Newsletter Articles : Cryogenic Transfer Hoses

Over the years I have conducted safety / purity audits of hundreds of laboratories and one of the items that undergoes a continuous battering is a cryogenic transfer hose and phase separator. The hose is commonly 4-6 feet long and is intended to deliver a cryogenic product from one vessel to another. The most common use is to deliver liquid nitrogen from a roll around dewar to a secondary vessel or chamber.

A phase separator is a brass sieve at the end of the hose that keeps the liquid nitrogen from splashing during the pouring process. It is common practice when a technician is done with the process to simply drop the hose with the phase separator on the floor or against the side of the tank. The problem is that the hose and phase separator are still at cryogenic temperatures. (Liquid Nitrogen is at -321 F)

The common result is three fold:

  1. The phase separator hits the floor and breaks because it is brittle at these low temperatures
  2. The phase separator hits the floor and freezes whatever it touches to itself.
  3. The phase separator hits the side of the tank and breaks due to the low temperature combined with impact.

If we look deeper at item two above the issue compounds itself dramatically.

Example: I was called into a customer's site in 2009 to take a look at foreign substances found on their product that came directly out of a liquid nitrogen freezer. Under a microscope I observed a compound that had been thawed and was the one of concern. Under a second microscope I observed a similar compound thawed from a different freezer. The two samples might as well been from different worlds as there was no similarity between them. The compound of concern was massed in particulates and unidentifiable substances.

Following my request I was led to the technician who was responsible for transferring the liquid nitrogen from the dewar to the portable freezer where the suspect compound was stored. Due to the color of one of the substances I saw under the microscope, I had my suspicions. The technician led me to the dewar of liquid nitrogen that had a 6' cryogenic hose and phase separator attached. The phase separator was on the floor. With the Lab Manager and Quality Control Manager present I picked the phase separator up off the floor to reveal a disgusting array of hair, dust, unknown particulates and a wad of chewing gum all covering the phase separator. It didn't take any discussion to identify the source of the contaminated samples. The color of the chewing gum under the microscope was unmistakable. Asked why he simply dropped the hose on the dirty warehouse floor the technician simply said there was no place to hang it on the tank.

This was an eye opener for me. This customer's science was interrupted and delayed due to a completely avoidable situation. Coming very soon from this writer and Middlesex Gases & Technologies is a Cryo-Hanger. It is an item designed to hang a cryogenic transfer hose on a dewar. It is in the final stages of development and will be released in Oct. 09. Another solution delivered by Middlesex Gases & Technologies.

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