Evaluation method for pipe wall thinning due to liquid droplet impingement

Abstract

In order to evaluate pipe wall thinning due to liquid droplet impingement (LDI), the analysis code system DRAWTHREE-LDI composed of the six steps has been developed. The wall thinning due to LDI is classified into two types which are LDI (corrosion) and LDI (erosion). In LDI (corrosion), the dominant mechanism to dwindle pipe wall thickness is flow-accelerated corrosion which is a chemical process. While in LDI (erosion), it is impact onto wall surfaces due to droplet impingement which is a physical process. The validations on DRAWTHREE-LDI were made through the comparisons of results calculated with those measured in feed water heater vent lines at an actual power plant. Most calculated results agreed with those measured within a factor of two which was the target in the development of DRAWTHREE-LDI. In order to confirm the calculation accuracy, it is strongly required to improve measurement accuracy, since the measured wall thinning rate was obtained by subtraction of the measured wall thickness during the regular inspection period from one during the previous inspection period. The measured wall thickness itself by UT techniques has some measurement errors, and the error increases a lot by the subtraction.