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

 

[lostsailor]

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

 

[dtn6770]

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.

 

[jte]

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

 

[dcasto]

In cryogenic servise, the owner may not want water.

 

[deanc]

Best thing I have found. Another benefit of the space program.

See Appendix A

http://smad-ext.grc.nasa.gov/gso/manual/chapter_07.pdf

 

[jte]

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

 

[johnnymist2003]

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

 

[toothless]

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.

 

[dcasto]

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.

 

[dtn6770]

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...

 

[deanc]

Water testing also has stored energy. Got to be careful no matter what.

http://www.llnl.gov/es_and_h/hsm/doc_18.02/doc18-02.html

see 4.5

Pneumatic test if you must,minimum risk in all cases,distance or shields.

 

[gr2vessels]

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

 

[deanc]

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.

 

[CodeRef]

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.

 

[SnTMan]

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

 

[dcasto]

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.

 

[zdas04]

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

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[deanc]

zdas04

Thank you

 

[shahdadf]

Thanks a lot friends,
it was really a good discussion.