What are the inspection methods for butt weld elbows after corrosion?

　　Butt weld elbows can corrode due to improper use. Corrosion typically manifests as thinning of the pipe wall, localized pitting, and pitting. Inspection methods for butt weld elbows after corrosion include:

　　1. Magnetic flux leakage method: This method is based on the high magnetic permeability of ferromagnetic materials.

　　The magnetic permeability at the corrosion defect is much lower than the overall permeability of the butt weld elbow. When the butt weld elbow is magnetized under an external magnetic field, most of the magnetic lines of force pass through the steel pipe, resulting in a uniform distribution. When there are internal defects, the magnetic lines of force bend, and some leak out onto the surface of the steel pipe. Detecting the leakage magnetic flux escaping from the magnetized butt weld elbow surface determines the presence of defects.

　　2. Ultrasonic method: This method uses the pulse reflection principle of ultrasonic waves to measure the thickness of the corroded pipe wall. This process uses a self-propagating centrifugal casting method for molding, mainly utilizing the material's own chemical reaction, exothermic combustion to generate high temperatures, and the synthesis of new materials during the propagation of the combustion wave. During testing, the probe emits ultrasonic pulses vertically towards the inner wall of the butt weld elbow. The probe first receives the reflected pulse from the inner surface of the pipe wall, and then the ultrasonic probe receives the reflected pulse from the outer surface of the pipe wall. surface reflects the thickness of the pipe wall.