Swagelok Tech BitsISSUE 3

2-3Understanding how Supply-Pressure E�ect, Joule-Thompson E�ect and Hysteresis a�ect the performance of pressure regulators

4-6Basics of Bu�er and Barrier Seal Support Plans

7-8What is Grab Sampling forLiquid System?

In ThisIssue

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- by Rajasegaran A/L Munion

Understanding how Supply-Pressure E�ect, Joule-Thompson E�ect and Hysteresis a�ect the performance of pressure regulators

Supply-pressure e�ect (SPE) or dependency is a ratio describing the change in outlet pressure per 100 psi (6.8 bar) change in inlet pressure. In other words, for every 100 psi (6.8 bar) drop in inlet pressure, the outlet pressure will increase by X psi. X is the SPE. For standard pressure-reducing regulators, the outlet pressure increases as supply pressure decreases. The opposite is true as supply pressure increases. This e�ect can also be realized on system start up or shut down.

To understand more on SPE, see Figure 1. This regulator is placed on gas cylinder outlet, where the initial pressure of the gas cylinder is 3600 psi and downstream of the regulator is set at 50 psi. As the pressure source from the gas cylinder depletes from 3600 psi to 2600 psi, you may now see an increase of 10 psi at the downstream of the regulator from the initial set pressure of 50 psi. The 10 psi increase at downstream of the regulator is observed based on the consideration that this

Supply-PressureE�ect

regulator has a SPE of 1% with reference to manufacturer product literature/ catalogue.

SPE is mostly experienced on a gas cylinder or tank application where the source depletes overtime due to application demands. It is recommended to use 2 stage regulator or balanced poppet design regulator to reduce the SPE.

Figure 1

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Hysteresis

Do you encounter icing on your regulator as shown in Figure 2, if yes then most probably your regulator is experiencing Joule Thomson e�ect. Joule Thompson e�ect occurs when the pressure of a gas is suddenly reduced, the heat energy needed for expansion has no time to flow into the gas from surrounding metal so it has to come from the internal energy of the gas itself. This loss in energy causes gas to cool down which is also known as adiabatic cooling. The average temperature drop is 1° Celsius for every 2 bar pressure drop. Hydrogen, Helium and Neon take exceptions to this phenomenon as they heat up when the gas pressure is suddenly reduced.

These swings in temperature can adversely a�ect a regulator’s function and harm the components. Transporting the fluid while controlling the temperature and pressure in stages may reduce this e�ect and prolong the life of your system. Additionally, the use of heated regulators, and utilizing 2 stage regulator to drop the gas pressure in stages may help to address this issue.

Hysteresis results from dynamic friction forces within the regulator but is usually not an issue when evaluating the performance of a regulator. However, it can be a point of confusion during system operation. See Figure 3 above. When reading left to right, flow is increasing. And the reverse is true when reading right to left. Depending on whether flow is increasing or decreasing, the curve di�ers slightly. Outlet pressure does not follow the same “Droop line” (Droop- known as reduction in outlet pressure, as the flow demand increases) or end at the original set pressure. This phenomenon is called hysteresis.

Let’s look at an example to understand more on Hysteresis, suppose an operator sets up a system to deliver an outlet pressure of 50 psig (3.4 bar) at 110 std ft3/min (3115 std L/min). The next day, the pressure is now 50.5 psig (3.48 bar), but the flow is still 110 std ft3/min (3115 std L/min). It is likely that something in the system temporarily created more flow demand downstream. Moving from left to right on the flow curve (Figure 3), the temporary flow increase slightly reduced the outlet pressure. Then, as the flow demand returned to 110 std ft3/min (3115 std L/min), hysteresis caused the outlet pressure to return to a point slightly higher than the initial set point. Hence it is recommended to approach set pressure from a lower pressure. Another best practice is to employ pressure gauges in the system to help fine tune regulator settings to achieve desired operating pressures.

Joule-ThompsonE�ect

Figure 2

Figure 3

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What is a Bu�erFluid Plan?

