Sulphide stress cracking test development for a weldable 13%CR supermartensitic stainless steel in simulated seabed environments

Walters, Matthew (2016). Sulphide stress cracking test development for a weldable 13%CR supermartensitic stainless steel in simulated seabed environments. University of Birmingham. Eng.D.

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Abstract

Weldable 13%Cr supermartensitic stainless steels are commonly used for subsea pipelines in the oil and gas industry. Although classified as corrosion resistant alloys, these steels can be susceptible to Sulphide Stress Cracking (SSC) when exposed to wet environments containing chlorides, carbon dioxide and low levels of hydrogen sulphide. Standard guidelines stipulate that laboratory SSC tests are performed at 24 °C and at the maximum design temperature, however some studies suggest that the risk of SSC could be greater at temperatures below 24 °C. Seabed temperatures can be as low as 5 °C, so in-service cracking could occur following shut-down conditions even if the material has been qualified at 24 °C.

Four-point bend SSC tests performed at 5 °C and 24 °C in simulated seabed environments showed the material was more susceptible to SSC at 5 °C, but only when the as-received pipe surface was compromised. A supporting stress and strain investigation highlighted strain concentrations on the test surface which were coincident with the location of cracking observed in the SSC tests. Finite element simulations were used to demonstrate that tensile stress-strain data should be used over flexural bend data to load four-point bend specimens to the desired loading strain.

Type of Work:

Thesis (Doctorates > Eng.D.)

Award Type:

Doctorates > Eng.D.

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