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pneumatic test
6

pneumatic test

pneumatic test

(OP)
hello guys,
am seeking your advise for pneumatic test pressure case in my project.
i have 1" s.s line sch.40s connecting to cold box,our client refuse to make hydro test on account of the sensitivity of the cold box so he insist to make a pneumatic test instead.
the design pressure for the line is 31 barg so when i calculated the test pressure according toASME B31.3 it will be 34.1 barg which i consider as extreemly high to apply, noting that the continuation to the line has design pressure of 3.5 barg and included within test limt(welded valve in between).

thanx in advace

RE: pneumatic test

A local company making flexible connections for the automotive and aircraft industries, did their pneumatic tests under water. In your case and not knowing anymore about the conditions imposed on your testing procedure, you could use an antifreeze solution, light weight oil or other low freezing point solution to do the pneumatic tests.

RE: pneumatic test

What the heck is the problem? I've done pneumatic tests with air, nitrogen, or methane to 62 barg. All were code compliant and done very safely (without submerging the lines).

If you have attached a 3.5 barg design pressure valve to your 31 barg system, then the system is now 3.5 barg design pressure. You can't test a low pressure valve to a medium pressure with gas or with water. Something has me quite confused here.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

RE: pneumatic test

I think that he meant 35 barg instead of 3.5 barg.

RE: pneumatic test

(OP)
thank you all for replies and sorry for some spelling mistakes above since i was in hurry.
chicopee: i do not see any prblem in testing itself but the pressure will be applied on the continuation line is too high compairing with DP for the line...
let me simplifiy the issue, i have line with DP 31 barg welded to a glob valve with DP 31 barg and the a contiuation line welded to the valve has a DP of 3.5 barg.
i tried to split the two lines into two test packages to test them with the valve in close position but for some reason(i believe he does not trust the valve)the client insist to test them as one package with the valve in open position..the material for both lines are the same(only DP is different),can we test them toghether under 34.1 barg????????

thanks again

RE: pneumatic test

(OP)
dazedit was zdas04 not chicopee

RE: pneumatic test

raptor,

In this case the client is correct. Testing against a closed valve is not normally allowed, but you might be able to make a case so long as the deign pressure of the valve (and it's seats and seals) is more than your 34.1 barg. However it's not a good way to work and shows a lack of forethought about how you were going to test this pipe. What you need to do if testing against the valve is not allowed, is cut off the 3.5 bar rated pipe d/s of your valve, weld a cap on, open the valve and then test at 34.1. Do the same thing for the 3.5 barg pipe then weld the two back together as a golden weld.

Next time start planning the hydrotest BEFORE you weld the pipes together...

For a pneumatic test, just make sure everything is well tied down and have an exclusion zone of 10m to 15 m during the test. DO NOT do any leak testing with soap at this pressure.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: pneumatic test

An alternative to LittleInch's reply would be to weld an ANSI 300 flange downstream of the globe valve and put in an insert blind for the two tests.

I would be pretty nervous about a spec break from ANSI 300 to 3.1 barg with only a globe valve between them. The globe valve will only give you any dP at all while flowing, when you stop flow the pressure across the partially open valve equalizes very quickly.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

RE: pneumatic test

That's another option - basically any form of positive physical isolation is required for the test

I didn't go into the design aspects - too many unknowns.....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: pneumatic test

". . .exclusion zone of 10m to 15 m during the test"

Try about 100 to 200 meters. In a catastrophic failure, large pieces may be thrown even farther than that. At 200m, I've got time to step out of the path of something comming my way. Yes, the risk of a serious failure is low, but the consequences are massive. And yes, I have pneumatically tested big-bore pipe at 35 bar/550 psi, and small-bore at 2300 psi. And I was worried.

FYI, at these pressures any pinhole leaks [like weld porosity] will be screaming. After reducing the full test pressure at least 10% and leaving someone to watch the guage to make certain that the cold gas you are testing with doesn't warm up and increase the pressure, then walk the line and listen for leaks. NEVER walk a line at full hydro pressure - unless you let me take out a life insurance policy on you.

