Session: 08-11: Computational Fluid Dynamics (CFD) and Applications - XI

Paper Number: 130797

130797 - Evaluation of Hydrodynamic Effects for Flow Accelerated Corrosion (Fac) at Weld Section 

Abstract: 

Flow accelerated corrosion (FAC) is well known ageing phenomena in power plants, and also is known that the thinning rate due to FAC is strongly influenced by the chromium content of the carbon steel piping.
Therefore, if the chromium content differs between base metal and weld metal or between base metals at welded sections of plant piping, the FAC rate of each part may differ.
In particular, if the chromium content of the weld metal is smaller than that of base metals, localised FAC at only the welding section. This local FAC phenomenon is known as “Weld FAC”, and has actually resulted in leakage from welds in some cases.
Furthermore, when only the weld thinning occurs due to Weld FAC, the localised depressions is formed and this may change the thinning tendency due to the formation of vortices and the increase of the turbulence caused by the fluid.
However, the hydrodynamic effects to Weld FAC are not clarified, and if changes of the flow field due to progressive thinning contribute to increased thinning, these effects should be taken into account in the evaluation of Weld FAC rate.
In this study, the hydrodynamic effects in the weld depression caused by the Weld FAC were analytically evaluated to assess the change in the wall thinning tendency with the progression of the Weld FAC and its correlation with the fluid conditions.
CFD (computational fluid dynamics) analysis was carried out with STAR-CCM+ code and straight pipe with welding is modeled with parameters such as the weld width and the depression depth of the weld. To evaluate the local turbulent effects at the weld properly, the Adaptive Mesh Refinement (AMR) method was used around the weld.
In this evaluation, to evaluate the effect of the hydrodynamic effects, “geometry factor”, ratio of the amount of wall thinning at the bottom of the weld depression to that at the straight pipe, was used. If the geometry factor exceeds 1.0, the hydrodynamic effects is considered to enhance the Weld FAC.
The results of the evaluation showed that when the aspect ratio (ratio of weld width to weld depression) is small, re-attachment flow is formed and the geometry factor is increased. Then, when we increase the aspect ratio and a circulating flow is formed in the weld depression, the geometry factor tends to gradually decrease.
In the presentation, the correlation between these parameters and the geometry factor will also be presented.

Presenting Author: Ryo Morita Central Research Institute of Electric Power Industry

Presenting Author Biography: 2001/3 finish master cource in mechanical engineering at Osaka UNIV.
2001/4 start working at CRIEPI
2006/3 take a doctorate of engineering at Osaka UNIV. with working at CRIEPI

Speciality
/Fluid Engineering
/Computational Fluid Dynamics (water, wet &dry steam, flashing)

Research Field
/ Wall Thinning (FAC(Flow Accelerated Corrosion), LDI(Liquid Droplet Impingement Erosion) and cavitation erosion)
/ Flow instabilities, Flow Induced Vibration and vibration fatigue
/ Risk-Informed Maintenance

Authors:

Ryo Morita Central Research Institute of Electric Power Industry
Tomohisa Yuasa Central Research Institute of Electric Power Industry
Yuta Uchiyama Central Research Institute of Electric Power Industry
Takayuki Yamagata Niigata University