Austenitic Stainless Steels in Chloride Solutions
Chloride stress corrosion cracking of austenitic stainless steels (Types 304, 316, 321, 347, etc.) can occur in
aqueous solutions containing chloride ions. Cracking is most severe where the chloride ion concentration is high, the solution is hot, the pH is neutral or low, and especially where evaporation builds up deposits on the stainless steel.
Stainless equipment hydrostatically tested with sea water has failed due to the residual sodium chloride film left behind. Other failures have been traced to chlorides leaching out of wet insulation. Many failures have resulted from not protecting stainless equipment from chlorides during shutdowns. There can be an incubation period of several hours to many weeks before cracking occurs in certain environments.
Cracking can be greatly reduced by stress relieving the stainless equipment in the 1550°F to 1650°F temperature range. However, complete freedom from chloride stress corrosion cracking can be assured only by protecting austenitic stainless steels from any chloride ions or by using the more expensive super stainless grades with 30% to 45% nickel. Duplex stainless steels have improved resistance to chloride stress corrosion cracking.
Recommendations to prevent chloride stress corrosion cracking include:
1. Do not select solid wall austenitic stainless steel construction for hot, aqueous chloride services. If stainless steel is required, use clad construction.
2. Stress relieve vessels made of solid austenitic stainless steel where no other economical material is available.
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