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Air test instead of hydrotest
5

Air test instead of hydrotest

Air test instead of hydrotest

(OP)
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

RE: Air test instead of hydrotest

shahdadf,
For pressure vessels either is acceptable.  Pneumatic (air or other gas) tests are often specified when moisture or residual water is a problem.
Regards,
RLS

RE: Air test instead of hydrotest

Due to the energy associated with them, there are usually a lot more precautions take with pneumatic tests that include, but are not limited to: 1) increasing pressure in steps, 2) relief valve(s), 3)limiting personnel access to the area during testing.

RE: Air test instead of hydrotest

Also keep in mind that the end user's spec's may require a hydro. This is important since typically a hydrotest will be at a higher pressure than a pneumatic test. I have never seen a vessel in the refining industry which could not be hydrotested when it was fabricated.

Post-construction hydrotests may be difficult to impossible due to several reasons including dealing with water contaminated by the residual process fluid, structural stability, foundation, etc.

jt

RE: Air test instead of hydrotest

In cryogenic servise, the owner may not want water.

RE: Air test instead of hydrotest

dcasto-

Can you explain your comment with regards to cryogenic service with a bit more detail. I do not understand the negative impact of a hydrotest (at reasonably warm temperatures for the purpose of the test) on a vessel in cryo service.

jt

RE: Air test instead of hydrotest

Hi all,

for R&R, normally the vessels are refractory lined.You do not want to test using water as it will damage the refractory lining.In this instance, pneumatic test should be specified.Be aware that during the pneumetic test the stored energy due to the compressability of the air used for the test is much higher and thus more damgerous than with water. For this reason, I have seen R&R specified with 100%RT, and the closing weld is done under more stringent conditions and nde tested thoroughly ("golden weld") in order to eliminate the need for further testing.
John

RE: Air test instead of hydrotest

I would NOT use air or any compressible fluid.

What if it fails?  There is a lot of energy that must be bled off (explode out) in compressed air.

Water, on the other hand, is non-compressible, so as soon as the failure occurs and a little water drains out, the water pressure immediately drops very low.

RE: Air test instead of hydrotest

I hope shahdadf see's that there are very resonable resons to air/nitrogen test a line. It is allow by the codes and standards and there are lots of resons. You need to think about every thing before you fall into the trap, NOT use, what if a 747 falls from the sky. You have to remember that a B31.3 test IS NOT a stenght test, you'll be lucky to get to 25% of yield strenght of the line.

Here is another one where an engineer what if himself, almost out of a job.

We needed a new 24" line in the piperack for natural gas.  The mechanical engineer looked at the existing supports and said they would not hold the weight of an additional new 24" line full of water. NOW WHAT.

The conservative engineer specified that we uninstall the line (cut it into about 8 pieces) and lower it back on the ground rewelded it back, xray 10% and test it with water,then cut it up, put it back in the rack and weld it up and then do a 100% xray on the new welds.  I tried to get him fired, it cost $200,000 vs a air test that would have run about $5000.  Oh to top it off the line fed a cryogenic unit so it took 2 days to dry the line with N2 to a -80F dew point.

RE: Air test instead of hydrotest

dcasto,

Similar to your 24" line saga...A long 24" flare line with all new 15'+/- supports.  Project engineering & management supported a pneumatic test to save money on the support system.  The plan was to take all the necessary and appropriate safey measures during the test.  Just before testing, some nervous nelly in the facility's management had enough stroke and trumped the projects plan.  It took a lot of cranes to support that line.  The couldn't be dumped and had to be transported (via truck) to another location.

Arg...

RE: Air test instead of hydrotest

Guys, guys,
Seems to miss the point. The testing of a new Reactor (which is a pressure vessel) and designed probably to high pressure and high temperature, requires conformance to ASME VIII, UG 99. The pneumatic test is a leak test only, that's way the hydrostatic test is required in the fabrication of pressure vessels, refer below:
UG-99 STANDARD HYDROSTATIC TEST
(a) A hydrostatic test shall be conducted on all
vessels after:
The alternatives are for special conditions only, testing on site, large vessel and no water around, residual water reacting with the process, etc..
Cheers,
gr2vessels

RE: Air test instead of hydrotest

gr2vessels:

Hello again and I do not agree with you.

 UG-100(2)"not readily dried". That is all one needs and according to the first post,may be the case depending on service. You may also exceed 1.1 MAWP if calculated for.

Check the Interps.,UW-50,and last paragraph/first column of the Forward.

RE: Air test instead of hydrotest

One mistake during a pneumatic test can cost someone their life. Not only "during" the test, but before or after the test (when applying and backing off the pressure)
I am quite familiar with an accident at a shop where an inadequately trained,yet qualified individual,lost his life.
Enough said for test procedures and qualifications, which were in place, but not strictly followed. I vowed since that time, never again would I defend the use of a pneumatic in lieu of a hydro.
I knew that people are fallible, but now, it takes more than just words in a Code book to convince me that a pneumatic test in lieu of a hydro is acceptable. Unless you know for certain, and are familiar with the safety concious environment within the shop, and are present around those who will be conducting the test, don't readily allow for pneumatic testing in lieu of a hydrotest.


There are three kinds of people in this world; those who can count and those who can't.

RE: Air test instead of hydrotest

dcasto, it took me a while, but...

So the line AS INSTALLED had no pressure test, just 100% x-ray. What was the point of all that preceeding activity? Could have just x-rayed he whole thing in the rack :)

Regards,

Mike

RE: Air test instead of hydrotest

Yep, thats all part of why I wanted to get rid of the engineer.  Here's another one the guy pulled.  We needed to use a 6" line that was in prior service.  The records and UT test confirmed the line was sch40.  The line had 300# flanges.  The test records showed the pipe was tested at 750 psig, giving the line a 500 psig rating.  The new service required a 600 psig rating.  The engineer would not release the line for new service because of an improper test.  We had to wait 4 weeks to get the line, it cost us about $300,000 in lost revenue.  

RE: Air test instead of hydrotest

The discussion above skirts what I see as the main issue--a properly designed test, executed per the design is safe regardless of the test medium.  I've done tests with air, nitrogen, methane, and water.  Each time I evaluated the environment, the specific piping/equipment being tested, the fluid characteristics, and the code.  For compressible-fluids test-media there are some extra safeguards that are clearly laid out in the code, but following those safeguards in the test-design will result in a safe and effective test.

I've looked at a lot of accidents involving static testing and in every case either the test design was shoddy or the execution didn't follow the design.  I don't think that there is a third reason for "accidents" during static testing.

David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

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RE: Air test instead of hydrotest

zdas04

Thank you

RE: Air test instead of hydrotest

(OP)
Thanks a lot friends,
it was really a good discussion.

RE: Air test instead of hydrotest

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

RE: Air test instead of hydrotest

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

RE: Air test instead of hydrotest

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.

RE: Air test instead of hydrotest

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

RE: Air test instead of hydrotest

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.

RE: Air test instead of hydrotest

TEAM MEMBERS

Please Review ASME PCC 2 2006  

RE: Air test instead of hydrotest

?????????? 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. ponder


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?? ponder

RE: Air test instead of hydrotest

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

RE: Air test instead of hydrotest

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

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