RE: pneumatic test

Duwe6,
I've got a few points about your post
  • Explosive decomprssion. A few years ago a summer intern at NASA did a calculation of the amount of energy potential in a multi-mile, big inch pipeline at very high pressure under a test compared to atmospheric pressure. His conclusion (published on NASA letterhead) was that in an explosive decompression the entire energy (MT of TNT-equivalent range) would be explosively vented. His conclusion was utter nonsense. Communication within a gas system is limited to the speed of sound, so the initial decompresison is limited to about one joint of pipe. The explosive decompression is ounces of TNT-equivalent, not mega-tonnes. When you look at the case studies that people keep trotting out for this discussion, the big-time failures (e.g., the top half of the vessel upside down on an upper floor of a structure) are all consistent with limited accesses to energy (the vessel that everyone points to was not part of the test, they were testing against shut valves and the pressure built up in the vessel until the stress in the vessel walls caused it to fail, you never would have tested to failure on purpose). Exclusion of 10-15 m is actually excessive. If you did get a catastrophic failure with shrapnel the bits of steel would be traveling at near-sonic velocity (call it 450 m/s) and you really think you could "get out of the way" in 200 mS? You've been watching too much TV.
  • Pinhole leaks. Flow is a function of dP and flow path. A pinhole leak in a pneumatic test has a big dP, but a very small cross-sectional area and relatively long flow path. I've seen weld porosity leaks that barely spit, certainly didn't sound like sonic flow, because it wasn't.
  • Full hydrotest pressure. I always walk the line (at least part of it, I generally have other people walk the rest of it because I don't walk very fast) at full hydrotest pressure. It hasn't killed me a single time. Upwards of 100 tests. Keeps not killing me. Guess I won't be buying the insurance policy in your name.
  • Pressure increase with temperature. You're kidding, right? If I start a test at 80°F and the sun shining on the pipe heats it to 90°F (almost impossible in a buried line, barely possible in an above-ground line), that is about a 1.8% increase in pressure (900 psig to 917psig) . On the other hand if I have a line full of water at 900 psig test and it heats from 80°F to 81°F then I've gone to 1000 psig, now that can be dangerous.
I live in the Rocky Mountains. Every test I do has more elevation variation than I can handle with a hydrostatic test. I often have major battles with clients over the attitudes that you are expressing in your post. They don't have any basis in fact, it is just fear and superstition. When my clients buy into that fear and superstition we are left with zero options. No way to segment a test to take the elevation differences out. No way to test prior to installation (nowhere with several miles of level ground and it is really hard to get a drag section to match field bends). Fear and superstition prevents a pneumatic test. Usually they (I won't sanction this procedure and I leave) end up with the test gauge at the bottom and never testing the top at all, not even a leak test.

Everything we do as Engineers has some amount of risk. I write test procedures that (so far) have a 100% track record of never hurting anyone and never spilling contaminated fluids (and I have had several tests fail without any projectiles). I don't want an unsupervised new hire to write a test procedure. But I've gotten good results from supervised new-hires writing good procedures. The problem comes in when we (as Engineers) can't pull ourselves away from meetings long enough to do the Engineering, so we rely on standard prohibitions against pneumatic tests, threaded connections, etc. "Standard prohibitions" should be an anathema to us all.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

RE: pneumatic test

Fair enough, I keep thinking of buried pipe. Most piping facilities have a pressure test area wish is suitably protected and this is 1" pipe, but the point is well made.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: pneumatic test

Dave, this is a pneumatic test. Temperature rise is enormous. Where did the 'pneumatic gas' come from? Comes out of 2300 - 3000 psi portable cylinders. Then the pressure is decreased by putting it into the pipe - causes a major drop in temperature. And that self-refrigerated gas also has to pass thru the high-pressure regulator; regulator gets cold and its diaphram gets stiff. Now you turn your back on that regulator as the flow slows down when the pressure in the pipe reaches the setpoint. Regulator rewarms, diaphram gets less stiff, more pressure is delivered. There is the first pressure 'overshoot'. Now, the autorefrigerated gas in the line warms up. Causes a major increase in pressure. These mechanisms are probably why B31.3 tells us to increase the pneumatic pressure in 10% increments - lets the temperature equilibrate, keeps from having unexpected pressure jumps.

Now step back and consider the whole system. It took the contents of one or more high-pressure nitrogen cylinders to bring this system up to pressure. Incorrectly handled gas cylinders are damn dangerous, due to the massive ammount of stored energy and the potential for a catastrophic release. All we did was move that stored energy from the cylinder(s) into an untried pipe system. That full ammount of energy still exists, and it wants out. One [very] bad weld, one flawed pipe seam [s/s sch40 is usually a seamed item - much cheaper] and something goes BOOM. The odds of this happeming are very low, but the consequences are high.

Anybody can walk an 8-inch wide beam 2-ft off the ground. Simple & safe. Now move that beam 100-ft up. Still the same probability of falling off, but the consequences of a failure just became unacceptable.

