A client called upset that they’d just received 20 liquid cylinders back from rehab and now had 18 in the yard “bad.” They wanted immediate attention and got it. Two things were obvious on arrival. The first was that there were no DOT-4L repair “K” tags on the vessels indicating right away that we’d never seen the vessels in question. Number two, and most upsetting to the client, was the very apparent indication that someone had intentionally punctured the rupture disk on 18 of the 20 liquid cylinders. This was obvious as the protective disk covers were missing and the disks were blown “in” instead of “out.”
The purpose of vacuum rupture disks for cryogenic tanks and liquid cylinders is to prevent rupturing of the outer vessel which has no pressure rating. Vacuum rupture disks are very thin, concave and surrounded by knife edges which are lined up just over the surface. A very low pressure build up in the annular space of an oxygen, nitrogen, argon or carbon dioxide cryogenic tank will cause the disk to protrude against the cutting edges and rupture allowing free flow of the gas to atmosphere. So- any CSI investigator who sees the disk blown out can readily tell that a vessel with a disk blown “out” probably has some type of inner leak.
A disk that is blown “in” indicates a leak occurred in the disk and the vacuum in the annulus sucked atmosphere from outside pulling the disk in. There are slip-on plastic protective covers installed over most disks to prevent damage that would cause a leak. Many manufacturers and service companies also install a warning between the cover and disk noting that removal or tampering will void any warranty of the vessel. This cover helps protect the disk from welding or cutting sparks and corrosion that could cause a vacuum space leak in the cryogenic tank.
When there is a good vacuum on a tank then rupturing the disk will cause a great whoosh of flow into the annulus. It is an all too common occurrence for vandals to remove the covers and puncture the disks. Whether their intent is malicious or just for entertainment the result is the same. The liquid cylinder now has no vacuum and will have to be sent in for a rather expensive repair.
Next, we’ll talk about responsibility and how cryogenic liquid suppliers can save hundreds of dollars by training their drivers to be alert to damage and consistent in documenting it on site.
The purpose of vacuum rupture disks for cryogenic tanks and liquid cylinders is to prevent rupturing of the outer vessel which has no pressure rating. Vacuum rupture disks are very thin, concave and surrounded by knife edges which are lined up just over the surface. A very low pressure build up in the annular space of an oxygen, nitrogen, argon or carbon dioxide cryogenic tank will cause the disk to protrude against the cutting edges and rupture allowing free flow of the gas to atmosphere. So- any CSI investigator who sees the disk blown out can readily tell that a vessel with a disk blown “out” probably has some type of inner leak.
A disk that is blown “in” indicates a leak occurred in the disk and the vacuum in the annulus sucked atmosphere from outside pulling the disk in. There are slip-on plastic protective covers installed over most disks to prevent damage that would cause a leak. Many manufacturers and service companies also install a warning between the cover and disk noting that removal or tampering will void any warranty of the vessel. This cover helps protect the disk from welding or cutting sparks and corrosion that could cause a vacuum space leak in the cryogenic tank.
When there is a good vacuum on a tank then rupturing the disk will cause a great whoosh of flow into the annulus. It is an all too common occurrence for vandals to remove the covers and puncture the disks. Whether their intent is malicious or just for entertainment the result is the same. The liquid cylinder now has no vacuum and will have to be sent in for a rather expensive repair.
Next, we’ll talk about responsibility and how cryogenic liquid suppliers can save hundreds of dollars by training their drivers to be alert to damage and consistent in documenting it on site.
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