Instrument Air Piping Testing 1

[Tuga29]

Hi. We are building a new tank farm and we are having now some problems with our Instrument Air lines testing. They were designed to be threaded and pneumatic tested. The issue is that the construction company is having problems with the criteria of zero leaks during the test (1.1 the Design Pressure, which is 1300kPa). They want to reduce the test to 1.1 the Operation Test (800kPa to 1000kPa). Is there any kind of an acceptance criteria for leakage during testing? Thanks.

 

[DGrayPPD]

What is your code of construction? If B31.3, why not just use a service test at normal operating pressure?

"Thinking is the hardest work there is, which is probably the reason why so few engage in it."

-Henry Ford

 

[Dhurjati Sen]

Dear Tuga29,

The code is B31.3? The material is GI coated CS pipes? Can be tested with DM water at the test pressure. Requires complete drainage of the water after hydro-test followed by nitrogen purging.

Regards.

DHURJATI SEN

https://www.nace.org/people/dhurjatisen

 

[Tuga29]

Yes, the Code is B31.3.

That service test at normal operation pressure possibility is only for Category D fluid service right? Our Design Pressure is 1300kPa.

I don't trust these construction guys to use water testing in these instrument lines.

 

[DGrayPPD]

Ah, I missed the 1300kPa part. My mistake.

"Thinking is the hardest work there is, which is probably the reason why so few engage in it."

-Henry Ford

 

[pennpiper]

Tuga29,
"DO NOT USE WATER TO TEST INSTRUMENT AIR SYSTEMS"

(1) Instrument Air Systems (IAS)/Lines are one of the most critical systems in a Process Plant. The IAS system should be installed with special care, by carefully trained workers and kept as dry and as clean as possible.
Introducing water into an IAS system will start corrosion and contamination throughout the whole system that can never be removed.

(2) Are you real sure about the "1300kPa"? It sounds like it's way higher than the normal Instrument Air system would normally have. Remember, Pneumatic instruments are very fragile.

Sometimes its possible to do all the right things and still get bad results

 

[EdStainless]

If these are threaded then you expect some minor leakage.
After all the thread sealant is the only thing actually sealing them.
I have seen such systems where there is an allowed (but very low) leak rate.
Getting zero in this system may be a dream.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[LittleInch]

The issue is the criteria of "Zero" leaks.

How is "Zero" being measured? With soapy bubbles? so one bubble every ?? seconds is a failure?

There has been much discussion previously on threaded joints and seal welding / welded joints and the comment often made that sealing threaded joints over a large plant is effectively impossible if the criteria is so stringent as "zero"

Amend the criteria.

This is Instrument Air. Someone needs to get real. I would aim for class IV valve leakage rates (metal to metal seal)

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[mk3223]

IMO, the Instrument Air piping can be service tested with the normal operation pressure if meet the B31.3 Cat. D fluid definition. Of course, it's subject to the Owner's approval.
I thought the experienced Contractor may tight up the screwed joint with the proper joint sealant, the screwed piping can be free of leaking.

 

[Tuga29]

The big issue that we are dealing is that the manufacturer is having leaks. They ddin't tell us yet the gravity, but it doesn't seam good. That's why I would like to know and asked about an acceptance criteria. They asked us if they could only do a service test... it seams they don't have leaks at that pressure. But according to the code we are above the Design Pressure to consider Category D fluid.
Testing at 1.1x1300kpa... what could be an acceptable pressure drop?

 

[mk3223]

@Tuga29
As stated that the design pressure of the instrument air piping is 1300kPa, what's the maximum "operation" pressure of the system?

I don't know any acceptable leak rate for the thread piping testing, because it could be leaking from the multiple screw joints.

 

[Tuga29]

The maximum operation pressure, given by the Design team, is 1000kPa.

 

[DekDee]

A bit lost following this post.
What pressure are the fittings rated for ?
If they are rated in excess of 1300 kpa x 1.1 then there should be zero leaks (if the installer knows what they are doing).
If less than then there is obviously a problem.
Unfortunately there is no alternative acceptance criteria - either instruct your contractor to provide a code-compliant system or take the responsibility yourself and accept it as non code compliant system.
As noted previously - it is only instrument air.