Non Destructive Testing Monitoring Thermal Power Stations

Non Destructive Testing Monitoring Thermal Power Stations S. Bhowmick Department of Mechanical Engineering, Indian Institute of Technology, Kharagpur, India

Abstract

Shortage of power supply is an issue of great concern in India. In recent years, decommissioning of many dependable units at the Thermal Power Stations has made this problem more acute. Among the major contributing factors, problem of Boiler Tube Failure deserves special mention. However, Condition Monitoring and Maintenance operations at the Thermal Power Stations have played vital roles to resist against this national disaster in power supply. Various advanced methods of Non Destructive Testing like Ultrasonic Inspection for Wall Thickness Measurement and Scale Detection, Eddy Current techniques for crack detection, Remote Visual Inspection at the Turbine sections during short term overhauling have proved to be technical remedial measures to prevent capital overhauling and thereby reducing forced outage at Thermal Power Stations. Every year capital overhauling i.e. complete shutdown of the Boiler Units adversely affects the state revenue. This paper highlights mainly upon the modernization of popular NDT Examinations viz., Wall Thickness Measurement & Crack Detection by Ultrasonic Techniques, Eddy Current Testing, Remote Visual Inspection, XRD Technique for analysis of Boiler Tube scale for research purposes and their applications at the Thermal Power Stations during short term or capital overhauling. Key words: - Non Destructive Testing, Thermal Power Stations, Maintenance Operations.

1. INTRODUCTION Innovations of the conventional methods of day to day methods of maintenance activities have resulted in the saving of both time and labour. But Thermal Power Stations in India are suffering from certain long term problems whose remedies are still in the future prospects of R&D activities. The challenges faced during the day to day operation and maintenance activities at the Thermal Power Stations affects adversely the National Economy and thereby endangering the country’s population into a dark future of Power Failure. However, the immediate technical remedy to this problem of Boiler Tube Failure has emphasized the concept of Condition Monitoring activities. Again, very specifically stating any noninvasive techniques utilized to determine the integrity of a material, component or structure or quantitatively measure some characteristic of an object i.e. measure without doing any harm can be considered as Non Destructive Examination. It is definitely for this reason Non Destructive Testing has occupied a vast region both in the industrial as well as in the R&D sector. Every year Thermal Power Stations under renowned PSU sectors spend several lacs for the Condition monitoring operations among which a handful of operations can be considered as Non Destructive Techniques. The concept of this paper is to highlight the several Non Destructive Testing practices at the Thermal Power Stations and thereby

emphasizing upon the professional skills and dedications of innumerable field engineers, technicians and scientists for successful implementation of these techniques during the present period of National Crisis in Power Generation. 1.1 Wall Thickness Measurement and Scale Detection using Ultrasonic Techniques: Scale deposition inside the Boiler Tubes is a region of perennial worry at the Power Stations. A handful of Boiler Tube Failure cases can be attributed to Scale Deposition. The scales are mostly composed of Iron oxides and in some cases CaCO3 and certain other compounds depending upon chemical reactions and the nature of water. Purification of river water by using some chemical compounds is a burning issue of research interest in Analytical Chemistry but Scale detection and Wall thickness measurement using Ultrasonic Techniques has proved to be an immediate remedial measure to this long term problem. A tube with scale deposition of more than 30-32 microns can be considered as failed tube. Accurate scale detection and Wall Thickness Measurement not only predicts the tube condition but also guides the Acid Cleaning procedure so that the tube can be saved before being discarded.

1.1a Basic Principal of Ultrasonic Inspection: Although theoretically any frequency about 20,000 cycles per second (cps) (20 kHz) can be thought of as an ultrasonic frequency but in practice ultrasonic transducers and equipment operate in the frequency range of