Compressed air safety

[Mike Ginn]

I have been following the posts on silver soldering boilers and the safety issues.
I would welcome advice regarding compressed air tanks. I have a steel tank (Draper twin cylinder compressor) with a 50Ltr capacity tank and a working pressure of 120psi. Water collects in the tank although this is minimized by the shop de-humidifier but water collects and, when released, it is naturally a rust colour. I have considered an automatic timed release valve but it is not fitted.
Do you guys have any advice on these pressure vessels or how they should be managed. How do I determine the expected life? Is there any internal tank treatment I could use to minimise rust penetration?
I would welcome your advice
Thanks
Mike

 

[minh-thanh]

That's still the problem with compressed air machines
Previously, I worked with an industrial compressed air system manufactured in Italy - a very modern system, although there are devices to limit moisture...but the tank still has water, However, it has an automatic water drain valve system, Setup time is about a few days / 1 time (I don't remember exactly).

 

[timo_gross]

Bumped into this video some time ago. Should I do an ultrasonic test on the tank from time to time

 

[minh-thanh]

Bumped into this video some time ago. Should I do an ultrasonic test on the tank from time to time

I don't know if the overpressure valve still works? Or is it damaged? Or did he remove its function?

 

[Mike Ginn]

I nearly dropped my cream cake when I saw timo's video!!! That was super scary. I subsequently found 2 more videos, one of a tank with no leaks but 40 years old having a 20% steel reduction and another with a pin hole leak which, on analysis, turned out to be very thin steel again on a 40 year old tank.

Moving forward I am going to install an automatic drain which will reduce the water pooling and I will only pressurise the tank when needed. I really don't know if this will help but since the compressor is next to my lathe (and of course me!) this might help me sleep at night.

I really don't know the occurrence of catastrophic tank failures. I can well see a leak occurring but would it explode? I am not sure that the function of the over-pressure valve is a factor since I suspect that the pump would not deliver much more than the top pressure - even if the tank were at half pressure that is an awful lot of energy.

Are there any industrial codes for small compressors?

Mike (who is still scraping of cream from the desk!)


https://www.youtube.com/watch?v=akAoznYEztsWas this old air compressor about to EXPLODE ?? – YouTube

 

[minh-thanh]

Automatic water discharge valve .. I think it is not necessary for an air compressor for a store. As long as the reminder board is hung in a prominent position, it's fine. The water discharge time depends on the time you use it and the weather.
Even though I bought the machine new, when I use it I always watch the pressure gauge for the first run, that tells me the overpressure valve is okay.
tank is over 40 years old...maybe it's too old
An interesting topic...How do you determine the expected life of a tank?
Hope someone has more opinions

 

[Mike Ginn]

Minh......but is 20 years too old? I was proposing to make the automatic valve discharge whenever the compressor was powered up thus minimizing the amount of water.

Having said that I really don't know what I am talking about when it comes to tank safety.

Lets hope one of our more experienced members can through some light on the subject!

Mike

 

[minh-thanh]

Minh......but is 20 years too old? I was proposing to make the automatic valve discharge whenever the compressor was powered up thus minimizing the amount of water.

As far as I know, only drain the water after use or after the tank is filled and cooled, because then water vapor / moisture can accumulate to form water.
I found some information

https://spikytools.com/how-long-do-air-compressor-tank-last/
https://wennigercompressor.com/2022...the frequency of,life expectancy of 25 years.

 

[GeoffR]

in the UK air compressor tanks are designed to typically EN286 and the HSE web site sets down how the equipment should be cared for.

The air compressor I have is made by Swan and has an epoxy coated internal surface. Made to ASME standards

GR

 

[Mike Ginn]

Geoff
I guess the majority of modellers simply order a compressor from the web and wind up with a branded (or not) unit manufactured in China. I find it is quite difficult to purchase any tooling or electrical device which is not made in China. I understand the reason for this and as time moves on it is likely that India will take on the China role. Coming back to the point of standards, I wasn't aware that it was possible to buy an internal coated tank or the existence of EN286 part 2. (I looked it up and it costs about £100! for the document). Draper provided the document of conformity shown below. I looked up (free) the Simple Pressure Vessels (Safety) regs 2016 (60 pages) and that seemed to cover the manufacturing process regarding safety.

