Steel tank overfill damage?

[Nemrod]

I have two of my small fleet of steel 72s that I have owned since the early 70s. They have endured many "cave" fills in the 2800 to 3000 psi range and they continue to pass hydro. I no longer cave fill because--uh--I no longer cave dive but think nothing of a 2500 psi fill especially when warm. They will cool down to a good fill. I watch fill stations that might overfill my tanks by accident,on occasion I have had tank monkeys fill them to 3000 plus not knowing any different. I began writing with a permenant marker the fill pressure on the shoulder so they could see it and a verbal reminder for each type of tank. N

 

[duckbill]

I have my fill pressure written in black ink on the shoulders of all my galvanized tanks, as well as the service pressure and latest hydro date (with the "+" circled in black when present) painted with OSHA yellow. This incident is the first time I've received a gross overfill, and the LDS knows my tanks, so it was just oversight, I'm sure.

 

[in_cavediver]

I have my fill pressure written in black ink on the shoulders of all my galvanized tanks, as well as the service pressure and latest hydro date (with the "+" circled in black when present) painted with OSHA yellow. This incident is the first time I've received a gross overfill, and the LDS knows my tanks, so it was just oversight, I'm sure.

I guess I am bad - I always thought that 2400 on my tanks was my turn pressure......

My opinion on overfills is this and when I say overfill, I mean gross overfill, 500psi+. IE 3800 in a 2640, 3000 in a 2250 etc. Not 3200 in a 3000 or 2500 in a 2250.

Anything less than a gross overfill isn't worth worrying about.

Al - don't do it at all.

Steels - well some LP tanks have a long history of no problems. There has been rumored data about some tank brands lasting 10,000 hydro cycles prior to failure etc.

Personally, I been cave filling PST 104's for the last 5 years. No problems. I am about to send them for the Hydro so I'll let you know if they fail.

 

[CompuDude]

I guess I am bad - I always thought that 2400 on my tanks was my turn pressure......

...

Personally, I been cave filling PST 104's for the last 5 years. No problems. I am about to send them for the Hydro so I'll let you know if they fail.

While I respect your experience (and number of dives), I think it is verging on gross negligence to encourage someone to overfill a tank. Just my take on the matter.

That said: 10% overfill is no big deal, on nearly any tank, but especially no big deal on hot fills, which cool to the correct fill.

And no offense, but if you have only been been cave filling PSTs for 5 years, that means you have NO IDEA if your tanks will fail hydro or not, since they only need hydro every 5 years.

I'm not saying any of your tanks will fail... in fact the odds are probably in your favor. But gambling with your tanks, and advising someone else to do the same with their tanks are two different things.

Sorry, I'm a little touchy on the subject since I bought a used PST tank that failed it's first hydro, 9 months after I bought it.

 

[paulwlee]

Sorry, I'm a little touchy on the subject since I bought a used PST tank that failed it's first hydro, 9 months after I bought it.

Which tank did you have?
May or may not be the case with yours, but I heard that PST tanks need a special pre-expansion cycle to prime the hot-dip galvanized layer otherwise they will fail to pass hydro. Apparently hydro stations that don't handle much of those tanks will just do the usual procedure and then fail the tanks.

But you are right, anyone doing overfills do so at their own risk.

 

[CompuDude]

Which tank did you have?
May or may not be the case with yours, but I heard that PST tanks need a special pre-expansion cycle to prime the hot-dip galvanized layer otherwise they will fail to pass hydro. Apparently hydro stations that don't handle much of those tanks will just do the usual procedure and then fail the tanks.

But you are right, anyone doing overfills do so at their own risk.

PST HP100, one of the last true 3500 HP tanks (skinny neck). The shop (which actually does most of the hydros in the entire area on site) did use the special PST procedures, which I grilled them on many times, and even handed them a print out of them along with the tank. They pointed at a copy posted on the wall.

Muchos suckos.

 

[lamont]

That said: 10% overfill is no big deal, on nearly any tank, but especially no big deal on hot fills, which cool to the correct fill.

in fact the letter of the DOT regulations is that the service pressure is 21C/70F and an overfill of up to 5/4 of the service pressure is allowed at 55C/131F. it only exceeds the specs if it cools to higher than the service pressure at 21C.

and i'm definitely with in_cavediver that a few hundred psi is nothing to lose any sleep over -- particularly with steel tanks that crack much slower than aluminum...

 

[CompuDude]

in fact the letter of the DOT regulations is that the service pressure is 21C/70F and an overfill of up to 5/4 of the service pressure is allowed at 55C/131F. it only exceeds the specs if it cools to higher than the service pressure at 21C.

and i'm definitely with in_cavediver that a few hundred psi is nothing to lose any sleep over -- particularly with steel tanks that crack much slower than aluminum...

I agree, and thanks for the actual specs, I couldn't recall exactly and didn't want to post poorly-remembered specifics.

(I agree re a few hundred PSI, I don't agree re the spectacular overfills (500+) favored in cave country)

 

[SparticleBrane]

People have been 'cave filling' 3AA cylinders for decades with tanks lasting several hydro cycles.
Personally I won't overfill (beyond ~2500) the 2250 older steel 72s, just because I'm absolutely careful with them since they're not made anymore--same for the lower pressure tanks.

Other than that, they're fair game. The newer LP tanks--85s, 95s, 104s, etc...can all handle at least 3600 no problem. The newer exemption tanks shouldn't have any issue at 3600 either, especially since that's only a ~150psi overfill from 3442. That, plus the metallurgy is different on the exemption tanks vs. the 3AA LP steels--the exemption tanks are stronger. Look up some of Leadking's posts on the subject. If I recall, the exemption tanks are usually ~20,000psi higher in tensile strength than 3AA LP steels.

In another topic, why is everyone so frowny on overfilling aluminum tanks? They have to go through the exact same strength tests that steel tanks do, to be put on the market. Luxfer lists their minimum burst pressure as 2.5x service pressure, or 7500psi for a 3000psi tank. I'm not going to worry about 3600 in an Al80...even if it does decrease the service life. If you bought it for $175 and it lasted you 10 years, you paid $17.50/year for your tank. Go get yourself a new one, they're cheap.

I'm not advocating overfilling cylinders, but I will say that it's been doing in North Florida for a long time. If someone can point me to an incident involving a tank exploding from a 3600psi fill, I'd love to read it.

 

[paulwlee]

PST HP100, ...
Muchos suckos.

Wow, sorry to hear that.
But then what was it being overfilled to? Surely not something crazy like 4500psi???

Which brings me to my question a couple pages ago in this thread.. most overfills I hear about are filling LP tanks to HP-like pressures. Grossly overfilling HP tanks seem as common as overfilling AL tanks. (Read: pretty rare.)

So do people actually overfill(more than the usual hotfill 10% or less) HP tanks too?