Hydrogen damage of steels: A case study and hydrogen embrittlement model M.B. Djukic ⁎, V. Sijacki Zeravcic, G.M. Bakic, A. Sedmak, B. Rajicic University of Belgrade, Faculty of Mechanical Engineering, Kraljice Marije 16, Belgrade 11120, Serbia article info Article history: Received 14 December 2014 Received in revised form 30 April 2015 Accepted 17 May 2015 Available online 3 June 2015 Many efforts have been made to understand the effects of hydrogen on steels, resulting in an abundance of theoretical models and papers. However, a fully developed and practically appli- cable predictive physical model still does not exist industrially for predicting and preventing hydrogen damage. In practice, it is observed that different types of damages to industrial boiler components have been associated with the presence and localization of hydrogen in metals. In this paper, a damaged boiler tube made of grade 20 – St.20 (or 20G, equivalent to AISI 1020) was investigated. The experimental research was conducted in two distinctive phases: failure analysis of the boiler evaporator tube sample and subsequent postmortem analysis of the via- ble hydrogen embrittlement mechanisms (HE) in St.20 steel. Numerous tested samples were cut out from the boiler tubes of fossil fuel power plant, damaged due to high temperature hy- drogen attack (HTHA) during service, as a result of the development of hydrogen-induced cor- rosion process. Samples were prepared for the chemical composition analysis, tube wall thickness measurement, tensile testing, hardness measurement, impact strength testing (on in- strumented Charpy machine), analysis of the chemical composition of corrosion products – de- posit and the microstructural characterization by optical and scanning electron microscopy – SEM/EDX. The HTHA damage mechanism is a primary cause of boiler tube fracture. Based on the multi-scale special model, applied in subsequent postmortem investigations, the results in- dicate a simultaneous action of the hydrogen-enhanced decohesion (HEDE) and hydrogen- enhanced localized plasticity (HELP) mechanisms of HE, depending on the local concentration of hydrogen in investigated steel. The model is based on the correlation of mechanical proper- ties to the SEM fractography analysis of fracture surfaces. © 2015 Elsevier Ltd. All rights reserved. Keywords: Low carbon steel Hydrogen-assisted cracking Hydrogen embrittlement Fractography Impact strength 1. Introduction Hydrogen damage of boiler evaporator tubes is a very serious problem in many industrial boiler plants worldwide, including even the most developed countries. This is due to a very specific and complex relationship between the hydrodynamic processes in an evaporator and the boiler water treatment regimes, as well as the design and operating characteristics of a particular boiler unit [1–3]. In practice, it is observed that different types of damages to industrial components of fossil fuel power plant have been associated with the presence and localization of hydrogen in metals [2–5]. Due to the complexity of the processes involved and difficulties to experimentally simulate the operating conditions of evaporator tubes of the steam drum boiler in power plants, there is a very limited number of available information items about necessary preconditions for the initiation and development of hydrogen damage of the boiler tubes made of low carbon steel. Engineering Failure Analysis 58 (2015) 485–498 ⁎ Corresponding author. Tel.: +381 11 3370 375; fax: +381 11 3370 364. URL: mdjukic@mas.bg.ac.rs (M.B. Djukic). http://dx.doi.org/10.1016/j.engfailanal.2015.05.017 1350-6307/© 2015 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Engineering Failure Analysis journal homepage: www.elsevier.com/locate/efa