Development Of Detection System For Oxide Skin Blockage In Stainless Steel Boiler Tubes

The stainless steel materials have excellent physical, chemical and mechanical properties such as anti-oxidation,resistance of high-temperature and corrosion. As a result, they are widely used in the manufacture of power station boiler tubes. However, there will be oxide layer exfoliation accumulations in the inside of many long-term use steel boiler tubes. When the exfoliation approaches a level, it will cause the blockage can burst, jamming of steam turbine main valve and solid particle erosion problems. All these put a serious threat to the safe operation of the plants. The commonly used methods, such as ultrasonic testing, radiographic testing and chemical cleaning method have many deficiencies and cannot solve the problem of oxide layer exfoliation. Based on the micromagnetic detection principle, this paper developed a portable detection system for oxide coating blockage in Stainless steel boiler tubes.First of all, this paper did some research and analysis on the exfoliation and structure of the oxide skin stainless steel boiler tubes. We found material properties characteristics of the oxide skin, which provide a theoretical basis for the analysis of test results. Next, according to micromagnetic detection theory, oxide skin itself and stainless steel tube exist magnetic conductivity differences and the areas of oxide skin blockage in stainless steel boiler tubes will be magnetic anomalies.We analyzed feasibility of micromagnetic detection for oxide skin in mechanism. And then combining the actual working situation of the plants, we developed a detection system for oxide skin based on micromagnetic principle. This system is mainly composed of array probe of micromagnetic sensor, signal collection and processing module, IPC and software module. We chose iron-based amorphous alloys as the substrate material according to the principle of fluxgate sensor and developed a small high-precision sensor probe. Combined with actual situation of boiler tube in plant, we designed an adjustable array probe tooling and developed the signal collection and processing module of micromagnetic sensor. The instrument was designed portably and can be used in narrow space like power plants owning to the usage of tablet computer as upper computer. Finally, we carried out the algorithm research and experimental verification. Finally, we carried out the algorithm research and experimental verification. Through the test analysis of processing quality of oxide skin and the relational model of the processing magnetic field intensity values, we designed the detection control software. The reliability of magnetic detection for oxide skin was verified by Ray DR technology. The detection precision of the quality of oxide skin is 20 g and blocking accuracy is 5%. The image quality is intuitive and visual as we expected.This system can be used in the field test of oxide skin in stainless steel boiler tubes and provides an effective security assurance of the plant.