Hydro's are very safe - very little stored energy due to an incompressible fluid. Pneumatics are a different animal. Bet that you are old enough to remember split-rim truck tires. They killed and maimed a bunch of mechanics; with only an internal volume of a few ft^3 and a pressure of 90-120 psi.

And yes, a pinhole leak on a 550 psi pneumatic will 'scream' at you. Ask a boiler operator about the noise from a tiny high-pressure leak.

RE: pneumatic test

This same thread comes up all the time. However, I guess about all I would say is that in general one should probably best have a very good reason to substitute a pneumatic for a traditional hydrostatic test (I guess not only done with water, but sometimes maybe even other fluids if water is objectionable), and when one nevertheless does they best do your homework as to all the hazards and preventions involved. Trying to save a little money or bother in testing, or engineering of same, or for that matter in testing pipeline designs or profiles that could have been done a little differently to begin with that would allow for conventional hydrostatic filling and testing, may not in the long run be good enough reason if someone (heaven forbid) is injured in the testing. In this regard, the juxtaposition of the following two statements are striking (if I am reading same correctly):
“Exclusion of 10-15 m is actually excessive. If you did get a catastrophic failure with shrapnel the bits of steel would be traveling at near-sonic velocity (call it 450 m/s) and you really think you could "get out of the way" in 200 mS? You've been watching too much TV.”
If pieces of steel, or for that matter virtually anything else, happen to be propelled at a velocity of 450 m/s, I guess I have to ask how is an exclusion zone of only 10-15m “actually excessive”? I am aware that a 28-feet long chunk of the San Bruno pipeline (originally buried) was reported by many sources including http://www.ntsb.gov/investigations/summary/PAR1101... found a hundred feet (>30m) from its original location (after the gas pressure in the line reported at http://articles.latimes.com/2010/oct/14/local/la-m... had climbed to only “386 psi” shortly before). For whatever it is worth also I have also seen one poor unfortunate soul was per the report at http://www.tedpelling.com/news/Pneumatic%20Shangha... and others reportedly/tragically killed within his dorm room “350 m away from the explosion” during pneumatic testing (I do suspect however this incident involved exposed as opposed to buried piping).

RE: pneumatic test

Believe it or not - "Get out of the way" is easy, at 200m. Guys at rock quarries do it daily. They 'duck & cover' for the initial blast due to possible supersonic small rocks. Then they pop up like a Major League catcher, scanning the sky for big chunks that got lobbed into the air. zdas04 got the velocity right, the big chunks will be slightly subsonic, or slower. If anything stays in your field of view, not drifting up or down, nor left or right -- it is going to land right where you are standing. Take a couple of steps to one side and don't stay where that big rock intends to land. Easy for an old, fat guy at 200m. Not enough reaction time at 20m.

RE: pneumatic test

I've never done a test from cylinders. I don't know why someone would do that. If the test is small enough for cylinders to make sense, the logistics of a hydrotest generally make more sense. I would be very reluctant to do a pneumatic test out of bottles. If drying the line was the big issue, I might use liquid propane for a test that small (then carefully control the rate of depressurization to minimize phase-change cooling).

Hydrotests are not nearly as benign as people seem to think. There was a case here a few years ago where a company was doing a hydrotest on a line that ran over an 1100 ft bluff. They put their test equipment at the top. Pressured the top toward 900 psig. The bottom got to somewhere above 1300 psig and a valve parted. Unfortunately it was pointed towards a road. More unfortunately a small vehicle was passing the site as the valve came off. The road was next to a river and the driver discovered that Volkswagens will definitely float, just not indefinitely. Could have been a catastrophe, no one was hurt so it just pretty funny. Hydrotest water is a hazardous waste that is really hard on aquatic life. Way too much of it has been dumped in ditches, dry washes, and rivers. Failed hydrotests usually just make a bit of a mess. Sometimes they put people at risk through flooding confined spaces. Sometimes they spray water into switchgears. Sometimes the part that comes loose is not captured and can be launched with enough force to do damage.

When I've done air tests I've used on-site air compressors and my problem was getting the gas cool enough that I didn't have to add much make-up gas during the soak periods.

With methane tests I've been able to purchase pipeline gas to run the test and the temperatures were basically ground temp.

