What to do with a tank that has failed hydro?

[captain]

Either way I know I won't buy anymore PST tanks. If they fail the ordanary Hydro procedure, they sound like they can't be as good as tanks that pass it. On top of that they ignored the email from me. They could have responded and said "sorry there is no warranty on that tank".

I don't know this to be fact, but I had heard that the round out procedure was needed because of the hot dipped galvanizing process affecting the shape the cylinder assumes when not under pressure.

Oxyhacker you can chime in, do any of the other manufactures of hot dipped galvanized cylinders also require the round out procedure.

 

[Luis H]

Not likely - the PST procedure has no official status, it's just a kludge that PST came up with to give their tanks a little extra help at hydro time, without actually breaking the law. So a hydro shop isn't required to follow it. And the PST that issued that bulletin doesn't even exist anymore.

The round-out procedure is not a kludge (I love that word ). It is commonly done to other thin wall pressure vessels in other industries. It guaranties a true cylindrical geometry and IMHO, it should be done to all thin wall cylindrical pressure vessels before testing.

Hydro testing is intended to test the elasticity of the material not how true is the cylindrical geometry. As an example a fireman’s hose can hold a lot of pressure when it is cylindrical, not flat, but the volume change from flat to a cylinder is huge.

In a thin wall cylindrical pressure vessel the walls are stressed in pure tension, not bending. If it is out of round it should just simply bend to form a cylinder without harming anything if it is within the material properties (and geometry) allowable limits.


A manufacturer requirement is not a law, but it is still a requirement. Your automobile manufacturer can require procedures to service the brakes, etc., as long as it doesn’t violate federal or state regulations. If you or the service technician doesn’t follow the requirements, don’t expect any sympathy or anything else from the manufacturer (in any case whether you will get anything is always debatable).

If I hire a technician/ shop to perform a service it is a requirement for them to follow manufacturer’s requirements (unless I specifically agree otherwise) if they are going to have my business.

 

[fweber]

Louis,

The fact is, they(PST) are requesting that the hydro tester use a "System Leak Check" that is allowed by DOT to perform a round-out that shouldn't otherwise be needed. Other galvanized cylinders don't require it. Other thin walled cylinders don't require it. And, even after performing the necessary round-out, a higher percentage of PST tanks WILL still fail when compared to other brands. It's a DOT 3AA cylinder. It should test somewhat like all the other 3AA cylinders. Perhaps PST simply selected too high a grade of steel and then thinned it too far. But, it's down right difficult to get their cylinders to pass, even after using a round-out. If one has been left at low or no pressure for long, there is little chance of getting it to pass. I've gone so far as to take such cylinders, that came in without valves, valve them, take them through several fill cycles, top them off and set them aside for days. After the aforementioned, and performing a system leak check/round-out they still might not pass. It's not the system that is amiss here..............

 

[oxyhacker]

The feds don't mandate any particular procedures for auto maintenance. So manufacturers and dealers have to provide their own, though independant shops will often disregard them, or, if they feel they are unreasonable, at least offer the customer the option of ignoring them.

In the aviation world, where the feds do mandate procedures, manufacturers are free to issue their own "mandatory service bulletins", but there is no requirement that the owner or mechanic pay any attention to them.

The situation is pretty much analogous to state motor vehicles inspections. There is, in most states, a fairly short list of things they look at, with a few minimum quantative requirements like remaining brake pad thickness and tire tread depth. A garage can not enforce its own, stricter, standards, nor can a car manufacturer, while performng the state inspection.

A manufacturer requirement is not a law, but it is still a requirement. Your automobile manufacturer can require procedures to service the brakes, etc., as long as it doesn’t violate federal or state regulations. If you or the service technician doesn’t follow the requirements, don’t expect any sympathy or anything else from the manufacturer (in any case whether you will get anything is always debatable).

If I hire a technician/ shop to perform a service it is a requirement for them to follow manufacturer’s requirements (unless I specifically agree otherwise) if they are going to have my business.

 

[pescador775]

Weber, one small correction. I presume the "thin walled" tanks which you speak to are HP? The PST HP tanks are not "3AA".
Pesky

 

[fweber]

Weber, one small correction. The PST HP tanks are not "3AA".
Pesky

Right you are. They are E series. Forgive me the error. But, iirc the lp 95's that the OP is talking about are.

 

[AbyssalPlains]

Sell it to some DIR guy. Not having to worry about keeping the hydro current eliminates another failure point.

 

[Jasonmh]

Sell it to some DIR guy. Not having to worry about keeping the hydro current eliminates another failure point.

Diving with a tank that failed hydro eliminates a failure point?

 

[tajkd]

RJP,

The exploding tank is on U-Tube already if you want to see it.
YouTube - Tank Shootout

 

[WD8CDH]

The flattened fire hose is really a good description of the round out procedure. Rounding out the tank doesn't prestretch the material, it just sets the volume. If anything, it would make a truely fatigued tank fail easier.