SSC Tensile Tests: Comparison between the Regular NACE Test, the SNEA(P) Test and a Modified NACE Test at pH 4

Abstract The only major differences between the NACE test procedure with subsize specimens and the SNEA(P) procedure are in the nature of the gas itself, respectively pure H2S and gas from Lacq (CH4 + 15% H2S + 9% CO2), and the amount of acetic acid added to the solution, 0.5% acid or adjustment to pH 4. Nevertheless, these differences induce a slight distortion in the ranking of materials. Thus, the most SSC susceptible materials, the high stress levels and the stainless steels are more penalysed in the NACE test than in the SNEA(P) one. On the contrary a variant of the NACE test with an initial pH value of 4 leads to results quite parallel to those of the SNEA(P) test. Furthermore, this modified NACE test seems to be much more representative of actual service conditions. This study also shows that provided that some additionnal experimental precautions are respected, the use of samples with a small diameter is quite possible in smooth tensile test procedures.