Assessing the influence of cyclic bending on pearlitic wire's microstructural evolution: a simulation of spiraling and armoring processing effects

Abstract

Flexible pipelines are widely used offshore for oil and gas transportation and are subjected to several complex stress modes during service. Stress tensors cause different alterations in the macro and microstructure of the material. Therefore, studies involving the relationship between mechanical behavior and the crystallographic orientation of tensile armor wires need deep investigation. This work investigated the role of complex plastic deformation during the spiraling tensile armor on the microstructure and crystallographic texture of pearlitic steel with 0.74 wt%C. A heat-treated sample was prepared as a starting point. Further specimens were subjected to cold bending to investigate the strain accumulation during spiraling and armoring processing and then compared to an industrial twisted tensile armor sample. The microstructural and texture evolution was characterized by scanning electron microscopy, X-ray diffraction, and backscattered electron diffraction. Specimens were submitted to the Vickers microhardness and tensile tests to evaluate the mechanical properties. Results revealed that the bending deformation causes a reduction of (001)//ND fiber and increases the mechanical resistance of the material, which may prevent the onset and crack propagation. (111)//ND fiber increased while (110)//ND decreased, leading to stability in the slip systems. The formation of shear band structural changes resulted from the increase of (110)//ND with armoring and a decrease of (111)//ND fibers. Bending strains enhance the desirable texture components while diminishing the undesirable ones. Deformations to which the materials were subjected provide less mobility of dislocations, which causes an increase in mechanical strength. Little change in texture and microstructure was also observed.