Preparation before flaw detection
Surface treatment: Use chemical cleaning, grinding or sandblasting to remove oil, rust, oxide scale and dust from the pipeline, check and repair existing defects on the surface to ensure detection accuracy.
Select equipment and materials: Select the flaw detector according to the pipeline specifications, select the magnetization method (AC or DC), prepare magnetic powder or magnetic suspension with high magnetic permeability, low coercivity and sharp contrast with the color of the pipeline, and the carrier must be compliant.
Calibration equipment: Use standard test blocks to verify parameters such as the sensitivity of the flaw detector to ensure that the equipment is normal and the results are accurate.
Magnetization operation
Determine method parameters: Select the magnetization method (such as axial power supply, magnetic yoke method, etc.) according to the shape of the pipeline and the direction of the defect, and set the magnetization current value and time according to the standards and detection requirements (continuous method power supply 1s - 3s).
Implement magnetization: Place the pipeline, ensure good contact, turn on the power supply and magnetize according to the parameters to generate a magnetic field inside.
Apply magnetic powder or magnetic suspension
Select the method and timing: For rough surfaces, use dry method to evenly sprinkle powder; for smooth surfaces, use wet method, and spray, pour or immerse magnetic suspension after stirring. The continuous method is applied while magnetizing, and the residual method is applied after magnetizing.
Observation and recording of magnetic traces
Create conditions: non-fluorescent traces are observed in a bright place with natural light or light; fluorescent traces are observed in a dark room with ultraviolet light.
Analysis and record: Distinguish the true and false magnetic traces, record the position, size, quantity and shape of the magnetic traces that are indeed defects, and take photos or use tape to stick them for preservation.
Demagnetization treatment
Demagnetization is required when the product technical requirements are met, multiple magnetizations have interference, and residual magnetism affects subsequent processing. Use AC or DC demagnetization method to change the direction of the magnetic field and reduce the intensity to zero.
Post-processing
Clean the residual magnetic powder in the pipeline (wipe with organic solvent or high-pressure water, etc.), prevent rust as needed (apply anti-rust oil, etc.), and prevent rust from affecting performance and life.
