Pressure Test on Sand Blaster

It depends upon which party is to undertake burst/collapse liability as a result of catastrophic self-disassembly:

• If it is to be insured in order to indemnify the owner and operator of the tank, then the term <...too expensive...> is either irrelevant or farcical, or perhaps both. Periodic insurance inspection is mandatory in many jurisdictions above an energy storage capability of 215-250 bar-litres.
• If this is a home-brew thing and the only person to die or to incur property damage is the homeowner and assorted relatives, then one can do what one likes. However, not putting the thing on a periodic insurance assessment would appear to be bad practice as it makes any survivors extremely unpopular with household insurers and life assurance policy providers.

This comes into the delicate realm of liability. This is why the outside pressure testing certifiers will not bring their equipment to you. Therefore all decisions on how much pressure and how many times you test and how often you retest must fall on you, r&ddoc.

My only critical advice is that I would pressurize only with dyed water and using a hand pump. This way no compressible fluid (gas, air) can store energy and a weeping leak will be more visible. A fluorescing dye and a black light might make it easier to see a weeping crack. I would also pressure test multiple times in each testing cycle. I would retest every one or two years if in constant use.

Yeah.... I know ...

The + part is that my 3/16 thick tank has a couple of inspection ports I peeped trough, only showing superficial rust; so rust would be no issue.

How to know / determine metal fatigue??? May be cutting a disk of the tanks wall and making a metalographic exam??? aint it too much???

..."According to Harvey⁽²⁾, the important factor is number of stress repetitions, not time in service. Fatigue in metals is a progression beginning with submicroscopic changes in grain structure of the metal, and consists of three main stages: crack initiation, crack propagation, and rupture. Once initiation of a crack occurs, the crack grows a finite amount with each stress cycle until the remaining cross sectional area is so small rupture occurs.

Before fatigue life of a pressure vessel can be determined, fatigue life of material(s) of which it is constructed (number of cycles at a given stress level) must be known. "...

..."As the vessel approaches predicted end of life, visual examination should be supplemented by other NDE methods in search for cracks in highly stressed areas of the vessel. The effect of any crack on fatigue life should be evaluated immediately as failure may be imminent. Failure may be a slow leak or may be catastrophic.

Regular examinations of vessels should be part of a plan to either replace the vessel at end of life, or to extend its life past its calculated fatigue life. A complete detailed history of the vessel is required to extend vessel life. History should include actual pressures and temperatures, inspection reports, etc. Actual operating loads may not have been of the magnitude used for fatigue analysis. It may be possible to extend vessel life when fatigue analysis is based on actual operating loads.

Obviously, not all parts of a pressure vessel are equally stressed. The most highly stressed areas occur at changes in geometry: nozzles, transitions in diameter, etc. Cracks can be repaired and cracked components replaced. Fatigue analysis of the repair or replaced component is required to ensure vessel life is extended past the original design life. Another alternative is to perform a fitness for service analysis per API⁽⁴⁾ 579-1/ASME FSS-1. Fitness for service analysis provides an estimate of number of cycles to failure."...

https://www.nationalboard.org/index.aspx?pageID=164&ID=441

A close-up of the surface of a steel pipeline showing indications of stress corrosion cracking (two clusters of small black lines) revealed by magnetic particle inspection. Cracks which would normally have been invisible are detectable due to the magnetic particles clustering at the crack openings. The scale at the bottom is in millimetres.

I´m 66 ... how many years you guess I would get if this thing explodes? I am perfectly aware that gases under pressure are very dangerous.... but what should I do? There are so many risk factors that my only alternative (even buying a new vessel) seems be to stay in bed hoping my place does not get hit by an meteorite....

Ha ha It's only information....you are certainly free to take or leave it as you choose...Your own risk tolerance is under your domain...I only seek to inform...It's better to know the risks involved before hand rather than after, don't you agree...Now get out there and do some blasting...

...and don't forget silicosis...

https://www.cdc.gov/niosh/docs/92-102/default.html

SolarEagle's warning about silicosis is critical. His referenced information starts with this:

"WARNING! Abrasive blasting with sands containing crystalline silica can cause serious or fatal respiratory disease...".

To my knowledge, "sandblasting" (i.e. using sand as the blast medium) has been illegal in my state in Australia for at least 40 years, yet I still see reference to "sandblasting" here and around the world - I can't understand why (maybe sand without silica content is available elsewhere)!

Please use a safe blasting medium and appropriate protective equipment.

