First in-situ Electrochemical Measurement During Fatigue Testing of Injection Pipe Steels to Determine the Reliability of a Saline Aquifer Water CCS-site in the Northern German Basin

Abstract

Abstract During carbon dioxide storage technology (carbon capture and storage, CCS) components are exposed to a corrosive environment and mechanical stress, which results in corrosion fatigue and inevitably followed by the a lifetime reduction of these components. In order to gain knowledge upon the corrosion fatigue strength of materials, Samples of high alloyed stainless injection-pipe steels AISI 420 X46Cr13, and X5CrNiCuNb16-4 AISI 630 were tested in a at T=60 °C and ambient pressure in a CO 2 -saturated synthetic aquifer environment similar to possible geological on-shore CCS-sites in the northern German Basin. Therefore a corrosion chamber applied to a resonant testing machine allowing for “in situ” test conditions was designed and successfully tested. In-situ tension compression experiments were established using a resonant testing machine at a frequency as low as 30 – 40 Hz. In addition technical CO 2 was introduced into the closed system at a rate close to 9 L/h to keep stable environmental conditions. Simultaneously electrochemical testing was performed to get information on failure causes and the mechanism of failure during the injection of CO 2 into deep geological layers. S-N plots, micrographic analysis, and surface analysis of the fracture surface were applied to obtain sustainable information on the corrosion fatigue behavior of injection pipe steels. Samples used have a surface roughness of Rz = 4, to simulate technically machined surfaces. X46Cr13 reached the maximum number of cycles (12.5 x 10 6 ) at a stress amplitude of 173 MPa. X5CrNiCuNb16-4 reached the maximum number of cycles (10 x 10 6 ) at a stress amplitude at 150 MPa. The scatter range of X5CrNiCuNb16-4 is very high (1:34); by comparison the scatter range of X46Cr13 is only 1:3.5.