Abstract: The base material of CRA composite piping is carbon steel, which is overlaid by 3 mm 625 stainless steel on inner surface. The CRA composite piping is applied more and more widespread in offshore project, because of its good ability of corrosion resistant and lower cost than stainless steel. RT is normally applied to evaluate the weld quality; however, it's difficult to overcome the inspection difficulty of too big thickness. This page develop the MUT technique, to solve the disadvantage of RT, this technique can well overcome the influence of material attenuation and interface. The technique reliability is verified by the prepared serial of artificial defect block, and can provide guidance for similar inspection.