The deal with expired air tanks

[Zone Drifter]

So I'm looking for a refresher in this tank topic. Here is my basic understanding:

-All aluminum tanks less than 2 feet long and 2 inches in diameter are exempt from testing. Use best judgement on condition.

-All aluminum high pressure air tanks (generally only 3000psi) are 5 year hydro, unlimited lifespan so long as it keeps passing hydro.

-All fiber wrapped tanks (in general) require hydro every 5 years with a 15 year limited lifespan. There are some exemptions but that is typical.


I only bring this up because I am amazed at the amount of expired lifespan fiber wrapped tanks for sale on eBay and other used sites. Is this enforceable by some kind of law or is it just up to the person if they want to take the risk and keep using the tank even if it's out of hydro or past the 15 year life? I also assume most fields won't allow those tanks from being used. That is up to the place of course, can't stop private fields from being shady if they want though.

Just looking for discussion on this. I recently rebuilt nearly all my tank regs and my shoebox compressor, so I was looking for old tanks not past life limit to refurbish and use. Caught me by surprise how many 20 year old fiber tanks were for sale!

[Nobody]

You can do 2 things with expired tanks. 1) you can self fill them, using them for home testing, or pirate ball or whatever is not regulated. You are taking your own responsibility for it. 2) cut it to make up cool planters, ash trays, really anything thatbis limited by your imagination. Now it is sort of confusing of what is a 3y hydro, and 5y but 15 years is the total lifespan of the tank and no reputable field would knowingly fill or allow an expired tank be used on their field.

this is my opinionNow, from what the welding industry & scuba dive shops have told me, is the 15 year lifespan is an arbitrary number. At some older ship yards and welding places, tanks can still be used actively that are 50+ years old, some are even nearer 100 years old. As long as there is no damage, no major problems, the tanks go on and on being used. One would surmise that carbon fiber wrap, that is a strong material in design, would continue to be able to hold the pressures, for as long as the structure remains intact. This is baring any clear coat problems of bubbling or cracking, and dents or dings going through into the wrap and subsequently the aluminium core. I truly believe that the lifespan limit was just a number, no one would think the sport would reach, or how a sub industry would be grown from it. Even then, the manufacturers built in a market where viable tanks have to replaced.

[caylegeorge]

I think that is a pretty well thought out opinion Nobody - I have always additionally wondered how the fiber wrap ages over time? After decades it seems like plastics often deteriorate and become more brittle and less structurally sound. Is the fiber in fiber wrapped tanks the same? Does it deteriorate with time? Sunlight? Temperatures?

For me, 15 years is long enough to not want to weigh $ versus my my own and other's safety. But it is interesting if the 15 years is based in science, mtbf testing, or who knows

[MrBarraclough]

As long as there is no damage, no major problems, the tanks go on and on being used. One would surmise that carbon fiber wrap, that is a strong material in design, would continue to be able to hold the pressures, for as long as the structure remains intact. This is baring any clear coat problems of bubbling or cracking, and dents or dings going through into the wrap and subsequently the aluminium core.

The problem, I believe, is that while carbon fiber is strong and largely flexible, it is also somewhat brittle in the long run, and the fiber/resin mixture is especially so. Every material has some inherent number of cycles to failure before it breaks due to fatigue. Each cycle of pressurization and depressurization expands and contracts the tank ever so slightly (imperceptible to the naked eye). That flexes and relaxes the fibers, which over time develop micro cracks. The purpose of a fiber/resin matrix is to allow other fiber strands to shoulder the load as a few individual fiber strands fail here and there throughout the life span of the tank. Each new failed strand increases the load on the remaining strands. Given enough cycles, it will reach the point that the load is too great for the dwindling number of good strands, at which point there is a cascade of breaks and catastrophic failure of the fiber. Thankfully, we have a pretty good idea of when that is likely to start happening, and can set the working life span of the tank well below that threshold by a comfortable safety margin.

