API Plan 13

API Piping Plan 13 FSA Knowledge Series

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Abstract This Fluid Sealing Association Knowledge Series training presentation introduces API Piping Plan 13. A description is provided on: ▪ What is an API Plan 13?

▪ How an API Plan 13 Works ▪ What does an API Plan 13 do?

▪ What an API Plan 13 cannot do ▪ Optional Features for an API Plan 13 ▪ Cost to Operate With an API Plan 13 ▪ How to Size a Plan 13 ▪ How to Install an API Plan 13 ▪ General API Plan 13 Commissioning Guidelines ▪ How to Operate an API Plan 13 ▪ General Troubleshooting of API Plan 13 ▪ Alternatives to API Plan 13 3

What Are Piping Plans?

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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.

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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.

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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 13?

API Plan 13 is the most common flush plan used in vertical pumps. This flush plan simply taps into a pressure source lower than the seal chamber pressure, typically the pump suction, and pipes process fluid from the seal chamber to the low-pressure source to provide continued venting of the seal chamber and cooling of the seal faces.

Flow direction

Pump suction flange 5

Flow controlling orifice Mechanical seal or seal chamber “Flush” connection

How an API Plan 13 Works An API Plan 13 works by creating flow using differential pressure between the pump suction pressure, and the pressure downstream of the seal chamber.

The direction of flow is from the high-pressure source, the seal chamber, to the lowpressure point, downstream of the seal flush port. This fluid flow enters the seal chamber through the seal chamber throat, and Flush fluid exit exits through a flush port located in either the from the seal chamber mechanical seal gland plate or seal chamber wall.

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As the fluid source is from the pump, the fluid flowing through the interconnecting piping and seal chamber is the same fluid that is being pumped.

Flush fluid entry to seal chamber

How an API Plan 13 Works The flowrate of fluid through the seal chamber can be controlled by adding flow control features. These features include: Flow Controlling Orifice Pipe/Tube diameter selection Flush hole diameter

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Seal chamber throat bushing clearance

What does an API Plan 13 do?

The flow of fluid through the seal chamber created by an API Plan 13 can be used to:

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Continuously remove any trapped gases in the seal chamber.

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Remove heat generated by the mechanical seal.

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Decrease seal chamber pressure when used in conjunction with a seal chamber throat bushing.

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Prevent the accumulation of debris in the seal chamber.

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Provide flow through the seal chamber when the differential pressure between the seal chamber and pump discharge is low (i.e. alternative to an API Plan 11).

What an API Plan 13 cannot do

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Cannot isolate the seal chamber from process fluid.

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Cannot remove debris from the seal chamber if flow is low.

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Cannot cool the process fluid flowing to the seal chamber.

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Cannot decrease seal chamber pressure without seal chamber throat bushing.

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Cannot lower emissions to the atmosphere.

What an API Plan 13 cannot do The main purpose of an API Plan 13 is to create flow through the seal chamber.

Sufficient flow cannot be created reliably when:

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Fluids freeze, solidify or thicken within the external piping

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Fluids containing high solids and abrasives that abrade and wear the flow controlling components

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Fluids that contains large particles that can clog the flow controlling components

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Fluids that polymerize and can clog the flow controlling components

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Pumps that have a low-pressure differential between the seal chamber and pump suction that is too low to generate sufficient flow

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Valves are installed in the piping to control flush flow

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Mechanical seal designs utilizing a distributed flush

Optional Features for an API Plan 13 Optional flow control types ▪ Flat Plate Orifice: Narrow plate with a small flow-through hole that restricts flow within the API Plan 13. These are commonly constructed from piping components and can be assembled either seal welded or threaded. Often used in hazardous fluid pumping applications.

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Threaded Joint

Seal Welded Joint

Optional Features for an API Plan 13 Optional flow control types

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Compression tube fitting with inbuilt orifice restriction.

Constructed using commercially available tubing and compression tube fittings. Offers great flexibility in installation and assembly.

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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 13 Optional flow control types

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Threaded coupling with inbuilt orifice restriction. Often custom fabricated from hexagonal bar stock to meet the design needs.

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Choke tube: Length of smaller bore tube, possibly coiled, utilizing flow resistance to reduce the flow through the API Plan 13. Used to control flow rates when high differential pressures exist.

Optional Features for an API Plan 13 ▪

To control flowrate 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 12 inches (300 mm) apart

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Pressure gauges can be installed upstream and downstream of the orifice to provide the ability to calculate the flow rate

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A temperature gauge can be added to measure the temperature of the flush fluid being delivered to the seal chamber. When installing, ensure the tip of the temperature gauge or thermowell does not obstruct the flow through the piping.

Temperature Gauge Thermowell Eccentric reducers to expand pipe size in region of the thermowell tip

Cost to Operate with an API Plan 13 There is a cost associated with operating an API Plan 13. 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 Plan 13 flush piping and is eventually returned to the suction of the pump.

The fluid that has flowed through the API plan 13 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 13 flush flow rate versus the total pump flow rate: 𝐴𝑃𝐼 𝑃𝑙𝑎𝑛 13 𝑃𝑜𝑤𝑒𝑟 = 𝑀𝑜𝑡𝑜𝑟 𝑃𝑜𝑤𝑒𝑟

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𝐴𝑃𝐼 𝑃𝑙𝑎𝑛 13 𝐹𝑙𝑜𝑤 𝑅𝑎𝑡𝑒 𝐴𝑃𝐼 𝑃𝑙𝑎𝑛 13 𝐹𝑙𝑜𝑤 𝑅𝑎𝑡𝑒 + 𝑃𝑢𝑚𝑝 𝐹𝑙𝑜𝑤 𝑅𝑎𝑡𝑒

Cost to Operate with an Plan 13 Typically, the volume of flush is very small compared to the capacity of the pump and therefore the efficiency effect is very small.

