In general, tensile armour wires of flexible pipes that are designed for sour applications have their strength limited to 850 MPa due to the possibility of embrittlement phenomena to occur. A Thermally Sprayed Aluminum (TSA) coating 250 μm thick was applied to high strength steels with UTS of 1470 MPa and YS of 1280 MPa. Three specimens conditions were evaluated: full coating, no coating and coating with a designed defect. The load was applied using a four point bending fixture, maintaining a constant stress of 90% of material’s yield strength. All tests were performed in accordance with recommendations of NACE TM 0177 method B. The test solution was distilled water with NaCl 5.0% saturated with a gas mixture of 10,000 ppm of H2S in balance with CO2 during 720 hours. It was observed that samples without coating were more susceptible to the effect of the environment presenting higher degradation and failure. The fractures presented typical characteristic of the Sulfide Stress Corrosion Cracking (SSCC). Furthermore, it was detected parallel cracks to the surface of the wires indicating the embrittlement phenomenon of Hydrogen-Induced Cracking (HIC). On the other hand, coated samples with and without defects did not fail during the 720 hours of testing. A posterior non-destructive testing and a metallographic analysis did not identify the presence of cracks. These results were attributed to the physical barrier of the aluminum coating and the cathodic protection generated by the preferential aluminum corrosion. This preliminary study shows that TSA coatings can be a good alternative to increase the corrosion resistance of armour wires in sour environments allowing the application of higher strength steels.
Evaluation of Aluminum-Coated Flexible Pipe Armour Wires Exposed to a Sour Environment
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Bertoncello, JCB, Tagliari, MR, Coser, TB, Kerpen, FS, Santana, LM, Paes, MTP, & Kwietniewski, CEF. "Evaluation of Aluminum-Coated Flexible Pipe Armour Wires Exposed to a Sour Environment." Proceedings of the ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering. Volume 5: Pipelines, Risers, and Subsea Systems. Madrid, Spain. June 17–22, 2018. V005T04A029. ASME. https://doi.org/10.1115/OMAE2018-78719
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