Investigation on air compressor blow up

[peterbatty]

Hi this is a typical lesson learnt through hindsight. I work in pressure vessel inspection in the UK I note that many of these simple pressure vessels have a cyclic life (number of times the pressure goes up and down) for this type of unit it will be considered 500 full pressure cycles. So if you use and empty the tank every day then the life is about a year and half. Most use the compressors far less often than this in a domestic environment and so many manufacturers estimate 10 years life. A fatigue crack generated by the cyclic operation cannot be detected with a "pick" hammer, for the cost of these units it would be far safer to dispose of the unit every ten years in addition to adequate maintenance over the period. Corrosion is still a problem though this does tend to manifest as a leak. Fatigue is the probable cause here, which may have been exasperated by corrosion ( Corrosion Fatigue). Thanks for sharing and I hoe to use this video in training of vessel examiners.

[timbylander]

I won’t second guess your diagnosis. But it has changed the way I do things. I just retired an old compressor with a patched tank thanks to your video. Thanks

[JustaGuy]

As an Engineer with over 15 years in the business, you need to fix your video.

1. NEVER, EVER hit your tank with a hammer to check integrity. If you cause a dent, it can lead to a stress concentration which can cause failure. Pressure vessels are designed for smooth walls, and ANY discontinuity affects the strength significantly. The proper way to check it is to use an ultrasonic thickness meter which use high frequency sound waves to determine wall thickness. Many states require annual inspections of pressure vessels using ultrasound for commercial applications- even hot water tanks.

2. Any signs of visual damage (dents, cracks, paint chipping off, etc) should indicate the tank needs replaced.

3. Do not attempt to repair pressure vessels of any kind. It looks like in your previous video that someone had patch welded on one side of the bung hole (drain hole), most likely because it started to crack or leak. NEVER DO THIS! If you see a crack forming, tank develops a leak, or paint starts to chip off, DO NOT USE IT! This is an indication of fatigue failure. Even if you fix the one area appropriately, it will continue to crack around and nearby anyways.

More than likely this failure was due to fatigue, with rust compounding the issue. The welded seams by their very nature are physical discontinuities, and when you include the Heat Affected Zone (HAZ) causing a discontinuity in grain structure of the steel, it is a prime location for fatigue failure. Once a crack starts, it is just a matter of a few cycles to cause it to grow to catastrophic failure.

Moreover, pressure vessels are only designed for so many cycles They should be replaced periodically to ensure that things like this are avoided, even without visual damage. If in doubt, read the manual or contact the manufacturer and ask the service life of your air compressor. If the tank is expensive, it may pay to hire a company to ultrasound the tank to certify that it is still in good shape.

[heydonray]

Glad you’re ok! Please note that simply cooling the compressed air before it reaches the tank will NOT prevent water from entering the tank.

[deanhoward]

As a former fire investigator & tank welder; I think you have more than a simple seam failure! The pressure relief valve may have temporarily stuck & contributed to the catastrophic failure; without x-rays & and a hands on inspection it is hard to be 100% certain, but from what I see in this video; I see what we call a B.L.E.V.E. or a Boiling Liquid, Expanding Vapor Explosion. Most likely your compressor ingested or inhaled a flammable gas of some type, such as gasoline vapor, propane vapor or even exhaust vapor from a running automobile, and yes even with catalytic converters, internal combustion engines still produce enough volatile fumes to do damage to a compressor like I see in your video. I don't think it was just a seam failure! Somehow your compressor got flammable fumes inside the tank & when the hot air was compressed in with the combustible vapor, that's most likely caused the explosion ! Did anyone use a spray lubricant, like WD 40 around the compressor? If so it could have sucked the fumes in and spray lubricants can explode under pressure! Sincerely Retired Captain Dean Howard. Riverside Vol.F.D. member # 11803 National Association of Fire Investigators.

[seanwatts]

*Seams are on the bottom for SAFETY... THINK ABOUT IT - if the seam was on top how much MORE shrapnel would the motor and compressor make?*

[bobuk]

Hmm. A coiled inlet pipe might well condense the moisture out. Guess what, it will then get blown straight into the tank! Don't work. You need a proper water vapour separator which drains into a bowl that can then be emptied.

