 175 deg.Cand Perfluoroelastomers shall not be used in seals operating at pumping


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Metal Components: SS 316Secondary Seals: Flexible Graphite

7.0 SEAL DESIGNS:

Mechanical seals designs are typically of the wet contact seal faces(designated as CW ) type. The API code has now included two additional

seal designs and these are as follows; Containment Seals (designated as CS ): These are seals typically

used as backup seals in a dual unpressurized seal arrangement.These operate at a pressure of 0.7 bar under normal conditions.When the inner seal fails, this seal is designed to operate under fullpressure conditions for a minimum of eight hours.

Non Contact Seals (designated as NC ): In this design of seals, thecontact face maybe profiled to achieve a hydrodynamic lift so as tocreate a separation of the faces. These are typically used in dualpressurized seal arrangements. These maybe considered for liquidand mixed phase applications.

8.0 SEAL ARRANGEMENTS and CONFIGURATIONS:

The seal arrangement defines the number of seals in the cartridge and theseal housing pressures. These are categorized as below;

Arrangement 1 :This is the conventional one seal per cartridge assembly.

Arrangement 2:This is a dual seal cartridge assembly with outboard seal is at a pressurelower than the seal housing pressure (outboard seal could be a containment

seal)

Arrangement 3:In this arrangement, dual seals are supplied with an external barrier fluidwhich is at a pressure higher than the sealing pressure.

R f h h b l


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T ABLE 2: S EAL A RRANGEMENTS AND C ONFIGURATIONS API 682 2 ND E DITION

9.0 SEAL ACCESSORIES:

9.1 SEAL COOLERS:

Seal coolers maybe specified to increase the vapor pressure of the fluid or improve its lubricating properties. The seal cooler sizing shall be adequate for the required removal of heat. The following shall be ensured;

1. Buffer/Barrier fluid temperature does not reach boiling point. A marginof 15deg.C is recommended between the maximum anticipatedtemperature and the boiling point.

2. Barrier/Buffer fluid temperature should not exceed allowable limits of the materials of construction.

3. The temperature rise of the fluid should be restricted to 20deg.C.


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Shaft seal size < 2.500 inchesMinimum tube size Minimum Tube thickness 0.065

Shaft seal size > 2.500 inchesMinimum tube size Minimum Tube thickness 0.095

9.2 Barrier/Buffer Reservoirs:

The minimum design criteria sizes of the reservoirs have been specified in thecode. The minimum volume for these reservoirs is indicated as;

Shaft seal size < 2.500 inchesVolume: 3 gallons

Shaft seal size > 2.500 inchesVolume: 5 gallons

Reservoirs for atmospheric or low pressure buffer liquid and accumulators for pressurized barrier liquid shall be sized for a manual refill interval time of atleast 25 days based on the seal leakage rate specified by the seal

manufacturer without compromising the specified seal life time.

9.3 Condensate Collection Reservoir:

The condensate collection reservoir is a vessel used to collect leakage from aPlan 75 system. This reservoir collects the leakage and is a place for liquidand gas phase leakage to separate and be piped to the appropriate recoverysystem. The reservoir maybe instrumented to monitor inner seal leakage. The

standard provides details of the construction for this vessel.

9.4 Buffer / Barrier Gas Supply Panels:

Gas supply panels are used on Plan 72 and Plan 74 systems to provide afiltered regulated inert gas to the mechanical seals. The supply panels musth t i i g l t l i g filt fl t l


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10.0 SEAL PIPING PLANS:

Primary seal plans, such as 11, 13, 21, 23 and 32, shall be executed in pipingwith welded or flanged connections.

The use of strainers or cyclone separators to trap sealant particulates is notrecommended. Standard seal flush plans 12, 22, 31 and 41 shall not be used.

A brief discussion on the various seal piping plans is included to aid theselection process;

Plan 01:

Internal seal chamber flush from pump dischargePurpose:

Heat removal from seal housing Venting of seal housing Reduce risk of freezing / polymerizing fluid in exposed and external

piping of Plan 11. Application

Clean and medium fluid temperatures Single seals

Limitation:Flush cannot be directed over the seal faces.

Plan 02:

Dead ended seal chamber with no flush.Purpose:

Simple, low cost Application

Clean and medium fluid temperatures Single seals

Limitations: Flush cannot be directed over the seal faces With higher fluid temperatures cooling water jacket is required for seal

housing. Construction Features:

Throat bush is removed.


