Abstract
An orifice is used widely as a flow meter or a contraction device in pipeline systems in hydro-power plants, thermal power plants, and chemical plants because of its simple construction, high reliability, and low cost. However, it is well known that flow-accelerated corrosion (FAC) occurs on the pipe wall downstream of the orifice. Some of the authors have examined FAC through experimental and numerical analyses and have reported that one of the major governing parameters of FAC for single-phase water flow is the pressure fluctuation p’ on the pipe wall, and also that pipe wall thinning rate TR can be estimated by p’. In addition, they have presented the effects of the ori-fice geometry on p’ or TR, and have described a method for suppressing p’ or TR. In the present study, FAC for a two-phase air-water bubble flow is examined and compared with the single-phase water flow experimentally. Further, it is shown that because p’ is also considered a governing parameter of FAC for a two-phase air-water bubble flow, TR can be estimated using p’. It is also indicated that, by using a downstream pipe with a smaller diameter than that of the upstream pipe, p’ or TR can be suppressed.
Highlights
The flow-accelerated corrosion (FAC), liquid droplet impingement (LDI) corrosion, and cavitation erosion (C/E)How to cite this paper: Shakouchi, T., Kinoshita, K., Tsujimoto, K. and Ando, T. (2016) Flow-Accelerated Corrosion in Pipe Wall Downstream of Orifice for Water and Air-Water Bubble Flows
It has been shown that there is a good correlation between the pipe wall thinning rate Thinning Rate (TR) and the turbulent kinetic energy k near the pipe wall as shown in Sections 1.1 and 1.2 or the pressure fluctuation p’ on the pipe wall downstream of the orifice for single-phase, water flow
This means that the Std-Dp orifice can decrease the pressure fluctuation or pipe wall thinning caused by FAC downstream of the orifice
Summary
The flow-accelerated corrosion (FAC), liquid droplet impingement (LDI) corrosion, and cavitation erosion (C/E). At the Mihama nuclear power plant, Japan, the pipe wall (diameter D = 560 mm) downstream of the orifice with an area contraction ratio of CR = 0.36 was broken by FAC after 21 years of use under the following conditions: flow rate of water Qw = 100 ton/hour, mean velocity um ≈ 2.2 m/s, pressure p = 0.93 MPa, and temperature T ≈ 142 ̊C [4] [5]. It has been shown that there is a good correlation between the pipe wall thinning rate TR and the turbulent kinetic energy k near the pipe wall as shown in Sections 1.1 and 1.2 or the pressure fluctuation p’ on the pipe wall downstream of the orifice for single-phase, water flow. The TR can be estimated by p’ [11] [15]
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