Browsing by Author "Abubakar, Shamsuddeen Ashurah"

Now showing 1 - 3 of 3
  • Thumbnail Image
    ItemOpen Access
    Effect of dissolved CO2 on the interaction of stress and corrosion for pipeline carbon steels in simulated marine environments
    (MDPI, 2023-06-22) Abubakar, Shamsuddeen Ashurah; Mori, Stefano; Sumner, Joy
    Offshore pipelines are subjected to stresses (e.g., from fluid flow, mechanical vibration, and earth movement). These stresses, combined with corrosive environments and in the presence of trace gases (O2, CO2), can increase the pipeline’s corrosion rate and potentially lead to cracking. As such, the impact of trace gases such as CO2 (linked to enhanced oil recovery and carbon capture and sequestration) on corrosion is key to determining whether pipelines are at increased risk. American Petroleum Institute (API) 5L X70 and X100 were exposed as stressed C-rings (80% or 95% of yield strength). The tests were conducted with either N2 (control) or CO2 bubbled through 3.5% NaCl, at either 5 °C or 25 °C. Linear polarization resistance was used to assess corrosion rate, while morphology and variation were determined using optical microscopy (generating metal loss distributions) and scanning electron microscopy. The control experiment (N2) showed that corrosion rates correlated with temperature and stress. In this low O2 environment, both alloys showed similar trends. Under CO2 exposure, all samples showed accelerated corrosion rates; furthermore, the morphologies generated were different for the two alloys: undercutting corrosion with discontinuous microcracks (X70) or deep, wide ellipses (X100). Understanding these changes in corrosion response is key when selecting materials for specific operational environments.
  • Thumbnail Image
    ItemOpen Access
    Monitoring of stress corrosion cracking under representative pipeline conditions.
    (Cranfield University, 2023-10) Abubakar, Shamsuddeen Ashurah; Sumner, Joy; Mori, Stefano
    Pipelines are subjected to various stresses during operation, which are induced from factors including fluid flow, ocean currents, mechanical vibrations, or earth movements. These stresses, in combination with the corrosive environment can cause an increase in pipeline’s corrosion rate and, subsequently, lead to stress corrosion cracking. The presence of trace gases (CO₂, O₂, H₂S), is expected to have an influence on this susceptibility. As such, the aim of the research is to access the impact of trace gases linked to CO₂transportation, carbon capture and storage, enhanced oil recovery and other pipeline operations. This is key to understanding whether pipelines are at increased risk of failure. In this research, the stress corrosion behaviour of API 5L X65, X70, X80 and X100 has been investigated. Tests were conducted in 3.5 % NaCl solution with either N₂, CO₂, or mixtures of O₂/N₂ and O₂/CO₂ bubbled through. Liquid temperatures were maintained at either at 5 ˚C, 15 ˚C or 25 ˚C. C-ring and 3-point bending specimens were stressed at 80 % or 95 % of yield strength. Linear polarization resistance monitored corrosion rates. Corrosion extent and morphology were examined by optical microscopy (to measure metal loss), followed by scanning electron microscopy analysis. The results from baseline experiment (N₂) showed correlations between corrosion rates and both stress and temperature. All samples exposed with mixed O₂/N₂ presented higher corrosion rates by 1 order of magnitude. Their damage morphology consisted of metal loss and pits features. These pits had deeper, elliptical morphology in comparison with N₂-only data. Results from the pure CO₂ gas showed more rapid corrosion rates than in pure N₂ and mixed O₂/N₂. However, with change in trace gas mixture from pure CO₂ to O₂/CO₂, a large increase in corrosion rates of about 70% was observed. Similar morphologies were observed on X65, X70 and X80 samples in solution with pure CO₂ and mixed O₂/CO₂ at all solution temperatures, with a deep undercutting morphology and discontinuous microcracks being observed. In contrast, X100 showed wide, deep ellipse-shaped pits.
  • Thumbnail Image
    ItemOpen Access
    A review of factors affecting SCC initiation and propagation in pipeline carbon steels
    (MDPI, 2022-08-22) Abubakar, Shamsuddeen Ashurah; Mori, Stefano; Sumner, Joy
    Pipelines have been installed and operated around the globe to transport oil and gas for decades. They are considered to be an effective, economic and safe means of transportation. The major concern in their operation is corrosion. Among the different forms of corrosion, stress corrosion cracking (SCC), which is caused by stresses induced by internal fluid flow or other external forces during the pipeline’s operation, in combined action with the presence of a corrosive medium, can lead to pipeline failure. In this paper, an extensive review of different factors affecting SCC of pipeline steels in various environmental conditions is carried out to understand their impact. Several factors such as temperature, presence of oxidizers (O2, CO2, H2S, etc.), composition and concentration of medium, pH, applied stress, and microstructure of the metal/alloy have been established to affect the SCC of pipeline steels. SCC susceptibility of a steel at a particular temperature strongly depends on the type and composition of the corrosive medium and microstructure. It was observed that pipeline steels with water quenched and quenched and tempered heat treatments, such as those that consist of acicular ferrite or bainitic ferrite grains, are more susceptible to SCC irrespective of solution type and composition. Applied stress, stress concentration and fluctuating stress facilitates SCC initiation and propagation. In general, the mechanisms for crack initiation and propagation in near-neutral solutions are anodic dissolution and hydrogen embrittlement.