[srl]

We had a used compressor (homemade from a farm) that we would regularly use to work on our cars . During the weekend we might have as many as 10 friends hanging in out all day. This air compressor exploded during the initial fill, as the contacts froze and the pressure relief valve was not working. My brother had gone in the house while it was filling. It blew out an entire wall with shrapnel everywhere. The fire department said they never saw anything like it. No one was hurt. I suggest that you NEVER purchase a used unit and do a routine safety check on everything.

[neilfromclearwaterfl]

Note that the factory weld was actually clocked towards the side of the tank so that water would have needed to accumulate to a fairly substantial level to reach it. That the feed line to the tank blew off its port is a good indicator that there was some blockage/restriction in the relief valve or its port leaving over pressurization as a very likely contributing factor in this failure.

The power of compressed air is very powerful and one of the worst examples happened at a commercial laundry that was over a city block in size where an entire city block was leveled by a boiler tank that got over pressurized after it ran dry and someone tried to refill the boiler manually before allowing it to cool down first. It was estimated that it only took one cup of water to develop enough pressure in a 2, 000 gallon boiler to level the city block. The worker along with all the concrete around the boiler were turned to dust and vapor. This happened at least 60 to 70 if not 100 years ago at what I believe was the White Rose Laundry facility if I remember correctly and was quiet a common event, though not at this magnitude, before safety standards were put into place.


An automatic condensate drain unit the vents the bottom port on the tank every time the compressor cycles on and off to me as an industrial maintenance technician is almost a critical component for a horizontal compressor to ensure continuous condensate removal and best practice is to verify its operation every day the compressor is in use along with regular checking of the pressure relief valve by manually opening it under full set pressure to ensure that even though its free that it actually vents the tank and stays open to below pump cut in pressure so if it fails to vent or fails to stay open after you release it, then that is an indication that the relief valve is in need of replacement with one with an equal or lessor relief pressure. As the tank ages you should never change to a relief that vents at a higher pressure.

Coils between the compressor and the tank only better ensure that condensate ends up in the tank and does not migrate into your air system however a dog leg condensate trap with its own drain cock (preferably and auto-drain unit) after the cooling coils/device between the compressor head and the tank is a much better option as the bulk of the condensate should accumulate there and not inside the tank.

Though inconvenient a steel safety cage around a compressor to contain any explosive events is best practice however is no substitute for good condensate mitigation and regular safety checks. Dinging the tank with a pick though can be a double edged sword and end up causing a failure. Sounding the tank by lightly tapping the tank with a smooth faces hammer with no sharp edges on its face after the tank has been drained completely of all pressure is a better practice as is opening the largest port on the tank and inserting an inspection camera to verify the condition of the tank.

Welding a repair on a non-industrial tank is indeed an invitation for disaster unless your turning it into a non-pressurized piece of art or a barbecue.

A additional danger today is that some manufacturers, for user convenience, are putting the tank drain off to the side so that you have to tip the tank in order to drain it. I've seen some where this will leave about an inch of water in the bottom of the tank if you do not tip the tank so that the drain is facing straight down and hold it there until all condensate has been removed.

Indeed Be Safe.

Best!

[ninjatech]

Drain bung had welds around it, so tank had shown signs of severe rust damage, it was 'patched up' instead of being disposed of as it should have been. Who ever welded that tank up and thought it was safe to continue using even though it had already rusted though in at least one spot was and idiot.

[jeffshannon]

Thank you for caring about other peoples lives and the time that it took to make this video

[mattfeil]

After watching your first clip I accidentally came across yesterday...I went to my air compressor and drained it! I havent done it for about 5-6 years, I dont use it very often. I have so far drained out about 1/3 of a gallon of water!!! I so want to GRATEFULLY THANK YOU for sharing all this info!!!! You may have just saved my life and others!!!! Shall be drained every time AND be run ONLY outside!!! Thank you

[scroungasworkshop]

