Old steels denied fills due to store "policy"

[Billy Northrup]

I’ve seen a few shops refuse tanks in hydro but had generic inspection stickers off EBay. They wanted to see a shop name on it

 

[BRT]

Just to clarify the OP has provided inaccurate information.
The tanks in question are 51 year old steel 72s . I wonder what other details my be in question

Do you have an example of a 51 year old steel 72 that exploded while in hydro and vis? None? Never? Do you know how high they pump those things? The guy I sold mine to told me they make great 100's.

 

[Wookie]

I’ve seen a few shops refuse tanks in hydro but had generic inspection stickers off EBay. They wanted to see a shop name on it

And that is maybe valid. But that isn't what's going on here. The cylinders had VIP stickers from the very shop that refused to fill them.

 

[Jiminy]

And that is maybe valid. But that isn't what's going on here. The cylinders had VIP stickers from the very shop that refused to fill them.

She should ask the GM for a refund on her VIP I think that would be fair

 

[swimlikethefish]

Again welding cylinders operate at a much lower working pressure and I stand by my assertion that praxair or air gas have never provided me with a rental tank older than 20 years. Yes I have seen many privately owned tanks that predate the first world War. ]

For thought I went out into my shop. I have a regular swap of 20+ tanks a week with airgas. Here are just 3 examples: argon, oxy, co2. All predate your 20 years assertion. You might want to go explain to them you no longer want their business because they are providing you with tanks that are over 20 years of age....

 

[Ana]

Just to clarify the OP has provided inaccurate information.
The tanks in question are 51 year old steel 72s . I wonder what other details my be in question

Wow... my tanks are rotten, from craigslist and now I'm a liar.

You got me... I exchanged sexual favors in a dark alley for the tanks in question. Then I walked into Force E demanding loudly to get my f'ing tanks filled right away. I then harassed them online and not happy with that I came here to slander them. Who knows maybe I'll throw poo to them next time I drive up US 1.

Dude.... what is wrong with you? I said the tanks are steels from 1970 and 1971, and so they are, but what if they are from 1961? or 1951?

WTF are you clarifying? Like tmassey said above ... I could do this all day.

 

[fullytek]

Let's see the vip?

 

[swimlikethefish]

Wow... my tanks are rotten, from craigslist
Dude.... what is wrong with you? I said the tanks are steels from 1970 and 1971, and so they are, but what if they are from 1961? or 1951?

I have 8 year old tanks that look worse than that... She looks pretty clean on the outside.

 

[txgoose]

Let's see the vip?

Because her first lie didn’t end up being the lie that you claimed it was? Dude. This is becoming beyond comical.

 

[Diving Dubai]

Okay... I am (was) a metallurgist, I worked within the Aerospace sector, with my speciality being Non Destructive Testing.

Allow me to pick up on a couple of points.

That's where vis comes in. It's a quick way to see if something has changed. Are you a trained visual inspector? If not, you should become. It's like $200 or so for the class. Even if you never vis a tank yourself (outside of class), it's worth it. The biggest surprise for me was how *MUCH* damage is perfectly fine. I don't have my book in front of me, but the amount of pitting that is allowed is *WAY* more than anyone's emotional "gut" would tell them is OK. Like I was shocked.

Visual Inspection is subjective - incredibly so. You might be surprised to learn that a professional visual inspection course for Level II that allows some to inspect and decide if a component is serviceable or not has a minimum course length of 40hrs and certainly doesn't cost a mere $200 A professional qualification has to be re-certified every 3 year - you go through the whole examination process again

The trouble with vis is that some inspectors can be absolutely spot on and well trained, at teh other extreme some might have been asleep in class or couldn't care that day. I've had the unfortunate responsibility of attending 2 air crashes where the prime cause was a defect clearly missed during inspection.

So vis is really only worth while to see if there are any major problems.

How do we *know* that tank is still safe? A hydro. A hydro does more than test the tank's ability to hold pressure. It does do that, but it's much pickier than that. It measures how much the tank *expands* while filling (which tells if the tank is being stressed at that level), and *contracts* when emptying (which tells if the tank is damaged by the process.) If the tank expands a certain amount (not too much and not too little!) we know the metal is acting like it's supposed to resisting the pressure. If the tank contracts back where it's supposed to, we know it's ready to do it again.

Sort of. A hydro measures the materials elastic properties which can change over time. A material can become both more or less elastic. So yes in that you are correct.

But that's all it does (apart from testing the ability to hold pressure) It cannot measure any stresses nor detect any fatigue cracks or stress corrosion for instance. A cylinder can have these underlying defects, pass hydro and vis and still go bang on a pressure fill.

How do we know all of this? Centuries of metal knowledge and experience. We know if the tank stays in the defined range, it is fine. No matter 'how many times it's been filled, tumbled, etc. etc. etc.' The tank is still working as designed.

Our knowledge of metallurgy is great, but we don't' know it all. I gave up being surprised when a component would fail unexpectedly havign been stressed modeled and designed to the nth degree. Cylinders are over engineered - massively so, because the raw material is of commercial grade and has the potential to include all sorts of defects. While batch testing of the raw material can pick up if its a bad composition or heat treatment and later poor manufacturing quality it can't guarantee the material is perfect. Hence they over engineer because the raw material is cheaper than 100% testing.

Cycle testing of cylinders is there to ensure they can stand pressure cycle fatigue. You can't fully test for environmental and handling conditions as there are too many variables.

Tumbling etc will remove material wall thickness which may have no effect on hydro but will cause stress concentrations. Generally not an issue but given teh right circumstances it will cause an initiation point for a failure. That defect might be fast or slow growing.


Now it's perfectly acceptable and rational to look at failure rates over time vs number of cylinders and declare that the risk of failure is low. We do it all the time. But using that as a bases to have unlimited life on a cylinder is
foolhardy.

The ONLY people who can give a predicted life expectancy in teh real world are the manufacturers, and they would err heavily on the side of caution.

We are all scuba divers who are cautious with our equipment. People debate until they go blue about "additional failure points, O rigs and plastic buckles" and yet will happily insist that cylinders are good to be overfilled and can be used forever because there hasn't been a problem...

I'll admit I'm an engineer and cautious - from experience. my personal opinion that a 50yr old cylinder is well overdue to be turned into a bell or astray

If you had more rigid and meaningful inspections that might not be the case, but the cost of such would not be cost effective.

Is 30 years too much I don't know (without data) but if a shop wishes to err on the side of caution then we should respect that.

$300 for a new cylinder and 5 years hydro free? Cheap I say