Desgaste abrasivo em materiais poliméricos utilizados na proteção de linhas flexíveis de condução de petróleo

Abstract

Abrasion due to rubbing of flexible pipes against sediment layer is an Emportant degradation mechanism in deep-water oil and gas production. In order to protect such flexible pipes against abrasive wear, polyethylene (PE), polyurethane (PU), polyamide (PA) or Rubbers may be selected. This is justified due to their excellent corrosion résistance to sea water, maintaining at the same time, the structural integrity and enough flexibility. However, at the touch down point region (TDP), the relative movement provoked by the sea streams and/or displacements of the platform can lead lo excessive abrasive wear of these polymeric sleeves. To evaluate the wear performance of some polymeric materials it was used a pin-on- drum tester. The main characteristics of this equipment are described in the DIN 53.516 norm. The wear tests were carded out in water at temperatures of 4, 25 and 4CcC. The normal applied lead was also varied (5, 10 and 15 N), Additionally, the Shore A and D hardness of the samples worn measured. Different materials were tested, such as: polyurethanes, rubbers, polyamides and polyetilenes. The structural characterization was performed by some experimental technique, like DSC, FTIR, TGA E SEM- EDS. To evaluate the wear performance, the samples were weighted before and after the teats by using a piece of equipment with a resolution of 10’5 g The wear mechanisms were characterized by means of SEM analysis. Since these materials can experience water induced reactions in the absence of light and microorganisms, leading to wear behaviour changes, a study was undertaken to investigate Ihe possible hydrolysis effects on their abrasive wear behaviour. The hydrolysis tests were carried out under hyperbaric pressure (200 bar) in synthetic seawater at a temperature of 25 °C. The polymeric materials were held in the hyperbaric vessel for 125 days and, after that, their wear behaviour were analyzed and compared with those observed on protection layer materials before their use. Additionally, it was performed an analysis of the degradation level observed in the metallic banding, that fixes the polymeric protection layer, The results showed that the tested polyurethanes have a wear resistance remarkably superior to the other materials and that, under the used test conditions, the temperature has little influence in the wear process. The wear behavior also did not suffer any modification after the induced degradation tests. Moreover, the hardness results showed no clear correlation with the wear results. The crevice corrosion observed in the Inconel® 625 banding can lead to a failure in a long term use. Finally, preliminary résulte of four months hydrolysis tests shewed that the investigated materials (PU, PE, PA and rubber} are not subjected to this kind of degradation.