Happy blasting.

Despite being a Neurosurgeon and not a Pulmonologyst, I have certain knowledge about the risks to health involved in this activity, but thank you anyway for your comment and advise! Yes, I will take care!

OK, sounds like you'd know

However, there are plenty of people who don't and some could be reading this. Recently we had a spate of kitchen bench installers (in Australia) ending up with lung disease caused by cutting stone bench-tops. While I wasn't a bit surprised to know they contracted a life-shortening illness from not using appropriate protective equipment, sadly, they obviously were. I believe there's a class action happening - cold comfort.

Having spent ~40 years inspecting pressure equipment including doing hundreds of hydro-tests - IMO your question has been well answered already. I also spent the 80's doing lots of blasting and painting inspection for power stations, enforcing "no sand" grit blasting among other things and saw a lot of unwell looking workers, so I still like to spread the word at any opportunity.

Cheers

Thanks again! I honestly appreciate your input and consider this is what forums are good for!

My pleasure and completely agree that this is what forums are good for.

Cheers

There are wet sandblasting rigs available,that use a pressure washer with a venturi to inject the sand into the water stream.This greatly reduces the dust hazard,but personal protection is still required.Not suitable for all situations,but a good fit for others. Of course,there are many other blasting media available as well.

I thank you both for your advises, and yes; I am aware about what might happen from the legal point of view if this thing decides to explode.

As legislation varies from one country to another, please lets only focus on the "how to" (mechanics / physics) of the actual testing.

I liked the idea of using a fluorescent dye and UV light ! Quite cool , easy to do and affordable!

First you need to test the tank metal thickness to see if there are any thin spots...

https://www.google.com/search?q=Ultrasonic+thickness+test&oq=Ultrasonic+thickness+test&aqs=chrome..69i57&sourceid=chrome&ie=UTF-8

already had it in mind! Thanks. Im gonna ask the guy who ultrasounded my boat´s hull to see if he would do the job.

If this thing is going to be pressurised without a hydraulic test to a higher pressure beforehand and without a testing regime to a recognised local code, then please ensure all other CR4 readers are well out of range beforehand...

Keep clear!

Pressure test will be performed next tuesday @ 9 AM local time

As Redfred mentioned earlier, you should only use a hand pump for this. They are readily available and fairly inexpensive.

Here is an example

Summing up the comments, I would conclude that your project is not reasonable. The pressure testing is far beyond what you would want to do for one unit. The welding should have been done by a certified pressure vessel welder.

A new tank, 60 gal, 200 psi, on Amazon is probably around $600.

I don't know if this helps. Scuba tanks are tested hydrostatically at 5/3 the rated pressure. It is done underwater and the amount of expansion is measured by measuring the displaced liquid.

"Hydrostatic testing

After the initial test, the results are stamped into the body of the scuba tank, along with the date (year and month) it passed. After that, the tank must be retested hydrostatically every five years. The test for each tank is on file at the DOT, and the testing station must contact them to obtain the correct test specification. A common hydrostatic test is to pressurize the scuba tank to 5/3 of its working pressure and to measure the flexing of the tank walls. Five-thirds of a 3,000 psi working pressure means that the tank will be pressurized to 5,000 psi. This is done by replacing the valve with a special hydraulic testing connection and filling the scuba tank with water under pressure – NOT air! Air would be too explosive if the tank were to let go during the test, as it sometimes will. Because water cannot be compressed, the tank cannot explode if it fails.

Testing is done inside an armored vessel. The one my hydro station uses is sunk into the shop floor for added protection. The tank is also under water, and they measure the amount that a water column rises as the tank is pressurized. This measures the amount of tank expansion. The water inside does not expand, but the aluminum or steel tank casing certainly does! They are looking for tanks that DO NOT expand as much under pressure, indicating that their walls have been work-hardened over the years. Like a piece of steel that is repeatedly flexed, the tank walls get hard to the point that they may suddenly fail with a snap. This is EXTREMELY rare outside the testing station. When it DOES happen, it’s almost always fatal to people standing close by.

You know it when they fail!
When a tank fails during hydro, it’s usually the valve threads that let go. It sounds like a loud “whump” if you are in the building when one fails. The other thing that sometimes happens, but not as often, is that the bottom of the tank bursts open. This is due to corrosion. If the tank fails to flex enough during the test, it can never be filled with air again, and no dive shop will do so. It will not be stamped with a current test stamp (one within the past five years) and is “out of hydro” as far as any dive shop is concerned. One possible use for a failed tank is to cut off the bottom with a carbide saw (a lengthy process!) and hang it far downrange on a rifle range to be used as a gong."

https://www.pyramydair.com/blog/2006/02/scuba-tank-testing-hydrostatic-and-visual-inspection/

I think it is reasonable.

