Brian Dalder Forum Moderator 177 Posts
Re: How can I prevent stress corrosion cracking?9 November 2010 at 1:29pm
It sounds like you have a severe case of caustic induced stress corrosion cracking (SCC) otherwise known as "caustic embrittlement." Caustic stress corrosion cracking occurs above threshold temperatures when stresses in the pipe exceed the yield point. Carbon steel pipe used for 50% caustic service should be stress relieved to relieve stresses caused by welding, cold forming, bending, field flaring etc. Is your line heated to keep the caustic from freezing (the freezing point of 50% sodium hydroxide is about 15 °C)? If so, heat tracing systems need to be carefully designed to avoid overheating or localized "hot spots" as elevated temperatures exacerbate caustic SCC. For more information, I suggest you consult Pamphlet 94 "Sodium Hydroxide Solution and Potassium Hydroxide Solution (Caustic) Storage Equipment and Piping System" from the Chlorine Institute. This pamphlet is available at no charge and can be downloaded from their website (http://www.chlorineinstitute.org.)
I have a 3-inch schedule 40 carbon steel line carrying caustic 50% getting in service for about 6 months. Repeated cracks in different welds and HAZ has occurred. This should be caustic embrittlement. What is the best action to avoid facing this problem in other welds in this line considering that there are always some parts of the line suffering general corrosion?
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