My overall conclusion is that I needn't be concerned for the next few years but it seems sensible to remove pooled water from the tank frequently - and that will be my next project to automate the process.

Good discussion guys but it would be good to have a US input especially since the scary video was from the US!

Mike

 

[ajoeiam]

Your common atmospheric conditions are going to have a large bearing on your compressed air tank life.
If you live where there are high temperature high humidity you will have a shorter tank life, high humidity is the issue even in not so warm climates.
I would bet that internally coated tanks is something fairly new.
As a point of reference semi trucks use compressed air tanks and I've seen some terrible outside looking ones but they seem to live quite a long time - - - but then they are supposed to be drained at least once each operating day.
IMO the tank depicted in the video had likely been rarely checked for moisture buildup.
Also most of the tank failures that I've heard of were pin hole leak types - - - catastrophic failure is quite a bit rarer (not saying it doesn't happen!!).
IIRC it is recommended that you park your compressor off to one side and not right in your working area.

 

[Ken I]

ajoeiam - couldn't agree more - I spent a good deal of my life as a professional engineer signing off on pressure vessel tests - conducting most myself.

Failure under hydraulic load is nowhere near as dramatic as shown above and pinhole failure is the most common form of failure.

I never had one split like that but I have seen similar images and videos.

The last pressure vessel I professionally tested was a 60 cu ft 120 psi rated Ingersol-Rand over 60 years old and quite badly corroded in places but is still passing (1.1X) test some twenty years hence.

My personal garage compressor gives me the willies but I hydraulic pressure test it to 1.25 rating approximately every two years - but I live in fear of just such a bang as reported above.

That tank in the video looks very thin - but even so I suspect pressure switch failure and a jammed / overset / gummed up relief valve.

My advice - perform an annual internal visual inspection - keep an OSHA or similar logbook (normally available free or low cost from local safety agencies) with notes of condition and testing, do a proper hydraulic test every four years and periodically inspect the relief / safety valve for correct operation. (Do this at the same time as the hydraulic test, set safety to relieve at 1.1X pressure before plugging to continuing to the final test pressure (if higher) - be guided by local regulations even if you don't intend to fully conform - keeping such records will always help if it all goes pear-shaped one day.

Besides, I've never seen a tank subject to routine inspections ever explode.

Regards, Ken I

 

[krypto]

There's your problem! Not a factory weld.

According to the guy who filmed the video, after 10 years the tank developed pin holes around the drain even after he drained the tank every day! Sure, OK, whatever. Rather than scrapping the tank like a sane person, he decided to cut the old drain out and weld in another plug with drain.

Did he clean out the tank before welding? Nope. Did he weld it upside down with all the sparks going inside? You bet! Did he hydro test the tank after the repair? Hydro-what?

His defense was that it didn't break at the weld. Fair enough and it ain't easy welding on that rusty, paper-thin *****. Unfortunately, all that heat puts a lot of stress on the rest of pressure vessel. It might not have torn right at the 1/4" layer of chicken ****, but I'm sure it had something to do with it popping.

Also, I think something went wrong with the pressure switch and it kept running. Even the cheapest compressor you can buy has an emergency relief valve and it's there for a reason. He said he was "charging it up" when she blew.

 

[Mike Ginn]

Krypto - thank you for throwing light on the "incident". I think that will help folk sleep more easily at night - especially those who sleep above their shop! I had always thought (without evidence) that the first sign of failure would come from pin hole leaks long before a rupture.

I guess this video should be subtitled with a warning that you must never try to repair a compressor tank.

Mike

 

[Charles Lamont]

After my first cheap chinese compressor developed a pinhole leak after about 10 years, I spoke to a guy I know who spent several years as a pressure vessel inspector. He said that was about the life he would expect. I don't use my replacement compressor as much as I would really like to, and it is drained down after use. I would certainly never try to plug a pinhole leak: if it has corroded through in one place it is going to be very thin in others and should be scrapped.

