Hydrostatic Testing 2

[jasonmuneton1]

What are the pros and cons of using water verses air for a hydro-static pressure vessel test? I have read places where they say that using water is better because it is virtually in-compressible but using air is dangerous because it is compressible? I guess there is something in ASME B31.1.

 

[metengr]

This topic has been discussed numerous times in the ASME Mechanical Code issues and Boiler and Pressure Vessel Engineering forums. I would recommend you use the search feature above and type in hydrostatic testing.

 

[Cockroach]

Oh man, don't ever use compressed air for vessel testing. How about the "con" being energy of compressed air during a sudden pressure envelope rupture?

This is extremely elementry. I would be asking a senior professional engineer for some supervision! Don't take this as a slam, but you don't want to risk property damage and possiblity of loss of life.

Compressed air for testing. Absolutely never!

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[pennpiper]

By definition "hydro-static pressure vessel test" means to test the vessel with water.
It is the only safe way to test large chamber objects.

 

[LHA]

Depends what you're testing. Most Municipal Authorities in the eastern USA require compressed air tests on san. sewer lines, vacuum tests on san. sewer manholes and hydrostatic on water lines. These air tests are low pressure though, about 4 psi.

Check out any typical CSI Div 02 spec for a job in the eastern USA. I'll bet a websearch for:

02651 Sewer and Manhole Testing
02653 Testing and Disinfection Water Mains

will get you a lot of required compressed air testing.

Engineering is the practice of the art of science - Steve

 

[zelgar]

Additionally, you'll be able to see where the leaks are occurring when you're using water.

 

[zdas04]

This discussion always gets out of hand very quickly and I'd like to interject another point of view before anyone reading the thread starts to really believe that you can't do an air static-test.

I'm several decades past being a "new engineer", in fact I'm one of those "senior professional engineers" that cockroach mentions and I rarely use anything but air for natural-gas pipeline static testing and I've done dozens of them to pressures in the 900-1000 psig range.

These tests are allowed by ASME in both B 31.3 and B 31.8.

Occasionally I've tested large lines (10 miles of 20-inch pipe on one occasion) with pipeline natural gas and then sold the gas that wasn't vented in the purge back to the pipeline. This is also allowed by B 31.8, but with reduced maximum hoop stress.

The "trick" is that I carefully follow the ASME limitations on hoop stress and don't test pipe to a significant proportion of SMYS with air.

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

 

[Cockroach]

I too am "senior" zdas04, but have witnessed first hand one of my valve designs letting go under an air pressure test. Fortunately for me, no one was killed, but the property damage and loss of product went almost to half a million dollars.

It was found that although the 8" valve was designed correctly and had sufficient safety factors, a twenty dollar pressure regulator on the line failed, allowing 2900 psi of compressed air into an ANSI Class 600 application. This is rated for 1440 psi maximumn.

A 60 lbf flange went 270 ft into a field after going through a cement wall, 130 ft away. Doing the mathematics, the force at the point of impact, approximately 20 ft of elevation, you get 3.2 tonnes of force. The recoil of the 1900 lbm valve fitted with an actuator was about 30 ft in the reverse direction. The valve technician was not injured but had ringing in his ears for several weeks following the incident.

This is a valve, volume is much less than that of a pressure vessel. In air pressure testing, ANYTHING can go sideways. Now you have all that energy stored in the working medium under compression. So I disagree that the conversation has gone out of hand quickly.

Ever stand beside a valve about to blow up under an air pressure test? Try it! It sounds like an angry women screaming hysterically.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[bingopin]

Shoulda had a PRV with an appropriate setting. Of course it could have failed as well. Pnuematic testing can be done safely. Having said that, hydrotestesting is usually much easier because of all of the additional requirements to pnuematic test.

 

[zdas04]

Cockroach,
I understand your point, but my point is that you did not have a "properly designed test" if one malfunctioning part could overpressure the fabrication being tested to a factor of 2 of your test pressure. "Proper test design" would have called for at least a PSV in the test rig and I don't know what else. The air tests I do are pressurized from compressors and at no time do I have a source of pressure connected that is higher than the current soak point.

The times I've done a test with high-pressure natural gas, I test PSVs prior to the test and carefully control the rate of pressure change with explicit proceedures (add WAY more soak periods than really necessary). My biggest fear in that case is always that rather than a purge, some genius will just open the gas source into a dead-ended line. I have never been successful in engineering stupid-proof, but when there is a risk of someone being killed by stupid I attend the test and monitor proceedures very closely.

