Review of Single Mechanical Seal Piping Plans

Requirements of Mechanical SealsLiquid sealsStable fluidsGood lubricating propertiesFluids do not flash or vaporize in seal chamberFree from contamination and solidsModerate viscosities

Requirements of Mechanical SealsGas sealsGas or vapor suitable for sealingConstant supply of external buffer/barrier gasProcess fluids free from contamination from both liquids and solidsProcess fluids which are not adversely affected by gas leakage

Purpose of Piping PlansCreate a more favorable environment for the mechanical sealFlushing to remove heatLowering fluid temperatureAltering the seal chamber pressureCleaning the process fluidsControl atmospheric side of seal

Purpose of Piping PlansProvide a means of detecting and controlling seal leakageCapture and/or prevent leakageDetect leakageRoute leakage to appropriate collection or disposal systemProvide fluid other than process fluid for the seal environment

Methods of Achieving GoalsPiping or routing of process fluidsIntroduction of external fluidsAuxiliary equipmentSeal coolersCyclone separatorsReservoirsInstrumentation

Piping PlansStandardized in:API 610API 682ISO 21049ASME B73Designated by numbersAPI example 11, 32, or 53ASME example 7311, 7332, or 7353

Plan 01WhatInternal seal chamber flush from pump discharge.Operates similar to Plan 11.

Plan 01WhySeal chamber heat removal.Seal chamber venting on horizontal pumps.Reduce risk of freezing or polymerizing fluid in exposed Plan 11 piping.

Plan 01WhereCustom seal chamber, most likely an ASME/ANSI pump.Clean, moderate temperature fluids.Used with single seals, rarely used with dual seals.

Plan 01Preventative MaintenanceFlush typically can not be directed over the seal faces and heat removal is limited.Calculate flush flow rate based on head loss through internal porting.

Plan 02WhatDead-ended seal chamber with no flush.

Plan 02WhySimplicity no environmental controls.

Plan 02WhereLarge bore or open throat seal chambers in moderate temperature services.Clean fluids.Top-entry mixers or agitators with dry seals.

Plan 02Preventative MaintenanceProcess must have adequate boiling point margin to avoid vaporization.Cooling fluid in seal chamber jacket may be needed at all times in hot services.Often used in combination with steam quench, Plan 62.

Plan 11WhatSeal flush from pump discharge through orifice.Default single seal flush plan.

Plan 11WhySeal chamber heat removal.Seal chamber venting on horizontal pumps.Increase seal chamber pressure and fluid vapor margin.

Plan 11WhereGeneral applications with clean fluids.Non-polymerizing fluids.

Plan 11Preventative MaintenanceUse an orifice with a minimum 0.125 (3 mm) diameter.Calculate flow rates to size orifice for adequate seal chamber flow.Increase boiling point margin with proper orifice and throat bushing sizing.Flush should be directed over seal faces with piping at 12 Oclock position.Typical failure mode is a clogged orifice check temperatures at pipe ends.

Plan 13WhatRecirculation from seal chamber to pump suction through orifice.Standard flush plan on vertical pumps.

Plan 13WhyContinuous seal chamber venting on vertical pumps.Seal chamber heat removal.

Plan 13WhereVertical pumps.Seal chamber pressure is greater than suction pressure.Moderate temperature fluids with moderate solids.Non-polymerizing fluids.

Plan 13Preventative MaintenanceVent piping loop prior to starting vertical pumps.Use an orifice with a minimum 0.125 (3 mm) diameter.Calculate flow rates to size orifice for adequate seal chamber flow.Reduce seal chamber pressure with proper orifice and throat bushing sizing.Typical failure mode is a clogged orifice check temperature at pipe ends.

Plan 14WhatSeal flush from pump discharge and recirculation to pump suction with orifices.Combination of Plan 11 and Plan 13.

Plan 14WhyContinuous seal chamber venting on vertical pumps.Seal chamber heat removal.Increase seal chamber pressure and fluid vapor margin.

Plan 14WhereVertical seal.Clean, non-polymerizing fluids at moderate temperatures.

