tank overfills HP vs LP

[CaveMD]

I know there is a thread about LP overfills already.


But out of curiosity, do people overfill HP rated tanks to the same magnitude? And just how high do they go? If people are filling lp tanks to just under 4000psi, what would keep people from filling HP tanks to 5000-5500?

How much pressure can most DIN 1st stages handle?

 

[Wookie]

DIN first stages are usually rated at 300 bar, or 4500 lb. Air compressors are usually rated at 3,000 psi, 4500 PSI, and 6,000 PSI. (200, 300, or 400 BAR, roughly) I would be surprised to see any scuba cylinder pressurized above 4500 lb.

 

[GrumpyOldGuy]

Deleted. I found I was passing on bad information.

 

[SparticleBrane]

Another factor is many of the new steel HP tanks and LP tanks are the same, except for the hydro and stamps on the cylinder. This saves tooling cost for the manufacturer.

Thus the LP tanks have a lot of tolerance for overfilling above their rated pressure since they are essentially overbuilt for their rated pressure. It sibling HP brother has a stamp that makes it legal for the HP, tested at hydro at HP values , but it really has no more designed strength to endure incrementally more pressure than its LP sibling.

While they might look the same, they aren't the same steel. They are made from different alloys and have different tensile strength. While I can understand the confusion due to the similar sizes between different series cylinders, they are made from different grades of steel.

From this thread:

A tank sold in the U.S. as a 2400+ cylinder which will be a DOT 3AA cylinder cannot have a tensile yeild greater than 125,000 psi and therefore would fall far short to qualify for a European HP cylinder. The confusion is that there are different steels used in construction. Manufacturers use the identical tooling to manufacure LP and HP cylinders, the difference is in the metallurgy not the dimensions of the cylinder.

I spoke with our engineers today and found that DOT 3AA cylinders have a typical tensile strength of 105,000-120,000 psi and Worthington's tensile strength on our X-Series (E-14157) is 135,000-155,000 psi with nominal at 145,000 psi which they tell me they hit "pretty well on the money" every time.

This demonstrates that a high pressure E cylinders is at least 30% higher tensile than 3AA cylinders.

Please pass this information on and do everything you can to stop the rumor that HP and LP cylinders are the same except for the markings.

Dive safe

So, there you have it:
LP cylinders have tensile strength in the 105,000psi to 120,000psi range, and the 3442psi-series cylinders have tensile strengths in the 135,000 to 155,000psi, with Worthington usually being around 145,000psi in the X-series cylinders.

They are NOT "the same cylinders, just stamped differently".

 

[dsdiving]

Well said Sparticlebrane. That myth has been floating around my area for some time, not too sure how these tales get started, but thanks for the post.

 

[GrumpyOldGuy]

I read your referenced thread, plus a few others. I believe I was wrong, I was passing on bad information. My bad.

Same tooling maybe, different steel. Thanks.

I will delete my original post to eliminate the chance of passing my information on.

 

[netmage]

But out of curiosity, do people overfill HP rated tanks to the same magnitude? And just how high do they go? If people are filling lp tanks to just under 4000psi, what would keep people from filling HP tanks to 5000-5500?

No.... In an area that overfills, Its not uncommon to get a cold 3800, regardless of tank designation.... It's extremely rare to get anything higher.

 

[SparticleBrane]

I read your referenced thread, plus a few others. I believe I was wrong, I was passing on bad information. My bad.

Same tooling maybe, different steel. Thanks.

I will delete my original post to eliminate the chance of passing my information on.

No worries...I apologize if I came across too harsh. After coming back and re-reading it I can see where it would appear that I was a bit snippy. Sorry about that.

 

[GrumpyOldGuy]

No problem, getting corrected on SB much preferable to getting corrected by reality.

 

[Scott L]

LDS's who utilize chilled wet-filling facitities regularily fill HP cylinders to 3800-3900 PSI.