Metallurgy Interview Question:

Is there a possibility of inducing stress cracking in an insulated stainless road tanker vessel (20 tonne capacity) if the vessel is subject to rapid filling (10 tonne /hr) with liquid methane (-160 C) assuming the vessel is at ambient. If so, where could I obtain suggested cooling rates?

Submitted by: Administrator

Assuming a two-hour load time, insulation in good condition and steel in good condition with no existing stress cracks at the welds, and a "pre-cool" period prior to rapid loading, the unit should hold up OK.

If you start with an ambient unit, and you have an inrush of liquid methane, the initial boiling of the methane in the unit will be very vigorous until the inner surfaces are cooled down. This violent boiling will result in liquid being ejected from the unit if care is not taken, and could result in damage to the insulation and liner. It would be best to load a small amount of the liquid methane into the unit and let it boil away, collecting the fumes and re-compressing if possible, thereby cooling the inner components of the unit. This will lessen the initial thermal shock and reduce the likelihood of stress cracking.
Submitted by: Administrator