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This Fluid Sealing Association Knowledge Series training presentation introduces API Piping Plan 14. A description is provided on:
▪ What is an API Plan 14?
▪ How an API Plan 14 Works
▪ What does an API Plan 14 do?
▪ What an API Plan 14 cannot do
▪ Optional Features for an API Plan 14
▪ Cost to Operate an API Plan 14
▪ How to Size an API Plan 14
▪ How to Install an API Plan 14
▪ General API Plan 14 Commissioning Guidelines
▪ How to Operate an API Plan 14
▪ General Troubleshooting of an API Plan 14
▪ Alternatives to an API Plan 14
What Are Piping Plans?
▪ Piping plans collectively are different piping arrangements of fluid used to improve the conditions the mechanical seal operates in with the objective of improving the mechanical seal’s life.
▪ The American Petroleum Institute adopted numbers and created definitions for each piping plan configuration, thereby allowing a common language across the industry to simply describe a particular configuration.
▪ The American Petroleum Institute standard API-682 is where the definition of each piping plan can be found and where they may periodically be updated.
What is an API Plan 14?
API Plan 14 is a combination of Plans 11 and 13, commonly used on vertical pumps. The Plan 11 taps into a pressure source higher than the seal chamber pressure, typically the pump discharge, or an intermediate stage in a multistage pump, and pipes this fluid to the seal chamber. The Plan 13 connects the seal chamber to a lower pressure source, typically the pump suction, to provide cooling and lubrication to the seal faces.
Flow controlling orifice
Pump discharge flange
Pump suction flange
Mechanical seal or seal chamber “Flush In” connection
Mechanical seal or seal chamber “Flush Out” connection
Flow controlling orifice
How an API Plan 14 Works
An API Plan 14 works by creating flow using differential pressure between a highpressure region (the pump discharge, or an intermediate stage in a multistage pump), a medium-pressure region (seal chamber), and then a low-pressure region (the pump suction).
Flush fluid entry or exit from seal chamber
The flush fluid enters and exits the seal chamber through the flush connections, located in either the mechanical seal gland plate or seal chamber wall. In addition, flush fluid can exit, or enter, between the seal chamber throat bushing and shaft.
Flush fluid entry to seal chamber
Flush fluid exit from seal chamber
How an API Plan 14 Works
As the fluid source is the pump discharge, the fluid flowing through the interconnecting piping and seal chamber is the same fluid that is being pumped.
The flow rate of fluid through the seal chamber can be controlled by adding flow control features. These features include:
What does an API Plan 14 do?
The flow of fluid through the seal chamber created by an API Plan 14 can be used to:
▪ Remove heat generated by the mechanical seal.
▪ Increase seal chamber pressure when used in conjunction with a seal chamber throat bushing to achieve an increased pressure margin above the pumped fluid's vapor pressure.
▪ Prevent the accumulation of debris in the seal chamber.
▪ Continuously remove trapped gases in the seal chamber during operation.
▪ Allow trapped gases in the seal chamber to vent before startup.
What an API Plan 14 cannot do
An API Plan 14 cannot:
▪ Isolate the seal chamber from process fluid.
▪ Remove debris from the seal chamber if flow is low.
▪ Cool the process fluid flowing to the seal chamber.
▪ Lower emissions to the atmosphere.
▪ Alter seal chamber pressure without a seal chamber throat bushing.
What an API Plan 14 cannot do
The main purpose of an API Plan 14 is to create flow through the seal chamber.
Sufficient flow cannot be created reliably when:
▪ Fluids freeze, solidify, or thicken within the external piping.
▪ Fluids contain high solids and abrasives that can abrade and wear the flow controlling components.
▪ Fluids contain large particles that can clog the flow controlling components.
▪ Fluids polymerize and can clog the flow controlling components.
▪ The pressure differential between pressure sources is too low.
▪ Valves are installed in the piping to control flush flow.
Optional Features for an API Plan 14
Optional flow control types
▪ Flat Plate Orifice: Narrow plate with a small flow-through hole that restricts flow within the API Plan 14. These are commonly constructed from piping components and can be assembled either seal welded or threaded. They are often used in hazardous fluid pumping applications.
Threaded joint
Seal welded joint
Optional Features for an API Plan 14
Optional flow control types
▪ Compression tube fitting with inbuilt orifice restriction.
Constructed using commercially available tubing and compression tube fittings. Offers great flexibility in installation and assembly.
▪ Threaded pipe union with orifice plate. Constructed from piping components and offers advantages where orientation of the connecting pipes is complex.
Optional Features for an API Plan 14
Optional flow control types
▪ Threaded coupling with inbuilt orifice restriction. Often custom fabricated from hexagonal bar stock to meet the design needs.
▪ Choke tube: Length of smaller bore tube, possibly coiled, utilizing flow resistance to reduce the flow through the API Plan 14. Used to control flow rates when high differential pressures exist.
Optional Features for an API Plan 14
▪ To control flow rate in pumps that have a large differential pressure, multiple orifice plates can be used. When using multiple orifice plates, they should be spaced a minimum of 300 mm (12 inches) apart.