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Increases seal chamber pressure and raises vapor pressure margin Application Clean service and medium fluid temperatures Single and dual seals

Limitations: Failure mode is due to chocking of orifice. Regular field checks to

include monitoring of temperatures upstream and downstream of orifice.

Plan 13:

In this plan, there is a recirculation from seal chamber back to pump suctionthrough an orifice. The orifice ensures seal chamber pressure greater thansuction pressure.Purpose:

Heat removal from seal housing

Venting of seal housing in vertical pumps Application Clean service and medium fluid temperatures Single and dual seals Vertical pumps

Limitations:Failure mode is due to chocking of orifice. Regular field checks to includemonitoring of temperatures upstream and downstream of orifice.Construction Features:

Need a vent in piping loop for venting prior to starting in vertical pumps

Plan 14:

In this plan, there is a seal flush from pump discharge through an orifice and arecirculation from seal chamber back to pump suction through an orifice.Purpose:

Heat removal from seal housing Continuous venting of seal housing in vertical pumps Increase seal pressure chamber and fluid vapor pressure margin

Application Clean and medium fluid temperatures Single and dual seals


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Plan 21:In this plan, there is a seal flush from pump discharge through an orifice and acooler.Purpose:

Cooling of seal Reduce fluid temperature to raise fluid vapor pressure margin

Reduce coking Application Clean and high temperature service, typically between 80 deg.C to 175

deg.C Single and dual seals

Limitations: Failure mode is due to chocking of orifice. Regular field checks to

include monitoring of temperatures upstream and downstream of orifice.

Construction Features: Seal coolers and piping need vents at highest elevation for venting

before start

Plan 23:

In this plan, the flush is circulated by an internal pumping device to the cooler in a closed loop. This lowers the cooling duty of the cooler and may allowlower flush temperatures.Purpose:

Cooling of seal Reduce fluid temperature to raise fluid vapor pressure margin Reduce coking

Application Clean and high temperature service, typically between 80deg.C to

175deg.C Single and dual seals

Limitations: Seal coolers and piping need vents at highest elevation for venting

before start Failure mode is due to chocking of orifice Regular field checks to


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Plan 53 - A:

In this plan, the pressurized barrier liquid is circulated through the reservoir.Barrier liquid is circulated by pumping ring. Barrier liquid is pressurized in thereservoir by gas which is in direct contact with a liquid.Leakage of the inner and outer seals is monitored.Purpose:

To provide a backup seal for the primary seal To provide seals with zero emissions, especially in applications of light

hydrocarbons (having high vapor pressure) No process contamination is allowed

Application Plan is used for dual seals in face to back arrangement High temperature, dirty, polymerizing, oxidizing, hazardous or toxic

serviceLimitations:

Requires regular monitoring of the reservoir pressure. Plan 53 A as pressurizing gas is in contact with the barrier liquid; gas

pressure can drop due to absorption Gas charging arrangement is required

Construction Features: Piping loop needs to self vent to vapor recovery system near

atmospheric pressure Buffer liquid to be compatible with process liquid and should preferably

have a good specific heat Inboard and outboard seal leakages are known by reservoir level

alone.

Plan 53 - B:

In this plan, the pressurized barrier liquid is circulated through the reservoir.Barrier liquid is circulated by pumping ring. A bladder in the reservoir separates the gas from the barrier liquid. Leakage of the inner and outer sealsis monitored.

Purpose: To provide a backup seal for the primary seal To provide seals with zero emissions especially in applications of light


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High temperature, dirty, polymerizing, oxidizing, hazardous or toxicserviceLimitations:

Requires regular monitoring of the reservoir pressure. Gas charging arrangement is required

Construction Features: Piping loop needs to self vent to vapor recovery system near

atmospheric pressure

Buffer liquid to be compatible with process liquid and should preferablyhave a good specific heat Inboard and outboard seal leakages are known by reservoir level

alone.