For nitrogen tests I've used liquid nitrogen trucks. The way you get liquid nitrogen up to pressure is by heating it. On any inert gas test, the first warning in the procedure is that you have to monitor injection temperature and that it must be within a very narrow band around current ambient temperature. I have seen several accident investigations and seen several accident reports on failures associated with inert gas and every single one of them has had a root cause of "incompetent Engineering" or "Failure to follow procedure".

There simply is no way to take the risk associated with pressures approaching SMYS to zero. You can get them close enough. A person wearing fall protection can walk that 8-inch beam 100 ft in the air time after time without significant harm coming to them--procedures are the "fall protection" of static testing.

I used to work in steam plants and have seen the mechanical operators that went looking for a 600 psig superheated steam pin=hole leak with their hands. They're usually called "stubby". Superheated steam has a whole lot more specific enthalpy than ambient temperature air or nitrogen. Even at that the pin-hole leaks I've seen were noisy, but not sonic. The rule of thumb from control valves is that if the "hole" is smaller than 1/6 the flow path length you will not have choked flow (e.g. for a pin-hole leak the flow path is the wall thickness and a hole diameter would have to be greater than 1/16" in a 3/8" thick pipe to get choked flow). 1/16" hole is pretty damn big.

Yeah, those split-ring rims were fun. I saw a tractor tire take out a rafter in a shop once when I was in High School, The tech was filling the tire with antifreeze. Energy is energy. What matters is the duration of the release event.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

RE: pneumatic test

A 1", sch 40 ss line requires nearly 10,000 psi to rupture. And I've tested 1/2" to 4", sch 40 lines to rupture to so determine. 35 barg doesn't produce enough stress in hoop to to cause rupture even with a very long, deep crack. The pneumatic test is quite safe to perform. You will need to assure that your blinds are properly sized and attached. I have seen instances where the blind shot off. The volume also has not been calculated and the stored energy is a function of pressure times volume. If the volume is low, even the NASA calcs will permit closer to a 10 meter or less exclusion radius.

Zdas is absolutely correct regarding "explosive decompression" There are a number of petrochem companies that use a length of 100 ft at the test pressure to determine the exclusion radius using the NASA calcs. Having said that, one of our customers required a 150 ft exclusion radius for a 55 psig test; the exclusion radius per NASA calcs for the full length of the test was only 30 ft.

RE: pneumatic test

rconnor,
Come on. San Bruno? Really? San Bruno was a fuel-air explosion on a pretty grand scale. Not explosive decompresison. The line split, gas mixed with ambient air and found an ignition source. Yeah, a 1.5 ton piece was thrown a ways. So what? When the US dropped an atomic bomb on a couple of Japanese cities in WWII there were some pretty heavy pieces of steel thrown a ways also. Is that relevant? Yes, when you ignite an explosive gas (or liquid for that matter), it can explode. Who knew?

The Shanghai case is relevant, but that report is premature ("the cause of the failure is under investigation"). I've seen several of these kinds of failures and the cause is usually that they started the test with the pipe below freezing or introduced inert gas a cryogenic temperatures. That is a failure of Engineering (or following procedures) not a condemnation of pneumatic testing.

Of course there is significant energy available to cause harm during a test. That is why you have Engineers design static tests.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

RE: pneumatic test

"San Bruno was a fuel-air explosion"

That explains why a well-buried line made such big blast. FAE's can be HUGE.


RE: pneumatic test

The thing that needs to be considered here (and all pressure tests - pneumatic and hydro), is a proper analysis and consideration for the failure events possible and what can / needs to be done to mitigate against the effect. The failure rate in pressure tests is fairly low thankfully, but nowhere near low enough to be in the "negligible" region

Hence pneumatic needs to consider things like crater size for a large buried line, what connected flanges, spools, end caps, valves, tees etc could potentially "fly off" and in which direction, how secure the pipe is against movement in such an event, things like that.

Then you can demonstrate what you are doing is sufficiently low risk once you take the required actions (e.g. testing against a blast wall / barrier to prevent things hitting anyone if they fly of, restricting access to certain areas, having a suitable exclusion zone.)

Each system is different, so you need to look at each one separately, but with the same procedure thinking all the time - what if it fails here and how Do I prevent that failure injuring someone. Testing is designed to demonstrate strength or find weakness prior to operational service. Most of the time it does the former, but occasionally the latter.

