The Design of an Enhanced Magnetostrictive Sensor and an Advanced Signal Processing Method for Detecting Corrosion in Through-wall Gas Pipe Risers

Description

In modern cities, natural gas is a major source of fuel for heating and cooking. In a high-rise building, an external piping system, which is erected along the external walls of the building, is used to deliver gas to each household unit. Risers are short pipes that connect the external piping system to kitchens and bathrooms through the building concrete wall. According to recent statistics provided by Towngas, over 14 million household units in China have such risers. Risers are prone to corrosion due to water leaks into the concrete wall. Corrosion often occurs in the sections of risers that are inside the concrete wall. Conventional inspection methods have failed to effectively detect the covered corrosion. The continuous degradation of corrosion may result in riser rupture. Consequently, serious gas leaks may occur and cause explosion. Incidents of sudden explosion caused by ruptured risers happened and killed a number of people. Hence, subjecting risers to safety inspections is a prime concern for every city. The goal of this proposal is to design an effective means to detect corrosion that often occurs in through-wall risers.Ultrasonic guided (UG) waves have recently become popular in the research on detecting defects in buried pipes because UG waves have low energy attenuation and are capable of long-length inspections using only a single transducer. However, the application of UG waves in risers is difficult. First, the surface of a riser is usually coated and partially encased in thick concrete, causing serious energy attenuation on the emitted UG waves. Second, the scattering of reflected UG waves generated by a corroded area is nonlinear, increasing the complexity of defect characterization. Third, risers are usually short in length, with both ends connected to elbows. The reflected waves generated by the elbows may overlap with those that are truly generated by defects. To overcome these difficulties, we propose the designs of a novel sensor called T-MsS, which is a torsional-mode- based magnetostrictive sensor embedded with flexible thin-film coils and smart-materials, an innovative nonlinear inspection approach and an advanced signal processing method named optimized matching pursuit. With the help from these innovative designs, the physical extents of a riser’s corroded area can be determined.Hence, an early warning can be issued after performing a quantitative analysis on the corroded riser. The maintenance staff can then arrange proper remedy to avoid the occurring of catastrophic gas explosion triggered by a ruptured riser.