What causes dewar wall failure in a cryogenic storage vessel and what are the warning signs before it occurs?
Dewar wall failure in a cryogenic storage vessel refers to the loss of vacuum integrity in the insulated wall space between the inner and outer vessel shells. It is not the physical collapse or rupture of the vessel wall itself but the degradation of the vacuum that makes the insulation effective. The vacuum in a new dewar is typically maintained at a pressure well below 0.1 millibar, achieved using molecular sieve material and getter compounds that absorb residual gases in the vacuum space. Over time, outgassing from the vessel materials, microperforations in the inner shell, and degradation of the getter compounds allow the vacuum pressure to rise, progressively reducing insulation effectiveness.
The earliest sign is a gradual increase in LN2 consumption that exceeds what changes in access frequency would explain. As vacuum degradation progresses, condensation or frost begins to appear on the outer wall surface, initially in patches and eventually across the full outer surface. At the point of significant frost formation, the vessel should be taken out of service for biological storage immediately and biological material transferred to a replacement vessel. We supply replacement storage dewars with a 3-year vacuum warranty as standard. Contact Cryolab to discuss planned vessel replacement for your facility.