When I was a student many years ago, we were testing plastic tubes repeatedly in a lab with water / nitrogen to use as rockets. One failed during a run scattering bits of plastic over a significant area (students were considered expendable in those days....). Only luck prevented any serious injury. After that they made us build a wooden frame very close to the tube to catch any subsequent explosion before the velocity was too high. A further failure saw the end shoot off and ricochet off an angle narrowly missing an observer. Both failures could have been prevented from creating injury potential by going through a proper failure analysis and review, but I was at the bottom of the learning curve in those days and practices like this not applied in university type situations.

So take note of all the posts above and individuals personal experiences and think about failures, do it properly and in all likelihood, your system will pass the test without incident or injury

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: pneumatic test

C'mon, guys- this is stupid. It's a freaking 1" line, steel rather than plastic, and only 500 psig! It's definitely possible to design a SAFE pneumatic test for those conditions. We do tests like that routinely, and we do them indoors, without immersion. We do set an exclusion zone, but it's nowhere near 15 metres! Above 500 psig, or when the compressed gas volume is greatly larger, tighter controls kick in.

A catastrophic failure at 500 psig of a line this small is going to occur only because of a) extremely poor material, embrittled AND nearly cracked through and somehow unnoticed during fabrication, or b) extremely incompetent workmanship. The likely mode of failure is leakage only. Actually, the largest single risk in this test that I can see is the risk associated with incompetent testing. A means to ensure that the pressure can't be suddenly increased greatly beyond the test pressure is essential.

What people here should be doing is engendering respect rather than fear for the damage that energy stored in compressed gas can cause.

RE: pneumatic test

"What people here should be doing is engendering respect rather than fear for the damage that energy stored in compressed gas can cause."

Call it 'respect' or call it 'fear', there still is a very low probability of catastrophic failure, but with REALLY BAD consequences. "8-inch beam at 100-ft in the air" Some form of mitigation has to be done, if you are a prudent test engineer. All LittleInch and I are saying is not to blythly pressurize a line pneumatically without a well-thought-out plan to mitigate the risks & consequences. A blow-out is a one-in-a-million [or even less frequent] incident, but it typically kills or maims someone. Just facts.
Airline crashes are a one-in-ten-million [or less] probability, but engineered mitigation is used, even in 3rd-world countries. Just sayin' ;)

RE: pneumatic test

Duwe6,
You really missed Moltenmetal's excellent point. Everything we do as Engineers has some amount of risk (or they would assign the tasks to less expensive talent). A competent assessment of the risks and appropriate processes and procedures to mitigate the risks to acceptable levels is what we are supposed to do.

Fear and superstition make zero sense. We were talking about a pneumatic test that was probably at 30% of SMYS and someone posts a link to the San Bruno explosion--that is fear mongering at its worst. When you look at incident investigations associated with pneumatic tests you see that every single one of them was a failure in Engineering or a failure to follow the test procedure. I have never reviewed an incident involving pneumatic tests that did not fall into one or the other of those two categories. Yeah, fill a line with -10C nitrogen and pressure it up to the warm SMYS and something is going to part. A competent procedure would say that you need to heat the nitrogen to near ambient temperature prior to injecting it. My procedures always say that and I make sure that I (or my inspector) confirms the injection temperature every few minutes. It is a critical variable that doesn't get specified. We specify exclusion zones of 5 parking lots, but we don't set a minimum injection temperature. The exclusion zone is fear and superstition, the minimum injection temperature is Engineering. We don't specify a minimum ambient temperature for tests, but we are really careful to fully specify the PPE that the testers must wear.

Attitudes like have been expressed in this thread are quickly leading companies and regulators to ban pneumatic testing. This is an absolutely horrible outcome. Take away yet another tool because people won't do their job? God I hope not, but I see it coming.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

RE: pneumatic test

I agree mainly with zdas04 and my aim was to describe what you need to do to make is as safe as practical. Just because there hasn't been a failure in other tests is no guarantee that it won't happen this time. Well thought out, written and supervised procedures are part of that mix.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: pneumatic test

"We specify exclusion zones of 5 parking lots, but we don't set a minimum injection temperature."

Exactly. I think you and I are on the same side of the pneumatics. That they are damn dangerous when done by folks w/o significant training/education in this specific form of testing. IF injection temperatures are reasonable, and if all the welds passed in-process and final inspections, a pneumatic test is no more dangerous than driving on the freeway to work. Nothing in this world is risk-free.

But most times in my experience, the client wants a pneumatic test to cut corners and save time/money. The 100% welding inspection didn't happen, so the welds are 'suspect' - not 'bad', just of an unknown quality, thus suspect. And I have never seen or heard of an outstanding test setup like you described: "For nitrogen tests I've used liquid nitrogen trucks. The way you get liquid nitrogen up to pressure is by heating it. On any inert gas test, the first warning in the procedure is that you have to monitor injection temperature and that it must be within a very narrow band around current ambient temperature." Doing it that way dials the test risk waaay down; excellent engineering, Dave!

