Pressure Relief For Cylinders

[StoneCold]

I am working on the pressure relief of cylinders for the fire case. The cylinders are originaly designed for refrigerant recovery and are made of carbon steel. We use them to transport various organic chemicals in solvents. I know the MAWP (240psig) and the Burst pressure (960psig) of the cylinders but the drawings for the cylinders have no design pressure. When I called the manufacturer they stated that those pressures were for ambient temperature (70F).

This is fine for everyday use but in a fire induced relieving scenario what pressure and temperature do you allow the cylinder to go to before it begins relieving?

One of the solvents we use is toluene so at 165 psia the relieving temperature is 437F. We are still well below the MAWP but I am concerned about the temperature.

What do you think the maximum temperature is that I should allow the cylinder reach before it begins relieving?


Here is a link to the manufacturer of the cylinders if you click on the section called "Refillable Specifications" you will see drawings of the cylinders.

http://www.worthingtoncylinders.com/recovery_refillable.html

For cylinders, would you use a fire load of 21000 BTU/hr x Area^0.82 or would you use 34500 BTU/hr xArea^0.82 ? Since the cylinders are shipped all over the world the fire may occur where there is no fire fighting efforts, so should I use the more conservative case? What do you think?


Is all this information in the CGA Handbook? I don't have that book but maybe I need to get it to solve this problem.
Comments on that?

Thanks
StoneCold

 

[CHD01]

Refer to DOT standards for shipping containers in cylinders and also CGA to determine relief requirements for fire. If you can determine the material spec you can refer to ASME Section VIII appendix for allowable stress at elevated temperatures to establish your MAWP. Or a Pressure Vessel Handbook can help you. I referred to ANSI B16.5 for carbon steel falnges just for an example and found for Material Group 1 carbon steel 150lb flanges that the allowable stress decreased about 20% in going from 100 to 300 Deg F (285 psig @100 F, 260 psig @ 200 F and 230 psig @300 F).

I would recall the vendor, there should be an associated design temperature for the design pressure or MAWP.

The more you learn, the less you are certain of.