Maximum test pressure

[duckbill]

Why would you condemn a cylinder alone based on going over the minimum test pressure? If the cylinder does not yield over the limits dictated by the specs you have not done any damage to the cylinder. Now if the cylinder yields and has deformation then yes, it needs to be condemned.

I, too, was wondering why it would automatically be condemned. However, as I understand it, damage is always done during a hydrotest if there is any permanent expansion, which there always is. The problem here is that more damage was done than the minimum necessary to get the test done.

 

[rjack321]

Agreed, I would avoid anyone that can't do simple math and turn a knob.
But I also know that $hit happens, we are all human. The sad part is I don't think very many people stand up anymore and say "Yep, I screwed your tank, here is a new one".

If elasticity limits are still ok its just aged a bit more than usual. I'm fine with chocking this type of event up to an "oops". But condemning a tank which is still within specs because its been overpressurized suggests to me that they don't understand the actual test reasoning in the first place.

The only circumstance I can see this as being remotely reasonable is vastly overpressurizing a 6351 cylinder and then being extremely cautious about SLC propagation that might be imminent (<5yrs away) but not yet showing up on a post hydro eddy test. And hence recommending condemnation for that reason. I.e. "We screwed up and your tank may be even more susceptible to SLC than it normally would be so here's $50 for our mistake, sorry."

 

[Cylinder Tester]

Originally Posted by Cylinder Tester
If we pressurized a cylinder over 10% of test pressure, I would condemn the cylinder immediately. I suggest you find another retester and retire your cylinders.

Roger

I assume if you did that you would replace the cylinders for the customer, correct?

Yes, there are several customers who either have new cylinders or were credited against other charges for our screw ups. I consider that the cost of doing business! I am in a business that has to be perfect every time; and we all know that only one person ever was or will be.

Originally Posted by fppf
Why would you condemn a cylinder alone based on going over the minimum test pressure? If the cylinder does not yield over the limits dictated by the specs you have not done any damage to the cylinder. Now if the cylinder yields and has deformation then yes, it needs to be condemned.

I would definately avoid hydro testers who condemn tanks which have not necessarily even exceeded their deformation specs just because they screwed up setting the TP

Has anyone ever heard of "Professional Liability"? Ever cylinder we touch could legally bind us to whatever happens to that cylinder for the life of the test cycle, and even further if it is not tested when the last test expires. My fault, your fault, nobody's fault, guess who gets sued if something happens to that cylinder. Please explain to me how it benefits me to let a cylinder leave my facility that I believe is unsafe! Is it worth losing my business over 1 cylinder.

And who are you to decide what the yield limit is for a specific cylinder? Everyone seems to quote the 10,000 cycle test performed by the manufacture as the end all, that ever cylinder the manufacture makes from that point on is perfect, that each cylinder exists in some perfect environment, that each cylinder will live on for eternity. Well guess what? 1 cylinder was pressurized 10,000 times as fast as they could pressurize it. And all it had to do was not leak, deform or blow up to prove the design. And after that 100's of 1000's of cylinders started getting popped out as fast as they could.

You want to bet your life on it, go for it. I expect to be here tomorrow and the day after.

Roger

 

[oxyhacker]

Many testers who grossly overpressurized a tank might give a nervous look around to see if anyone was watching, then bleed the pressure down a bit and do a normal hydro, rather than dutifully logging the overpressure the way this guy did, and leaving proof of the crime for everyone to see.

That gets me wondering whether the tester was operating on a misconception rather than just pure carelessness. Which is why it would be interesting to hear his explanation of why those particular pressures.

BTW I've never been able to find in CGA C-1 or anywhere else any mention of a maximum test pressure limit for the standard test. C-1 does say that in the event of a retest the cumulative increase shall be limited to no more than 10% of the minimum prescribed test pressure, but that is clearly in reference to retests only. While it's pretty clear from this and other references that the CGA doesn't think a tank should be pressurized to more than 10% of test pressure, nowhere that I can find do they actually come out and say across the board not to do it, far less specify automatic condemnation should it occur. And anyhow the CGA says the publication is "voluntary and non-binding".

This is worth noting because if one has a tank that has been overpressurized at test time, and wanted the tester to replace it, it would be hard to make a case as long as the tank passed hydro afterwards. It also would put a shop that condemned a tank after they overpressurized it in an awkward position since they would not be able to point to any DOT or other regulation that authorized them to do so. But then if they were replacing the tank with a new one as one assumes any reputable shop would I doubt anyone would complain.

I would definately avoid hydro testers who condemn tanks which have not necessarily even exceeded their deformation specs just because they screwed up setting the TP.

