An atomic force microscopy study of the effect of tensile loading and elevated temperature on polyvinylidene fluoride from flexible oil pipelines

Flexible pipelines and risers have been used for more than 20 years for the transport of oil and gas in the petroleum industry. In the current study, a phase II polyvinylidene fluoride based pipeline material was subjected to varying degrees of tensile deformation, and microtomed sections were examined by atomic force microscopy (AFM) in order to investigate the resulting topographic changes. The effects of annealing at 100 and 130 degrees C on the maximum load and on topography were also studied. Annealing at 130 degrees C for varying lengths of time gave an increase in the maximum load which was found to be dependent upon crystallization kinetics. AFM studies showed ridges running perpendicular to the loading axis, which are attributed to flow lines resulting from the extrusion process. In annealed samples these ridges were closer together than in unannealed samples. The ridges were absent in quenched samples, but they gradually reappeared after storage at room temperature. These observations were further verified by transmission electron microscopy studies.