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Performance of Advanced Dissimilar Metal Weld SA508-52M-316L in Simulated PWR Primary Water Environment

Author: LiGuanJun
Tutor: LiGuangFu
School: Research Institute of Mechanical
Course: Materials Science
Keywords: Dissimilar metal welding parts Stress corrosion cracking Pressurized water reactor to the loop water environment Electrode potential Dynamic strain aging Welding defects Low temperature crack propagation
CLC: TL421.1
Type: Master's thesis
Year: 2011
Downloads: 50
Quote: 1
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Abstract

International scale nuclear power plant experience has shown that long-running nuclear island structural materials in the environment of high temperature and high pressure water to stress corrosion cracking (SCC) mainly environmentally assisted cracking has become one of the main issues affecting the security and economy of the whole system running, rupture performance testing and evaluation of the quality of these materials in the relevant environment is crucial. In this context, the work carried out AP1000 reactor pressure vessel to take over the third-generation pressurized water reactor nuclear power plant - the secure side of dissimilar metal welding parts SA508-52M-316L research, based on accumulated experience in related engineering and laboratory research data, carried out the experimental work, and to draw the appropriate conclusions: 1) the various parts of the microstructure of the weldment analysis showed that low-alloy steel SA508 matrix structure after post-weld heat treatment on bainite in the heat affected zone can be observed in the region of three characteristics carbide precipitation were less thin-layer zone, coarse grained region as well as the approximate base metal. 52M weld area of ??the nickel base alloy microstructure is the maximum cooling direction preferential growth of dendrite structure, suspected of weld hot cracking fine defects exist in some grain boundaries significantly in the composition change of the transition region adjacent to the weld lines and the tissue morphology is more complex. Stainless steel 316L matrix organization for single equal austenite crystal axis. 2) using the slow strain rate tensile (SSRT) method and the monitoring and control of the electrode potential, the welding of SA508-52M-316L joint multi-notched specimen in the 290 ℃ simulated pressurized water reactor (PWR) primary circuit high temperature water environment SCC in characteristics. The material is closely related to the electrode potential and the dissolved oxygen content of water of the high temperature and the water flow rate and other engineering parameters. Experimental potential of -780 mV to 200mV range, the analog 'loop water chemistry to dissolved oxygen from the state of hypoxia ideal low potential of hydrogen-containing significantly exceeded the high potential of the state service environment. The results show that, its susceptibility to SCC in high temperature water environment is essentially increases with increasing potential shows that the SCC should be anodic dissolution mechanism exist the potential Escc a critical rupture between -300 ~ 200mV (SHE). This article, the definition Escc the specimen due to the occurrence of significant SCC lowest potential fracture failure. Potential in the range from-780mV to-300mV, SSRT sample is always broken form of ductile fracture in nickel-based alloy weld Central. When the potential to rise to the range of -200 mV to 200mV, the sample occurred significantly SCC brittle fracture, SA508-52M interface area is surrounded by the most vulnerable parts of the weldment, occurred in the heat affected zone of the interface and near the SA508 transgranular SCC (TGSCC), - interface thin layer of nickel-base alloy weld occurrence of intergranular SCC (IGSCC). 3) the SSRT plus potential measurement and control method, the basic same SA508-52M and 52M-316L smooth specimens of two single connector in the SCC in the same 290 ° C high temperature water environment. SA508-52M SCC characteristics SA508-52M-316L joints more gap sample is similar to the SCC sensitivity also increases with increasing potential, but the critical rupture potential Escc at 200 - 300mV (SHE) in the most sensitive parts of the SA508-52M at the weld interface, when the potential is higher than Escc occurred significantly SCC brittle fracture, crack like initiation SA508 heat affected zone. 52M-316L susceptibility to SCC with the potential changes in the relationship is more complex, 316L sometimes high strain under conditions of low potential occurrence of the SCC, when the potential to rise to 400 mV (SHE), 52M-316L sector SCC crack indications . Furthermore, the weldment sample temperature water SSRT curve showing the serrated yield characteristics indicate that the sample in this condition, the dynamic strain aging (DSA) characterized; 4) using the same method, weldment samples characteristics of SCC in to 54 ℃ simulated PWR a loop heated environment, in the different strain rates, the surface state and the potential under the conditions of the experiment, were not found in significant SCC; the SSRT curve compared to 290 ℃ the SSRT curve 54 ° C under not showing obvious jagged yield characteristics, that is, without apparent sensitivity of the DSA; 5) showed significant susceptibility to SCC because of low alloy steel weldment parts necessary to carry out further research. Weldment on the material, so that to complement experimental study carried out under the same conditions and welding parts, low alloy steel components, the basic process similar domestic low-alloy steel SA-508 Ⅲ. Experimental results show that the SA-508 Ⅲ welding SA508-52M single joints smooth specimens of low alloy steel good consistency: SCC sensitivity generally the same increase as the potential rise in SCC characteristics were in the 200 - 300mV (SHE) between Escc; slight difference in that the low alloy heat-affected zone on the welded parts is presented below for a wider potential range in Escc slight signs of the SCC, this should be by welding impact. The above experimental results will help the industry to conduct a preliminary evaluation of the service performance of the material or component, the author of this article in this preliminary study.

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