Fatigue and Static Crack Growth Rate Study of Carbon Steel for Corrosion Prevention of Natural Gas Transmission Pipelines (original) (raw)

Abstract

Internal metallic and non-metallic coatings are being considered as parts of answers to allow current natural gas transmission pipelines to safely batch transport a variety of products, including natural gas, carbon dioxide and hydrogen. Sacrificial anode coatings, that contain Zn, are being considered for internal corrosion protection of standard carbon steel pipeline as they are known to galvanically protect steel. However, this can lead to the creation and ingress of hydrogen into the line pipe material, resulting in increased susceptibility to cracking under high static and cyclic loads associated with both steady state as well as startup and shut down conditions. The current study simulates the conditions expected to be encountered in field by performing crack growth rate measurements under static and fatigue loading conditions on fracture mechanics-based specimen extracted from API 5L X-65 steel. The effect of cyclic loading frequency on fatigue crack growth rate (FCGR) and the effect of applied cathodic polarization on static crack growth rates (SCGR) was investigated in a 3.5% NaCl solution in contact with CO2 at 25°C. The partial pressure of CO2 (pCO2) was 101.325 kPa. The applied cathodic potentials were those associated with mixed potential of the Zn- based coatings.

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