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API 598 closure leakage bubbles compared to milliliter
2

API 598 closure leakage bubbles compared to milliliter

API 598 closure leakage bubbles compared to milliliter

(OP)
Hi,

API STANDARD 598 TENTH EDITION, OCTOBER 2016 says:
a: For the liquid test, 1 mL is considered equivalent to 16 drops. For the gas test 1 mL is considered equivalent to 100 bubbles.

So for a 8in Valve for example which has a allowable leakage rate of 32 bubbles/min it would be less than a mL.
A !48in! valve would have a leakage rate less than 2 mL!

I can not believe this strict leakage rates.
Is this correct?

RE: API 598 closure leakage bubbles compared to milliliter

Per MSS SP-61, Pressure Testing of Valves, Table 4, Note (b), 25 bubbles is 1 ml, which is the equivalent of a spherical bubble having an approximate diameter of 5/32 inch (0.4 mm).

Per ANSI/FCI 70-2, Table 2, 1 bubble equals 0.15 ml, so 6.67 bubbles equals 1 ml.

Both MSS and FCI explain how the bubble size is determined. API 598 also explains how bubble size is determined in paragraph 5.9.2.5, and it is essentially the same as FCI 70-2. Clearly API 598 is wrong. API 598 is due to be revised next year (every 5 years). I expect that this will be corrected in the next revision.

RE: API 598 closure leakage bubbles compared to milliliter

(OP)
As said in API 598, P 5.9.2.5, measured by mylself and colleagues a bubble = 0.35ml. But this Standard is very un-specific. I mean you can choose a tubing between 2-4mm thats a big difference. Also it makes a big difference if you put the tubing 3 or 6mm deep into the water…
But like you said… this standrad gets revised soon and hopefully they correct it!

RE: API 598 closure leakage bubbles compared to milliliter

We are revising API 598, however, there are currently no plan to update this area. The 2 ml/min is written mainly to address low pressure gas test with isolation valves and valve manufacturers currently have no problem meeting this requirements.

If there are desired wording changes, perhaps to section 6.5 High-pressure Closure test, please propose it and I can propose it.

Thanks,

Luke | Valve Hax | https://valvehax.com/

RE: API 598 closure leakage bubbles compared to milliliter

(OP)
Sure at low pressure gas test @80psi (5,5bar) usually it is not a problem.
But what about an gas test for example an 8in CL600 or even CL2500 valve at around 1500psi (103bar) or 6000psi (430bar).
I am pretty sure then it is nearly impossible to meet 0,32ml/min for 8in metal seated ball valves (I work as an engineer for a large ball valve company).
For my understanding there should be a different leakage rate table for high pressure testing.
Shell MESC SPE 77-300 Standard which is widely known in ball valve Industrie for beeing very strict for example refers to ISO 5208 rate B at ambient temp which would be 3,6ml/min for an 8in valve.

Also i have a Problem with the bubble to ml comparsion. We set up the tube in water like in API 598 and compared a bubble to ml with a calibrated flow meter.
Always one bubble is around 0,4ml which would be 13ml/min or 32b/min for 8in Valve. This is what my compandy assumes for decades… Also customers like Shell, Total, ExxonMobil did not complain ever
during acceptance tests.

RE: API 598 closure leakage bubbles compared to milliliter

just fyi, the meeting this fall will be digital in format, perhaps you'd be interested in joining and see what happens. Additionally, if you guys have documented experiment results from the bubble to ml conversions, we will definitely take that into consideration and perhaps make updates.

Thanks,

Luke | Valve Hax | https://valvehax.com/

RE: API 598 closure leakage bubbles compared to milliliter

(OP)
Thanks for the Information!
I will check if it is possible to document the experiment properly within the next days.

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