All-metal tanks don't fail in quite the same way. They develop cracks that grow in size which can be detected by various testing methods (even high dose X-ray in some cases). It's easier to pinpoint a growing crack in a solid aluminum wall than it is to detect and count micro-cracks in individual fiber strands and determine how close that total number is to some threshold critical mass of broken strands. That's especially true given that the number of broken strands needed to precipitate a rupture will vary with placement (fewer needed if concentrated together). There are some century-old metal tanks in use today in welding and industry because we have pretty good methods of spotting problems and predicting failures with metal.

An out of date fiber-wrapped tank that still has years of usability left in it and one that is going to tear your face off tomorrow can look horrifyingly alike.

Is a 15-year maximum overly cautious? Maybe it is. Do manufacturers have a financial interest in this kind of planned obsolescence? Sure they do. We absolutely should push the industry to deliver fiber-wrapped tanks with better longevity and to set working lifespans based on reliable and transparent scientific data. In the meantime, I'm going to follow the stated limits unless and until professional engineers produce a body of data supporting longer limits. The cost savings of squeezing more life out of old tanks just doesn't compare to the potential downsides of having one fail.

[going_home]

Immortal Air already sells 38 year minimum to lifetime bottles.

Heres from the Immortalair.com website:

https://www.immortalair.com/product/immortal-air-immortalite-77-4500-carbon-fiber-system-1-tank-package/

[GoatBoy]

AFAIK, finding breaks in composite fiber parts is an ongoing topic of research. As noted, it's really hard to know when a fiber part is broken, and this doesn't just apply to paintball tanks. Anywhere these new fangled composite parts are used, particularly hard-to-reach places of complicated life-critical machinery, this problem exists.

The 15-year lifespan is apparently not arbitrary.

The act of hydrostatic testing on fiber tanks technically damages them in some small way. So you can only "test" a tank so many times until it's been damaged beyond a comfortable safety margin. So the lifespan is a multiple of hydro test interval. (15 happens to be divisible by 3 and 5...)

[Zone Drifter]

Very good point. So how would this apply to all aluminum tanks? Do they retain more flexibility therefor can be ran until it fails hydro? That makes me assume that when they hydrotest those tanks, if they fail then they were close to failing but weren't on the verge of exploding. Also, I wouldn't expect an all aluminum tank to just explode. If it was punctured, then it would burst out of the hole like a burst disk, right? More query than anything, I've never purposely tried to rupture a tank. This just makes me think that all aluminum tanks, despite the weight and less air capacity, are far safer and worth the value.

AFAIK, finding breaks in composite fiber parts is an ongoing topic of research. As noted, it's really hard to know when a fiber part is broken, and this doesn't just apply to paintball tanks. Anywhere these new fangled composite parts are used, particularly hard-to-reach places of complicated life-critical machinery, this problem exists.

The 15-year lifespan is apparently not arbitrary.

The act of hydrostatic testing on fiber tanks technically damages them in some small way. So you can only "test" a tank so many times until it's been damaged beyond a comfortable safety margin. So the lifespan is a multiple of hydro test interval. (15 happens to be divisible by 3 and 5...)

[GoatBoy]

Very good point. So how would this apply to all aluminum tanks? Do they retain more flexibility therefor can be ran until it fails hydro? That makes me assume that when they hydrotest those tanks, if they fail then they were close to failing but weren't on the verge of exploding. Also, I wouldn't expect an all aluminum tank to just explode. If it was punctured, then it would burst out of the hole like a burst disk, right? More query than anything, I've never purposely tried to rupture a tank. This just makes me think that all aluminum tanks, despite the weight and less air capacity, are far safer and worth the value.

I wouldn't extrapolate any value judgements like "safer" or "about to explode". It boils down to numbers and statistics.

A 15 year lifespan means... 15 year lifespan.

I have to admit I like my little 2" aluminum tanks for the lifespan reason. I've got a bunch of expired fiber wrapped tanks that I think I'm going to use as large air dusters around the house...