Insulation covers for sodium hydroxide piping

[chicagoeng]

I am trying to determine the most appropriate (and cost effective) insulation covers for piping and vessels containing sodium hydroxide in concentrations ranging from 25% to 50% and temperatures from 100F to 350F. Aluminum is not appropriate because the NaOH will dissolve it if it leaks, and I've received various positive and negative comments about 304SS covers. Any thoughts or arguments from personal experience would be appreciated.

 

[mbeychok]

chicagoinc:

You have a more serious problem than insulation covers to be concerned about. Hot caustic causes stress corrosion and embrittlement especially at welded joints. Carbon steel vessels and piping will suffer stress corrosion and embrittlement at temperatures above about 150 deg F (66 deg C). Stainless steel will have the same problems at temperatures above about 250 deg F (121 deg C).

Vessels handling hot caustic must be stress relieved.

Piping must avoid temperatures higher than those given just above. If you are steam tracing caustic piping and then covering the piping and steam tracers with insulation, you should wedge pieces of insulation between the piping and the steam tracers to prevent high pipewall temperatures. Piping handling caustic hot caustic at temperatures higher than those given above can quite literally fall apart.

Milton Beychok
(Visit me at www.air-dispersion.com)
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