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TOPIC: Pressure Testing requirement for Natural GasPiping

Pressure Testing requirement for Natural GasPiping 4 years 8 months ago #8793

  • AbhijitN
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Dear all knowledgeable fellow pipers,
We have a 20” NG piping going to the customer after metering now I want to know the Testing criteria for the same.
This came in picture when we were designing our sleepers safe support spans. If we need hydro test for this line that means I need to consider liquid filled weight of this pipe & if we can live with Pneumatic test then I can straight away consider this as gas filled weight for the support spans from the standard span chart.

I read in NFPA-54 that it need to gas tested with test medium as-
8.1.2 Test Medium. The test medium shall be air, nitrogen, carbon dioxide, or an inert gas.
OXYGEN SHALL NEVER BE USED.

However I am not sure with the governing codes itself for this situation. Is it ASME B 31.3 as it is inside plant situation.
if yes, pls guide me to the exact point.

Design Pressure- FV/98
Design Temp.- -20/60
Material-LTCS
Class- 600#
Non-insulated

I also read in a company standard Pneumatic testing is not a recommended one. So it is all becoming very confusing for me.

Can somebody help me out at the earliest?

Pressure Testing requirement for Natural GasPiping 4 years 8 months ago #8794

  • Jop
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Abhijit,
You have three issues here that need to be addressed.
1. Pipe support spacing
2. The Code
3. Safety

Issue #1 - This Pipeline has the potential for being used to transport either a Gas or a liquid. There is also the possibility for additional lines (Liquid or Gas) to be added in the future to this same rack, therefore you should always set your pipe support spacing for liquid filled lines. If you study the spacing of supports for your line size (you did not tell us the line size or the distance), a gas filled line and for a liquid filled line what is the real difference in the number of supports?
Issue #2 - You mentioned ASME B31.3, Is this the actual Code in effect for this part of your Project? If so, what does the Code say about the testing of this line? What does the Client say about the testing of this line? Is there an 'Authorized Inspector' (AI) involved in this situation, if so what does he say?
Issue #3 - Safety should be your primary consideration. Hydro Testing is considered the safest way to test a piping system. Why would you consider any other method?
Do it once and Do it Right

Pressure Testing requirement for Natural GasPiping 4 years 8 months ago #8796

  • AbhijitN
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Thanks for the reply Jop.

Issue #1 - Line size is 20" gas transport line. & the distance of travel is 500 meters.
The difference in the spans Liquid v/s gas is as follows 18 v/s 11 which is a considerable difference.

WRT the ASME B 31.3 it is mentioned that “345.3.2 Temporary supports. Piping designed for vapor or gas shall be provided with additional temporary supports, if necessary, to support the weight of test liquid."

So the conclusion would be Design the sleeper for vapor filled spans however the provision for temp. Test supports are to be taken care for Hydro test.

Issue #2- ASME 31.3 talks about both type of test hydro as well as pneumatic however our company std. gives a caution on pneumatic testing should be only used when we can't do hydro testing & pneumatic testing decision is mostly discouraged. Issues in Hydro testing like corrosion or where the traces of any liquid testing medium can't be acceptable etc. but it seems in my case of NG the hydro test will not be an issue as long as we clean it with hot air, steam etc. (what you guys think? is it ok for NG service).
AI in not involved in this situation however I think I need figure out if I can get him in.

Issue #3 - Agreed as per my company std. however the Code talks about both. SAFETY consideration says Hydro test if for NG service the traces of water is not an issue.

I think I have got some idea now with this research & Jop's answer that
1-Hydrotest is a way forward.
2-Support span to be considered should be preferably for liquid service but check with civil for cost impact about the sleeper design & decide whether we can live with vapor span & introduce temp. Supports when hydro testing.

Thanks Jop for the guidance & also all of you pls provide inputs for the said situation.
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