More than three years ago, a large waste-to-energy plant initiated a large-scale test of a spray-and-fuse alloy from Wall Colmonoy Corp., Madison Heights, Mich. The plant had a job shop overlay 86 boiler tubes with Colmonoy 88, coating the 25' long, 2.5" dia. tubes with the protective material.

Since the alloy was applied, tube-metal temperatures approached 900°F (482°C), and the boiler has run 24 hours a day, seven days a week. The tubes are vital components of the energy plant’s superheater, which is a part of one of the boilers. The coating has helped extend the tubes’ life from a one-year cycle to three, tripling their lifespan. Colmonoy 88 extends boiler tube life, especially in the secondary superheater section of a boiler where the most severe environment exists for mass burn and refuse-derived fuel boilers.

The Colmonoy coating offers four advantages for superheater tubes and panels, according to Wall Colmonoy.

• Longer life than tube shields, stainless tubes or any type of Inconel overlay, including Inconel 625, 622, 52 and 72.
  
• Improved high temperature erosion properties compared with other alloys tested.
  
• Reduction of molten salt or slag buildup on the tubes.
  
• Better heat transfer properties than shielding or overlays.
  
• Reduced maintenance costs from labor and material savings.

Satisfied with the results, the waste-to-energy plant now plans to test Colmonoy 88 in two of its other facilities, according to Wall Colmonoy.