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Energy to operate

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Carbon footprint

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Initial investment

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Cost of operation

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Refer to the Fluid Sealing Association’s Lifecycle Cost Calculator (LCC) for a more detailed analysis.

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How to Size an API Plan 13 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 with volatile or hot pumped fluids.

The Fluid Sealing Association recommends working with your mechanical seal vendor whenever 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 need:

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Mechanical seal heat generation

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Target flow rate

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Actual flow rate through the API Plan 13 piping system

How to Size an API Plan 13 Seal heat generation is influenced by many factors, including seal design, materials of construction and balance ratio. The governing formulae are: 𝑃𝑓𝑎𝑐𝑒 = ∆𝑃 𝐵 − 𝐾 + 𝑃𝑠𝑝𝑟𝑖𝑛𝑔 𝑄ℎ𝑒𝑎𝑡 = 𝑃𝑓𝑎𝑐𝑒 𝑉𝐴𝑓 Where: Pface = Seal face contact pressure ∆ P = Differential pressure across the seal faces (Sealed Pressure) 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 18

How to Size an API Plan 13 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:

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8°C (15 °F) for water and low volatility hydrocarbons

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16°C (30 °F) for lubricating fluids

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3°C (5 °F) for volatile/flashing hydrocarbons

Frequently the target flush rate is relatively low, often less than 4 l/min (1 GPM) 19

How to Size an API Plan 13 The temperature rise occurring with a heat input and ideal mixing occurring can be calculated by: 𝑄ℎ𝑒𝑎𝑡 Δ𝑇 = ṁ𝐶𝑝 Where: Δ𝑇 = Temperature rise (T2 – T1) Qheat = Seal heat generation ṁ = Flush fluid mass flow rate Cp = Fluid specific heat

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How to Size an API Plan 13 The actual flow through an API Plan 13 piping system can be quite complex. Typically, the known pressures are the pump suction and discharge pressure. To calculate the flow the intermediate pressures must be calculated through an iterative process: P1 Impeller

P2 Seal Chamber

Gland Orifice P3

P4 Pump Suction

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Orifice Plate

How to Install an API Plan 13 An API Plan 13 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.

When using piping components, the orifice is formed With a plate having a central hole sandwiched between 2 flanges with gaskets.

When using tubing 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 inch).

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How to Install an API Plan 13 API 682 recommends: ▪ For shaft diameters up to 60 mm (2.5 inch): ▪ ▪

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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.

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How to Install an API Plan 13 To achieve self venting of the seal chamber, the flush connection should exit the seal chamber at the highest point

High point flush connection

Horizontal Shaft 24

Vertical Shaft

General API Plan 13 Commissioning Guidelines To commission an API Plan 13: 1) Using the mechanical seal assembly drawing, verify that the flush piping is connected to the correct port in the mechanical seal.

2) Check that the orifice size has been indicated on the externally visible surfaces of the orifice.

3) With the pump casing primed, vented, and pressurized prior to startup, check all the joints on the API Plan 13 for leaks. Correct any if found.

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How to Operate an API Plan 13 Operation of an API plan 13 is inherently connected to the operation of the pump. As soon as the pump generates a differential pressure, flow will automatically occur through the API Plan 13 piping.

Periodically check for leaks at the joints There are no external adjustments that can be made to an API Plan 13 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.

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General Troubleshooting of an API Plan 13 As flow is continuously moving through the API Plan 13 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 are 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 duty, in climates where winter temperatures are low, or wind that can cool the external piping.

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General Troubleshooting of an API Plan 13 Inadequate or excessive flow – An improperly sized orifice can result in excessive or insufficient flow rates for the mechanical seal. For between bearings pumps, the API Plan 13 for both ends of the pump may terminate into a common connection to the pump suction. The piping design and orifice locations need to ensure flow is distributed evenly from each seal.

Incorrect connection point – Connecting the API Plan 13 piping to the wrong connection port on the mechanical seal can result in the flush fluid not providing the intended cooling, or possibly leakage to atmosphere.

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General Troubleshooting of an API Plan 13 Excessive flow can cause:

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Cavitation due to the high velocities through the orifice. This can be detected as noise occurring at, or downstream of the orifice.

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Erosion of the orifice. This can be detected as increased seal chamber pressure

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Erosion or cavitation damage of the seal chamber throat bushing. This can be detected as an increase in seal chamber pressure.

Alternatives to an API Plan 13 Alternative piping plans that are similar:

API Plan 11 Flush from discharge to seal chamber

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API Plan 21 API Plan 11 with heat exchanger

API Plan 14 API Plan 11 plus API Plan 13

API Plan 31 API Plan 11 with cyclone separator

API Plan 13 Summary ▪ ▪

Flow to the mechanical seal is created by the differential pressure between the seal chamber and the pump suction.

Flow is used to: ▪ ▪ ▪ ▪

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Provide continuous venting of the seal chamber.

Remove heat generated by the mechanical seal.

Decrease seal chamber pressure.

Prevent the accumulation of debris in the seal chamber.

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