Study on the loss of ductility of the API 5L grade b steel using the isothermal aging process

• Ductility loss quantification for an aged steel pipeline material. • Natural aging can be replicated using an artificial isothermal aging technique. • Fracture area, elongation and area reduction studied as random variables. • Ductility loss of the material indicates embrittlement as aging process advances. Fossil hydrocarbons will continue to be of great importance in the energy network in the foreseeable future. The most cost-effective way to move these hydrocarbons is through pipelines. The steel used in these pipelines needs to be able to sustain significant plastic deformation before rupturing. These pipelines tend to be in service for very long timespans, thus undergoing an aging process. In the literature, it has been found that the natural aging process tends to decrease the ductility in the pipeline steel. Using an artificial aging process (isothermal), we studied the loss of ductility in API 5L Gr.B steel, analyzing samples already used in tension tests and Charpy impact tests, which were carried out in previous works, and estimating the percentage of the brittle fracture area, elongation, and area reduction. These variables were analyzed as random variables and were fitted to a theoretical probability function. The gamma and lognormal distributions correctly fit the steel characteristics studied. In addition, it was found that the percentage of elongation and area reduction tended to diminish as the material aged. This study confirms the loss of ductility in API 5L grade B steel and allows for the quantification of the changes in this property, which can help to model the material deterioration in the future or carry out mechanical behavior studies using some computational techniques.