145 PSI is not a lot of pressure on a 3/16" wall tank.

What was the tank rated for before welding?

It depends very critically on the diameter of the tank, corrosion allowance in the design, and the proficiency of the welder.

Why was your opinion rated as "out of topic"??? ... just because it was not as fateful as the rest ?

It was rated 250 PSI.

Perhaps the other members who expressed their OPINIONS (and that's all they are is opinions) didn't like the fact that I went against their "scholarly" opinions, based on my 72 years on this Earth.

These are the same members who, without hesitation, give high voltage electrical wiring and component advice almost every day to people with a demonstrated lack of knowledge and competence.

It's be interesting to see what the testing house has to say and if they require a "hold harmless" disclaimer for their work. Did they say to what pressure cycle they would use?

I voted your post OT not because it went against anyone's grain, but because it was flat-out dangerous and incompetent.

I removed the OT vote that someone gave you. You are entitled to your opinion, even if it is wrong.

Filling the tank with water/oil or other liquid and pressurizing it incrementally does not seem dangerous to me. But, there we go again, that's just my opinion.

Tht 2x pressure is not what I criticized. It was the comment about the 3/16 inch thickness.

The dependency of thickness on diameter is not a matter of opinion; it is rock-solid fact.

In order for your argument to hold water (pun intended) we must assume that the original pressure vessel was incorrectly manufactured and certified.

De rating, because of welding MAY be a factor. We don't know that, thus the post weld testing.

Also,we do not know any detains of the death and destruction photos posted by SE.

10 bar is not a lot of pressure for a 3/16" wall tank, if properly sized and constructed.

It will be interesting to see the test results.

Most of that is dangerously irrelevant. If you ever knew anything about pressure vessels, you have apparently forgotten it.

This is especially bizarre from someone who frequently berates supposedly unqualified persons.

I have been some days away...

The ext diameter is of about 800 mm

That was already explained in post 17. Without the diameter, 3/16" wall thickness is utterly meaningless.

Can you please confirm that this is the blasting media tank?

I've not seen any sand blasting process where the media storage was pressurised. They were always downstream from the air flow control and either fed media by gravity or venturi into the air stream. In both cases, the media tank was not sealed.

The fact that you have welded the tank means that the original metallurgy will have changed in the weld zone and also for whatever you have added. Wall thickness of those (now unknown) materials will not be sufficient information for safety conclusion.

Hi, My blaster works more or less as seen below, therefore tank / pot is under pressure during operation.

Are you a certified welder? In my country welding on a pressure vessel has to be done by a certified welder, with an identification number issued by the state. This number must be stamped on every device welded. Are you aware of hydrogen embrittlement, which causes hairline cracking due to hydrogen absorption by certain metals and alloys or moisture in welding rods/flux? This can cause unexpected failure (which most explosions are). As the old saying goes: "a stitch in time saves nine." In this case it may save many painful stitches, or perhaps even a toe tag. Of course, you packed the parachute, you can jump with it if you please.

I hired a company to do the testing. They will inspect the entire equipment next week. Nevertheless I´m already considering suicide as an alternative!

I'm sure everything will be fine.....

right!

We test pressure vessels all the time.

Redfred is correct about using a hand pump.

Also, the tank should be placed in a water filled vessel for testing (hydrostatic test).

Two times rated pressure is normal.

The numbers I most commonly see on required tank hydrostatic tests in The US Code of Federal Regulations is 1.5 times rated pressure. Fill the tank solid with water and use a manual pump to reach test pressure. Previous comments about seeing weepage when using incompressible fluid are correct. A test tank filled with incompressible fluid, such as water will not explode or grenade on you.

You will also likely benefit from a post-weld stress relief of the weld area. Typically the tank is not a heat treated alloy, but residual stresses and chill lines in heat affected zones significantly reduce the available strength margin in the steel and could easily lead to an unexpected brittle failure, which would be contraindicated if you have an aversion to pain and suffering.

I am surprised no one has asked you what you welded on the tank ad or whether it was a penetration or surface weld?

Most have offered safe information but have not asked what your weld procedure was stick tig or mig with or without pre heat etc.

