The Experimental Investigation Of Stress Corrosion For Q345R Steel Welding Joint Containing Defects In Wet Hydrogen Sulfide Solution

Q345R steel is mainly used for making types of low-pressure vessels and welding is the main manufacture process, according to the characteristics of welding technique such as rapid cooling and heating, adding welding materials, which is determined the inhomogeneity of organization and performance, so it will become the failure part and inevitably caused the stress corrosion cracking (SCC) when encountered wet H2S as a result of high hydrogen and residual stress. In view of many defects and quality problems of Q345R steel welding joint and much loss for equipments failure, it will be important to research the stress corrosion of Q345R steel welding joint containing defects in wet hydrogen sulfide solution.The Q345R steel welding joint was chosen as the research object in this paper. Slow strain rate test (SSRT), pre-crack (CT) tensile test and wedge opening loading (WOL) test were adopted to study the stress corrosion in the wet hydrogen sulfide solution in the lab. The sensitivity of SCC, the crack propagation rate and the critical stress intensity factor of stress corrosion of Q345R steel in hydrogen sulfide environment were investigated, which provided experimental data for corrosion protection and safety assessment of in-service equipment containing defects.The main conclusions of this paper are summarized as follows:1. SSRT tests show that the fracture time and elongation of Q345R steel welding joint containing defects decrease obviously since suffered from stress concentration and H2S solution. The SCC sensitivity is higher than without defect. The sensitivity of Q345R steel welding joint containing defects increase with the concentration of H2S increase and the typical stress corrosion fracture surface is observed in 200ppm H2S solution.2. SSRT tests show that the SCC sensitivity of Q345R steel welding joint containing defects are almost the same in three different strain rate (1.06×10-6s-1, 2.12×10-6s-1, 3.18×10-6s-1).3. Pre-crack tensile corrosion tests of Q345R steel weld zone (WZ) and heat affected zone (HAZ) show that the average propagation rate of WZ in 200 ppm and 400ppm H2S are 2.626×10-5 mm/s and 2.583×10-5 mm/s, while the HAZ are 1.463×10-5 mm/s and 1.429×10-5 mm/s. The propagation rate of WZ is faster than HAZ. In the same zone, the rates are almost no change in two concentrations, but initial crack time in 400ppm is earlier than in 200ppm.4. WOL tests show that the SCC crack propagation rate of Q345R steel welding zone without defects are within the range of 3.147×10-7 mm/s ~4.126×10-7 mm/s,whileⅢlevel slag are 3.367×10-7 mm/s~6.873×10-7 mm/s andⅡlevel slag are 1.092×10-7 mm/s~2.800×10-7 mm/s,the crack growth rate ofⅢlevel slag is faster thanⅡlevel slag and no defects. The critical stress intensity factor (KISCC) of without defects are less than 75.245MPa m ,ⅢandⅡlevel slag KISCC are respectively less than 74.124MPa m and 77.612MPa m。...