The Role of Slow Strain Rate Testing on Evaluation of Corrosion Resistant Alloys for Hostile Hot Sour Gas Production

Abstract

The slow strain test is an effective technique for evaluating the application of high-nickel corrosion resistant alloy tubulars for hostile deep sour wells. To increase that effectiveness, it is important that maximum exchangeability among various data from different laboratories be established. In order to accomplish this, it is necessary to minimize data scattering and maximize the consistency of phenomena by controlling test methods, i.e., specimen dimensions, test machine characteristics including strain rate control, test procedures, and degradation indices. Effect of strain rate on the SCC susceptibility of CRA in such hostile environments tends to be the highest at 1 × 10-6 to 10 × -6s-1, similar to the active pass SCC of carbon steels reported so far. The use of SSRT to assess the contribution of environmental factors on SCC and corrosion is objective and mostly consistent with the results from the other SCC test methods. The effect of electrical insulation between specimen and test equipment and application of anodic polarization on the SSRT is analyzed in this paper. From the engineering viewpoint for material selection, it is recommended that such a galvanic effect should be avoided. It is also recommended that SCC data at the off-gage section should be eliminated and vacuum evacuation in the deaeration process should be used. A test machine that minimizes fluctuation of strain rate control has been developed and used at one of our mills for corrosion resistance quality assurance of mass-produced CRA tubulars.Results are discussed in this paper.

Technical Letter Report of Slow-Strain-Rate Tensile Tests on Irradiated Stainless Steels in a PWR Environment

“…With a given material/environment system, SCC can be revealed at a certain range of applied strain rates. 48,49 If a test was performed at too high a strain rate, there is not enough time for SCC to develop. On the other hand, if the strain rate is too low, the film-rupture rate would be too slow and an active condition at the crack tip cannot be maintained.…”