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An unpressurized fluid system with a reservoir (seal pot) that is used to provide cooling or lubrication to fluids with poor lubricating characteristics, such as light hydrocarbons

Bu�er fluids should have a lower vapor pressure than the sealed fluid

Allows the process fluid leakage to bubble through the bu�er fluid and be vented to flare

What is BarrierFluid Plan?

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It is a pressurized fluid system with a reservoir (seal pot) that is used when the process fluid must be isolated from the environment to prevent flashing, crystallization, polymerization, or when the pumped fluid is toxic/hazardous

Barrier fluids are usually pressurized 15-30 psi above the seal chamber pressure

Basics of Bu�er and Barrier Seal Support Plans– by Alfred Low

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Plan Description Design

Plan 51 •

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Dead-ended to quench connection

Used with auxiliary sealing device

Valve closed before startup

Plan 52 •

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Unpressurized bu�er fluid circulated with pumping ring

Cooling coils in reservoir (optional)

Typically coupled with a flush plan

Note: Per API 682, this plan is only recommended for vertical pumps, but in practice it has also been used on horizontal pumps.

Note: A bu�er fluid drain is to be located on the lower point of the bu�er inlet.

Typical Reservoir(Seal Pot) Requirements

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2 types of configurations- Fully welded- Flanged end (for cleanout)ISO 15649 or ASME B31.3 compliant

• Typical volumes- 12L (≤60mm pump shaft)- 20L (>60mm pump shaft)

Plan 53A •

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Pressurized barrier fluid

Cooling coils in reservoir

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Source: Swagelok Mechanical Seal Support Systems Training

Plan Description Design

Plan 53B •

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Bladder accumulator isolates pressurizing gas from barrier fluid

Prevents gas entrainment in barrier fluid

Note: A barrier fluid drain is to be located on the lower point of the barrier inlet.

Note: A barrier fluid drain is to be located on the lower point of the barrier inlet.

Plan 53C •

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Piston Accumulator (intensifier) references seal chamber pressure and provides positive di�erential to barrier fluid

No external pressure source

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Closed loop systems provide a sample that is fresh, extracted and held under the same process conditions that existed at the time of the sample. The precision of your facility’s chemical products relies on the ability to collect accurate samples. Grab sampling is one way for your plant to reduce costs iteratively through consistently accurate sample grabs—diminishing product waste.

Here are some grab sampling modules designed for liquid sampling. It can be customised to your needs depending on whether you require a fastloop or purge feature.

GSM-L-1(-N)Standard Liquid Sampler without Purge

Use:General use for liquid sampling

Recommended for:• Fluids that are non-toxic and are not susceptible to settling in the sampler • Fluids with sample return sent to atmospheric drain or open drain Front Back

What is Grab Sampling forLiquid System?– by Sharon Sng

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GSM-L-1(-P)Standard Liquid Sampler with Purge

Use:General use for liquid sampling. Purge option (using gas or a solvent) clears fluid before and/or after sample collection.

Recommended for:• Fluids that are toxic or may settle in the sampler • Fluids with sample return sent to closed drain Front Back

GSM-L-2(-N) Continuous Flow Liquid Sampler without Purge

Use:General use for liquid sampling when continuous flow is required from inlet to outlet.

Recommended for:• Liquids that are non-toxic and are not susceptible to settling in the sampler • Samplers installed directly in the sample stream, on a fast loop, or where long sample transport lines are used

GSM-L-2(-P)Continuous Flow Liquid Sampler with Purge

Use:General use for liquid sampling when continuous flow is required from inlet to outlet. Purge option (using a gas or solvent) clears the sample fluid from the sample transport lines before and/or after sample collection.

Recommended for:• Liquids that are toxic and may settle in the sampler • Samplers installed directly in the sample stream, on a fast loop, or where long sample transport lines are used Front Back

Front Back

For technical queries, please email us at inquire@swagelok.com.sg

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