On the Changes in the Properties of an API 5L Steel Through Isothermal Artificial Aging

Abstract Despite the emergence of renewable energies, oil and gas will continue to be critical factors in economic growth, specially in developing countries. An immense amount of these hydrocarbons are moved using steel pipelines. However, these pipelines are becoming older each day and will continue in-service for several more years. Traditional inspections using “smart-pigs “ or UT techniques only help to obtain the size of the corrosion defects, they cannot measure in the field the mechanical properties of the material. In this context, studying the changes in the steel that can happen through years of service is necessary, but this is not a simple issue because the current real characteristics need to be compared with the original ones when the pipeline was built and commissioned. For this reason, an approximation based on an artificial aging method (isothermal method) can be helpful for estimating some mechanical characteristics. Likewise, the impact of these changes is assessed by computing the pipe failure pressure using semi-empirical models. The aforementioned mechanical characteristics are studied statistically with the purpose of determining the pipeline failure probability. Furthermore, the results of evaluating the changes in the corrosion susceptibility using electrochemical techniques are shown. Finally, the results point to the conclusion that the changes in the material properties could be significant, particularly when estimating the failure pressure of the pipe, this could lead to underestimate or overestimate the risk at the time of operation because the mechanical characteristics tend to show a more significant variance. Therefore, it would be recommended that the oil and gas industry propose to develop a methodology to monitor these changes.