Avaliação da resistência ao desgaste abrasivo de risers flexíveis proposição de nova metodologia de teste

Abstract

The oil and gas extraction in deep waters by Petrobras has been expanded progressively in the recent years. In this condition, oil and gas can be extracted by Jacket type and semi-submersible platforms, which are connected to the wells through flexible risers. These components are constituted of a multilayer system with internal and external coatings made of polymers. On inspection of these risers, scratches and a significant reduction of the riser protection layer were observed. These damages were found to be related to the relative movement of the pipe in the area of the touchdown point (TDP). In order to reduce this problem the risers have being coated externally with plaques of polyurethane. High chemical inertia and good mechanical and abrasion resistance characterize these materials. Besides, they allow the riser to have a good flexibility. Thus, the abrasive wear of these risers was reduced. However, optimizations still must be reached. Currently, the abrasive wear resistance of these materials is evaluated by means of abrasive wear tests according to the DIN 53.516 norm and the single-pass scratching technique, both at a temperature of 4ºC. The latter one is appropriate for testing polymeric riser protections but it does not simulate the repetitive action of hard particles acting against the plaques. In the present work, a new test rig for abrasive wear testing is presented, which is based on multiple interactions between indenters and plaques. So, the deep water wear conditions were simulated and the wear micromechanisms of different polyurethane materials were observed to be similar to those of field application. The wear rate results showed that wear in these materials is basically due to microcracking. It was also noticed that materials with a good wear performance have a high tearing elongation and strength and a high resilience. A correlation between abrasive wear and mechanical properties of five different types of polyurethane was proposed. The obtained equation showed no linear relation with these results, suggesting that terms of higher degree may be important.