RE: pneumatic test

What I object to is the fear mongering- the same as David.

Hazards have to be assessed in terms of both probability and magnitude of resulting harm. We're trying to mitigate the risk of a hazard (failure of this line in service with a commodity presumably more hazardous than compressed air or nitrogen), by doing an ENGINEERED TEST. Blowing the potential harm of that test out of proportion isn't helpful to anyone. Pointing out the hazards of pneumatic tests carried out on systems with a greatly higher P*V is all well and good, as long as it's then properly related to the poster's specific conditions.

I agree with David- what we risk as a result of over-reaction by well-intentioned but ignorant people is an outright ban on pneumatic testing. That would be a tragedy, and could result ultimately in unnecessary injury or loss of life.

RE: pneumatic test

Guys,
Found some interesting info in the Pneumatic Field Testing Specification from a major US O&G company.

FIGURE 2: EXCLUSION ZONE
NOTES:
1. The projectile model selected, a DN 50 x 300 mm long nozzle detaching from the main pipe or
equipment item results in the following exclusion zone distances which have all been rounded up
to multiples of 10 m. These distances shall be observed for all pneumatic tests as a minimum
and increased if any concerns of safety are raised before any test.

APPENDIX I: EXCLUSION DISTANCES
1. Credible Failure Modes
1.1 The access to the system to be pneumatically tested is determined by calculating the
distance travelled by a projectile, which is considered to be the most likely type of failure.
1.2 The distance travelled by such a projectile is a function of mass, initial velocity after
detachment and its aerodynamic profile.

1.3 For piping systems the possible types of failure are:
• Brittle fracture of a pipe creating small shrapnel projectiles with small aerodynamic profile
• Butt weld failure of pipes up to DN 150 causing them to whip or “snake”. However, the
remainder of the pipe still attached restricts this effect and therefore the exclusion distance
• Although it would be catastrophic, butt weld failure of pressure vessels, exchangers or
equipment within a piping system is not considered to be a credible event during a pneumatic
test, since all this equipment will have been shop hydro tested.
• Sudden detachment of a branch welded nozzle connection or other pipe attachment. This
would result in a tumbling projectile, which could travel a large distance and could cause
significant injury or loss of life. It is not practicable nor possible to 100% radiograph branch
welds due to their geometry. Therefore, a failure here is considered to be far more likely than
butt welds which have been 100% radiographed.

1.4 Exclusion distances have therefore been calculated for the "guillotine failure" and
detachment of a small nozzle connection welded to a larger pipe or to an item of equipment.


3. References and Equations Used To Calculate Exclusion Distances
3.1 References
Baker W E et al "Explosion Hazards and Evaluation"
Elesevier Scientific Publishing Company, Amsterdam, 1983, pp 463-474
Baker W E "Blast and Blast Fragments from Bursting Pressure Vessels" ASME Journal
83-PVP-61.

It is interesting that the exclusion zone noted in this specification for 34 bar (3400 kpa) is 180 metres,
Cheers,
DD

RE: pneumatic test

Company policies are written by folks. That bit of official looking prose could have been written by the people in this thread who object to the concept as too risky. You can bet that more than a few of the people who have commented in this thread have written company policy, maybe even that one.

I had a boss once that contended that company policies and standards are written based on the "cat on a hot stove principle" which says that if a cat jumps on a hot stove, he'll burn himself, and after that he will never jump on a stove again regardless of its temperature. This guy strongly contended that the company standards manuals get so full of prohibitions against one-off activities that they should be discarded and started over about once a decade. Life would be so much better if that happened. I went through a complete re-write once (we invalidated the standards and specified that industry standards as published would govern our Engineering activities). Within a couple of years we were writing add-ons to the code again. It was a nice couple of years.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

RE: pneumatic test

David,
I am sorry, I fail to understand your response.
I have mentioned numerous times on this forum that IMHO there is nothing wrong with pneumatic testing if performed in accordance with requirements/regulations and I have personally been involved in some huge tests over the last few years.

