Failure of Secondary Superheater Tube by Caustic Stress Corrosion Cracking (CSCC)
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CASE HISTORY—PEER-REVIEWED
Failure of Secondary Superheater Tube by Caustic Stress Corrosion Cracking (CSCC) Alireza Katamipour . Mohsen Shamshirsaz . Abdolhossein Fereidoon
Submitted: 14 May 2015 / in revised form: 8 July 2015 ASM International 2015
Abstract Failure analysis of a ruptured superheater tube from a boiler has been carried out. Experiments revealed that the chemical composition of the tube was in correspondence to SA213-T22 standard and had ferrite-pearlite microstructure of 2.25Cr-1Mo steels. Investigations showed that caustic stress corrosion cracking (CSCC) was the predominant mechanism of cracking and failure of the tube. Misuse of boiler feed water, as the supplying water through the attemperator to the superheated steam, in the secondary superheater, and carryover from the steam drum to the superheater resulted in scale buildup and cracking of the CSCC type. Keywords Failure analysis ASME SA213 Gr22 Creep-resistant alloys Caustic SCC Stereomicroscopy SEM EDX Hardness Vickers (HV)
Introduction Since steam generation is an important stage prior to different processes in different industrial units such as refineries, power and petrochemical plants, and so on,
A. Katamipour (&) Abadan Faculty of Petroleum Engineering, Petroleum University of Technology, Abadan, Iran e-mail: [email protected] A. Katamipour M. Shamshirsaz Equipment Inspection Department (E.I.D), Abadan Refinery, Abadan, Iran A. Fereidoon Faculty of Mechanical Engineering, Semnan University, Semnan, Iran
boilers play an important role in industry. Working of these assets in harsh conditions of high-temperature and water environments makes them susceptible to different kinds of failures. Superheaters are parts of boilers experiencing both hot steam inside and high temperature from flames outside of their tubes. These conditions necessitate the choice of alloys of high resistance to these conditions in manufacturing the tubes. Many case studies are reported in the literature about boilers and especially superheater failures, most of which are caused by creep [1–3, 9–12]. Movahedi-Rad et al. [1] studied a case of superheater tube failure in which lowgrade fuel was used, tubes were overheated, and scale and carbide formation resulted in the final fracture. Psyllaki et al. [2] focused on the metallurgical factors influenced during high-temperature operation of a pipeline that resulted in its short-time failure by creep rupture in a lignite power plant unit. Purbolaksono et al. [3] studied failure of the SA213-T12 primary superheater tube by visual inspection, in situ measurements of hardness, and finite element analyses. They came to the conclusion that localized short-term overheating of the tube due to localized and concentrated flue gas flow resulted in a failure of the primary superheater tube. In this work, we studied failure of a secondary superheater tube from a boiler. The tube has ruptured along the weld metal.
Information from the Client Table 1 shows designer’s feed and boiler water conditions.
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