Corrosion behavior of low-alloy steel used for flexible pipes exposed to a seawater environment

Abstract

An immersion experiment was carried out to illustrate the corrosion behavior of low-alloy steel used for flexible pipes in a seawater environment in terms of corrosion kinetics, corrosion phases, surface morphology, cross-sectional morphology and elemental distribution. The experimental results show that the corrosion rate with an exponential format is linear with respect to the corrosion time with an exponential format. The main corrosion phases are goethite (a-FeOOH), lepidocrocite (g-FeOOH), iron oxide (Fe2O3) and magnetite (Fe3O4). Corrosion products become denser and thicker with the increasing corrosion time. Cr-rich compounds are the first to be formed on the coupon surfaces. The effects of the alloying elements on the corrosion products are different. Chromium is rich in the area near the steel substrate. Iron, oxygen and molybdenum are homogeneously distributed throughout the corrosion products. Keywords: corrosion behavior, low-alloy steel, flexible pipe, seawater Avtorji so izvajali preizkuse potapljanja fleksibilnih cevi iz malo legiranega jekla v morsko vodo, da bi ugotovili njihovo odpornost proti koroziji z vidika kinetike korozije, nastajanja korozijskih faz, morfologije povr{ine in preseka cevi ter porazdelitve elementov. Preizkusi so pokazali, da je hitrost korozije eksponentno odvisna od~asa. Glavne korozijske faze so getit (a-FeOOH), lepidokrokit (g-FeOOH), hematit (Fe2O3) in magnetit (Fe3O4).^im dlje je cev v vodi, tem bolj nara{~a debelina in gostota korozijskih produktov. Najprej nastajajo s Cr bogate faze. Vplivi razli~nih legiranih elementov na korozijo so razli~ni. Krom je najve~v obmo~ju blizu jekla. @elezo, kisik in molibden pa so homogeno porazdeljeni po korozijskih produktih.

Sea water corrosion behaviour of T2 and 12832 copper alloy materials in different sea areas

“…The Cu 2+ /Cu + ions released during the electrochemical corrosion process of T2 in sea water would destroy biological cells. When Cu 2+ /Cu + ions reached a certain concentration, it could effectively kill sea creatures and prevent their growth on the surface [18,19]. In particular, Cu 2 O formed on the surface played a crucial role in inhibiting marine biofouling [20].…”

“…As can be seen from Table 3, the corrosion rate of 12832 copper alloy was less affected by these sea water environmental factors such as pH, salinity and temperature, but the surface fouling conditions (including sediment deposition) had a crucial impact. On the one hand, XRD results showed that the content of Cu 2 O in the corrosion products of 12832 copper alloy was very small, and the dealloying corrosion products played a role of physical isolation, which contributed to the occurrence of biofouling [18,19,22]. On the other hand, only when the corrosion rate of copper alloys reaches 0.025 mm y −1 , a better antifouling effect can be achieved [1,23].…”