CATHODIC PROTECTION AT A SIMULATED DEPTH OF 2500m

摘要

The hydrogen embrittlement and cathodic protection characteristics of several subsea pipeline and flexible riser / hose steels were investigated in simulated deepwater service conditions. Static four-point bending loads were combined with an impressed potential of-1.1 V Ag/AgCI, at a pressure of 250 bar in a synthetic seawater solution. The experiment applied a static load to welded pipeline steel specimens and un-welded flexible hose armour wire specimens by four point bending. Sacrificial cathodic protection from aluminium bracelet anodes was simulated by a multi-channel potentiostat. The specimens were immersed in synthetic seawater and pressurised to 250 bar, equivalent to 2500m depth. After 30 days in this test condition, none of the specimens had failed due to hydrogen embrittlement. Thick cathodic deposits had formed on all the specimens, but these proved much less effective at reducing the required cathodic current than deposits formed at atmospheric pressure. This would reduce the throwing capacity of the sacrificial anodes in deepwater. The stainless steels were less affected by the quality of the cathodic deposit than low alloy carbon steels, due to the properties of the oxide passive film.