▪ The addition of a floating bushing to the seal chamber throat can tighten the clearances in that area and increase pressure in the chamber, which is advantageous for increasing vapor pressure margin around the mechanical seal faces.
Optional Features for an API Plan 14
▪ In multistage pumps, an intermediate stage can be used as the pressure source used to create flow, lowering the differential pressure across the Plan 14 system.
▪ Pressure gauges can be installed upstream and downstream of the orifices to provide the ability to calculate the flow rate and to measure the pressure being delivered to and from the seal chamber.
▪ A temperature gauge can be added to measure the temperature of the flush fluid being delivered to and from the seal chamber. When installing, ensure the tip of the temperature gauge or thermowell does not obstruct the flow in the piping.
Eccentric reducers to expand pipe size in the region of the thermowell tip
Cost to Operate an API Plan 14
There is a cost associated with operating an API Plan 14. Energy has been added into the pumped fluid to raise its pressure to the discharge pressure. Most of this fluid flows out of the discharge piping, but some of the flow enters the API Plan 14 flush piping and is eventually returned to the suction of the pump.
The fluid that has flowed through the API Plan 14 piping needs to have energy added to it again to raise its pressure back to the discharge pressure.
This energy consumption, and hence energy cost and carbon footprint, can be calculated as the motor power multiplied by the ratio of the API Plan 14 flush flow rate and the total pump flow rate:
Cost to Operate an API Plan 14
Typically, the volume of flush is very small compared to the capacity of the pump and therefore the efficiency effect is very small. ▪ Energy to operate $ $$$$
Carbon footprint
Initial investment
Cost of operation
Refer to the Fluid Sealing Association’s Lifecycle Cost Calculator (LCC) for a more detailed analysis.
How to Size an API Plan 14
There are some general rules of thumb often used to estimate required flush flow rates. The most commonly used target is a flow rate of 0.16 l/min per mm of shaft diameter (1 GPM per inch of shaft diameter).
These rules generally work well in cool aqueous pumped fluids; however, a more precise calculation may be needed, particularly with volatile or hot pumped fluids.
The Fluid Sealing Association recommends working with your mechanical seal vendor if a more precise target flush flow rate is required.
The calculation method is based on an energy balance to evaluate performance. To make this evaluation the following calculations are needed:
▪ Mechanical seal heat generation
▪ Target flow rate
▪ Actual flow rate through the API Plan 14 piping system
How to Size an API Plan 14
Seal heat generation is influenced by many factors, including seal design, materials of construction, and balance ratio. The governing formulae are:
Where:
Pface = Seal face contact pressure
∆P = Differential pressure across faces
B = Balance ratio
K = Pressure gradient
Pspring = Spring contact pressure
Qheat = Seal heat generation
V = Mean velocity
A = Seal face area
f = Coefficient of friction
How to Size an API Plan 14
A target flush rate is necessary to obtain the optimal performance of a mechanical seal as determined by an energy balance calculation. Heat generated between the seal faces is assumed to be absorbed by the flush through ideal mixing. This raises the temperature of the flush as it passes through the seal chamber.
For best practices, the maximum temperature rise through the seal chamber should be limited to:
▪ 8 °C (15 °F) for water and low volatility hydrocarbons
▪ 16 °C (30 °F) for lubricating fluids
▪ 3 °C (5 °F) for volatile/flashing hydrocarbons
Frequently the target flush rate is relatively low, often less than 4 l/min (1 GPM).
How to Size an API Plan 14
The temperature rise occurring with a heat input and ideal mixing occurring can be calculated by:
Where:
Δ�� = Temperature rise (T2 – T1)
Qheat = Seal heat generation
ṁ = Flush fluid mass flow rate
Cp = Fluid specific heat
How to Size an API Plan 14
The actual flow through a Plan 14 piping system can be quite complex. Typically, the known pressures are the pump suction and discharge pressures. To calculate the flow, the intermediate pressures must be calculated through an iterative process:
How to Size an API Plan 14
Flush fluid entry to seal chamber
Plan 14 flow calculation is an iterative process dependent on orifice, bushing, and piping sizes in order to optimize seal chamber pressure, seal flush rate, and flow velocity underneath the bushing. This calculation is a balance of flow rates and pressures into and out of the seal chamber, and across the bushing, based on the principle of conservation of mass.
For flow optimization and component selection (e.g., tubing and orifice sizing, bushing selection) consult seal provider.
Flush fluid entry or exit from seal chamber
Flush fluid exit from seal chamber
How to Install an API Plan 14
An API Plan 14 is typically constructed using tube or pipe components or a combination of both. When using pipe components, the joints can be threaded or, when the pumped fluid is hazardous, welded joints.
With pipe components, the orifice is formed with a plate having a central hole sandwiched between two flanges with gaskets.
When using tube components, the orifice is formed with a tube fitting union with a reduced diameter through-hole.
To prevent clogging, the minimum orifice diameter should be no smaller than 3.2 mm (0.125 inches).
