Hydrostatic testing of ASTs at low temperature 1

[rkchalla]

I am looking for chemicals that can be added to test water for a hydrostatic test of an aboveground storage tank at a temperature of -20 deg. F or thereabouts. I am looking for a vendor or a trade name.
Desirable characterestics of the chemical are non corrosiveness and does not contaminate petroleum prodcuts.

 

[JStephen]

If the only point of the chemical is to prevent corrosion while the tank is hydrotested, normally no chemical additives would be used. Time involved in hydrotesting should be minimized (ie, don't drag it out for weeks and weeks). Chemical additives are undesirable due to disposal of the water when testing is completed.

If you intend that the hydrotest liquid is to be at -20F, I suppose you would be looking for antifreeze as in car radiators?

 

[RNDguy]

Ethylene glycol, propylene glycol or triethylene glycol may be good for this application. Many companies make them, try e.g. Lyondell Chemical Company:

http://www.lyondell.com

Glycols are the anti-freeze of common parley. Their compatibility with petroleum products is good (I am sure the solution will be drained after hydrostatic testing). For instance, ethylene glycol is the most important component of most engine antifreezes.

 

[jte]

rkchalla-

Can't help you with chemicals but wanted to be sure you had considered brittle fracture. There have been plenty of hydrotest failures due to the steel beeing too cold. If you have well chosen steel and weld procedures, though, you could be ok.

jt

 

[JStephen]

If you are looking to hydrotest with low ambient temperature, you might be better off to look at heaters, rather than antifreeze solutions, or some combination of the two. Can you rent portable boilers or heaters? They can put temporary insulation on tanks for field stress relief; if you run into enough money, it might be feasible to do this for a hydrotest as well.

It might be worthwhile to put some thought into heat loss calculations. You mention the -20F. Is this the Lowest One Day Mean Temperature? If so, it might be overly conservative for purposes of this calculation. You could probably get weather forcasts enough in advance to let you dodge a period of extreme cold. By the way, NFPA-22 includes some information on tank heating, aimed at fire protection tanks.

What I recall about hydrotest temperature- I remember hearing at a tank seminar long ago that if a crack was loaded above the brittle-ductile transition temperature, it would tend to blunt the end of the crack, making it less susceptible to cracking at low temperatures. So it is always advantageous to hydrotest at high temperatures rather than low. I recall reading a requirement about this somewhere, but couldn't find it in API-650 last time I looked, so I may be remembering customer specs (or maybe it's in API-653.)

API-650 does allow leak testing with penetrating oil rather than hydrotesting. If your tank is very large, I think the cost of the antifreeze would be enormous. If it is small, especially small enough that minimum thickness controls rather than hydrostatic pressure, the hydrotest wouldn't be as critical.

You mentioned rust prevention. Regular antifreeze like you put in your car has rust preventive additives. But I hate to think of the cost of hauling truck after truck of Prestone out to some jobsite.

Thermal storage tanks routinely have chemicals added for corrosion protection also; you might try searching for chilled water tank additives.

 

[rkchalla]

Thanks for the input. We will look at glycols.
Brittle fracture was considered in selection of the steel. We are preparing for the possibility of a hydrotest at -20 deg F.
We thought of using heaters but the cost will be prohibitive to try to account for thermal losses.