Free tank

[Citation]

OK. I was gonna let this all rest, but there is too much bad info getting posted on the subject of air tank integrity.

First, I'll offer my chops ... I'm a registered Mechanical Engineer in Ohio, hold an ASME Section 1 Pressure Piping Inspection Certificate, and hold a National Board Boiler Inspector stamp. Also, a certified pressure piping welder.

Regarding tank design ... tanks are NOT designed to leak first ... via pinhole or anything else. Tanks are designed not to leak at all. I will admit that in the petro-chemical industry there are some designs that use pre-drilled "pits" in specific vessels for active corrosion detection, but that does not apply to air tanks.

Pinholes develop due to internal corrosion ... typically from the accumulation of moisture. If the corrosion becomes severe, a through-wall pinhole will often develop. BUT, a single pinhole seldom occurs alone ... if there is one, there are probable more (like cockroaches ... if you find one, there are probably more). You might weld up the one leaking, but that doesn't repair the remainder and, unless you take appropriate action, the corrosion in the other pits will most likely continue.

If you get enough of these pits (not yet through-wall) you will begin to weaken the tank wall, and if the weakening gets bad enough the tank can fail (another corny analogy ... it's sort of like pulling on a piece of perforated notebook paper, at first the paper holds, but then suddenly rips along the perforated line). Result is a catastrophic burst of the tank.

I really find it rather baffling that anyone would argue against performing a static hydrotest on a tank with unknown provenance. It's a simple test and is basic common sense. And it could save someone's life or save you a lot of bucks in damage repair.

I agree when you see one pin hole there are going to be more. However, as someone who also has a long list of degrees I think you are going to have to do more to convince me that the tanks in this class (not the large scale industrial tanks you are working with) are not designed with leak before burst in mind.

I don't disagree that inspection of tanks is a good idea but why wouldn't OSHA et al just make this a legal requirement if the problem was that significant? I hope you aren't suggesting that Leak Before Burst is some sort of invented concept.
https://www.researchgate.net/publication/275386718_Leak-Before-Break_What_Does_It_Really_Mean

Perhaps you can get us some stats on tanks in the 10-80 gallon range on failure rates and causes. I can certainly say that when my 20 gallon tank failed it was clearly a leak before break case. I cut the thing open to inspect it.

 

[John in OH]

I agree when you see one pin hole there are going to be more. However, as someone who also has a long list of degrees I think you are going to have to do more to convince me that the tanks in this class (not the large scale industrial tanks you are working with) are not designed with leak before burst in mind.

I don't disagree that inspection of tanks is a good idea but why wouldn't OSHA et al just make this a legal requirement if the problem was that significant? I hope you aren't suggesting that Leak Before Burst is some sort of invented concept.
https://www.researchgate.net/publication/275386718_Leak-Before-Break_What_Does_It_Really_Mean

Perhaps you can get us some stats on tanks in the 10-80 gallon range on failure rates and causes. I can certainly say that when my 20 gallon tank failed it was clearly a leak before break case. I cut the thing open to inspect it.

If you will re-read my post, you’ll note that I never said that a tank would NEVER leak before burst. What I said was that these small air tanks are not DESIGNED with a leak before burst (LBB) feature (except in some unique petro-chemical applications). Further, regarding your reference, note the types of applications cited for LBB:

“LBB has been applied to missile casings, gas and oil pipelines, pressure vessels, nuclear piping, etc.”

Suffice it to say, small mass produced air tanks for small shop air compressors do not fall into the rarified level of missile casings, etc.

I was trying to make the point (perhaps poorly done) that if a tank does have a through wall pinhole leak, it is probable that there are an additional (maybe 10, 20, or 30 ???) similar pinholes lined up in the bottom of the tank that have not yet penetrated the wall. Thus, setting up the “tear on the dotted line” catastrophic failure …. possibly with NO further pre-failure leakage!

Also, bear in mind who makes the majority of these small shop air tanks … most are mass produced from some unspecified grade of carbon steel by some small fab shop (maybe in China, India, or god knows where) and I can pretty well say with confidence that these small thin-wall tanks are NOT engineered with the sophistication to be able to exhibit a DESIGNED-IN leak before burst (LBB) feature. The determination of the wall thickness and their serviceability is typically done via a “proven experience” process, not a rigorous design process.

Most are un-stamped, non-ASME tanks (unless you are buying a very high end tank) with wall thicknesses of not much greater than 3/32”-1/8” and sized with little or no corrosion allowance.

I’m not going to go into any research effort to find tank failure stats. I’m simply offering my recommendation based on my experience and professional training.

If you or anyone else doesn’t want to do a static hydrotest on an unproven air tank prior to use … well, that’s your choice. I’m done with this topic.

 

[Dh3256]

I’m not going to go into any research effort to find tank failure stats. I’m simply offering my recommendation based on my experience and professional training.

Thanks for sharing your expertise, it's very helpful to have such good information from someone with the experience and training to give accurate recommendations and guidance.

 

[Citation]

If you will re-read my post, you’ll note that I never said that a tank would NEVER leak before burst. What I said was that these small air tanks are not DESIGNED with a leak before burst (LBB) feature (except in some unique petro-chemical applications). Further, regarding your reference, note the types of applications cited for LBB:

“LBB has been applied to missile casings, gas and oil pipelines, pressure vessels, nuclear piping, etc.”

Suffice it to say, small mass produced air tanks for small shop air compressors do not fall into the rarified level of missile casings, etc.

