An external inspection agent was appointed for investigating the root cause of the failure. During investigation, manufacturing defect was ruled out after checking all QC documents and manufacturing procedure. Sample analysis of material from the corroded part indicated starvation of oxygen in the corroded part.
Operating conditions of bottom channel is more severe in terms of temperature, carbamate concentration and lack of Oxygen content due to stripping action. However, titanium part did not show any deterioration in the top or bottom channels. The 25-22-2 materials in the top channel were found intact. Hence, it was concluded that 25-22-2 material cannot resist corrosion for the severe condition prevailed in the bottom channel without additional supply of Oxygen.
From the 4th Licensers symposium held in Oct 2004, it was reported that bimetallic stripper without additional passivation air has failed during first year of operation in 3 other plants in Argentina, India and Pakistan.
Direct cause of failure:
The direct cause of the bimetallic stripper failure is “Inadequate Air Passivation” at the bottom channel, where 25-22-2 could not resist the severe corrosion due to non-conducive operating condition.
Root cause of failure:
The root cause of the failure is “improper design“ of the bimetallic stripper which failed to recognize that 25-22-2 couldn’t withstand the severe operating conditions prevailing in the bottom channel of the stripper.
The material 25-22-2 material requires more air passivation comparing Titanium.

s5_002 Bi- Metallic Stripper Failure.pdf