EMAT Integrated with Vertical Climbing Robot for Boiler Tube Inspection

National Thermal Power Corporation (NTPC) has signed an MoU with Bhabha Atomic Research Centre (BARC) for design and development of automated boiler tube inspection system for vertical water wall tubes. A vertical climbing robot has been developed for this purpose at Division of Remote Handling & Robotics (DRHR), BARC. Recently, an Electromagnetic Acoustic Transducer (EMAT) has been integrated with the Robot and field trial tested at one of the NTPC’s power plants at Dadri, UP. The paper discusses working principle of EMAT, brings out comparison with other methods of non-destructive testing (NDT), covering design detailing of vertical climbing robot. The typical tube thickness measurement data acquired during plant inspection is also presented. results in revenue loss. Localized wall thinning of the boiler tube is of primary concern to boiler operators. In general, boiler tube failure occurs due to various reasons like Caustic attack, Oxygen pitting, Hydrogen damage, Acid attack, Stress corrosion cracking, Waterside corrosion fatigue, Superheater fireside ash corrosion, High temperature oxidation, Waterwall fireside corrosion, Fireside corrosion fatigue, Short-term over heat, Long-term over hear, Graphitization, Dissimilar metal weld failure, Erosion, Mechanical fatigue, etc. Apart from metallurgical aspects, internal tube damage is mainly due to water chemistry and the temperature, while external tube damage is due to temperature and ash deposits. 1.2 Inspection challenges Boiler tube inspection poses a unique challenge in terms of limited accessibility at inspection location as well as for transporting the inspection equipments into the boiler; limited available time; limited exposed external tube surface; difficulty in X-ray / ã-ray radiography and the affordability. Immediately after plant shutdown, it takes about 2-3 days to cool down, after which scaffolding is erected. Thereafter, external tubes (heat transfer surfaces) are cleaned using water jet. During tube inspection, main objective is to have increased inspection coverage in minimum possible time. This helps in reducing plant down time. Once the inspection technique is selected, it is preferred to automate the inspection of boiler tubes. This paper also focuses the development of vertical climbing robot for carrying the inspection probe onto the boiler tubes, as an attempt to automate the tube inspection. Due to limited access, it is difficult to automate the inspection, covering all the areas of boiler. So, tube inspection and automation is limited to vertical water wall tubes only. Design of vertical climbing robot for given payload and working at required linear speed with desired manoeuvrability is a real challenge. Unlike other