 

[minh-thanh]

View attachment 149883

There's your problem! Not a factory weld.

According to the guy who filmed the video, after 10 years the tank developed pin holes around the drain even after he drained the tank every day! Sure, OK, whatever. Rather than scrapping the tank like a sane person, he decided to cut the old drain out and weld in another plug with drain.

As far as I know, the drain valve is made of brass and is much thinner than the tank and it is a "passive" overpressure valve for the tank.

 

[Joe]

Your common atmospheric conditions are going to have a large bearing on your compressed air tank life.
If you live where there are high temperature high humidity you will have a shorter tank life, high humidity is the issue even in not so warm climates.
I would bet that internally coated tanks is something fairly new.
As a point of reference semi trucks use compressed air tanks and I've seen some terrible outside looking ones but they seem to live quite a long time - - - but then they are supposed to be drained at least once each operating day.
IMO the tank depicted in the video had likely been rarely checked for moisture buildup.
Also most of the tank failures that I've heard of were pin hole leak types - - - catastrophic failure is quite a bit rarer (not saying it doesn't happen!!).
IIRC it is recommended that you park your compressor off to one side and not right in your working area.

Modern commercial trucks use very effective air driers and spitter valves, water build up in the tanks is a sign that something isn't working as it should. My truck is 4 years old now, my tanks are and always have been dry. There is just shy of 6000 hours on it and I couldn't guess how many compressor cycles.

John

 

[xtal_01]

I worked for an air house (air compressors and vacuum pumps) back in the 90's. No matter how many times we told people to drain their tanks, they didn't. I remember having one tire service truck come in and say his compressor would start and kick right out. I checked the tank ... filled to the top with water. This was not surprising as I was living in South Carolina ... very very very humid.

So, in the end, we just told every customer they "needed" an automatic drain.

There are several times .. some had a float ... some were just a solenoid valve with a timer.

My brother just bought a new compressor ... I told him to put an automatic drain on it. Again ... just in case you don't think about it for a few months ... and people with best intentions forget to drain their tanks ... the automatic drain won't forget.

Mike

 

[HMEL]

Geoff
I guess the majority of modellers simply order a compressor from the web and wind up with a branded (or not) unit manufactured in China. I find it is quite difficult to purchase any tooling or electrical device which is not made in China. I understand the reason for this and as time moves on it is likely that India will take on the China role. Coming back to the point of standards, I wasn't aware that it was possible to buy an internal coated tank or the existence of EN286 part 2. (I looked it up and it costs about £100! for the document). Draper provided the document of conformity shown below. I looked up (free) the Simple Pressure Vessels (Safety) regs 2016 (60 pages) and that seemed to cover the manufacturing process regarding safety.

My overall conclusion is that I needn't be concerned for the next few years but it seems sensible to remove pooled water from the tank frequently - and that will be my next project to automate the process.

Good discussion guys but it would be good to have a US input especially since the scary video was from the US!

Mike
View attachment 149877

My experience in the US dealing with pressure vessels that are part of the air systems was driven home by the insurance carriers inspections. They required that the safety valves be inspected or replaced annually. I do not ever recall they demanded wall thickness test be conducted. Nor did they ever require pressure tests on these units. Not so for the other unfired pressure vessels they were in the facility. I never gave it much of a thought till now but it may be the tanks operated at lower temperatures and the risk is lower. If the tanks did show evidence of corrosion they would have been replaced since a small leak would be very costly to sustain. But if you ever welded on one you better have the paper work to prove it was a good weld.

 

[TonyM]

My small compressor only contains compressed air when it is needed. It is never left with air in overnight or when not being used. If it has been used it is drained each day from the main airline and only the last couple of pounds go through the drain valve which is left open till I use it again. If the air is drained through the drain valve at any speed then turbulence is caused in the tank and the tank walls can remain wet with all the air released.
When it is used I wait till its full to check the cut off each time I use it. I check the safety valve also when first started. I printed a list and attached it to the compressor.

I worked with compressors, air receivers, and steam vessels most of my life. Never underestimate the potential for catastrophic failure of any pressure vessel.