Principal Research Results

Development of Evaluation System of Liquid Droplet Impingement Erosion

Background
Liquid droplet impingement erosion (LDI) is defined as an erosion phenomenon caused by high-speed droplet attack in asteam flow. In a power plant, pipe wall thinning by LDI is observed in steam piping systems. Because LDI usually occurs very locallyand is difficult to detect, prediction of LDI location is required for the safety of the plant system.
Therefore, as the ultimate objective, we set the development of a tool for predicting LDI location that can be easily used inpower plants (LDI Prediction Code).
In previous researches, we were able to evaluate all the local flow conditions that affect LDI materially ＊ 1. But, as LDI is acomplex phenomena affected by fluid and material, it is difficult to predict the LDI position by applying these results and past knowledge individually.

Objectives
This study aims to suggest the evaluation method for LDI position (LDI prediction system) through organizing the previousresults and past knowledge systematically.

Principal Results
1. Suggestion of LDI prediction system
We constructed the LDI prediction system by providing “fluid conditions at the inlet and exit of piping system” and “pipingisometrics” as input conditions (Fig.1). The steps are as follows;
1. Global flow evaluation: Calculation of the flow condition in arbitrary piping position by in-house code “MATIS-SC ＊ 1” or“MATIS-SP ＊ 2”
2. Local flow evaluation: Calculation of the droplet behavior at the elbow and definition of “the percentage of droplet collision”
3. Evaluation of the LDI sensitivity: Evaluation of the LDI sensitivity by past findings, knowledge and the results of 1 and 2.
2. Test calculation of LDI prediction system
Test calculation of suggested LDI system is conducted in steam piping model with orifice (Fig.2). After the calculation ofglobal and local flow (Fig.3), we constructed the model to evaluate the ranking of LDI possibility by using a function of LDI sensitivity considering the percentage of droplet collision in addition to the velocity and wetness, the effects of which on LDI are well known
as conventional knowledge.
As a result, we found that the percentage of droplet collision affects LDI in addition to the velocity and wetness (Table1).
Main Researcher: Ryo MORITA Ph. D.,
Research Scientist, Pipe Wall Thinning Unit, PLM (Plant Life Management) Project
Reference
R. Morita, 2007, “Investigation of Flow Characteristics Affecting Liquid Droplet Impingement Erosion (Part 2) - Improvement ofFlow Evaluation Method -”, CRIEPI Report L07016 (in Japanese)
R. Morita, 2006, “Development of “MATIS-SC Code” for High Speed Steam Flow with Non-equilibrium Condensation”, 4th ICCFD＊1：Multi-dimensional Accurate Time Integration Simulation for Steam with Condensation＊2：Multi-Phase Accurate Time Integration Simulation for Steam in Piping985. Nuclear

Fig.1 Overview of LDI Prediction SystemAssuming fluid conditions at the inlet and exit of piping system and piping isometrics to be the input conditions,
possibility of LDI at all elbow positions is evaluated.

5Fig.2 Steam Piping Model
As a test calculation of LDI prediction system,
steam piping flow with orifice is calculated and LDI
sensitivity is evaluated at elbow 1-5.

Fig.3 Flow Distribution along Flow Direction in Piping
Global flow condition is calculated by 1D code.

Table 1 LDI Evaluation Results at Elbow ①-⑤
LDI possibility is calculated at elbows ①-⑤ by using a function of LDI sensitivity considering thepercentage of droplet collision in addition to the velocity and wetness.
We found the percentage of droplet collision affects the LDI possibility.
LDI Possibility

Velocity

Wetness

Percentage of Droplet

u [m/s]β[%]Collision, w [%]f (u , β)※f (u 4, β, w)

①

178.4

2.62

40.7

55②

183.8

2.59

44.0

44

③

187.8

2.58

56.9

32④

192.1

2.56

40.9

23⑤202.8

2.53

42.8

11Elbow※In case of not considering the percentage of droplet collision, w

994