Failure analysis of boiler steam drum material

Madan, M and Bhuvana, R and Sujata, M and Venkataswamy, MA and Bhaumik, SK (2008) Failure analysis of boiler steam drum material. Project Report. National Aerospace Laboratories, Bangalore, India.

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During Remnant Life Assessment of a boiler drum, several cracks were noticed on the inner surface of the drum. Two representative samples, one from the cracked region and the other from the unaffected region, were submitted to this laboratory for analysis. Examination revealed several branching cracks emanating from the major cracks. The crack surface was found to be covered with a firmly adherent thick oxide layer. The oxide layer was peeled off by repeated replica cleaning and the crack surface was examined under a scanning electron microscope. Fractographic study showed that the cracks were intergranular in nature. Subsequent metallographic study also confirmed this finding. Detailed microstructural study of the cracked regions discovered that the cracking was associated with repair welds. The cracks were found to have initiated in the heat affected zone (HAZ) adjacent to the weld and propagated progressively to the surface. In most cases, the cracks were found to be filled with oxides. Study showed variation in microstructure in the cracked region similar to that generally associated with welding. However, there was no significant variation in hardness at the welded region. This indicates that post-welding heat treatment was carried out in the boiler drum. Evidences suggest that the boiler drum has failed by intergranular cracking. The cracks were associated with welds and have initiated in the heat affected zone. The nature of cracks suggests that they are typical of cold cracks. Cold cracks are generally caused by hydrogen and it appears most probable that the hydrogen was absorbed in the steel during the repair welding process. It is believed that the hydrogen content in the steel was substantial even after post-weld heat treatment. The reason could be inadequate protection against moisture/hydrocarbon during welding. A detailed analysis of the failure is presented in this report.

Item Type: Monograph (Project Report)
Uncontrolled Keywords: Boiler steam drum;Welding;Cold cracking;Hydrogen cracking
Subjects: AERONAUTICS > Aeronautics (General)
CHEMISTRY AND MATERIALS > Chemistry and Materials (General)
Depositing User: Ms. Alphones Mary
Date Deposited: 19 Jul 2011 04:55
Last Modified: 19 Jul 2011 04:55

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