Effect of ultrasonic cleaning on decontamination efficiency, microstructure, and properties of pipeline welds

The weld seams with uneven surfaces on the nuclear power plant pipelines have led to radioactive hotspots formed by long-term accumulation of radioactive contaminants within the pipelines, which has increased the radiation dose rate for the operators. This article establishes a simulation model for pipeline welds and conducts ultrasonic cleaning tests, which studies the effect of pipeline welds on ultrasonic cleaning, as well as the effect of different installation methods on the decontamination efficiency, microstructure, and properties of the pipeline welds. The research results show that the pipeline welds have a relatively small impact on the ultrasonic cleaning effect. Meanwhile, the decontamination efficiency of the dual-transducers operation mode for pipeline welds is approximately three times than that of the single-transducer mode. This is attributed to the superposition of the acoustic fields generated by the dual-transducers at the welds, which enhances the mechanical vibration effect and cavitation effect, thereby increasing the decontamination efficiency. Before and after decontamination, both the substrate and the weld area exhibited as austenitic structure and columnar crystal structure. The microhardness remained consistent basically. The element distribution was uniform, and there was no significant fluctuation in the composition content. The tensile strength remained unchanged, and there were no defects on the surface of the sample after bending. The surface of the salt spray corrosion samples with single-transducer and dual-transducers presents metallic color and no corrosion, ultrasonic cleaning doesn’t reduce the corrosion resistance at the weld seams. Therefore, the ultrasonic cleaning under different operation methods will not affect the microstructure and properties of the pipeline welds. Under the condition that on-site conditions permit, the dual-transducers cleaning method should be given priority for the cleaning operation of the pipeline welds, which can improve the cleaning efficiency at the welds. This has an important guiding role in the implementation of the ultrasonic cleaning scheme for pipeline welds.