In general any welding on a pressure vessel will de certify it but not necessarily damage it.

Hello! I was actually waiting for your question! This pot was originally designed for two blasters working simultaneously, or one operator working uninterruptedly. It was divided in two compartments one above the other. Compartments got pressure simultaneously, but each had its own exit tube connected to a blasting line. Truth is that it did not work (not even close) to the way it was supposed to. So I connected both compartments, made a single exit for the blast media at the bottom's center, welded a cylinder connected to the pot by means of a pipe with an elbow pointing downwards for generating a whirl to prevent media getting accumulated against the inner walls (as it actually happened), etc.

All were MIG welds without preheat.

As I am not THAT confident about my welding, I want to test pressure the pot before actually putting it into service.

So think in terms of Process Intensification:

• Fit a smaller vessel that doesn't need periodic testing and certification under the regulations in force; in the UK this would be below 215 bar-litres.
• Get rid of the vessel altogether. Can a long length of pipe of suitable diameter fulfil the same purpose (rhetorical question - NNTR)? Can a suitably-rated mounted vehicle tyre/tire fulfil the same purpose [tyres/tires fall outside the pressure systems regulations in many jurisdications] (rhetorical question - NNTR)?

"What you don't have, cannot leak." - with apologies to the late Dr. Trevor Kletz, process safety guru.

Numerous replies advise your options. Mine is to consider what have you got to lose?

If it is only you involved, then it is your problem, your time, your money, your decision, and your life.

.....the latter being the important factor where all the testing has to be carried out by law that normally requires a report from an independent third party (themselves, probable registered as well).

But if DIY is viable for you, then fill the tank with water to the brim (absolutely evacuating any air pockets). Then pump it up in increments, pausing to see if pressure remains steady (invisible leaks) - typically to 1.5 x 'rated' pressure' - this is the tank rating (on the label) that might be more than your 10 bar working pressure.

Initially you are looking for leaks (see advice by others) - thus wasteful on air usage if ignored - but seriously not - because they warn of weakness - calling for the reason to identified.

Also wrap a steel tape measure tight around the tank to measure the girth as the tank expands - marking expansion versus increments of pressure - and record this to compare with acceptable limits (if you can get hold of them).

If it was me, I would go up to 20 bar, and if in any doubt - next step the scrap yard.

Or, before all this hassle, an obvious solution is to buy a new certified tank.

A little off topic,but even when used in properly designed compressed air systems,some leakage is very hard to prevent.It is the most expensive utility,costing more than steam to produce.Industry is constantly searching for new ways to detect leaks,such as ultrasound,infrared,etc. Not dismissing the importance of properly tested equipment,a totally leak proof compressed air system is very hard to find.

Thanks for your input! A Engineer will test the tank in two days. (which no need to say has not been pressurised so far).

About buying a new tank> yes I have considered it as well, but a pot (with the same constructive quality as mine) is very expensive down here, so if it does not pass the test, I will scrap it and quit the blasting project.

If you cannot afford to lose,you should not gamble.

Depends to a high level on the stakes and the payout.

Would you play Russian Roulette for a million dollars?

If it was a rubber band gun.

The next <...change...> that needs to be made is to feed it into a recycling shredder.

Hi, Just wanted to tell you all that I had the blasting pot as well as the air tank from my diesel driven screw air compressor tested yesterday. The technician made a visual inspection, measured the wall thickness of the vessels, and pressure tested them.

The preliminary report says that both passed the inspection, but I will get a full written report within this week.

Thanks a lot for your input !

Let the blasting commence....

You made me laugh!

Thanks !

Are you working part time making your own devices?

https://www.todaysmedicaldevelopments.com/article/full-story---will-medical-blasting-go-robotic--/

Well, it is a long story...

There is a jung man I got acquainted to at the shipyard that made the half life maintenance to my boat. This fellow was always very helpful good mannered and proactive and did a great job, and we eventually developed a father to son relationship. A time ago he told me he would like to start his own business and wanted me to be his partner, so we reached an agreement I would purchase a second hand equipment, he would do the job and incomes would be split in two. When out of the red figures, he would start returning me the money I invested on his behalf. I don't know if this will ever happen (to own a profitable business)... but well, I felt I had to lend him a hand.

About the company I work for in the Medical Device business, although it is not the core of our business we do some fancy coatings on metal implants. So far, by hand. I f this business branch grows, we certainly will robotise the operation.