Plan 53 - C:

In this plan, the pressurized barrier liquid is circulated through the reservoir.Barrier liquid is circulated by pumping ring. The reservoir has a pistonaccumulator. The barrier liquid is pressurized by the process liquid from thepump discharge. Leakage of the inner and outer seals is monitored.Purpose:

To provide a backup seal for the primary seal To provide seals with zero emissions, especially in applications of light

hydrocarbons (having high vapor pressure) No process contamination Need higher pressure than in Plan 53A Dynamic tracking of system pressure

Application Plan is used for dual seals in face to back arrangement High temperature, dirty, polymerizing, oxidizing, hazardous or toxic

serviceLimitations:

Reference line can get chocked.Construction Features:

Piping loop needs to self vent to vapor recovery system near atmospheric pressure

Buffer liquid to be compatible with process liquid and should preferablyhave a good specific heat

Inboard and outboard seal leakages are known by reservoir levell


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To provide seals with zero emissions, especially in applications of lighthydrocarbons (having high vapor pressure) Isolate the process liquid

Application Plan is used for dual seals in back to back or face to face arrangement High temperature, dirty, polymerizing, oxidizing, hazardous or toxic

service Seal cannot induce circulation

Limitations: Availability of reliable source of compatible barrier liquid at the requiredpressure

Circulating system must be pressurized and energized at all timesConstruction Features:

Piping loop needs to self vent to vapor recovery system near atmospheric pressure

Buffer liquid to be compatible with process liquid and should preferably

have a good specific heat Inboard and outboard seal leakages are known by circulating systemlevel gauge.

Plan 62:

This plan provides external quench on the process side of the seal.Purpose:

Prevent solid build up or icing on atmospheric side of the seal. This prevents seal hang-up situations

Application Used typically in single seal arrangements with self flush Service that can cause polymerizing, oxidizing, coking, icing,

crystallizing in atmospheric conditionsLimitations:

Need continuous supply and drain of quench media Needs monitoring of choking of supply or drain connections of

quench mediaConstruction Features:

Quench side pressure to be limited to 0.3 bar (2 psi)

Pl 65


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Limitations: Need periodic checking of the drain line for choking Requirement of close clearance throttle bushing may require

extended glandConstruction Features:

Requires a close clearance throttle bushing to aid directing leakageto the collection vessel

Plan 71:This plan provides supply of gas buffer for dual gas seals and containmentseals.Purpose:

Provide for low pressure containment seal with gas buffer as backupfor primary seal.

Application Typical application is in face to back seal arrangement where outboard

seal is a containment seal in dead ended seal cavity. High temperature, hazardous or toxic service

Limitations: Gas buffer supply pressure to monitored on a regular basis

Construction Features: With containment seals gas buffer pressure is limited to 0.7 bar (10 psi)

Plan 72:

This plan provides supply of gas buffer for dual gas seals and containmentseals. This is selected when it is beneficial to sweep the containment sealcavity with an inert gas.Purpose:

Provide back up for primary seal using a low pressure containmentseal with gas buffer

Application Typical application is in face to back seal arrangement where outboard

seal is a containment seal. High temperature, hazardous or toxic service

Limitations: Gas buffer supply pressure to monitored on a regular basis


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Construction Features: With containment seals gas buffer pressure is limited to 0.7 bar (10 psi)

Plan 74:

This plan provides supply of pressurized barrier gas for dual gas seals.Purpose:

To provide seals with zero emissions, especially in applications of lighthydrocarbons (having high vapor pressure)

Isolate the process liquid Application

Where liquid barrier for seals cannot be used Plan is used for dual seals in back to back or face to face arrangement High temperature, dirty, polymerizing, oxidizing, hazardous or toxic

service Moderate temperatures

Limitations: Clean and reliable supply of barrier gas supply is required.

Construction: Barrier gas supply is typically 1.75 bar above the seal chamber

pressure Gas flow meters indicate leakages of the inner and outer seals Bottled gas supply system maybe required as an emergency backup

system

Plan 75:

This plan provides for collection of drain from containment seal cavity. Thedrain may then be led to a liquid collection system and/ or for vapor recovery.

Purpose: Leakage collection for zero/low process emissions Safety indicator for primary seal

Application Used alone or with Plan 72 Fluids that may condense in ambient conditions Service that maybe hazardous or toxic or with high vapor pressure Clean, non-polymerizing, non-oxidizing fluids

Li it ti


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Hook up vent collection reservoir to low pressure vapour recoverysystem or flare system Primary seal leakage is indicated by increase in level / increase in vent

pressure

Plan 76:

This plan provides for vent from seal cavity of containment seal to vapor recovery.Purpose:

Leakage collection for zero/low process emissions Safety indicator for primary seal

Application Used alone or with Plan 72 Fluids that do not condense in ambient conditions Service that maybe hazardous or toxic or with high vapor pressure Clean, non-polymerizing, non-oxidizing fluids

Limitations: Regularly monitor liquid level, valve settings and low vent pressure.