This topic comes up often and in every discussion people point to specific cases where an air test launched steel across the landscape. I've never seen one of those examples that could be called a properly designed test. Many of the examples are brittle failure of parts tested to 150% of MAWP at ambient temperatures below freezing. A good test should specify a minimum ambient temperature for a test

People that have had a bad experience with an air test are unlikely to ever do another air test or to allow their subordinates to do one. I contend that air tests are exactly as safe as the design-engineer is competent to do the task.

Bingopin,
I know that the OP was asking about a vessel test, but many of the issues are the same for pipeline tests and I've formulated most of my opinions on pipeline tests. For pipeline tests it is getting very difficult and expensive to dispose of hydrotest water. Current NPDES regulations proscribe just letting it run down the bar ditch, many UIC disposal wells are refusing to take it, and drillers won't have anything to do with it anymore.

Determining what test pressure exists in a hydrotest at each point is a major problem in hilly country (I did a test on a 300 psi line with 1,000 ft of elevation change, a gauge a the top would give me 744 psi at the bottom, a gauge at the bottom would have the top empty and at atmospheric pressure). Actually getting the water out of the pipe in hilly terrain can require pushing a pig with nearly the test pressure behind it.

Either kind of test has its own strengths, weaknesses, and limitations. It is our job to pick a test media, test conditions, and test proceedure that are appropriate for the specific test underway--that is what we get the big bucks for.

David

 

[Yorkman]

I would really want to know what substance the vessel was going to hold. I've seen one or two large refrigeration systems totally fouled up because the mechanical contractor descided to hydro test rather that use presurized nitrogen. We were months trying to dehydrate this system using vacuum pumps (much of this system was outside) before we could get the system to hold a vacuum at 1000 microns. If the vessel is a.s.m.e, rated and proper safety relief valves have been installed I would see no problem.
You would have a greater risk of over pressurization using water given it's rate of volumetric expansion if the vessel were to be exposed to ambient or radiant heat sources.

I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int.

 

[jasonmuneton1]

I forgot to mention that it is an Air Receiver meant to hold 100 psig compressed air. Another question would be how do you clean an Air Receiver? Acid Wash? Chem Wash? And how do yo check the pressure vessel for cracks? Is the hydrostatic test the only test on a pressure vessel for checking failures in the vessels walls. I understand that hydrostatic means using water. But I have heard that sometimes it is more pratical even though less safe to use air? And you guys should stop attacking each other in these threads jeez? I thought this is about professionals asking for professional help? Or novice little kids like me just looking to understand a little bit more.

 

[metengr]

Another question would be how do you clean an Air Receiver?

Reply; Power wash or mechanical methods to remove sludge, debris, etc

And how do yo check the pressure vessel for cracks?

Reply; It all depends on the size of the vessel. If you can gain entry, wet fluorescent magnetic particle, or remote field eddy current testing. If you can’t gain entry, examination can be performed from the OD surface using radiography (x-ray) or even ultrasonic testing.

Is the hydrostatic test the only test on a pressure vessel for checking failures in the vessels walls.

Reply; No.

 

[Ashereng]

And you guys should stop attacking each other in these threads jeez?

I don't think Cockroach and zdas04 are not attacking each other. The tone of their writing suggests debate more than heat. Of course, I am not speaking for them.

They each bring up their points, and more importantly, they ALLOW others to examine their points. This is something that I am finding more and more rare. Many of my peers do not like examination of their product. Too bad, because this is how I learn.

I quite enjoy the many debates that various posters hold - it is a good way to see the many facets of the same arguement. In the end, I make up my own mind.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[Montemayor]

I join Ashereng in emphasizing that when two experienced professional engineers such as Cockroach and zdas04 talk, I listen and take note. I am convinced that they also listen equally well to each other. They are proven professionals and when they make a point it is because they believe they can be or service in offering another way of working a problem sucessfully and safely.

I've been on these Forums with them long enough to know that they wouldn't waste words on other engineers that they don't respect. As engineers we are not bound to only one way of thinking and one way to solve a problem. Our diversity in problem solving is our strength and when shared with others gives us even greater strength.

Good, strong arguments guys - on both sides. It made a good thread even better.

 

[zdas04]

You guys did pretty well speaking for me. I think this is the most civil discussion of this topic I've ever participated in. The more I know about this topic the more confident I am that I don't know nearly enough.

David

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