LP & HP tanks

[lamont]

The impression of the diving public toward overfilling steel cylinders with the thought that is acceptable is confusing to me. If filling a steel to hydro pressure is considered reasonable, why not fill an aluminum 3000 psi cylinder to 5000 psi and get 52 more CF?

What is the reasoning? Both cylinder designs have been tested to a minimum of 10,000 hydro cycles without fail for DOT approval. How does the diving public rationalize this?

I just want the rationalization not a war!

Steel inherantly cracks very slowly and most steel cylinders are condemned due to rusting and not hydro failures. They also don't have the SLC tank neck cracking issues. Plus there's the 10,000 cycle testing, plus there's the safe track record of actual use this way in cave country. By overfilling a steel tank you're making it crack faster and making it more likely that it will fail a hydro at some point in its life, but given the already slow rate of cracking of steel, it probably won't matter. However, if you start pumping it up signficantly above its hydro testing pressure then you start getting into areas where the metallurgical guarantees about cracking are no longer valid, and there's at least one case of a ~6,000 psi fill in a steel tank resulting in a fatality.

All my tanks are HP tanks, though, specifically because its worth (to me) the cost and the hassle of getting the new HP tanks to not have to get into this argument with dive shops...

 

[500 PSI]

As long as you all are talking tanks how many fill cycles is a typical Aluminum 80 cf good for? I have often wondered what the life of an aluminum tank is if it is well maintained! Comments??

 

[Leadking]

Aluminum cylinders have also gone through the same 10,000 hydro cycle test as steel.
Cylinders are designed under a "equivalent level of safety" protocol.
I talked with a local hydro facility who does the bulk of hydros in the MPLS/ST PAUL market for all cylinders (scuba/medical/industrial). His statement to me that 90% of all cylinders that they have hydro'd are aluminum but most of the cylinders condemned are steel. PSI's website states about 6351 alloy "Several of the recent aluminum cylinder ruptures have attracted considerable industry attention while the more than 24 steel cylinder ruptures over the years are forgotten."

I sell both steel and aluminum cylinders, so either way it make no difference to me. My only concern is to the safety of the diving community and fill station operators (they usually are innocent victims).

 

[WarmWaterDiver]

Are there alloy composition differences for the 24 steel tank ruptures referenced vs. current 'steel' tank alloy compositions, similar to the aluminum 6351 vs. current aluminum alloy used?

 

[Leadking]

I can not say as fact but I would be very confident in saying they were 3AA steel, the same as being used today except in exempt cylinders.

 

[Paul F]

does any one happen to know of a place that has a couple PST E7 80 HP Tank in stock preferably in the NW or western canada

 

[TSandM]

For me, the argument for an LP Steel 95 is that they are cheaper than the HP ones, and trim me out perfectly . . .

 

[divematt]

So, is an LP steel 95 or 108 filled to 3700 safe or not? My tanks have DIN valves. The LDS allows the higher pressure fills regardless of the DOT. I like it that way but is it really unsafe? Do I have to go out and buy the 130's from Worthington that take 3440 psi just because of the DOT? I've heard they fill them to 4500 in Europe. I can get over 130 cubic feet filling the tanks as I do now but just wondered how foolish or not it was.

Thanks,
Matt

 

[lamont]

So, is an LP steel 95 or 108 filled to 3700 safe or not?

this does not answer your question, but may help you on your quest:

http://www.sportdiverhq.com/tanktalk.htm

 

[Leadking]

I've heard they fill them to 4500 in Europe. I can get over 130 cubic feet filling the tanks as I do now but just wondered how foolish or not it was.

Thanks,
Matt

Every tank design by every manufacturer must pass a minimum of 10,000 hydro cycles without fail (6-10 times a minute until fail, new cylinder without corrosion or fatigue issues) as required by DOT
Faber makes no tank greater than 7 inches that can take 4000 psi

U.S.tensile strength (105,000-125,000 psi) is not the same as European tensile strength (135,000-155,000 as required by EN 1964 part 1 and ISO 9809 part 1) and I have test data that shows Faber cylinders delivered to us show a tensile strength of 115,000-123,000 psi (as required by DOT)