Construction: Collection reservoir is located below seal drain and downward sloped

piping Hook up vent collection reservoir to low pressure vapour recovery

system or flare system Primary seal leakage is indicated by increase in level / increase in vent

pressure


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11.0 SEAL SELECTION PROCEDURE:The following criteria maybe be considered for seal selection;

Dual seals shall be applied in the following services:

Hazardous servicesHazardous services shall be defined on the following basis

o Category 1: Liquids containing hydrogen sulphide in concentrations

above 600 mg/kg. Liquids consisting of or containing lethal substances as

indicated in the data/requisition sheet. Examples of lethal substances include but are not limited to: HF acid,

phenol, concentrated sulphuric or nitric acid.

o Category 2:

Liquids consisting of or containing very toxic substances These are substances with TLV-TWA rating of 5ppmv and lesser

The value maybe extended to TLV-TWA rating of 20 ppmv if the location / site of the pump isfrequently visited by personnel

Liquids that are known to be proven carcinogensand or have been to known to be causing cancer in animal experiments.

Hydrocarbon liquids at an operating temperature abovetheir auto-ignition temperature.

o Category 3: Hydrocarbon liquids with a seal chamber vapour pressure higher than 5 bar (abs) .Hydrocarbon services of butane (C4) or lighter .

Services in which the required three year operation cannot be ensuredwith a single seal application due to the physical or chemical propertiesof the liquid to be sealed.

Services in which it is not permitted for the pumped liquid to enter theflare or atmosphere. In this case, dual pressurized seals shall beapplied


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Plan 54 for dual seals in Category 1 liquid services Dual unpressurized face to back seals with Plan 52 in Category 2services

Single seals with Auxiliary seals, other than dry gas seal types

A wet contact seal with containment seal may be considered only for liquids specified under Category 3 and are not classified as hazardousor toxic as per the definitions in Category 1 and 2.

Dual pressurized non-contact (NC) (dry gas) seal arrangements with apressurized nitrogen barrier are recommended for liquids that are notclassified as hazardous and have a maximum vapor pressure at pumpingtemperature of 1.05 bar (abs). Careful attention shall be paid in thisapplication to ensure a reliable nitrogen supply system.

Non-contacting primary seal with containment seals in a face to backconfiguration maybe considered for fluids in supercritical state or vaporizingliquids after validating that the design ensures vaporization of liquid before itenters the seal faces and also that it does not condense or cause icing as itexpands to a lower pressure.

12.0 SEAL MAINTENANCE and BEST PRACTICES:

12.1 Observation Maintenance:

Temperature monitoring of seals and sealing systems is most effective.Use of IR thermometers should be encouraged to record temperatureof seal housing of pumps and ensure these are same or lower than thepump inlet or suction casing.

It is a good practice to record differences in temperature on seal flushlines that are installed with orifices. This is applicable for seal piping

plan 11, 13, 14 and 21. Difference in temperature can detect cloggedorifices which is the most common failure mode.

Temperature measurement of flush lines downstream of cooler in Plan21, 23, 52, 53 will highlight the condition of the coolers.


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All pumps provided with quench should be checked for proper supply and drain of quench media.

12.2 Preventive Maintenance:

The following activities are suggested during the normal PM schedulesof the pump.

Opening and cleaning of sealant lines, orifices, vents and drainsespecially for unclean services

Back flush or cleaning of seal coolers. Ensuring adequatecooling water supply and return

Calibration of instrumentation for Plan 32, 52, 53, 72, 74, 75, 76

12.3 Corrective Maintenance:

The recommended practice is the use of seal cartridges in allapplications. These cartridges maybe be restored and tested in-houseor by the seal vendor. In any case, the following shall be the guidelinesfor repair as a minimum.

1. Surface Finish: The seal faces shall be lapped and finished to a maximum

tolerance of 3 light bands or 0.87 microns The surface finish of the sleeve shall be a minimum of 0.8

microns Ra Surface finish of the seal housing face shall be 1.6 microns Ra The seal housing bore shall be machined to a finish of 3.2

microns Ra

2. Geometric Tolerances:

Shaft/sleeve runout at seal face area should be within 0.05 mm Radial shaft deflection at seal face area should be within 0.05

mm Squareness of the seal housing (dial base on shaft and pointer

in axial direction on face of seal housing) shall be within 0.05mm

Concentricity of the bore of seal housing (dial base on shaft and


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maybe subjected to during static (shutdown) and dynamic(operating) conditions of the pump.

