Stress Corrosion Cracking Of Stainless Steels Welded Plate For Liner Of Normal Temperature Pools Of Nuclear Power Plants

Stress corrosion cracking(SCC)is one of the main reasons for the failure of stainless steel liner of normal temperature pools in nuclear power plants(NPPs).In this work,the SCC behaviors of stainless steels for the liners of the pools in various environments were studied by using chemical immersion tests.The test materials included the base metals and welded joints of the 304L/ER316L austenitic stainless steel weld plate for the second-generation NPPs and the S32101/ER2209 duplex stainless steel welded plate for the third-generation NPPs.The test specimens were divided by stress situation into three types,i.e.U-bend specimens,double-beam specimens and three-point bending specimens.The test environments were divided into four types,i.e.sulfuric acid solution,acidic sodium chloride solution and self-designed simulated solution for service environment,with the temperatures being 20?,40? and/or 60? near service temperature for these three types,and the conventional boiling magnesium chloride solution at 143? for SCC of stainless steels in industries.The main research results are described as follows:1.The SCC behaviors of the four materials in boiling magnesium chloride solution were studied by using the U-bend specimens and the double-beam specimens immersion tests,The results showed that in boiling magnesium chloride solution,base metal 304L,S32101 and the welded joint S32101/ER2209 showed transgranular SCC,but welded joint 304L/ER316L had a mixed intergranular and transgranular SCC.The susceptibilities of all materials to SCC were ranked from high to low as:304L/ER316L>304L>S32101/ER2209>S32101.The susceptibilities ranking of the 304L/3 16L was heat affected zone>the base metal>the weld metal,but that of S32101/ER2209 was fusion line>affected zone>the base metal>the weld metal.The susceptibility of SCC resistance of welded joint S32101/ER2209 to stress was higher than that of welded joint 304L/ER316L.The susceptibility ranking of SCC resistance of 304L/ER316L was the base metal>heat affected zone>weld metal.The SCC susceptibilities of the materials in this solution were the highest among the four environments.2.The SCC behaviors of the four materials in sulfuric acid solution were studied by using the U-bend specimens immersion tests.The results showed that in sulfuric acid solution,the base metal 304L and the welded joint 304L/ER316L had transgranular SCC,and the susceptibilities to SCC were increased with increasing temperature.The susceptibilities of heat affected zone of 304L/ER316L was the highest.The base metal S32101 and the welded joint S32101/ER2209 only had general corrosion.The corrosion resistance of the weld metal was better than that of the base metal,and the corrosion resistance increased with decreasing temperature.3.The SCC behaviors of the four materials in acidic sodium chloride solution were studied by using the U-bend specimens immersion tests.The results showed that in acidic sodium chloride solution,the base metal 304L,S32101 and the welded joints 304L/ER316L,S32101/ER2209 did not show any SCC,but only general corrosion,and the corrosion resistance of the weld metal of S32101/ER2209 was better than the base metal.4.The SCC behaviors of the four materials in simulated solution were studied by using the U-bend specimens and the three-point bending specimens immersion tests.The results showed that in simulated solution,the welded joints 304L/ER316L and S32101/ER2209 had transgranular SCC,and the susceptibilities to SCC were increased with increasing temperature.The base metal 304L and S32101 had general corrosion,and the corrosion resistance increased with increasing temperature.The susceptibilities of the welded joints 304L/ER316L and S32101/ER2209 increased with the increasing of the stress.The susceptibility ranking of the two welded joints from high to low was S32101/ER2209>304L/ER316L.