Plan 14Preventative MaintenanceUse an orifice with a minimum 0.125 (3 mm) diameter.Calculate flow rates to size orifice for adequate seal chamber flow.Increase boiling point margin with proper orifice and throat bushing sizing.Flush should be directed over seal faces.Vent piping loop prior to starting vertical pumps.Typical failure mode is a clogged orifice check temperatures at pipe ends.

Plan 21WhatSeal flush from pump discharge through orifice and cooler.Cooler in Plan 11 flush increases heat removal.

Plan 21WhySeal cooling.Reduce fluid temperature to increase fluid vapor margin.Reduce coking.

Plan 21WhereHigh temperature service, typically less than 350 F (177 C).Hot water over 180 F (80 C).Clean, non-polymerizing fluids.

Plan 21Preventative MaintenanceSeal cooler and piping must have air vents at highest elevation vent before starting.When using 682 Seal Cooler, pipe with series flow to maximize heat transfer.Use an orifice with a minimum 0.125 (3 mm) diameter.

Plan 21Preventative Maintenance (continued)Calculate flow rates to size orifice for adequate seal chamber flow.Increase boiling point margin with proper orifice and throat bushing sizing.Regularly monitor device inlet and outlet temperatures for signs of clogging or fouling.

Plan 23WhatSeal flush from internal pumping device through cooler.Standard flush plan in hot water services.

Good Piping PracticesMinimize line lossesLarge diameter tubingUpward sloping linesLong radius bendshigh point ventVerticalEquipmentHorizontalEquipment18 - 24 in.(0.45 - 0.6 m)3 ft. (0.9 m) maxlow point drainPlan 23 Example

Plan 23WhyEfficient seal cooling with low cooler duty.Increase vapor margin.Improve water lubricity.

Plan 23WhereHigh temperature service, hot hydrocarbons.Boiler feed water and hot water over 180 F (80 C).Clean, non-polymerizing fluids.

Plan 23Preventative MaintenanceSeal cooler piping must have air vents at highest elevation vent before starting.When using 682 Seal Cooler, pipe with parallel flow to minimize head loss.Seal chamber requires close clearance throat bushing to isolate process fluid.

Plan 23Preventative Maintenance (continued)Tangential seal gland taps should enter at bottom and exit at top.Regularly monitor cooler inlet and outlet temperatures for signs of plugging or fouling.Process fluids with iron should flow through magnetic separator before cooler.

Plan 31WhatSeal flush from pump discharge through cyclone separator.Centrifuged solids are returned to pump suction.

Plan 31WhySeal chamber heat removal.Solids removal from flush and seal chamber.

Plan 31WhereDirty or contaminated fluids, water with sand or pipe slag.Non-polymerizing fluids.

Plan 31Preventative MaintenanceCyclone separator works best on solids with a specific gravity twice the process fluid.Seal chamber pressure must be nearly equal to suction pressure for proper flows.Piping should not include an orifice and is not expected to vent the seal chamber.Typical failure mode is a clogged separator or pipes check temperatures at pipe ends.

Plan 32WhatSeal flush from an external clean source.

Plan 32WhySeal chamber heat removal.Process and solids removal from seal chamber.Increase seal chamber pressure and fluid vapor margin.

Plan 32WhereDirty or contaminated fluids, paper pulp.High temperature service.Polymerizing and/or oxidizing fluids.

Plan 32Preventative MaintenanceUse throat bushing sized to hold pressure or maintain flow velocity.To restrict dirty process fluid, regulate injection flow rate.To increase fluid vapor margin, regulate injection pressure.Injection fluid must be compatible with process fluid.

Plan 32Preventative Maintenance (continued)Regularly monitor control system for closed valves or signs of plugging.

Plan 41WhatSeal flush from pump discharge through cyclone separator and cooler.Combination of Plan 21 and Plan 31.

Plan 41WhySeal cooling.Solids removal from flush and seal chamber.

Plan 41WhereHigh temperature service, typically less than 350 F (177 C).Dirty or contaminated fluids, water with sand or pipe slag.Non-polymerizing fluids.

