In CGA Pamphlet G-8.1, "Standards For Nitrous Oxide Systems at Consumer Sites", it states that nitrous oxide cylinders should not be exposed to temperatures in excess of 125oF (52oC) due to the highly combustible nature of nitrous oxide.
In CGA pamphlet C-6.1, "Standards For Visual Inspection Of High Pressure Aluminum Compressed Gas Cylinders", it states that cylinders heated to metal temperatures in excess of 350oF (176oC) must be condemned.
Common evidence of exposure to elevated temperatures that may heat the metal temperature to 350oF (176oC) include:
* discoloration, charring, or blistering of the cylinder paint, protective coatings or labels;
* distortion of the cylinder;
* melting of non-metallic (i.e. plastic, etc.) valve components;
* activation of valve pressure relief device; or
* activation of a heat indication system
Catalina Cylinders recommends that if there is evidence, or it is believed, that a nitrous oxide cylinder has been exposed to temperatures above 125oF (52oC) but the temperature of metal of the cylinder is not believed to have reached 350oF (176oC) for any duration of time, the cylinder must still be subjected to hydrostatic testing or condemned. A cylinder that has been exposed to temperatures great enough to change the temper of the cylinder could show an increase in total or permanent expansion as measured during hydrostatic testing. Cylinders showing unusually high total expansion or exceeding the regulatory limits for the relationship of permanent expansion to total expansion (i.e. DOT = 10% and TC = 6%) should be condemned.
DOT 3AL and DOT 4E aluminum cylinders subjected to fire must be removed from service according to section (f) (4) of CFR 49 part 173.34, "Qualification, Maintenance, and Use of Cylinders". No testing for acceptance or re-heat treatment is authorized.
Stolen from:
http://www.catalinacylinders.com/tempn2o.html
