September 15, 2006

Cleaning and inspection of stainless steels and nickel alloys for FGD service

Richard E. Avery and William L. Mathay, Nickel Institute

Lessons learned

Proper inspection and cleaning practices help to maximize the corrosion resistance of stainless steels and nickel alloys in FGD systems. Pay close attention to the following issues.

Know your materials. The need for pickling or passivation treatments varies depending upon the alloy. The presence of heat tint and iron contamination on the surface of stainless steels can reduce corrosion resistance, whereas with NiCrMo alloys, neither the removal of heat tint nor embedded iron is normally considered necessary.

Conduct good housekeeping. Prior to and during fabrication, materials should be properly identified, stored, and maintained free of contaminants that could affect weld quality and in-service performance.

Meet the criteria. Weld acceptance criteria should include full-penetration butt welds; welds free from cracks, overlaps, and cold laps; and meeting agreed-upon acceptance standards for undercut and weld reinforcement.

—Richard E. Avery and William L. Mathay are consultants to the Nickel Institute (www.nickelinstitute.org). Avery can be reached at 603-434-2625 or richardea@aol.com. Mathay can be reached at wlmathay@adelphia.net.