How long for a PCP tube's life span

[AirGunShooter]

As long as the pressure tube does not receive any damage from corrosion or some other damage, the useful life of the tube comes down to cycles - fatigue cycles with respect to how close each cycle comes to reaching or exceeding the yield strength of the material used. 

[KnifeMaker]

I do know that the Germans require a test at 10 years if I have the time right. However the Germans are so anal that I rarely pay attention to them.

My wife is German, and well, I do pay attention to her. LOL!

I am Half German, so I only pay attention half arss to myself. 

My Cherokee half will beat it with a stick if it doesn't work right. GRRRRR!!!

Knife 

[RAJOD]

The steel tube on my Regal is supposed to be replaced 10 years after the date of manufacture.

Mine said 10 years too but would be interesting to see how they came up with 10 years.  Why not 8? 7? 11?   Just seems like they pulled it out of a hat.   

Hand pumping will introduce some water but most of it is shot out of the gun.  If you point the gun straight up and shoot it a few times any water will be expelled out the port.   I saw a test on this where they introduced water on purpose.   They found almost all of it was shot out the barrel and pointing the gun up and shooting removed most of it.   
Agreed.  I've had most of my gun apart, but not the air tube.  Next winter, I may pull it off and lube the inside with a very light coat of silicone grease, just to protect it.  Also, I want to see if hand pumping has caused any issues within the year that I've been doing it.

[RAJOD]

As long as the pressure tube does not receive any damage from corrosion or some other damage, the useful life of the tube comes down to cycles - fatigue cycles with respect to how close each cycle comes to reaching or exceeding the yield strength of the material used.

Exactly, I want to see how many cycles from 2000 psi to 3000 psi it takes to bust the tank.   That is the bottom line worry is the tank could have some kind of catastrophic failure and blow up.   If its just a slow leak or fizzle type failure then I would not worry about it at all and just use it until that day comes.   

With so many cheap low quality pcps out there you would think there would be these types of failures showing up by now.  I've not read about any (not counting modder failures) 

[RobertMcC]

[rsterne]

A properly designed PCP tube should have a cycle life of millions of cycles.... Steel has a virtually infinite cycle life if the stress is below 50% of the yield strength of the material used.... Aluminum will fatigue even at lower stress levels, but if the material and thickness is properly chosen for the MSWP, again millions of cycles are possible without the tensile strength dropping to the point a failure would occur.... Here is a chart of cycle life at various stress levels for steel and aluminum.... Note that 10⁶ cycles is 1,000,000 cycles, or 27 cycles every day for 100 years....



Having said that, overfilling a PCP increases the stress, and so reduces the number of cycles before possible failure.... While an occasional, slight, accidental overfill is not an issue (again, assuming the manufacturer did their homework).... continuous overfilling is NOT safe for that reason....

Bob

[AirGunShooter]

As long as the pressure tube does not receive any damage from corrosion or some other damage, the useful life of the tube comes down to cycles - fatigue cycles with respect to how close each cycle comes to reaching or exceeding the yield strength of the material used.

Exactly, I want to see how many cycles from 2000 psi to 3000 psi it takes to bust the tank.   That is the bottom line worry is the tank could have some kind of catastrophic failure and blow up.   If its just a slow leak or fizzle type failure then I would not worry about it at all and just use it until that day comes.   

With so many cheap low quality pcps out there you would think there would be these types of failures showing up by now.  I've not read about any (not counting modder failures)

Do some online research for fatigue life cycles with respect to yield strength of material.  I believe it will answer most of your questions. 

Edit: Just saw rsterne's latest post and he nailed it when looking at the big picture.  (And then he edits it to add more detail.     )

[Ribbonstone]

Are some rifles I'm a little suspicious of at the factory rating, and others folks seem to find a change of valve retention screws enough to warrant using at even higher pressure.

So far, I've replaced two tubes, but it wasn't work hardening....was a "swelling". Not something I'd trust, but at least a soft temper-welling beats a hard-temper crack.

[RAJOD]

As long as the pressure tube does not receive any damage from corrosion or some other damage, the useful life of the tube comes down to cycles - fatigue cycles with respect to how close each cycle comes to reaching or exceeding the yield strength of the material used.

