Failure analysis of leakage on titanium tubes within heat exchangers in a nuclear power plant. Part II: Mechanical degradation

Abstract

Serious failure incidents like clogging, quick thinning, and leakage frequently occurred on lots of titanium tubes of heat exchangers in a nuclear power plant in China. In the Part I of the whole failure analysis study with totally two parts, factors mainly involving three kinds of electrochemical corrosions were investigated, including galvanic corrosion, crevice corrosion, and hydrogenassisted corrosion. In the current Part II, through microscopically analyzing the ruptures on the leaked tubes by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS), another four causes dominantly lying in the aspect of mechanical degradation were determined -clogging, erosion, mechanical damaging, and fretting. Among them, the erosion effect was the primary one, thus the stresses it exerted on the tube wall were also supplementarily evaluated by finite element method (FEM). Based on the analysis results, the different degradation extents and morphologies by erosion on the tubes when they were clogged by different substances such as seashell, rubber debris, and sediments were compared, and relevant mechanisms were discussed. Finally, countermeasures were put forward as well.

Failure analysis of O-ring gaskets of the electric hydraulic system in the nuclear power plant

“…However, due to the complexity of the actual working conditions and the lack of appropriate detective methods, few researches have been devoted to solving the actual O-ring gaskets failure incidents in the nuclear power unit. Our lab has lots of experience on solving the actual failure accidents of nuclear equipment [15][16][17][18] and polymeric materials [19] , which helps us analyze this current case effectively and efficiently.…”

Modelling and fault analysis of APROS-based moisture separation reheater

“…Due to the condensing heat transfer in the reheater, there is a two-phase flow and temperature difference inside the tube [7], which leads to thermal fatigue of the tube bundle [8] and can lead to pipe rupture during long-term operation. Microscopic analysis of the heat exchanger tube leakage yields erosion effects as the main cause [9]. The above literature analyses the modelling simulation of MSR and the cause of rupture failure but lacks the specific performance and impact of small rupture failure to provide early warning for field operation.…”

Failure Analysis of Duplex Stainless Steel for Heat Exchanger Tubes with Seawater Cooling Medium

“…Several failure modes of heat exchangers have been identified; the most common modes are fatigue [7,8], creep [9,10], oxidation [11], and hydrogen attack [12]. The common causes of heat exchanger failure include weld defects [13,14], vibration [15,16], erosion [17,18], stress corrosion cracking [19][20][21], and microbial-induced cracking [22][23][24][25]. Considering its numerous failure modes, the failure of the heat exchanger should be analyzed by recognizing the possible root cause, especially the lessons learned from previous studies.…”