 

[Couv]

CylinderTester,

You probably have noticed, this is a well informed and sometimes rough crowd. I think I know you. If this is the facility that you work/manage, Western Sales & Testing of Deer Park, Inc, please allow me to commend you on the service I received from you last year. It is quite a haul for me to bring my bottles all the way to Deer Park, but it was certainly worth the trip. Not only did I find the price very reasonable, but several of the staff there took time to answer every question I had in person and over the phone.

When I got to this facility, it was very apparent that SCUBA is a very small part of their operation, but never-the-less I was treated as an important customer. Not only was the charge for the hydro was very reasonable, but the VIP was as well. The valve neck o-ring installed was a high quality polyurethane duro 90.

For my neighbors in the Houston area, it is worth the trip out to Deer Park for a hydro/vip especially if you have several tanks.

Couv

 

[duckbill]

This is worth noting because if one has a tank that has been overpressurized at test time, and wanted the tester to replace it, it would be hard to make a case as long as the tank passed hydro afterwards. It also would put a shop that condemned a tank after they overpressurized it in an awkward position since they would not be able to point to any DOT or other regulation that authorized them to do so.

That's what I was thinking. A hydrostatic retest is not a subjective test.

But then if they were replacing the tank with a new one as one assumes any reputable shop would I doubt anyone would complain.

Not a safe assumption. I dive vintage, and my tanks are valuable to me. They cannot just be pulled off of a retail shelf, and I wouldn't want a new, modern tank as a replacement. But that's just my cup of tea.

BTW I've never been able to find in CGA C-1 or anywhere else any mention of a maximum test pressure limit for the standard test. C-1 does say that in the event of a retest the cumulative increase shall be limited to no more than 10% of the minimum prescribed test pressure, but that is clearly in reference to retests only.

Hhmmm. Now that sounds right. The +10% or +100psi, whichever is less retest pressure is also stated in 49CFR, so it is binding.

That gets me wondering whether the tester was operating on a misconception rather than just pure carelessness. Which is why it would be interesting to hear his explanation of why those particular pressures.

Yes. Those are the same numbers that were run on previous tests and on similar cylinders. It was not an accidental over-pressurization.

I think I might have figured out his reasoning, thanks to oxyhacker.

The 2250 psi cylinders are plus ratable cylinders. I knew the hydro man would give a plus, so I requested it. As oxyhacker said, he probably just upped the test pressure by 10%.
2250 x 5/3 + 10% = 4125. Very close to the 4166 at which they were tested.

The 1800 psi cylinders are also plus ratable cylinders. Here's where it gets interesting. It appears that not only did he do the same math as above, he also added 10% to the service pressure, which he did not do to the 2250 psi cylinders.
(1800 + 10%) x 5/3 + 10% = 3630. Just 3 psi off from the pressure at which he tested the cylinders.

I'll bet that's what he did. Betcha. Yep.

I'm sure glad he didn't add the 10% to the service pressure of the 2250 psi cylinders like he did to the 1800 psi cylinders. Had he done that, those steel 72s would have been subjected to 4537 psi!

 

[Cylinder Tester]

DB,

So now that you've figured out how they got the test pressures what do you do with the cylinders?

Roger

 

[duckbill]

DB,

So now that you've figured out how they got the test pressures what do you do with the cylinders?

Roger

Technically, the steel 72 should be retested, but not because of the test pressure. The retester's license was not valid when he tested and stamped my cylinder. Due to his apparent lack of knowledge and laxidasical actions regarding his license status, I'm not really sure I want him doing any more of my cylinders. However, the price of a retest should not have to come out of my pocket. I'm not sure how I want to pursue this.

 

[oxyhacker]

Getting them retested would be real low on my list of priorities. It might matter to to the DOT whether or not his license was valid at the moment he tested your tanks, but I can't see how it really could make any difference to you. That is to say, retesting won't make them safer and won't make them easier to get filled. Come to think of it, the DOT knows the guy was running without a valid license for a while, and didn't make him do a recall, so I suspect they aren't very concerned about it either.

Just out of curiosity, did you take it to this particular tester because it is the only one handy, or because it was willing to "+" your old tanks?

Technically, the steel 72 should be retested, but not because of the test pressure. The retester's license was not valid when he tested and stamped my cylinder. Due to his apparent lack of knowledge and laxidasical actions regarding his license status, I'm not really sure I want him doing any more of my cylinders. However, the price of a retest should not have to come out of my pocket. I'm not sure how I want to pursue this.

 

[duckbill]

Just out of curiosity, did you take it to this particular tester because it is the only one handy, or because it was willing to "+" your old tanks?

Well, both.

Our only LDS uses the guy, even though he is 40 miles or so away.

I know at least one dive shop in Sacramento that uses him too, and I'm sure there are others as well.

He is also the only hydrotester in this general area that I know of who offers the "+" rating, and that is (read "was") my biggest determining factor considering there are other hydrotesters nearby.