Hydrogen Damage in Carbon Steel Tubing: An Investigation of Various Macro-Failure Morphologies Observed in Boiler Water Wall Tubes Manifesting as Hydrogen Damage Failure

Hydrogen damage is a serious problem in power plants, especially carbon steel tubing. In the water wall tube sections, fish mouth- or window-type opening is the most common and widely reported type of failure. However, the present failure investigation of various water wall tubes highlights that hydrogen damage can manifest itself in different forms and on a macroscale appear differently. Based on the extent of hydrogen attack, the four types of failures were observed and were categorized, viz. puncture-type failure (PTF), slit-type failure (STF), wave-type cracking (WTC) and fish mouth opening (FMO). Microstructural and fractography examination of these failed tubes revealed the extent of the hydrogen attack, localization and aggressiveness of the attack, which dictated the final failure morphology. Erratic hardness values were observed due to uneven hydrogen ingress and attack. Fractography examination revealed inter-granular fracture mode suggesting hydrogen-enhanced decohesion (HEDE) mode of embrittlement as the dominant one.