Tank temp change ?

[NorthernShrinkage]

This cant be good for my Tanks.

The other night we were doing class 2 of a BOW course and outside air temp was -18c we have a 20 minute drive to the pool I had all the tanks in the back of my truck and once unloading at the pool all tanks immediately began to get a heavy layer of frost on the outside . Tanks probably sat on the pool deck for 15 minutes before they hit the pool 85f so im guessing this would have been a pretty good shock to them .

Just thinking if I should take the tanks to the pool earlier in the day to allow them to warm up slowly instead of shocking them ?

 

[Jorbar1551]

na, it shouldnt matter. the air might have compressed a little more due to the cold outside temperature, but i wouldnt think it would matter, especially for a pool dive.

if canada ever gets hot as it does in california, i put my tanks under a towel to keep them in the shade. it can go from 110 degrees farenheit to 55 degrees in the water.

 

[cool_hardware52]

This cant be good for my Tanks.

The other night we were doing class 2 of a BOW course and outside air temp was -18c we have a 20 minute drive to the pool I had all the tanks in the back of my truck and once unloading at the pool all tanks immediately began to get a heavy layer of frost on the outside . Tanks probably sat on the pool deck for 15 minutes before they hit the pool 85f so im guessing this would have been a pretty good shock to them .

Just thinking if I should take the tanks to the pool earlier in the day to allow them to warm up slowly instead of shocking them ?

I wouldn't worry about it too much. You are talking about a ~85 degree F swing in temperature. Consider the "shock" a tank see's with a hot fast fill, i.e. big change in temp accompanied by a big swing in pressure.

If you placed cold tanks into a warm humid environment, like along a indoor pool deck, the frost you see condensing on the bottles is actually warming up the tanks. The latent heat of condensation and the latent heat of freezing of the moisture that collected on the tanks is actually raising the temps of the tanks.

To convert water vapor to liquid water requires removing heat from the vapor, and converting liquid water to ice requires further removal of heat from the water.

The latent heat values for water are quite high, IIRC, 540 calories per gram to condense and 80 calories per gram to freeze.

I'd worry a lot more about the "shock" to me of leaving an indoor heated pool and walking back into a 0 F environment, burrr. My thin socal blood would protest.


Tobin

 

[engdiver]

It would be intereresting to see what the pressure in the tanks would read at -18C. If you started diving with them at this temperature you might see your pressure actually increase as you did your pool dive until they warmed up to the water temp.

 

[FredT]

A steel tank starts to have difficulty around -70F, and is right brittle if vibrated at about -100F. Aluminum behaves silmilarly, but with different temperature limits. Above -40 most engineering metals behave quite well.

The shock you describe is a "non-event".

FT

 

[tedwhiteva]

Like everyone said - overheating is the problem. All temperature change does in the range you're talking about is change the pressure. About 4 psi per degree F as I recall.

 

[AXL72]

A steel tank starts to have difficulty around -70F, and is right brittle if vibrated at about -100F. Aluminum behaves silmilarly, but with different temperature limits. Above -40 most engineering metals behave quite well.

The shock you describe is a "non-event".

FT

You have to order cold temperature steel or aluminum with the appropriate Chary impact values.

Alot of forgings will not meet needed ductility values lower than -20F.

However, good reeading can be found with American Association of State Highway Transportation Officials (AASHTO), who have adopted ductility requirements (ie Charpy v-notch impact testing) at test temperatures that are allowed to be 70F warmer than the materials minimumm intended service temperature. The reason has to do with the rate of loading during a Charpy test compared to teh rate of loading for a highway bridge application.

so, if the ductility transition temperature for a scuba tank is 0F, it is porobablt good to be used at -70F, as long as you dont hit or bang it around. Be very very delicate in handling it. However, Ameerican Society of Mechanical Engineers (ASME) have not adopted this varience between testiung temperature and minimum in-service temperature for pressure vessels (ie pipelines and scuba tanks).

It would be wise to take the proper precautions with cold tanks. An exploding tank filled with air or any other gaseous fluid can be extremely catestrohic, This is not the same case with liquid filled pressure vessels because liquid does not expand to the order of magnitude that gases do.

If you immerse the tanks in water when cold, it will probably take about 6 minutes for the inside diameter of the un-insulated tanks to warm up by a temperature delta of 70F.