Detection of Creep Damage and Fatigue Failure in Thermal Power Plants and Pipelines by Non-Destructive Testing Techniques. A Review Aakash Kumar* Dept. of Material Science and Metallurgical Engineering Maulana Azad National Institute of Technology Bhopal, M.P., INDIA Sudheer Mathuriya Dept. of Chemical Engineering and Technology Maulana Azad National Institute of Technology Bhopal, M.P., INDIA Supriya Shilpi Dept. of Mechanical Engineering Kalinga Institute of Industrial Technology Bhubaneshwar, Odisha, INDIA Abstract — Analysis of creep damage in steels used in the power generation industry is usually carried out by means of traditional creep detection techniques, but the several shortcomings of these methods have induced a search for alternative non-destructive testing techniques, varying from ultrasonic to electromagnetic methods. During high temperature creep there are significant changes in the microstructure such as dislocation movements and grain boundary cavities. Magnetic hysteresis measurements have been used to evaluate fatigue and creep damage in power plant welded joints. A critical review of the main results obtained for the different stages of creep is presented in this paper, and the pros and cons of each method are discussed separately. Some methods are very promising like ultrasonic testing method, but the limitations are to be removed with further research before they are employed on industrial scale. Keywords— Creep, ultrasonic, pipeline steels, hysteresis INTRODUCTION Creep is the phenomenon of a material to deform permanently under influence of different mechanical loads. It can occur due to the influence of high levels of mechanical and thermal stresses that are below the yield strength of the material. Three stages of creep are shown in the plot of strain versus time as shown in Fig. 1. After the application of load, a sudden strain is observed, followed by the primary stage during which the strain rate decreases, until a steady creep rate is reached, this secondary stage of creep, characterized by a slow but constant plastic flow of material, usually accounts for the longest part of the creep life of a component. Then finally it reaches the tertiary stage, the strain increases considerably and the component finally fails. This behavior is the cumulative result of several mechanisms operating independent of each other. In the ranges of temperature and stress commonly encountered in engineering applications, the most significant causes of creep at a micro level are the motion of dislocations and the diffusion of vacancies [1]. It is commonly accepted that the voids that are created by the nucleation of cavities due to dislocations due to grain boundary sliding, tend to align themselves perpendicularly with respect to the direction of the applied load [2,3] subsequently converging into microcracks and finally macrocracks which lead to creep damage and fatigue failures [4,5]. Since cracks may grow and propagate very quickly, which may cause sudden failure of the materials, it is of great importance to detect creep damage in its early stages. It is rational to assume that, in components subjected to uniformly distributed mechanical loads and thermal stresses, creep and fatigue damage will also be wide spread (throughout the volume of the component) and multiple cracks will grow and propagate over a considerable large part of area of the component. [6]. Critical locations are to be monitored regularly where failure is likely to originate. In particular, initial failures due to localized creep in welded parts of the component are of primary concern for the power generation industry. Following a suggestion by [7], cracks in welded parts are commonly classified into four types, depending on their location. Fig 1. Typical creep curve with evolution of microstructural damage along with the various techniques studied. International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181 www.ijert.org IJERTV3IS110800 (This work is licensed under a Creative Commons Attribution 4.0 International License.) Vol. 3 Issue 11, November-2014 1147