Among different form of anodic oxidation on titanium plasma electrolytic oxidation (PEO) is recognized to produce oxide layers up to two orders of magnitude thicker that the ones produced by standard anodization. This treatment increases corrosion resistance in a variety of environments. However the micro-arcs produced during film growth induce nanoporosity in oxide film. This porosity limits oxide barrier effect and allows aggressive species to approach metallic titanium. In this work pulsed signal at different duty cycle values and different frequencies is applied to reduce the energy of each spark and create a smoother surface. The obtained samples are characterized for corrosion resistance in halides rich environment. Process parameters are optimized in order to achieve the best corrosion resistance for each given anodizing potential.
Top of Line Corrosion (TLC) occurs in a multiphase flow when water vapor condenses at the top and the sides of the pipeline leading to a severe corrosion attack. This study investigated the probabilistic risk of TLC for wet sour gas subsea pipeline using flow modeling and corrosion predications. The flow assurance hydraulic study showed that most of water drops out over the first few kilometers as the gas is cooled and becomes much less through the rest of the offshore part until they reach onshore area where the gas temperature drops further due to Joule-Thomson effect. It was anticipated that corrosion activities will be higher at the high condensation locations. The corrosion prediction modeling revealed high corrosion severity driven by Top of Line Corrosion (TLC). In order to maintain the system integrity the internal coating supplemented by V-jet batch inhibitor injection has been selected to protect against TLC. This study has realized the challenge to apply the batch treatment as it requires process interruption to meet scraper speed limitations. Therefore the industry path forward should consider the development of novel TLC treatments that to be applied with no impact on operations.
Oxygen diffusivity Dox is a key parameter in modeling corrosion rate of steel in concrete. Measuring Dox can be a complicated and slow process in conditions or geometries not always representative of those encountered by rebar in concrete. A method is introduced that eliminates someof those difficulties by using transient cathodic current measurements in reinforced concrete specimenssubject to alternating air/nitrogen mixtures. Experimental examples and modeling simulations are presented.
Direct Electrical Heating (DEH) is applied to subsea oil and gas flowlines for hydrate control and avoiding flow problems during production and after shut-ins. In a DEH system the flowline to be heated is thermally insulated and the steel wall of the flowline is made an active conductor for electric current. Single-phase alternating current (AC) from a topsides power supply is introduced into the wall of the flowline via apiggyback electrical cable resulting in resistive or joule heating which maintains the pipe contents above the wax melting point and hydrate formation temperature. The flow of AC can lead to electromagnetic interference in other metallic components and structures that are proximal to the flowline. Such components include collocated umbilicals and the armor wire used in the protective sheathing of such umbilicals. A laboratory investigation was conducted to study the effect of AC interference on the corrosion of two types of umbilical armor wire – zinc-galvanized and bare carbon-steel. AC corrosion testing in mildly-sour anoxic synthetic seawater conditions representative of the anticipated deep-sea service environment revealed significant differences in the corrosion behaviour of the two types of wire as a function of the average AC current density.
Deposits can play an important role in the corrosion rate and morphology of carbon steel in a production environment as well as affect the efficacy of an inhibitor. A test method has been developed to investigate the corrosion characteristics of carbon steel in a stratified flow regime where deposits of solids accumulate in the bottom of a pipeline.Previous testing showed higher under deposit corrosion rates of API X-65 carbon steel when the deposit consists of iron sulfide (FeS) versus sand in a 100%H 2 S environment. There is a needto investigate the effect of CO2 on these findings as the lower pH should affect the corrosion rate morphology and galvanic action particularly with respect to the FeS deposits.This paper presents the effect of mixed gases (50%H 2 S + 50%CO2 ) on corrosion behavior of API X-65 carbon steel coupons in the FeS and sand deposits. The average corrosion rate thickness loss of the coupons and pitting at the solid/liquid interface will be presented.Keywords: Under deposit corrosion Iron sulfide (FeS) sand mill scale acid gases