Stress Corrosion Testing For Q345R Steel Welding Joint Containing Defects In Wet Hydrogen Sulfide Environment

Q345R steel is becoming more popular as the material of choice for medium and low pressure vessels because of the advantages it provide such as perfect comprehensive mechanical performance and low price-to-yield ratio. Welding pays a key role in production process of the vessels and the welded joint is one of the most significant points in the weld-quality-controlling. But some defects which the important ones are pit, porosity, and slag inclusion, are often detected in the welded joint in the practical production, because of the characteristics of welding technique such as rapid cooling, local overheating, and adding welding materials. Although the defects have little effect on the mechanical properties of material, they may be one of the main causes of stress corrosion crack initiation and brittle fracture, when exposed to the wet H2S service.In this paper, the effect of the defects in the welded joint on the SCC behavior of Q345R in wet H2S solution were studied by using slow strain rate test (SSRT), wedge opening loading (WOL) test and pre-crack(CT) tensile test to assure good performance of Q345R steel and explore the strength design and service life prediction of the structure.The main research works and conclusions were summarized as follows:(1) The slow strain rate tests(SSRT) of Q345R welded joints indicated that, at an initial concentration of204and612mg/L wet H2S service, the stress corrosion cracking susceptibility indexes F (A) of all of the SSRT specimens was higher than35%, and the stress corrosion cracking (SCC) sensitivity was decreased with the radius of notches increased because of the synergistic effect of wet hydrogen sulfide and stress concentration. And the smooth specimen was the least susceptible to SCC in wet H2S service. The specimens with the same radius of notch were more susceptible to SCC at an initial concentration of612mg/L wet H2S service;(2) The wedge opening loading (WOL) test of Q345R welded joints indicated that, at an initial concentration of400mg/L wet H2S service, after3600h, the crack growth rate of all of specimens was higher than10"9mm/s; The crack growth rate of III slag inclusion was the fastest, while the III porosity was the slowest. In addition, The critical stress intensity factor (K1scc) of WOL specimens without any defects was less than80.734MPa?m1/2; The K1scc of III slag inclusion and III porosity K1scc was respectively less than76.434MPa-m1/2and83.314MPa-m1/2;(3) The pre-crack tensile corrosion test of Q345R welded joints indicated that, at an initial concentration of612mg/L wet H?S service,the displacement rates in the range of lxl0-5～5xl0-4mm/s, when the displacement rate were5X10"5mm/s and1x10-4mm/s respectively, the peak value of the load-time curves were8162.67N and8365.22N correspondingly, lower than the others; when the displacement rate was1x10-5mm/s, the SCC fracture surface could be observed in the compact tension (CT) specimens;(4) the SEM showed that, at an initial concentration of204and612mg/L wet H2S service, river-like patterns were observed from the SCC fracture surface in SSRT specimens; at an initial concentration of400mg/L wet H2S service, some river-like patterns and expansion of secondary crack were observed from surface of all the WOL specimens.