ASME B31.3: Clarification on inspection and testing for low pressure low temperature piping 1

[SGHO]

I would like to design an argon gas recirculation system where the fluid temperature will not go beyond 40 ^oC. Maximum pressure (Design pressure) of the piping system will not be more than 1000 mm of water column. The piping system comprises of 1/2-inch, 1-inch, 1-1/2-inch and 2-inch seamless pipes connected to each other by butt weld fittings (elbows (long radius), concentric reducers etc.). for such application, can we recommend (or insist on) X-ray radiography of welds or qualification by only liquid penetrant examination is sufficient. ASME B31.3 2014 341.4.1 (b)) suggests 5% random sampling of welds for each pipe lot and subjecting them to radiography.

Can I get some more clarification on the application of B31.3 for such piping application? Total number of weld joints in this case is not more than 100.

Thank you

SGH

 

[XL83NL]

Hi, and welcome to eng-tips.

for such application, can we recommend (or insist on) X-ray radiography of welds or qualification by only liquid penetrant examination is sufficient. ASME B31.3 2014 341.4.1 (b)) suggests 5% random sampling of welds for each pipe lot and subjecting them to radiography.

First of all, you dont recommend Xray, short RT. The Code, B31.3, tells you when RT is required (or, as you mentioned, it insists on, although I wouldnt use such a phrase). Same for other types of NDE, like dye penetrant testing or PT.
What do you mean by qualification of NDE? 'Qualification' (using NDE) that your system meets design code requirements? Usually, when such terms are used, people mean qualification of welding procedure or welder performance qualification. I know, it's semantics, but when it comes to Code issues, such words play an important role.

Ultimately, your Fluid Service will determine the scope of your NDE. Given the details provided, I assume this would Normal Fluid Service. Then, 5%RT per 341.4.1(b) is required. Make sure you, your client and your contractor understand what a designated lot is.

 

[DekDee]

Agree 100% with XL83NLs comments.
What is your design pressure ?
You may well fall under Cat D which doesn't require testing but as the designer you can stipulate anything you want (with the Client/Customers approval)

 

[moltenmetal]

At a pressure of 1 metre of water column (much less than 15 psig) and 40 C, you are below the scope of any pressure piping design code. You can do whatever you and the owner like. You can do any level of RT, or no RT.

But if you claim that you're going to meet B31.3, you have to actually follow B31.3. B31.3 doesn't waive the RT requirement but will allow clients to waive the pressure integrity test (mislabelled "leak test" in the code) with owner permission for Category D (nonhazardous) services, which it certainly sounds like yours would be.

 

[XL83NL]

mm is right. This may as well be put outside the scope of B31.3.

 

[DekDee]

MM,
Agree with your comment regarding being outside the scope of the code but respectfully disagree with the comment regarding RT.
" B31.3 doesn't waive the RT requirement"
Category D does not require any RT.
Regards,
Shane

 

[SGHO]

Sirs,

Thank you very much for the responses. I would like to slightly modify the specifications of the argon gas. Keeping all the experimental conditions same, if we assume that argon has 0.005% probability of containing Cd vapours (chemically hazardous) and <0.001% probability of radioactive aerosols, then whether we require 5% RT, 100% RT or not at all.

Does pressure integrity test sufficient for the above case as well?
Thanks

 

[moltenmetal]

DekDee has it right- it's been a while since I built anything Category D that required welding that could be inspected meaningfully by RT. We usually do this kind of piping threaded or with Victaulic type connections.

So the OP's question now is what RT is appropriate, given that there is a (low) hazard to personnel associated with the compounds in the low pressure, low temperature recirculating argon.

My feeling is that RT would be less useful than a high integrity leak test for this kind of service. Using 5% spot random RT would probably be appropriate just to keep the welders honest.

 

[XL83NL]

Using 5% spot random RT would probably be appropriate just to keep the welders honest.