Abstract
The purpose of this paper is to understand the mechanism of non-axisymmetric wall-thinning that caused a pipe break in the pipeline of the Mihama nuclear power plant in 2004. The wall thinning was caused by the flow accelerated corrosion which affects low carbon steel pipelines. The mass transfer rate measurement of the wall thinning behind an office in a curved swirling flow is carried out in a closed-circuit water tunnel using a benzoic acid dissolution method. The experimental results indicate that the high mass transfer rate is observed on one side of the pipe behind the orifice, which is similar to the observation of the wall-thinning rate in the Mihama case. This result suggests that the influence of the secondary flow in the long elbow combined with the swirling flow can produce the non-axisymmetric mass transfer phenomenon behind the orifice.
Highlights
The wall thinning is one of the important topics of interests for the safety management of the pipelines in nuclear/fossil power plants
The purpose of this paper is to provide a key to understand the complex mechanism of non-axisymmetric wallthinning of a pipeline by the mass transfer rate measurements using a benzoic-acid dissolution technique
Note that the results are shown at an axial distance of x/d = 1 behind the orifice, where the maximum pipe-wall thinning was observed in the Mihama case
Summary
The wall thinning is one of the important topics of interests for the safety management of the pipelines in nuclear/fossil power plants. The most interesting point of the pipe-wall thinning is the non-axisymmetric wall thinning in the cross-section of the A-line behind an orifice, which results in a higher thinning rate on one side of the pipe than on the other side. It was found from the scaled model experiment that the swirling flow was observed in the pipeline [7], the magnitude of which was estimated by the swirl number defined by the ratio of the circumferential momentum to the axial one and equal to 0.26 in the upstream of the orifice. Several studies have been carried out in literature [8,9,10,11,12,13] to elucidate the mechanism of wallthinning of the pipe
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