General

This standard establishes a SSR test method for evaluating susceptibility of carbon steels to ethanol SCC. It relates to the evaluation of SCC that may be observed in equipment involved in handling, storage, and transportation of ethanolic environments. This equipment primarily includes storage tanks and pipeline system components typically associated with the distribution of ethanolic environments, which includes FGE and FGEfuel blends. This test method may also be used for research related to the effects of environmental or metallurgical variables on susceptibility to ethanol SCC. Field samples of FGE and FGE-fuel blends present under natural service conditions, as well as synthetic ethanolic solutions prepared in the laboratory, may be used with this test method.

This test method is an evaluation method for screening or ranking susceptibility of carbon steels to ethanol SCC or for determination of the propensity of ethanolic environments to produce ethanol SCC in carbon steels. Further research or field experience may be required before using the results in engineering decisions.

This standard addresses the test environments, test specimens, test equipment, determination of baseline material properties, environment test conditions, mechanical test conditions, test procedure, data analysis and reporting of test results.

Two types of SSR test specimens are allowed in this standard: (a) a notched tensile test specimen, and (b) a nonnotched tensile test specimen.

The test procedure is summarized as follows: A SSR test specimen is exposed to a continuously increasing uniaxial tensile stress imposed by a slow and constant extension rate in the presence of an ethanolic environment until fracture is observed. The environment test results include: (a) determination of the tensile strength, (b) determination of the plastic elongation, and (c) assignment of the fracture classification based on examination of the fracture surface morphology. A similar SSR test specimen is pulled at the same extension rate in the presence of an inert environment (e.g., laboratory air) to determine the baseline values of tensile strength and plastic elongation. The ratios of the tensile strength and plastic elongation values in the environment test to their respective average baseline values are determined.

The values of tensile strength and plastic elongation determined in the environment test, the ratios of tensile strength and plastic elongation in the environment test to their respective average baseline values, and the fracture classification based on the fracture surface morphology in the environment test serve as indicators of the SSR test specimen material's susceptibility to SCC in the ethanolic test environment. Ratio values that approach 1.0 indicate high resistance to SCC, whereas lower ratio values normally indicate some degree of susceptibility to SCC.

Acceptance criteria based on values of tensile strength and plastic elongation in the environment test, ratios of the tensile strength and plastic elongation values in the environment test to their respective average baseline values, and fracture classification based on the fracture surface morphology in the environment test are outside the scope of this standard. It shall be the responsibility of the user to define the limits of acceptable behavior for these SSR test results.

Procedures for SSR testing shall be consistent with those provided in ASTM⁽¹⁾ G129,¹ unless specifically defined differently herein.

Other optional techniques may be used as required for particular applications of the data, but these are beyond the scope of this standard. These techniques may involve: (a) fracture energy, (b) crack growth rate, and (c) in the case of a notched SSR test specimen, application of fracture mechanics.

⁽¹⁾ ASTM International (ASTM), 100 Barr Harbor Dr., West Conshohocken, PA 19428-2959.