Look, I’m no expert but the steel in that receiver looks and sounds very thin. The fact that it let go along the weld seam is suspicious to me as well. I’m thinking that the problem isn’t rust but metal fatigue because the metal used to make the tank is so thin every time the compressor kicks in the tank expands slightly from the pressure and then contracts as you use the air. This cycle would be repeated thousands of times over ten years. If this is the case then I would fully expect it to fail at the weld seam as that is where the greatest amount of flexing would be because you have the thin metal of the tank meeting the thick metal of the weld. This would then act as a hinge point and although it’s only a tiny amount of movement given enough cycles that is where I would expect it to fracture. As you pointed out, if a pin hole developed in the tank from rust then, like you, I would expect it to just leak. Most aerosol cans run at 70 - 100 psi and I have punctured plenty of those and never had one explode. By the way, the cans have a warning not to puncture them even when empty because most of them use butane or propane as the propellant so one spark even when empty and it’s all over rover. There’s a good reason they use those gasses but that’s another story. It might be worth your while running a magnifying glass over the point of failure to see if there are any signs of a rust hole but I’ll be surprised if you find one. I think once the seam had failed the sudden release of air was big enough to rip the tank apart like a balloon popping where as when you get a pinhole there is enough metal around the hole to stop the rest of the tank from tearing open. I wouldn’t mind betting that it’s a cheap Chinese compressor. Do yourself a favour and buy a decent quality American made unit. I have two Australian made compressors in my workshop, a triple cylinder I use for sand blasting and a twin cylinder I use for everything else. Both compressors have tanks that have a 50mm plug at each end that can be removed to allow cleaning and inspection of the tank. I service them once a year and each time I take the compressor outside, remove the plugs and clean out the tanks. I even have a wire brush on a stick so I can clean the gunk off the bottom of the tank and eye ball the inside. Something to watch out for is that I have noticed some of the quality brand names here are now using Chinese compressor pumps and electric motors and maybe even tanks for all I know and assembling them here and whacking “made in Australia” stickers on them. I hope what I have said makes sense and I am happy to be proved wrong so please let me know what you find. All the best and stay safe. Cheers Stuart 🇦🇺

[hootinouts]

Sir, thank you for sharing this. This post may save a life in the future. I have several compressors and one is a Craftsman about the size of yours. This one I use for sandblasting and the cabinet is about six feet from the compressor. Well it won't be in the future. I'm getting it as far from me as I can. Something to point out is that the metal adjacent to any weld, which is referred to as the Heat Affected Zone (HAZ) undergoes a change in the grain structure as a result of the high heat. When a weld fails, it is generally in the HAZ if the weld is not stress relieved; known as post weld heat treatment. This would have been the manufacturer's fault had they skimped on this step.

[montyxmontyx]

Adding coiled tubing will lower compressed air temp into tank, but will not remove moisture. Moisture content in the atmosphere is what you will find entering the tank.

[alpaca]

I only run vertical compressors and the drain is always slightly cracked open. I loose air, but not enough to make a difference. Self draining and if i don't hear air leaking, leads to an inspection. I also check the pressure release. I pull it under pressure and let it bleed until it resets. I've had debris come out of the the pressure release valve, so i check frequently to make sure the valve doesn't freeze up. On another note, don't neglect your water heater safety valve. Years ago a water heater blew up in our area, shot it through the roof of the building and it landed in the street. Glad to see your focus on safety.

[oddballdynamics.]

Thank you for sharing this. I recently built a small shop. I had an area under a bench set up for my compressor. I will now be adding a small room outside to put the compressor in instead.

[keithnoneya]

I want to thank you for posting this video. I've always been a little leery about old air compressors and I have an older one than that. Because of this video I intend to use a camera to inspect both my 20 and 60 Gallon tank and am considering placing the one in use outside when I intend to pump them up. In my opinion both your videos are a must watch for all compressor owners. I always wondered why large compressors at shops were outside in a chain link fenced area instead of the shop. On my tanks when not in use I always leave the drain open.

[brianf]

these tanks can be pressure tested with a gauge and a pressure washer pump. typically tests should be minimum 1.5 x max working pressure. if it fails it fails. if it dosnt you can now be confident the tanks not going to rupture under normal pressure and they should be tested every x amount if years(idk the number). its called a hydrostatic pressure test iirc

[union]

Never hit a pressure vessel with a pick!!! Internal inspect with a torch and camera. Hydraulic pressure test every five years. Drain every day.