I posted this information purely as an example - two seemingly knowledgeable people (yourself and Duwe6) on this forum had given totally different examples of exclusion zones - one was 10-15 metres, the other was 100 - 200 metres.
I posted this to show what one of the largest O&G companies in the world considers a safe exclusion zone - I would rather work for a company who errs on the side of caution than a company who says 10-15 metres is acceptable !
Regards,
DD

RE: pneumatic test

I think you'll find the 10-15m was my guess, based mainly on buried pipe and the potential for crater forming. Wholly above ground testing of pipework clearly carries some level of risk, the key issues are how best to mitigate that risk and prevent injury to people and destruction of equipment. That does mean that you need to look at potential failures, the amount of NDT undertaken, the extent of any "temporary" (I hate that term) pipework or fittings and make sound reasonable judgements.

To get back to the OP, a 1" line at 30bar - we don't know how long or what fittings are on it - has some risk from an end cap or other fitting coming loose / brealing during the test and becoming a projectile. The key is identifying what those projectiles could be and either pointing them into the ground or a large wall or behind an earth bund or just retreating a long way. I would consider this prudent engineering and risk assessment, not risk avoidance. I have some sympathy with the view that standards are written in part to try and solve every problem found in isolated occurrences where the lowest common denominator is used and it removes the potential risk as the expense of common sense and responsible engineering.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: pneumatic test

David, you and I agree completely here. The trouble with company standards is that they are often treated exactly like religious texts: written by the ancients who have long since departed and hence can't be consulted to obtain context, and treated as holy and inerrant wisdom by the modern acolytes- people who have zero motivation to challenge the received wisdom of the ancients because these standards help them avoid the necessity for these folks to develop and use, and be accountable for, their own engineering judgment. The standards are often decorated with threats of fire and brimstone to those who violate the rules, but little actual design guidance to permit the user to determine when they apply and when they don't.

Then there are the interactions between and among the standards- standards which individually make sense, but in combination become a monster. We've seen a $50 air pig used as a backup receiver to hold a small double-acting actuated valve closed during an air failure, become a custom-built monster with 2" minimum flanged nozzles with XXS nozzle necks, legs, lifting lugs, ASME U stamp, 3-part paint system etc., and the air failure pressure switch replaced with a 0.075% accuracy industrial pressure transmitter...and it wasn't one, it was something like 10 of them on one little project.

A standard which requires a 180 m exclusion zone around a pneumatic test on a 1" sch40 line at 500 psig has proven itself to be useless, in my opinion.

RE: pneumatic test

DekDeee,
I did not mean to demean your post. I was just pointing out the reality of company policies. This one could have been written by Duwe6 who suggested 150-200 m exclusion zone above. He probably even believes that that exclusion zone is appropriate. If I had written it (and I've written dozens of procedures/policies/standards for various companies) it would have looked different.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

RE: pneumatic test

I respect all opinions and experience shared on this thread, and welcome debate on sound technical grounds. I will of course agree that there is a whole lot of difference at least in potential energy involved between a larger as compared to a quite small pipelines in pneumatic tests. When it comes to the particular/general subject of designing systems and choosing means of field tests, however, I think it is helpful to have different views expressed in threads that can be read by future (some admittedly impressionable, and not limited to the OP) readers who might not have detailed knowledge of the subjects but before they themselves dive into same. Unexpected failures in even quite small pipelines could conceivably initiate much larger problems in perhaps non-obvious ways (e.g. chain or domino-type reactions with other pipelines, structures or equipment etc.) Particularly in crowded industrial environments e.g., perhaps near "Final Destination" type scenatios are not out of the question. There is thus perhaps a fine line between “fear mongering” or “over-reaction” as opposed to promoting a healthy respect for all hazards of pneumatic as opposed to at least generally more preferable (by a great many organizations and standards) air removal and hydrostatic testing.

I will also agree that are likely some individuals or organizations who in some circumstances have or believe they have sufficient knowledge and control of/over all manner of risk factors in the life cycle of piping systems, that can even be quite lengthy and complicated by the time even new (not only existing) pipelines are tested, to make recommendations for properly run pneumatic testing. Some of these may even be capable of arguably reasonable/defensible e.g. FMEA-like hazard-risk analyses in this regard (see http://en.wikipedia.org/wiki/Failure_mode_and_effe...). In the modern age when unfortunately much material and even skill/engineering is "outsourced", and even vandalism, sabotage and terrorism have become some increasingly visible considerations, the picture has become no less complicated. I agree however with Duwe6 that there could very well be many others who are enticed to pneumatic testing out of expediency or “value engineering”, though maybe with much less of a “clue” as to what including all manner of measures/proper procedures and risks are involved. Perhaps as Shakespeare once verbalized, “therein lies the rub”.

