Baking Tanks in the Oven for O2 Cleaning

[hydro12]

So I was reading the DOT and Military specs for O2 cleaning and testing of AA and AL cylinders, and came across this bit of RR-C-901D, section 4.3.2.1 at http://assist.daps.dla.mil/docimages/0004/03/71/901D.PD5 regarding testing for Oils and hydrocarbons in cylinders after an O2 cleaning. It specifically refers to the Evaporation Method by "[evaporating] the extract to dryness at slightly below the boiling point and finish[ing] the drying in an oven at 221 ºF (105 ºC) ± 1.8 ºF (1ºC) for 15 minutes. Cool, weigh, and report as milligrams of extracted oil."

What I'm specifically curious about is whether anyone's used the baking in an oven at 221 F for 15 mins to merely dry the cylinder after running solvent (eg. Simple Green solution) through. I'm having a hard time rigging a blow dryer to effectively dry the inside and thought this might be easier ;P

 

[SparticleBrane]

Exposing cylinders to such high heat isn't really recommended...

 

[Mako Mark]

I have always been under the belief that anything over 80 degrees Celcius had the potential for annealing (softening the metal through chrystaline restructuring) and therefore was a big no no.

regarding drying tanks, the tanks should be inverted and an air hose inserted and air blown through it for about 20 minutes. Works a treat.

 

[Gilldiver]

For most aluminum alloys the trigger temp for changing the heat treat is between 225 and 250F.

If you are doing it in a calibrated over it can be done safely, at your house - don't even think about it. I work at a Aerospace aircraft manufacturer and do a lot a aluminum heat treatment (at one time I was the guy who did the oven cals). We only certified an oven if it kept a uniformed temp throughout the box of +-10F. Your oven at home will not even be close. Even then we would do a conductivity check on the sample parts of each alloy processed to make sure we didn't screw up.

For the scale, do you have one that can read to .1 gram at 30-40 pounds?


As for the spec, I'll look it over but many of these are real old and no longer used.

 

[Gilldiver]

OK, I see what they are doing. The test method doesn't heat the tank at all. What they are doing is a solvent extraction, pour in some solvent and slosh it around inside the tank, collecting the solvent, and then evaporating the solvent and weighing the residual.

See para 4.3.2.1

With these specs you have to keep track of the para numbers in order to figure out what they are doing. The alternative method (4.3.2.1 I think) to the evaporation and weight method is to use an IR to look for residual organics. In practice, I would collect the solvent, evaporate it in a clean dish, and then look at it under the IR scope. We do this just about every day at work looking for extractions from composite materials and structures.

 

[Rainer]

When we clean our tanks, we just blow them out with O2-clean compressed air. 30 seconds and the cylinders are bone dry.

 

[hydro12]

Yeah, I figure Gravimetric Analysis isn't exactly for me either considering my lack of a scale that would be that precise or accurate. I noticed on Luxfer's site, they list the melting point of their Aluminum cylinders at about 1200 F - surely that gives me enough wiggle room, right?

Additionally, I've leant out all my supply of IR hydrocarbon analyzers I normally keep handy, so that's a no-go. In seriousness, I'm not very concerned about measuring remaining hydrocarbons (though it would be cool if there was an easy empirical way, like dropping alka-seltzer tablets into the solvent and if there's no "plop-plop-fizz-fizz," you're safe). I'm just looking for a bit better way of quickly drying out my tanks since my compressed air sucks and my blow-dryer, Rube Goldberg-device isn't working like I'd hoped.

When we clean our tanks, we just blow them out with O2-clean compressed air. 30 seconds and the cylinders are bone dry.

Unfortunately, we have no O2 clean compressed air 'round these parts of which to use. I actually have reason to slightly suspect the air our only LDS pumps, so I'd be afraid of using it at all for this purpose.

 

[Rainer]

Have access to N or O2 you trust? If so, just use that. You need something clean and dry. Even a hairdryer hooked up to some tubing. Check the OxyHacker's guide for many solutions.

 

[oxyhacker]

I like a system that drains the tank as well as dries it, since evaporating pooled water as opposed to removing it only concentrates any contaminants that might be left in it. So and inverted washing/drying rack and a hair dryer or other heater/blower is hard to beat. You need the stand anyway to wash and rinse effectively, so hooking the dryer up is only another minutes work.

The heat thing bothers me too - I do not like to uncessarily heat aluminum tanks even if it is theoretically well below the trouble point. Seems just like asking for trouble. Also, heat levels that may not be high enough to damage the tank can still damage the finish which can in turn cause problems next inspection.

 

[Rainer]

Agree on the use of a stand (we built one like that pictured in Vance's book).