Hydrogen Damage Mitigation by Boiler Chemical Cleaning
By Andrew G. Howell, Ph.D.
Boiler tube failures resulting from hydrogen damage are characterized by corrosion beneath locally heavy internal deposits. The mechanism requires that hydrogen atoms generated by corrosion enter boiler tube metal and react with carbon in the steel. The heavy local deposits provide an environment where corrodents can concentrate at the tube metal surface, and hydrogen atoms resulting from corrosion can be generated at high concentrations. Concern is often expressed that incomplete removal of heavy local deposits may result in a high-risk situation, as corrodents such as chloride (from hydrochloric acid cleaning) could initiate hydrogen damage upon return of the unit to service. Experience at Xcel Energy suggests that incomplete removal of heavy local deposits is not necessarily a high-risk situation, as post-chemical clean operation has provided dramatic reduction in the frequency of hydrogen damage failures in nearly all such cases to date.
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