Eventos Anais de eventos
COBEM 2023
27th International Congress of Mechanical Engineering
Analysis of Fatigue Crack Growth Behaviour and the Influence of Corrosion of ASTM A285C Steel Applied in Kraft Continuous Digester
Submission Author:
alexandre nakayama , pr
Co-Authors:
alexandre nakayama, ANDRE LUIS MOREIRA DE CARVALHO, João Paulo Gabre Ferreira
Presenter: alexandre nakayama
doi://10.26678/ABCM.COBEM2023.COB2023-1074
Abstract
Fatigue failure is a common and critical issue in mechanical components and structures. As such, it is vital to study and understand it for the design, operation, and maintenance of industrial systems. In the cellulose pulp and paper industry, the cooking process is essential in producing cellulose fibers. This process involves removing lignin and other impurities from wood chips using an alkaline aqueous solution called white liquor under high temperatures and pressures. The continuous digester, which is a vertical pressure vessel where the cooking takes place, is subjected to severe operational conditions in the Kraft cellulose pulping process. The white liquor used in the cooking process is highly corrosive to carbon steels. Fatigue is one of the most important damage mechanisms that can occur during the operation of the continuous digester. It is difficult to detect and is usually only detectable through non-destructive inspections during equipment outages. Furthermore, the rate of fatigue crack initiation and propagation is variable and dependent on cooking parameters. This paper presents the results of fatigue tests conducted on ASTM A285 grade C steel specimens, a common material used in the upper part (impregnation zone) of Kraft continuous digesters. The aim was to investigate the stable crack propagation (stage II) of the fatigue crack growth curves and to evaluate the influence of the corrosive alkaline cooking environment on the fatigue process. Compact tension type specimens were used, and fatigue tests were conducted according to ASTM E647-05 standard, with the resulting da/dN x ΔK curves obtained. Additionally, the compact tension-specimens underwent corrosion immersion tests in white liquor, similar to the impregnation zone of a real process, according to ASTM G31 standard. After cleaning and drying, the specimens were fatigue tested using the same standard as for the as-received condition. The fracture surfaces were analyzed with optical and electron microscopy. The results showed that, in the early part of the stage II, the fatigue crack growth of the corroded specimens had a lower rate compared to the as-received condition. However, in a ΔK range of approximately 15 to 40 MPa√m, the fatigue crack growth rates of the corroded specimens surpassed and were higher than the as-received condition. It was noticed that during a substantial part of the stage II, the corrosion played a role in increasing the growth rate, possibly due to surface damages and the influence on the crack tip conditions.
Keywords
fatigue, Digester pressure vessel, corrosion
