Chemical Compatibility of Glycerin-Filled Pressure Gauges

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 Do glycerin filled pressure gauges present an explosion hazard when mounted on tank CIP arms? I see gauges with warnings about oxidizing media use. Would 2% caustic solutions/boosted peroxide caustic and 1-2% Peracetic/other acid solutions pose a risk? 

Safety Exchange says: Thanks for inquiring about the chemical compatibility of glycerin-filled pressure gauges with common brewery cleaners and sanitizers.

The design of most pressure gauges used in breweries and food processing is a tried and true concept credited to Eugene Bourdon, a French engineer, in the year 1849. The principle is that a curved, flexible, gas- or liquid-filled tube will tend to straighten itself with increasing pressure. The curled tube is attached to a gear mechanism that moves the needle as the tube begins to straighten out. (Think about the party horns with the curled up paper tube; when you apply pressure from your breath the paper tube sticks straight out.)

In a Bourdon tube gauge, the important fact is for the curled tube to be compatible with chemicals in the application. Be sure to buy stainless steel gauges with 304 or 316 grade stainless construction. The glycerin is merely a viscous liquid that is used to fill the gauge dial. This reduces the twitching of the needle which can make it difficult to make an accurate measurement. In a normally functioning gauge, the glycerin is never in direct contact with the gases or liquids inside the Bourdon tube.

Some gauges have a liquid-filled Bourdon tube, in which case there is a chemically resistant diaphragm below the tube that isolates process fluids from the fluid in the gauge.

It is true that glycerin can react with nitric acid to form an explosive compound (i.e. nitroglycerin), but that reaction requires additional proton donors, say from sulfuric acid, carefully controlled temperatures, and caustic scrubbing to purify the explosive. (Don’t try this at home kids!!) Our recommendation is that gauges which have failed for any reason, be promptly replaced before resuming normal brewing/cellaring activities.

First step is to get an SDS from the gauge Manufacturer to confirm the chemical. (Note some are actually filled with silicone.) They will probably tell you the volume of glycerine used to fill it.  We can compare that with the cleaner and sanitizer SDSs.