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How to Prevent Gas Regulator Failures

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Gas regulators are at the forefront of process control.  Engineers and technicians rely on them to maintain precise pressure control often under severe conditions.  Regulators are taken for granted until they fail, then confusion reigns.  Here are tip on how to prevent Regulator failure, improve corrosion resistance, and keep your calibration or process gas system running at it's best.

Regulators may seem simple, gas goes in at one pressure and comes out at another, hopefully lower, pressure; simple right?  Well there's a lot going on inside that block of steel that can go wrong.  Take a regulator apart and you'll see lots of parts, all of which are precision components that can cause loss of process control and can result in a potentially hazardous conditions.  

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How to prevent gas regulator failures

The single stage regulator section drawing below shows that a typical regulator consists of lots of moving parts.  The wetted Flow Path (area below the diaphragm) can be compromised by environmental and internal process gases.  The regulator body is not the only component to worry about.  The diaphragm, poppet, seat, closing spring, and filters can all be problem areas if regulators are not properly maintained and specified.

Single stage regulator drawing-072890-edited.gif

OK, there are lots of potential problem components, what can I do to be sure I don't have a gas regulator failure?

Set up a maintenance plan to manage problems.  Companies like Air Liquide, or Concoa offer general maintenance guidelines that are a good starting point for crafting your own gas regulator maintenance plan.  The maintenance schedule from Air Liquide (below) is a good example of a general maintenance plan.  Your plan should be tailored to your process environment and Flow path conditions.

Maintenance Schedule

SERVICE
LEAK
CHECK
CREEP
TEST
INERT
PURGE
OVERHAUL
REPLACE
Noncorrosive
Monthly
annually
Not Applicable
5 years
10 years
Mildly corrosive
2x Month
6 months
at shutdown
2 years
4 years
Corrosive
2x Month
3 months
at shutdown
1-2 years
3-4 years

Taking additional steps

Chemical process, oil & gas, semiconductor, and analytical laboratories face problems specific to their industries, but all can benefit from taking some additional steps to improve regulator performance.  Wise material selection, including inert, corrosion resistant coatings can improve regulator corrosion resistance, inertness, and moisture management.  Here are some examples:

Corrosion

Often compressed corrosive gases like hydrochloric acid, ammonia, H2S, or HBr are anhydrous which generally reduces the risk of corrosive attack.  Unfortunately, internal flow paths can be exposed to ambient moisture during cylinder changes which can dramatically increase corrosion and pitting which can impair performance or lead to failure.  Pitted surfaces can be great hiding places for analytes or corrosives which can lead to carry-over.  Selecting a corrosion resistant material like Dursan® to line the flow path will extend the life of surfaces by 10x or more.  The hydrochloric acid example below demonstrates the improved corrosion resistance of a Silcolloy® or Dursan® coated surface.  After 24 hours of immersion in 6M HCl, the stainless steel coupon is severely corroded with a very high 160 mpy corrosion rate.  The Dursan coated test coupon shows minimal corrosion after the same exposure.

Dursan_HCl_corrosion-263514-edited.jpg

Inertness

Gases move through a somewhat tortuous regulator flow path which includes exposure to filters, seats, bodies, chambers, and diaphragms; all of which can adsorb reactive calibration gasses.  VOC's, H2S, ammonia, and others can react with and be adsorbed by stainless steel or other alloy surfaces.  This can impact calibration results, especially when calibrating low level or trace gas samples. 

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Lining the flow path and filter surfaces with SilcoNert or other inert coatings will minimize adsorption.  Even sintered metal filters can be coated without significant impact to filtration or flow.  The comparative ammonia adsorption study below shows that SilcoNert® 2000 coated stainless steel is less adsorptive and more inert than PTFE and PFA.  Stainless steel surfaces are extremely reactive which can distort calibration results.*** Read the complete ammonia adsorption presentation.

Ammonia_Adsorption_Graph.jpg

Freezing and moisture management

High flow, low ambient temperatures and moisture can result in freezing and failure of the regulator.  Heated regulators or heat jackets will prevent freezing but won't address the underlying moisture contamination.  Moisture can build up in flow paths, exacerbating freezing and increasing failure potential.  Hydrophobic coatings like Dursan repel moisture and prevent build-up on the regulator body or other components, reducing purge time and making regular purge cycles more effective.  The graph below compares stainless steel vs. hydrophobic Dursan moisture purge time.  Saturated surfaces were dried at the same rate.  The Dursan surface released moisture over 3x faster than the uncoated stainless steel surface.

Moisture_purge_time.jpg

Particulate management

Particles in the flow path can interfere with gas regulation.  The solution is to install a fritted metal filter in the flow to capture particles.  Unfortunately the extreme surface area in filters can react and adsorb calibration gas samples and distort calibration results.  Don't throw out that filter and risk particulate damage, treat the filter with SilcoNert® or Dursan® to prevent adsorption, improve corrosion resistance and keep the flow path particulate free.

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SilcoTek® offers coating services but we also team up with manufacturers to make it easy for the customer to buy coated products.  Go to our web page to find manufacturers offering coated products.  Or contact our Technical Service Team to discuss your application. 

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*Image credit: Air Liquide.  https://industry.airliquide.us/single-stage-versustwo-stage-regulators

** Image credit: ASGE.  http://www.asge-online.com/Regpg21.html

***Data credit: Olavi Vaittinen1,Markus Metsälä1, Stefan Persijn2, Markku Vainio1,3 and Lauri Halonen1
1 University of Helsinki, Finland
2 VSL, The Netherlands
3 MIKES, Finland



This post first appeared on SilcoTek Coating, please read the originial post: here

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How to Prevent Gas Regulator Failures

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