Exactly, I want to see how many cycles from 2000 psi to 3000 psi it takes to bust the tank.   That is the bottom line worry is the tank could have some kind of catastrophic failure and blow up.   If its just a slow leak or fizzle type failure then I would not worry about it at all and just use it until that day comes.   

With so many cheap low quality pcps out there you would think there would be these types of failures showing up by now.  I've not read about any (not counting modder failures)

Do some online research for fatigue life cycles with respect to yield strength of material.  I believe it will answer most of your questions. 

Edit: Just saw rsterne's latest post and he nailed it when looking at the big picture.  (And then he edits it to add more detail.     )

I think that is what Bobs chart in the previous post is all about.

But the definitions of a stress cycle on the chart is not the same as a stress cycle of filling a pcp tube.   Some fill from 1000-2000, some fill 2000-2900 etc.  Is that 1000 psi of stress the same as a calibrated stress cycle of a given material?   Probably not, its some fraction of it though.  Just don't know what that fraction is.

Many unknowns here.  Like thickness of the tube, what its made of, did the manufacturer over build it or maybe used metal with more impurities etc.    Example, if the tube was made a little too thin in areas or maybe it has some weak points of more stress.    I'm thinking they use 10 years just to be on the safe side.   Bob is probably correct that unless its rusted or poorly made its going to last 100 years.

[Ribbonstone]

It's the cummulative effects...same reason tanks have a hydro date.  Not that a few fills stresses them, but +10 years worth of fills.  Most of the current cheap guns haven't had the cycles (yet).

Will say thathavingt an expiration date (as one poicture shows) would certainly pout-off a commercial filler....the home-filler would likely ignore that date.

[RAJOD]

It's the cummulative effects...same reason tanks have a hydro date.  Not that a few fills stresses them, but +10 years worth of fills.  Most of the current cheap guns haven't had the cycles (yet).

Will say thathavingt an expiration date (as one poicture shows) would certainly pout-off a commercial filler....the home-filler would likely ignore that date.

For sure the carbon tanks won't be filled by a scuba shop if past the hydro date (most) That photo is not a carbon tank its a PCP gun so that would be home filled.

Even carbon tanks were found to be probably good for 30 years.  10 years was found to be too much on the safe and more profitable side of things.   They burst at around 26,000 psi.
I've talked with fireman they say when they fail its more of a fizzle not a BOOM. 

Time will tell because I am pretty confident that most air gunners wont be replacing the air tubes in a timely manner.   Another 5-10 years we should have some real world data on types of failures if any.

[DHunter]

Keep in mind that pump airguns cycle the pressure way up and back down to nearly zero with every single shot.

I know from the road bicycle world and bike science that carbon fiber does not fatigue like the metals do.  It's not that they don't fatigue at all, but that if you take the amount of force it takes bending back and forth to break it in ten cycles, and cut that force in half, it takes ten million cycles to break it.  If you cut the force in half again, it takes ten trillion (not billion) cycles to break it.  After two times of breaking a nice steel frame from fatigue, I decided  I didn't want to do that anymore, so I got carbon fiber.  So far I have 43,000 miles on it, ie, more than twice as many miles on it as it took to break the steel, and it's like new as far as I can tell (although I've broken an aluminum crank arm, and a pedal, and mashed teeth on a steel cog in a sprint), and I've read of other people with three times as many miles on their carbon-fiber frame and they said it was the same as new as far as they could tell.

[Bentong]

Thanks to this post i got now a reason to get more AGs so  I don't have to stress about tube life and stuff...the more  the merrier distribution of happy tube life. 🖖

[rsterne]

Cycling is cycling, but obviously going from empty to 3000 psi  is harder on the tube than just going from 2000-3000.... The maximum stress, however, is at the highest pressure used, and THAT is the stress that is important in determining the cycle life.... The large the tube OD and the thinner the wall, the higher the stress at any given pressure.... If that maximum stress is below about 50% of the Yield strength of a steel tube, the cycle life is virtually limitless....

Incidently, if your tube permanently increases in diameter, that means it is being subjected to stress greater than its Yield strength.... NOT a safe condition, and every cycle is fatiguing and weakening it.... Every tube acts like a "yo-yo" and grows and shrinks with every fill.... but the amount may be so little you can't even measure it.... I can't tell you what a "safe" increase in diameter is, but obviously the more it grows, the closer the stress is to the yield point.... and the shorter the cycle life....

Bob