As to the earlier statements however that “San Bruno was a fuel-air explosion on a pretty grand scale. Not explosive decompression”, as a pipe geek and that it was in the news I followed the investigation of the San Bruno incident as closely as I could (including speed-reading the voluminous and quite detailed NTSB report that eventually came out at https://www.ntsb.gov/doclib/reports/2011/PAR1101.p...). As I didn’t remember seeing any statements that read exactly like that stated in this thread by others in that formal investigation, I went back and again looked over the detailed report a little closer. While it is quite obvious that there was a whole lot of “ignition” and fire etc. that did a whole lot of damage to folks and property, nowhere did I read a specific statement by the experts in charge of examining this particular incident that claimed it was the ignition of the “fuel” that opened this gaping pipe rupture, self-excavated the crater, or even hurled the big pipe piece(s). I also saw that it was found the rupture occurred at the pressure it did due to a faulty weld, and then furthermore that the report also prominently criticized the "grandfathering" of this particular line so that it apaprently was not required to be field high pressure hydrostatically tested like some other lines (saying that the required level of stress from same would have brought this defect to light, presumably without all the fatailities and property damage etc.) I have also heard there have even been some fairly spectacular craters reported opened up in pneumatic testing and/or somehow in a few cases some very spectacular ones also without ignition even in gas transmission pipelines (these get little press particularly when they happen in remote areas). Contrary to what was stated in anothers post, pneumatic testing can involve huge fluid expansion energy (several hundred or even thousands of times that of water, depending on pressure?) - e.g. about 5 MJ/m^3 of contained volume at ~500 psi pressure. While not necessarily to be "feared", I believe it deserves a great deal of respect, for I believe just that volume is said to be the blast energy equivalent of nearly 2-1/2 pounds/> one kilogram of explosive trinitrotoluene (TNT)! That being said, there is of course no question that at least suitably confined gas mixed with air (e.g. in some sort of suitable volume enclosures etc.) can really do some additional concussive damage when it ignites, and I am aware that at least one third-party critic after the fact has claimed and presented at least some technical arguments that fuel-air explosions have not been given their fair due by at least some of these formal investigative panels in San Bruno and elsewhere (see http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29P...). In one other case I noticed this gentleman brought out as evidence that that particular pipeline was backfilled with (otherwise hard to dispose of?) sections of scrapped pvc pipeline that could have collected somewhat confined gas-air mix pockets large enough to be problematic. While I’m not going to claim specific relevance to the OP, I just want the record to be as clear as best I understood to these formal findings.

As to modern fault-finding “investigations” by panels or for that matter juries etc. when a catastrophe occurs, I guess I also agree someone is likely in the modern world and with modern experts/tools to find things they can argue have been done wrong (and now often multiple things that have been done wrong by multiple folks!) While that can be attributed as “incompetence” or worse of professionals or others that might stick, some of us who have been around the real world for some time and agree that these have been done wrong also acknowledge these incidents as further proof that even despite good intentions human beings and many procedures etc. are not perfect (we don’t think at least most folks really want to hurt others). It is some interesting that I saw some records in legal proceedings not long ago that appeared to find that the greatest fault in pneumatic test gone awry with fatality was assigned to the dead/maimed man (while I guess he could indeed have been most at fault, I think this was likely of little consolation to him or his family, though I guess this may however have been in effect a rather painless satisfaction of even the harshest Code of Hammurabi though protecting others who may have been associated with the incident and were left unhurt/unpenalized and with all their limbs etc.). [In disclosure these particular cases I remember reading were indeed with type(s) of plastic pipe instead of steel.]

Finally, I agree also hydrotests need to be done as safely as possible, and particularly when large pipelines and very high pressures/thrusts etc. are involved (water is not really totally “incompressible”, particularly when there is a whole lot of water in large diameter pipelines, or after all where there happens to be a lot of air either known or unknown trapped within a test reach). It should thus be common sense to not stand behind exposed unblocked hydrostatic test closures or other thrust foci of any piping when you can stand somewhere else, though it may be helpful to tell/remind some folks who may not realize risks!

While I don't dictate nor write "policy" for any company, as to the stove and burned cat scenario, the contrapositive is of course when the so-learned cat does not jump up back onto the stove, he/she will assuredly not get burned whether or not it is hot or cold (if after two or three weeks being locked in the house, with all the mice gone and that is where the only food is, I guess they might however have second thoughts. Everyone have a good weekend. ]

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