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Air Products and Chemicals, Inc. -- Metals Solutions -- Ask the Expert
     
  Ask The Expert - Zurecki

Zbigniew Zurecki
Research Associate

     
  Ask the Expert -- Question What causes stainless steel to turn green in a continuous belt furnace?
 

Ask the Expert -- Answer

 

 

 

 

 

The green color that you see on stainless steel parts is chromium oxide (Cr2O3). It forms when there is too much oxygen and/or moisture in the furnace atmosphere, which is usually caused by a water leak, poor atmosphere tightness, or overly low flow rates of atmosphere gas.

In addition to the traditional steel and copper test, some companies run a piece of stainless through the furnace to check for high moisture and oxygen levels. A better and more precise way of measuring moisture and oxygen levels is to install an oxygen analyzer and dew point meter. It's inexpensive and highly accurate. If a green oxide film is forming on your stainless steel parts, that's an indication that the furnace or atmosphere is not optimized.

For a complete evaluation and audit of your process, give us a call at 800-654-4567. Also learn whether you're following best practices in atmosphere supply and other operational areas by assessing your process a www.metalsassessment.com.