Plan 41Preventative MaintenanceSeal cooler piping must have air vents at highest elevation vent before starting.When using 682 Seal Cooler, pipe with series flow to maximize heat transfer.Cyclone separator works best on solids with a specific gravity twice the process fluid.

Plan 41Preventative Maintenance (continued)Seal chamber pressure must be nearly equal to suction pressure for proper flows.Typical failure mode is clogged separator or pipes check temperatures at pipe ends.

Plan 62WhatExternal quench on atmospheric side of seal.Quench fluids typically steam, nitrogen, or water.

Plan 62WhyPrevent solids buildup on atmospheric side of seal.Prevent icing.

Plan 62WhereUsed with single seals.Oxidizing fluids or fluids that coke.Hot hydrocarbons.Crystallizing fluids or fluids that salt out.Caustic.Cold fluids less than 32 F (0 C).

Plan 62Preventative MaintenanceQuench inlet should be on top of gland with drain/outlet on bottom.Quench pressure should be limited to 3 psi (0.2 bar) or less.Use throttle bushing on atmospheric side of seal to direct quench flow to seal drain.Monitor regularly, checking for closed valves, blocked lines, and steam trap condition.

Quench Details

Plan 65WhatExternal drain with leakage detection on atmospheric side of seal.Normal leak drain is through the orifice to drain lineIncase of excess leak, the overflow chamber with level switch (high) will detect.The overflow line will bypass the orifice and send the fluid to drain.

Other Piping PlansPlan 12 Flush through a strainerPlan 22 Flush through a strainer and seal coolerPlan 61 Porting to atmospheric side of seal plugged for future usePlan 71 Porting to containment seal cavity plugged for future use

What are piping plans? Why are they necessary? How do we select the correct plan? How do we troubleshoot them?

Piping plans are an important part of any seal application. The selection, installation, and operation of the piping plan is critical to the success and reliability of the seal. Over the next hour, we try to answer most of these questions and give you some insights into the application of piping plans with mechanical seals.

Before we can talk about piping plans, we need to understand what is important to the proper operation of a mechanical seal. We will break this up into two sections liquid seals and gas seals.

A liquid seal is, very simply, a mechanical seal that is designed to seal a liquid. In practice, the fluid film between the seal faces is very small something on the order of 20 millionths of an inch or one-half micron. This fluid film helps separate and lubricate the seal faces. When we consider the pressures, temperatures, and speeds under which seals can run, this is an incredible technical achievement. This is only possible if we have a good fluid film.

What makes a good fluid film? The fluid must be stable and not breakdown under operating conditions. The fluid must be a relatively good lubricant. The fluid must be maintained in a liquid state and not flash or vaporize in the seal chamber. The fluid should be reasonably clean and free from contamination or solids. Lastly the fluid should be of a moderate viscosity.

Many of these terms are intentionally vague at this point. It is clear though that many applications do not meet these requirements. We are constantly required to seal fluids that are not ideal for sealing applications.Gas seals are designed to run with a film of gas separating the two seal faces. These seals have some benefits since they are non-contacting and generate very little heat. They can also have simpler seal support systems. They have their own set of requirements and are generally less tolerant of upset conditions.

The first requirement is simple; the gas must be suitable for sealing. This covers both the aspects of availability and well as safety and environmental concerns. The gas supply must be constant and reliable. It must also be free from contamination from both liquids and solids. Lastly, the process fluid must be compatible with the barrier gas. This includes leakage of barrier gas into the seal chamber and the pump.

Just like for liquid seals, the environment around the gas seal is critical to obtaining good reliability. And just like the liquid seals, very often we are required to put seals into applications where we do not have the ideal environment. This is where piping plans come in. Piping plans are designed to modify the environment around the seals. In addition, piping plans can provide valuable feedback on the condition of the seal and as well as provide safety backup for the sealing system.The purpose of a piping plan is to create a more favorable environment for the mechanical seal. This can be broken down into a number of specific effects.

