Effect of service exposure on KCl corrosion attack of AISI 347H FG steel
- 41 Downloads
The effect of ageing of AISI 347H FG austenitic steel on KCl-induced corrosion was investigated by comparing the corrosion attack on tube material previously service-exposed for 100000 h and that on an as-received tube. Cr-rich σ-phase precipitates were found mainly along grain boundaries in the microstructure of the service-exposed material, whereas no σ-phase was present in the as-received condition. Laboratory corrosion experiments were carried out using KCl-free and KCl-covered samples in a 15% (v/v) H2O (g) + 5% (v/v) O2 (g) + N2 (g) (balance) atmosphere at 600 °C for 168 h. Microstructural characterisation was performed before and after the corrosion experiments using light optical microscopy, X-ray diffraction spectroscopy, scanning electron microscopy with energy-dispersive X-ray analysis (SEM/EDX) and scanning transmission electron microscopy with energy-dispersive X-ray analysis (STEM/EDX). The presence of KCl resulted in increased attack, and the service-exposed material had increased attack compared to the as-received TP347H FG material; thus, the deepest attack was observed for KCl-covered previously service-exposed material where grain boundary internal attack occurred. The experimental investigations indicate preferential attack of the Cr-rich precipitates and the presence of chlorine at the corrosion front and Cr-rich precipitates (σ-phase) ahead of the corrosion front for KCl-covered service-exposed material. The findings suggest that service-exposed AISI 347H FG material may experience an increased KCl-induced corrosion attack caused by selective attack of the Cr-rich σ-phase.
This paper was written as part of the FORSKEL project ‘Biomass Corrosion Management’ with financial support from Energinet.dk (Grant no 2015-1-12289) and Oersted. Thanks go to Aalborg Forsyning for providing the exposed tube.
- 30.Korcakova L, Montgomery M, Jensen HT, Ab V (2013) Investigations of superheater materials from Nordjyllandsværket coal-fired plant after 100000 hours service. In: Auerkari P, Veivo J (eds) International conference on life management and maintenance for power plants. VTT Technology 106, pp 458–476Google Scholar
- 31.Astm Standard (2012) E112-12:Standard Test methods for determining average grain size. ASTM Int E112-12:1–27. https://doi.org/10.1520/E0112-12.1.4
- 42.Streicher MA, Begum S (2016) Corrosion, intergranular. Reference module in materials science and materials engineering. Elsevier, Amsterdam, pp 3–5Google Scholar
- 44.Kim CS, Moon SJ, Kong WS (2016) Effect of sensitization treatment on corrosion properties in austenitic stainless steel 304. Mater Sci Forum 857:232–236. https://doi.org/10.4028/www.scientific.net/MSF.857.232 CrossRefGoogle Scholar
- 48.Teranishi H, Sawaragi Y, Kubota M, Hayase Y (1989) Fine-grained TP 347 H steel tubing with high elevated-temperature strength and corrosion resistance for boiler applicationsGoogle Scholar
- 50.Fujikawa H, Iijima Y (2013) Effect of grain size on the high temperature oxidation behaviour of austenitic stainless steels. Defect Diffus Forum 333:149–155. https://doi.org/10.4028/www.scientific.net/DDF.333.149 CrossRefGoogle Scholar
- 57.Bender R, Schütze M (2003) The role of alloying elements in commercial alloys for corrosion resistance in oxidizing-chloridizing atmospheres. Part I: literature evaluation and thermodynamic calculations on phase stabilities. Mater Corros 54:567–586. https://doi.org/10.1002/maco.200390129 CrossRefGoogle Scholar