HYDROGEN UPTAKE AND CRACKING IN 22-PERCENT CR DUPLEX STAINLESS-STEEL UNDER GALVANIC COUPLING CONDITIONS

Tests were conducted to evaluate the performance of 22% Cr duplex stai nless steel (DSS) coupled to carbon steel (CS) in acid brine environme nts at 80 degrees C with and without hydrogen sulfide (H2S). Measureme nt of coupled potentials and currents were made in parallel with a det ailed evaluation of the effects of H2S, pH, and coupling current on hy drogen uptake. Hydrogen contents generated under coupling conditions w ere large, on the order of 100 ppm (by wt) total hydrogen. At low char ging currents, hydrogen uptake was independent of pH and H2S and propo rtional to the square root of the charging current density (i(1/2)). A s the charging current increased a critical value was reached above wh ich hydrogen uptake was independent of charging current in H2S-free so lution. In H2S-saturated solution hydrogen uptake remained proportiona l to i(1/2). The measurements of hydrogen uptake provide a reference f ramework for identifying critical parameters for stress corrosion test ing and interpretation of results. Preliminary stress corrosion tests were conducted using the slow strain rate testing (SSRT) technique. Th e threshold total hydrogen content for environment-assisted cracking w as between 100 ppm and 250 ppm (by wt) for the alloy tested No reducti on in strain-to-failure relative to oil was observed in H2S-free envir onments. Results from permeation and cracking tests suggested cracking will occur only in H2S environments at coupling currents > 100,mu A / cm(2). Nevertheless, currents of this magnitude may be realized in pra ctice.