Flushing to remove heat. Liquid seals create heat which must be controlled. This is done by providing a flush of liquid into the seal chamber to carry away the heat and control the temperature rise.

Lowering the fluid temperature. In some cases, the temperature of the fluid is too high for good seal performance. In these cases, the temperature must be lowered to improve the fluid properties.

Altering the seal chamber pressure. In some cases it may be necessary to either increase or decrease the seal chamber pressure to improve performance. This may be done to suppress vaporization or to reduce the heat load on the seal.

Cleaning the process fluids. If the process fluid contains unsuitable solids or contamination, it may be necessary to clean the fluid in the seal chamber. In extreme cases, it may even be necessary to provide a clean fluid from outside the seal system.

Control the atmospheric side of the seal. As process fluids come into contact with the atmosphere, they may dry out, crystallize, or coke. It is important to prevent any interaction with the atmosphere from adversely affecting seal performance.

Piping plans also provide a means of detecting and controlling seal leakage.

Capture and/or prevent leakage. Piping plans can provide a means of preventing leakage from reaching the atmosphere. They can also provide a safety backup for a primary seal. This may give the user the opportunity to run with a failed seal for short time and allow for a more orderly shutdown of the equipment.

Detect leakage. Piping plans can be selected so that it is possible to measure amounts of seal leakage and monitor seal performance.

Route leakage to appropriate collection or disposal systems. Piping plans allow users many options for collecting or disposing of seal related leakage.

Provide fluid other than process fluid for the seal environment. Fluids can be provided continuously from another process or can be a stand-alone system which recycles a small amount of barrier/buffer fluid.It is clear that piping plans allow the seal to operate more reliably and provide other benefits to user. How do we do this? What exactly is a piping plan?

Piping plans in their simplest sense are a design of piping or routing of the pump process fluid. As this fluid is circulating, it may be removing heat or altering the pressure acting on the seal. As it circulates, it may also be conditioned by cooling or cleaning. At a minimum, a piping plan normally consists of piping or tubing connecting the pump, seal, and other auxiliary equipment.

Piping plans may also introduce external fluids. These may be injection liquids or barrier and buffer fluids. These external fluids help create the sealing environment for the system.

Auxiliary equipment can be any other device added to the seal and pump. This may include seal coolers, cyclone separators, reservoirs, bushing, orifices, etc.

Lastly, the piping plan may include instrumentation to monitor the pressure, temperature, and flow rate of fluids in the piping plan.

Since there are many different applications for seals, there are many different requirements for the sealing system. There are also a great many permutations of routing the fluid flow and applying the auxiliary equipment. Fortunately, the most popular and useful arrangements have been identified and standardized.

API 610 was one of the first standards to identify piping plans for mechanical seals. These became almost universally referred to as API piping plans. These have now been removed from API 610 9th edition.

API 682 has become the location for all API mechanical seal piping plans. The first edition simply duplicated the older API 610 piping plans. The second edition has expanded on this adding piping plans for gas seals and containment seals.

ISO 21049 is international version of API 682.

ASME (formerly designated as ANSI) B73.1 and B73.2 also contains piping plans which where suited for the chemical industry. These are duplicates of the API plans preceded by the number 73.

Whichever standard we use, piping plans have been defined that will cover almost any requirements in modern sealing applications. We will review the most common piping plans discussing What is the plan, Why it is used, Where is it typically applied, and what Preventative Maintenance is normally required for the plan.There are a few other standard piping plans that we have not covered in this presentation.

Plan 12 consists of a seal flush through a strainer. Plan 22 consists of a flush through a strainer and a seal cooler. While these have been used successfully in some cases, there are many instances where the strainer gets plugged resulting in a seal failure. These are generally not used for new applications.

A Plan 61 is porting to the atmospheric side of a seal that is plugged and may be used in the future.

A Plan 65 describes the collection of atmospheric liquid phase leakage into a collection reservoir. This is used to monitor seal performance and alarm for a seal failure. This plan is new to ISO 21049 and API 682 3rd edition.

A Plan 71 is porting to the containment seal cavity that is plugged and may be used in the future.