Because the intergranular microstructure of nickel-based alloy weld exists in Austenite morphology and its acoustic characteristics are similar to those of austenitic stainless steel,it is difficult to detect defects quantitatively,locatively and qualitatively.This paper mainly introduces the UNS N08825 nickel-based alloy pipeline of the high sulfur well station of Sinopec Group(diameter is DN100-DN150 and the thickness 8.5-15mm)and the specific method of ultrasonic detection used in welded seam inspection.
When detecting butt welds of nickel-based alloy pipelines, it is easy to generate surface waves, and placing the finger close to the front of the probe can hinder the propagation of the surface, thus avoiding the influence of surface waves on the flaw detection. At the same time, pay attention to the discernment of pseudo defect wave when detecting. Nickel-based alloy pipeline pseudo defect waves are mainly: (1) caused by weld root shaping; (2) stagger (or weld aneurysm) defects caused by the variant wave; (3) coarse austenite grains caused by the noise wave.
The defects of ultrasonic detection of nickel-based alloy pipeline weld can be assessed by referring to Appendix I of NB/T47013.3, and the grade of safety condition of pressure pipeline can be assessed by referring to the "Regulations for Periodic Inspection of Industrial Pipelines".