How to Install an API Plan 14
API 682 recommends:
▪ For shaft diameters up to 60 mm (2.5 inch):
▪ Pipe: DN15 (½” NPS) Schedule 80
▪ Tube: 12 mm (0.5 inch), 1.5 mm (0.065 inch) wall thickness
▪ For shaft diameters above 60 mm (2.5 inch):
▪ Pipe: DN20 (¾” NPS) Schedule 80
▪ Tube: 20 mm (0.75 inch), 2.0 mm (0.095 inch) wall thickness
High process pressures may require increased wall thickness.
How to Install an API Plan 14
When the connection to the discharge pressure is in the pump volute, typically found in between bearing pumps, use the connections on the side of the volute for the "flush in" to prevent solids from being centrifuged into the Plan 14 flush line to the seal chamber.
How to Install an API Plan 14
To achieve self venting of the seal chamber, the flush connection should connect to the seal chamber at the highest point.
High point flush connection
Horizontal shaft
Vertical shaft
How to Install an API Plan 14
To achieve self venting of the seal chamber, the flush should connect to the seal chamber at the highest point. The piping connecting the flush connections to the pump suction and discharge should have a continuously rising slope, minimum 40 mm rise per 1000 mm run (0.5 inch rise per 12 inch run).
For pump designs where self venting cannot be achieved, a high point vent should be added to enable manual venting of the pump prior to commissioning.
General API Plan 14 Commissioning Guidelines
To commission an API Plan 14:
1) Using the mechanical seal assembly drawing, verify that the flush piping is connected to the correct ports in the mechanical seal.
2) Check that the orifice sizes have been indicated on the externally visible surfaces of the orifices.
3) Proper venting procedure should be followed prior to pump startup to prevent dry running of seals.
4) With the pump casing primed, vented, and pressurized prior to startup, check all the joints on the API Plan 14 for leaks. Correct any if found.
How to Operate an API Plan 14
Operation of an API Plan 14 is inherently connected to the operation of the pump. As soon as the pump generates a differential pressure, flow will automatically occur in the API Plan 14 piping.
Periodically check for leaks at the joints. There are no external adjustments that can be made to an API Plan 14 during operation.
During routine maintenance of the mechanical seal, the flow control devices should be inspected for wear, damage, or clogging. Replace or repair as necessary.
General Troubleshooting of an API Plan 14
As flow is continuously moving through the API Plan 14 piping, there should be almost no changes in surface temperature along the piping.
A noticeable difference in temperature indicates there is little to no flow occurring, indicating a blockage.
Plugged orifice –The orifice can become plugged if there are particles in the process stream which are larger than the hole in the orifice, or if there is a high concentration of solids or other debris in the process fluid.
Plugged piping (solidification, freezing) – Fluids pumped at elevated temperatures may solidify when they cool down. This can occur in a spare pump on hot standby, in climates where winter temperatures are low, or due to wind that can cool the external piping.
General
Troubleshooting of an API Plan 14
Inadequate or excessive flow – An improperly sized orifice can result in excessive or insufficient flow rates for the mechanical seal. For between bearing pumps, the inlet and outlet flush for both ends of the pump may originate and terminate at a common location, the pump discharge or crossover and pump suction, respectively. The piping design and orifice locations need to ensure flow is distributed evenly to each seal.
Excessive differential pressure – In multistage pumps, the pressure at the discharge may be very high and cause excessive flow that requires complex flow control devices. Connecting the flush inlet piping to the crossover or an intermediate stage can reduce the differential pressure.
Incorrect connection point – Connecting the API Plan 14 piping to the wrong connection ports on the mechanical seal can result in leakage to atmosphere or the flush fluid not providing the intended cooling.
General
Troubleshooting of an API Plan 14
Excessive flow can cause:
▪ Cavitation due to the high velocities through the orifices. This can be detected as noise occurring at, or downstream of the orifices.
▪ Erosion of the orifices. This can be detected as a change in seal chamber pressure. It may be difficult to isolate the problematic orifice, but it would most likely be the inlet orifice since that is where the highest flow generally occurs.
▪ Erosion or cavitation damage of the seal chamber throat bushing. This can be detected as an increase or decrease in seal chamber pressure.
▪ Erosion of the mechanical seal from inlet flow impingement directed to a single point. This can be detected as increased atmospheric leakage.
Alternatives to API Plan 14
Alternative piping plans that are similar:
API Plan 11
Flush from discharge to seal chamber
API Plan 13
Flush from seal chamber to suction
API Plan 21
API Plan 11 with heat exchanger
API Plan 31
API Plan 11 with cyclone separator
API Plan 14 Summary
▪ Flow to the mechanical seal is created by the differential pressure between the pump discharge (or intermediate stage in a multistage pump), the seal chamber, and the pump suction.
▪ Flow is used to:
▪ Remove heat generated by the mechanical seal.
▪ Increase seal chamber pressure when used in conjunction with a seal chamber throat bushing to achieve an increased pressure margin above the pumped fluid’s vapor pressure, depending on pump configuration (consult seal provider for piping plan sizing/arrangement).
▪ Prevent the accumulation of debris in the seal chamber.
▪ When connected correctly, the API Plan 14 piping can also allow trapped gases in the seal chamber to vent.