I was trying to make the point (perhaps poorly done) that if a tank does have a through wall pinhole leak, it is probable that there are an additional (maybe 10, 20, or 30 ???) similar pinholes lined up in the bottom of the tank that have not yet penetrated the wall. Thus, setting up the “tear on the dotted line” catastrophic failure …. possibly with NO further pre-failure leakage!

Also, bear in mind who makes the majority of these small shop air tanks … most are mass produced from some unspecified grade of carbon steel by some small fab shop (maybe in China, India, or god knows where) and I can pretty well say with confidence that these small thin-wall tanks are NOT engineered with the sophistication to be able to exhibit a DESIGNED-IN leak before burst (LBB) feature. The determination of the wall thickness and their serviceability is typically done via a “proven experience” process, not a rigorous design process.

Most are un-stamped, non-ASME tanks (unless you are buying a very high end tank) with wall thicknesses of not much greater than 3/32”-1/8” and sized with little or no corrosion allowance.

I’m not going to go into any research effort to find tank failure stats. I’m simply offering my recommendation based on my experience and professional training.

If you or anyone else doesn’t want to do a static hydrotest on an unproven air tank prior to use … well, that’s your choice. I’m done with this topic.

Every 20 gallon and above tank I've dealt with is ASME certified. My 20 gallon Campbell Hausfeld was certified. Its the only tank I've personally dealt with that rusted through. It was a pinhole failure. I cut the vertical tank open. This was not a case where it would zipper open so long as the tank was scraped once it leaked.

I don't recall the rules for when ASME or similar certification is required for a tank. I know my small California Air Tools tank is not certified. I've never heard of something like a 60+ gallon tank not being certified.

If you are going to come on here starting expertise it would be good if you had something to back those statements like the actual rules from the code or an explanation why OSHA, et al think it's ok to sell these things off the risk of catastrophic tank rupture is so high. Keep in mind that SCUBA tanks are certified and dive shops will not fill them if the inspections are out of date. Why don't we have the same rules for compressors? Is it the compressor lobby putting their interests above the consumer? Or is it that these systems reliably experience a "safe" failure before the metal unzippes.

I have no doubt you can tell us how to properly repair such a tank if one was so inclined but if you can't cite actual failure rates or *why* the regulators have chosen their current path I'm not sure you are actually enlightening us. Certainly your suggestion is the most cautious but you haven't offered a reasonable explanation why, given the actual harm a tank failure can cause, tanks aren't more regulated. The failure rate data I asked for would certainly help make the case.

 

[Dh3256]

If you are going to come on here starting expertise it would be good if you had something to back those statements like the actual rules from the code or an explanation why OSHA, et al think it's ok to sell these things off the risk of catastrophic tank rupture is so high.

That is great advice, do you have something to back up your opinions?

To answer part of your question, OSHA only applies to commercial use, they don't regulate home use. That's why so many of the 60 gallon and smaller tanks are not certified and the manufacturer prohibits commercial use. If one uses such a tank commercially, the manufacturer is not liable since their terms of purchase and use were violated.

 

[Citation]

That is great advice, do you have something to back up your opinions?

To answer part of your question, OSHA only applies to commercial use, they don't regulate home use. That's why so many of the 60 gallon and smaller tanks are not certified and the manufacturer prohibits commercial use. If one uses such a tank commercially, the manufacturer is not liable since their terms of purchase and use were violated.

My 20 gallon tank was ASME certified. Perhaps the rules changed between 2003 and now? This is the model I had (until the tank got a leak). Note the tank data plate under the motor.
https://www.google.com/imgres?imgur...Ag#imgrc=MqawHZJaw9fSNM&imgdii=bmjNeaI40pbSvM

Specific information isn't always easy to find. I'm not in this line of work but in my field (heavily regulated and with good reason) you sometimes have to really know the various rules to understand where a specific requirement comes from. Many of these regulations are not readily available without paying for a copy.

Anyway, this page suggests California has certification rules for compressor tanks over 11 gallons require a one time certification. Tanks over 187 gallons require reinspection.
https://www.vmacair.com/blog/faq-air-compressor-regulations-california/
I get the feeling that is rules for vehicle mounted tanks but I'm guessing the basis for the rules are some other specification. The ~11 gallon limit is what I recall in the past but I could be mistaken. Tanks under that size weren't required to be certified. Tanks over that size were. I'm certain that 60 gallon tanks were supposed to be certified.

You would be correct that OSHA doesn't apply to home/private use. However, did you notice I said "et al" after saying OSHA. That means I'm not trying to list any/every regulatory body that might have jurisdiction over the mfr, distribution, sale and use of air compressors.

 

[Sleeper]

Link to a thread from today discussing in part, Non-certified tanks on 30 gallon compressors.

https://www.garagejournal.com/forum/showthread.php?t=461584

 

[niget2002]

Ok, oh wise ones...

On to the next part of the discussion... The pressure switch.

The pump is only rated to 135 psi, so I bought a pressure switch that would shut off at 125psi. Made sense to me. However, when it came in and I took the cover off, I see that the switch is only rated to 12A at 240v, or ~2hp.

I'm assuming I should have bought this switch?

https://www.amazon.com/dp/B008ZFLRVS/?tag=atomicindus08-20

and while we're on the topic of acquiring parts for this machine, will this motor work? From the reading I've done and the measurements I made on the pulley, I think this is correct.

https://www.amazon.com/dp/B07GVNWJ6T/?tag=atomicindus08-20

 

[shadetree_mech]

This may sound silly, but would there be any way to seal the tank from the inside like when doing gas tanks with POR-15, or Red-Kote etc. to keep the tank from rusting on the inside?

I know this wouldn't help after the tank was old and already rusted, but doing this on a somewhat new tank to prevent it from happening?