12.4 Spare parts Management:

1. A master list of all installed seals shall be maintained indicating their interchangeability

2. Seal cartridges or spares maybe categorized as consumable or durable spares Their reorder level and reorder quantity shall bedetermined accordingly. Ordering information on slow or non-moving seal spares shall be reviewed annually.

3. All seal components shall have the information about their shelf lifeand storage instructions. It is recommended to store all elastomersin low temperature and humidity free environments

4. There shall be annual inspection of the condition of the stocked sealparts.

13.0 DOCUMENTATION AND RECORDS:

For effective maintenance and troubleshooting, it is essential to havethe following documentation for mechanical seals and sealing systems;

Original seal specification document Seal cross-section drawing with dimensions and tolerances. It

should also include bill of materials indicating MOC, installedquantity and OEM part number Seal piping plan details, documents and drawings Seal and seal plan manufacturing and testing records Repair / refurbishing procedures and check sheets with protocol

values.


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14.0 REFERENCES:

API 610 - Centrifugal Pumps for General Refinery Service, 10 th Edition API 682 - Shaft Sealing Systems for Centrifugal and Rotary Pumps, 2 nd

Ed. 2002 Shell DEP - Shaft Sealing Systems For Centrifugal And Rotary Pumps:

DEP 31.29.00.33-Gen. - July 1998 Overview of API 682 and ISO 21049 Michael B Huebner Proceedings

of 21 st International Pump Users Symposium 2004 Overview of API 682 Second Edition - Michael B Huebner Proceedings

of 20 th International Pump Users Symposium 2003 Advances in Mechanical Sealing An introduction to API 682 Second

Edition M.B.Huebner, J.M.Thorp, G.S.Buck, C.L.Fernandez -Proceedings of 19 th International Pump Users Symposium 2002

Containment Seals for API 682 Second Edition P.E.Bowden, C.J.Fone -Proceedings of 19 th International Pump Users Symposium 2002

Use of Non-Contacting Seals in Volatile Services B.Goodenberger,D.E.Barron, J.Marquardt - Proceedings of 20 th International Pump UsersSymposium 2003

Understand Mechanical Seals A.S.Godse Hydrocarbon processing April 1995

Mechanical Seal Piping Plans Flowserve Document FTA160 Rev12/03 Flowserve Solutions Division

Advanced Gas Sealing Systems for Hydrofluoric Acid Alkylation and Other Extremely Hazardous Duties D. Kozlowski, E.Jahromi. J.R.Wasser-Proceedings of 20 th International Pump Users Symposium 2003

Burgmann Mechanical Seals Catalogue


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Appendix 1.0

Seal Type A and its Alternative

Seal Type B and its Alternative

Seal Type C and its Alternative


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Prepared by: Paresh Girdhar Page: 25 of 25Checked by : K Gopalakrishnan

Group Manufacturing ServicesEngineering Services Dept Date: 9-Mar-07

Approved by : A Venkatraman DOC. No: GMS/RP/26 Revision no.: 0.0

Appendix 2.0

MECHANICAL SEAL PIPING PLANS

Single Seals

Self FlushExternal flush

Dead Ended Positive Pressure Difference

Sealant is dirty/solids/polymerizing ?

Product Temperature ?

Plan 01

Plan 14

Plan 13

Plan 11

Plan 23

Plan 21Sealant Cooler

Plan 02

Vertical Pump?Needs venting ?

Normal

High

No

Yes

Plan 32

Flush Type ?

Multiple Seals Seals

W et Contact Seals Wet / Non Contact + Containment Seal Non Contact Seals

Back to Back (BB) / Face to Face (FF)Face to Back (FB)

Inboard Seal

Outboard Seal

Inboard Seal - Wet

Outboard Seal

Induced Circulation

External PressurizedBarrier liquid

Plan 54

External UnpressurizedBuffer liquid

Plan 52

I nd uced C ircul at io n I nd uced C ir cu la ti on UnperssurizedBuffer Gas

Dead Ended

Plan 71Plan 72

Gas Supply System

Drain-Mixed Phase

Plan 75

Drain-Completely Dry

Plan 76

External PressurizedBarrier Gas

Plan 74

Wet Contact Seals

External PressurizedBarrier liquid

Plan 54A

AOptional Fluid

Quench

Plan 62

Possibility of Gas absorption?

No

Plan 53-A

Need dynamic trackingof system pressure?

Yes

No

Plan 53-B

Plan 53-C

Yes

Inboard Seal - NC

PressurizedBarrier Gas

Plan 74

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