steel tanks refinish?

[Gilldiver]

Gilldiver, where did you get those numbers?

Allow me to clarify
I got the number of 130F as the maximum operating temperature for filling a cylinder.
That's our standard for UCSC Fill Station Operators.
I merely take it as what it is and don't question it.
The manual also says that you should not store cylinders in temperatures that exceed 130F.
So as for the cylinders near the equator: personally I wouldn't want to use them. But that's just me.

But the temperature for using a cylinder on a dive will be different from that. I don't know what that number is.

I sent PSI an email and will post what they say about the process here.

The danger temp for aluminum comes from AMS 2770 for 6061 alloy ageing. I don't recall the AMS for steel but I can find it later today.

The surface temp for tanks, and most metals, came from acctual readings with a meter in the UAE, I was getting 150's and 160's for dark colored and 120-140's for silver and light colored things left out in the sun. You can fry an egg off of tanks at these temps. There is a reason why white is a popular color in the Mid East (cars may even have their bottom painted white) .

 

[WorkHorse]

I looked at Zinc Nation's video of Zinc metalizing.
I would strongly suggest not doing this unless you consult PSI.
The way Zinc Nation does it, is they heat up the metal while applying the zinc coating.
You should NOT HEAT your cylinders in anyway if you can help it.

The maximum operating temperature of a scuba cylinder is 130F.

Any temperature beyond that may compromise the structural integrity of the steel.
It will definitely be worse for an aluminum.

ASK PSI about this before commiting. Even if Zinc Nation says it's fine, they don't do exclusively scuba cylinders. It wouldn't hurt to get a second opinion.
I'll shoot PSI an email myself and check with them.

well my tanks passed hydro after the refinishing. so the integrity must not be compromised too much. and more than likely if you drop your tanks off at your LDS to get refinished they will end up with this type of finish, especially in california. EPA laws have restricted hot dip galvanizing.

 

[g1138]

If it passes hydro after it's refinished then there's really nothing I can argue against.
I got an email back from PSI
Here's what he said:

Ryan,
Who ever told you the operating temp is 130 is completely misguided, all cylinders are rated at 70 degrees F regarding all aspects including volume, testing and filling. This is tribal knowledge that continues to be passed around and is completely false. His cylinders MUST be condemned in accordance with DOT regulations.

DO NOT EVER HEAT YOUR CYLINDER BY ANY COATING PROCESS, THE DAMAGE IS CUMULATIVE AND IRREVERSABLE! ONLY A DOT APPROVED MANUFACTURE MAY GAIN APPROVAL FOR THIS PROCESS.

I'm still shooting emails back and forth trying to figure out if there's a magic temperature where cylinders are compromised.

In any case take it as you like. If it passes hydro and doesn't hide corrosion then I say all for it.

 

[g1138]

The danger temp for aluminum comes from AMS 2770 for 6061 alloy ageing. I don't recall the AMS for steel but I can find it later today.

The surface temp for tanks, and most metals, came from acctual readings with a meter in the UAE, I was getting 150's and 160's for dark colored and 120-140's for silver and light colored things left out in the sun. You can fry an egg off of tanks at these temps. There is a reason why white is a popular color in the Mid East (cars may even have their bottom painted white) .

Was this danger temp just for the allow or specifically set for a cylinder filled with 3000psi of air?

 

[JohnBhutch]

Ok the Aluminum Temps are due to the fact that both alloys that are in scuba tanks are T6. This means that they were heated to a specific temp and then speed chilled to harden the aluminum. If you heat the aluminum to a high enough temp you will anneal the metal once again making it workable. Aka no longer hardened and now it can rupture. I have the numbers someplace for tanks and will post them when I can find them.

 

[Gilldiver]

Mostly correct, ALUMINUM solution heat treatment (solutionizing) which will reverse the heat treatment of ALUMINUM is done at 850F-950F, Anneal which will soften the aluminum is done lower in the 600F-650F range, and Age temperatures where the final aluminum hardness and elastic properties is done at 250F and 350F. The specific temps and times are per AMS 2770. Also, solution quenching (speed cooling if you will) is only done in Solution heat treatment never in anneal or age were aluminum is air quenched or oven quenched. This meanes it is either cooled just out in the air or the oven is vented and the cooling rate is controled.

When using a powder coating, most commercial powders cure temps are usually in the 350-450F range as they are mostly used on steels or aluminum where the age (T-3/T-6/T-73/..) do not matter to the final product. So the danger of powder coating is that if you cure above 250F you are distorting the age and may actually be starting an annealing- so don’t do it. In practice I don’t like to take aluminum above 200-225F and in aircraft we start going to titanium and stainless steel for areas that see normal temps of this range. On helicopters this is limited to the engine and exhaust areas.

As for this

“Who ever told you the operating temp is 130 is completely misguided, all cylinders are rated at 70 degrees F regarding all aspects including volume, testing and filling. This is tribal knowledge that continues to be passed around and is completely false. His cylinders MUST be condemned in accordance with DOT regulations.

DO NOT EVER HEAT YOUR CYLINDER BY ANY COATING PROCESS, THE DAMAGE IS CUMULATIVE AND IRREVERSABLE! ONLY A DOT APPROVED MANUFACTURE MAY GAIN APPROVAL FOR THIS PROCESS.”

Who ever gave you this must not live on the earth and never took much aluminum material science. 70 degrees F is exceeded just about 24/7/365 anywhere below 20-25 degrees of latitude north or south. I have also been DIVING in water temps above 80F so am I damaging the tank by using it AT PRESSURE in the water? Where I am putting in an aluminum aircraft parts shop in India the avg temp is 85 with lows at 70 and highs in Aprial, May, and June of 115F.

As for normal temps seen by critical aluminum structures, what temp were the wings of the last aircraft you were on sitting out in the sun in the islands? I’ll bet that it was well over 100F and we see aircraft skins and main structural members at 150+ in the Middle East all the time.

 

[g1138]

Thanks Gilldiver for clearing that up.
I was a little curious when I talked to PSI and he gave me 70F as the only answer. I was prying at him again for a little bit of elaboration and he gave me this:

Ryan,
There are absolute high temperatures established by DOT for all cylinders that require the cylinder to be condemned;
Steel = 600 F
Aluminum = 350 F

This being said cylinder can be condemned for exposure to temperatures lower than the aforementioned, example a group of aluminum cylinders were in a room adjacent to a fire and after inspection they visually appeared to meet standards, when they were hydrostatically retested all failed the test due to permanent expansion exceeding 10%. The approximate room temp was established by forensic evaluation and determined to be 230-240.

We are currently experiencing a similar situation regarding last week’s cylinder rupture where steel cylinders were exposed to the fireball accelerated by oxygen causing a rather large fireball and structure fire. All but one are visually ok so a prudent person should retest all the cylinders to determine suitability for continued service / condemnation.

Regards,

Mark A. Gresham

I guess he didn't want to give me a high number in case I decided to push it with my cylinders =\

 

[Gilldiver]

Thanks Gilldiver for clearing that up.
I was a little curious when I talked to PSI and he gave me 70F as the only answer. I was prying at him again for a little bit of elaboration and he gave me this:




I guess he didn't want to give me a high number in case I decided to push it with my cylinders =\

I would agree with this as he is giving temps in the mid 200's F which is getting to the age range. A very quick exposure may not damage the tank structure but prolonged exposure for more than a few minutes to hours will. In a fire or near a fire a tank can be above 225/250 for more then a few hours.

But this is way diffrent then saying tanks are only rated to 70F.