General

This standard covers the testing of metals subjected to tensile stresses for resistance to cracking failure in low-pH aqueous environments containing H₂S. Carbon and low-alloy steels are commonly tested for EC resistance at room temperature where SSC susceptibility is typically high. For other types of alloys the correlation of EC susceptibility with temperature is more complicated.

This standard describes the reagents, test specimens, and equipment to use, discusses base material and test specimen properties, and specifies the test procedures to follow. This standard describes four test methods:

Method A—Standard Tensile Test

Method B—Standard Bent-Beam Test

Method C—Standard C-Ring Test

Method D—Standard Double-Cantilever-Beam (DCB) Test

Sections 1 through 7 of this standard give general comments that apply to all four test methods. Sections 8 through 11 indicate the test method to follow for each type of test specimen. General guidelines to help to determine the aptness of each test method are given at the beginning of each test method description (Sections 8 through 11). Reporting of the test results is also discussed.

Metals can be tested for resistance to EC at temperatures and pressures that are either ambient (atmospheric) or elevated.

For testing at ambient conditions, the test procedures can be summarized as follows: Stressed test specimens are immersed in acidified aqueous environments containing H₂S. Applied loads at convenient increments can be used to obtain EC data.

For testing at temperatures higher than 27°C (80°F), at either atmospheric or elevated pressure, Section 7 describes an alternative test technique. All methods (A, B, C, and D) are adaptable to this technique.

This standard may be used for release or acceptance testing to ensure that the product meets a certain minimum level of EC resistance as prescribed in API⁽²⁾ Specification 5CT, ISO⁽³⁾ 11960, or as prescribed by the user or purchaser. This standard may also provide a quantitative measure of the product’s EC resistance for research or informational purposes. This rating may be based on:

Method A The highest no-failure stress in 720 hours.

Method B The statistically based critical stress factor (S_c) for a 50% probability of failure in 720 hours.

Method C The highest no-failure stress in 720 hours.

Method D The average K_ISSC (threshold stress intensity factor for SSC) for valid tests of replicate test specimens.

Safety Precautions: H₂S is an extremely toxic gas that must be handled with care. (See Appendix A.)

⁽²⁾ American Petroleum Institute (API), 1220 L St. NW, Washington, DC 20005.

⁽³⁾ International Organization for Standardization (ISO), 1 rue de Varembé, Case postale 56, CH-1211 Geneva 20, Switzerland.

 

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