Nuclear power uses Inconel 690 / HY-industry to break technical difficulty

November 25, 2019

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Today, HY will discuss the application of the Inconel 690 U-tube of the nuclear generator steam generator heat transfer tube.
At present, only a few companies in the world such as Valinox of France, Sandvik of Sweden, and Sumitomo of Japan produce Inconel 690 (TT) alloy pipes, which almost monopolizes the high-performance heat transfer pipe supply market for steam generators.
In China, HY-industry completed the trial production of CPR1000 heat transfer tubes. The localization of China’s AP1000 unit Inconel 690 heat transfer tube is at a critical moment.
Selection of heat transfer tubes for steam generators
International selection of steam generator heat transfer tubes has basically gone through three stages:
The first stage was in the early 1950s and 1960s, when the development of nuclear power was mainly used, 18-8 stainless steel tubes were mainly used;
The second stage was in the 1970s and 1980s. Due to the large number of chloride ion stress corrosion problems in stainless steel pipes, material engineers selected nickel-base superalloy Inconel 600 alloy tubes or iron-nickel alloy tubes according to their experience in petrochemical engineering.
The third stage is after the 1980s, in order to solve the stress corrosion problem of the Inconel 600 alloy tube in the first and second side of the steam generator, France, the United States, Japan and other countries jointly developed the high-resistance Inconel 690 (TT ) Alloy tubing, officially applied to engineering in the early 1990s.

heat exchanger tubesChina began to develop steam generator heat transfer pipes from the 1970s, initially 18-8 stainless steel pipes, and subsequently developed new No. 13 alloy pipes. Since the development of nuclear power in China, the nuclear steam generator heat transfer pipe is basically the introduction of foreign pipe. It is worth noting that the varieties of imported pipes are also subject to the cooperation and the state of the art at that time. The Qinshan Phase I nuclear power plant designed by China has more connections with Europe. The Incoloy800 alloy tube that was favored by the Germans at that time was selected; The Daya Bay Nuclear Power Plant selected Inconel 690 (TT) alloy tubing, which was developed very late at that time; Qinshan Phase II and Ling Ao Nuclear Power Plants used the most popular Inconel 690 (TT) alloy tubing.
At present, almost all new designs and steam generators under construction in nuclear power plants use Inconel 690 (TT) alloy pipes as heat transfer tubes, and many steam generator units that originally used 18 – 8 stainless steel tubes or Inconel 600 alloy tubes have also been replaced with Inconel 690 (TT) heat transfer tube. According to the third-generation nuclear technology, the demand for Inconel 690 alloy pipe requires at least 350t of Inconel 690 pipe in the country to meet the construction of 2 million kW nuclear power unit.

nickel radiating pipeThe role of each element in Inconel 690 alloy Stellite 6
Ni: Increasing the Ni content reduces the stress corrosion cracking sensitivity of Incone1 690 alloy in lye.
Cr: Increasing the Cr content reduces the sensitivity of Inconel 690 alloy to stress corrosion cracking in high temperature water containing chloride and oxygen. Controlling at 30% gives the alloy high corrosion resistance.
Fe: Early studies on Inconel 600 alloys found that Fe has stress corrosion cracking sensitivity in deoxygenated pure water or chlorinated water, that is, Inconel 600 alloy has the main cause of stress corrosion sensitivity in these environments, while increasing Cr content can be Reduce stress corrosion sensitivity.
C: In the Inconel 690 alloy, the C content has little or no effect on the stress corrosion cracking resistance under rolling annealed conditions. However, after low temperature TT treatment, the higher carbon content (between 0.02% and 0.03%) appears to have better stress corrosion cracking resistance than the lower carbon content (about 0.01%). In addition, high carbon (0.03%) materials show more potential for precipitation of intracrystalline carbides than low carbon (0.01%) materials. A lower carbon content (0.017%) leads to a larger grain growth tendency than high carbon (0.027%).
Nb and B: Like Mo, the addition of Nb and B has a detrimental effect on the stress corrosion cracking resistance of Inconel 690 alloy.
AI: Increasing Al (<0.05 to 0.14%) seems to increase the depth of intergranular stress corrosion cracking.
Ti: When Ti is present in the Inconel 690 alloy, the grain boundary can be pinned.
S, P : This is two deadly harmful elements in nickel-based alloys, especially S. If a very low S content is not obtained, it will seriously affect the processing properties of the alloy and even make the alloy difficult to process. In the Inconel 690 alloy treated by TT, it was found that P, B and AI also had grain boundary segregation in addition to C. But the degree of segregation is much smaller than in the Inconel 600 alloy.
N: Some people think that there is an appropriate amount of N (about 0.2%) in the alloy, which can refine the grains without jeopardizing the grain boundary lean Al and lean Cr.