Hydrogen Damage in a Waterwall Boiler Tube Section

The rear wall tube section of a boiler that had been in service for approximately 38 years was removed and examined. Visual examination of the tube revealed a small bulge with a through-wall crack. Metallography showed that the microstructure of the bulged area consisted of a few partially decarburized pearlite colonies in a ferrite matrix. The microstructure remote from the bulged area consisted of pearlite in a ferrite matrix. EDS analysis of internal deposits on the tube detected a major amount of iron, plus trace amounts of other elements. The evidence indicated that the bulge and crack in the tube resulted from hydrogen damage. Examination of the remaining water circuit boiler tubing using nondestructive techniques and elimination of any heavy deposit buildup was recommended.