Air test instead of hydrotest 5

[shahdadf]

hi dear friends,
in one of our projects, contractor requested to do Air test instead of hydrotest for Reactor and Regenerator. consultant replied shop hydrotest is acceptable but proper nozzle to be provided for drain the water.
which one is correct???
Thanks a lot

 

[zdas04]

My favorite bone-head static test story was the "engineer" (really closer to a "fry cook" than a "chef") who wrote a 50 page hydrostatic test procedure (cut and paste is a wonderful thing). He was testing 30-inch S20 pipe to 150% of 600 psig MAWP (he thought that the pipe MAWP of 434 psig was close enough to 600 psig, or maybe he didn't look it up) on a pipeline in the rockies. He set his test gauge at the highest point in the line (so he could tie into the vent) not thinking about the 1,100 ft of elevation change over the lenght of the line. He got to 900 psig on his gauge and the pipe held the 1,384 psig at the bottom for almost 15 minutes. Ten miles of pipe drained 2 million gallons of water in about 10 minutes. Washed a car off the road, destroyed a building. I never knew why the pipe failed at 99% of SMYS, that is why we test.

Yep, hydrostatic testing is a lot safer than pneumatic testing, keep telling yourself that.

David

 

[nambutler]

Points to consider:

Hydrotest is a great deal safer
Failure of pneumatic test can be catastrophic both to surrounding equipment and personnel
Hydrotest has stress relieving benefits
100% xray may not show porosity in welds - believe me, I've been caught out with this

As professional engineers, we all need to consider our actions, and asking for advice from others if key. There is a consequence however....when we ask for advice, sometimes it may not be the answer we want to hear, but we should be professional enough to assess and analysis the advice given.

Pneumatic or hydrotest?? My vote goes with hydrotest for 99% of the time. If everything else has been exhausted, maybe a pneumatic.....now about classifying the workmanship as a "golden weld"? This then becomes wholly driven by procedures and checks through the manufacture....ideal conditions, best welder, best ndt, non critical system (low pressure, water etc). If the duty is non critical, then a non tested closure weld may - depending on insurance requirements - be acceptable.

Regards,
nambutler

 

[dcasto]

OK, if we must 100% test everything, including super douper nuclear stuff, after it is assembled, the how did we test an assembled nuclear bomb? I recommend all engineers take a course in SPC and testing.

 

[AravindSujay]

Hi,

Usually it is a general practise that all the pressure vessels will be hydro tested in the field at the time of comissioning. Hydro test will be a better option.

Regards,
Aravind Sujay

 

[Wadoka]

I've used UG-100 pneumatic testing for a few projects. All involved small Code vessels that were filled with a process material prior to closure that could not be exposed to water - zeolite, getter material, that sort of thing. The test pressure in one instance was about 940 psi. We fabricated a plate steel bunker open to the sky and put the vessels in the bunker to test them.

 

[LSThill]

TEAM MEMBERS

Please Review ASME PCC 2 2006

 

[robsalv]

?????????? I can't decide whether this thread is constructive on the matter of hydro versus pnuematic testing.


A fundamental point seems to be missing from the discussion - the purpose of a pressure test.


Why specificaly can't the OP's pressure vessel be hydrotested during fabrication? A reactor vessel isn't fabricated with a refractory lining, so why can't it be hydro'd before the lining goes in? IMO The extra benefits and confidence afforded by a hydrotest, definitely outweighs the short term concerns of drying the vessel out.


A pneumatic test wont get you the benefits (notch blunting, shake down, integrity testing etc) of a hydrotest and has substantially more danger involved - remember, we're testing an untested vessel for it's integrity - the potential stored energy can not be overlooked.


Australia's pressure vessel code includes an appendix to calculate the pneumatic stored energy and the the recommended exclusion zone required for a pneumatic test. If you post up the dimensions, I'll run the numbers. For kicks I sometimes work out the equivalent kg of TNT that a pneumatic test represents - it helps put things in perspective.


If in building a vessel I know that I must do a pneumatic pressure test (and that's rare), apart from many controls during the test, I also specify that the vessel is extensively NDE'd during fabrication. This helps increase the confidence level that there isn't a defect lurking that might cause the vessel to fail.





On the topic of testing and rerating lines, let me ask you this question. Using round numbers, say you have a pipe with 100psi DP, hydrotested to 150psi. Now the process dept need it rerated to 125psi but don't want to get the line wet - so hydrotesting is out. A 1.1DP pneumatic test is still within the original hydrotested envelope... would there be any benefit in a pneumatic test? Do you give the line carteblanche approval to operate at the new condition without any pressure test? Additional NDE??

 

[LSThill]

Team Members:

ASME PCC-2–2006, page 139 -141
Article 5.1, Appendix II
Stored Energy Calculations for Pneumatic Pressure Test

Article 5.1, Appendix III
Safe Distance Calculations for Pneumatic Pressure Test

Article 5.1, Appendix IV
Risk Evaluation Considerations for Pneumatic Pressure Test

Article 5.2
Repairs and Alterations Without Pressure Testing

 

[LSThill]

Team Members:

ASME PCC-2–2006, page 139 -141:

Article 5.1, Appendix II
Stored Energy Calculations for Pneumatic Pressure Test

Article 5.1, Appendix III
Safe Distance Calculations for Pneumatic Pressure Test

Article 5.1, Appendix IV
Risk Evaluation Considerations for Pneumatic Pressure Test

Article 5.2
Repairs and Alterations Without Pressure Testing