Ying Huo

Investigating effects of potential excursions and pH variations on cathodic protection using new electrochemical testing cells

Excursion from safe cathodic protection (CP) potentials occurs on buried steel pipelines due to various forms of electrical interferences such as stray currents. Variations in pH can also occur over some pipeline sections such as seashore and river crossing pipes. Currently, the exact effects of potential excursion and the pH on CP efficiency have not been sufficiently quantified preliminary due to difficulties in measuring these effects. In this work, these effects have been investigated using electrochemical cells designed to mimic the high resistivity and pH conditions observable over underground steel pipes, including a new electrochemical cell that has been designed to facilitate the effective simulation and control of pH, potential excursion and other CP testing parameters. The pH has been shown to be a key factor affecting the patterns of corrosion and CP efficiency. Localised corrosion has been found to be the dominating form of corrosion under potential excursions conditions.

Measuring and understanding the critical duration and amplitude of anodic transients

ABSTRACT Anodic transients are known to affect buried pipeline cathodic protection (CP) systems; however, their actual effects on pipeline corrosion have not been sufficiently quantified due to the lack of direct experimental evidences. In this work, a novel methodology developed based on an electrochemically integrated multi-electrode array has been used to visualise the dynamic effects of anodic transients on localised corrosion processes occurring on buried steel surfaces. It is shown that anodic transients do not necessarily cause steel corrosion, as long as their amplitude and duration are below critical values. The electrode array is able to determine these critical values accurately due to its ability to detect localised corrosion initiation, while the conventional coupon electrode is only able to estimate these values. The critical anodic transient duration has been explained as the incubation period for the breakdown of passivity formed on the steel surface exposed to CP-generated high pH conditions.

Localised corrosion of cathodically protected pipeline steel under the effects of cyclic potential transients

ABSTRACT Cathodic protection (CP) may lose its effectiveness for protecting buried steel pipeline from soil corrosion due to the effects of potential excursions caused by stray currents. In this work, dynamic localised corrosion processes of buried steel due to the effects of cyclic potential transients have been visualised using an electrochemically integrated multi-electrode array, often referred to as the wire beam electrode (WBE). The focus has been on the understanding of the effect of cathodic transients. The WBE maps suggest that the amplitude of cathodic transient, as well as the ratio of anodic cyclic to cathodic cyclic, can significantly affect the corrosion rates and patterns. In particular, if the cathodic transient leads to a very negative potential, e.g. −1350 mVvs.CSE, rapid corrosion would occur on buried steel surface. These results have implications for CP parameter selection for preventing stray current-affected buried steel pipelines.

Effects of high salt concentration and residue on copper and aluminum corrosion

Traditional researches on metal corrosion under salt solutions deposit conditions are usually carried out by visual, electron microscopic observations and simple electrochemical measurement via a traditional one-piece electrode. These techniques have difficulties in measuring localized corrosion that frequently occur in inhomogeneous media. This paper reports the results from the experiments using specially shaped coupons and a relatively new method of measuring heterogeneous electrochemical processes, namely, the wire beam electrode(WBE). Preliminary results from copper and aluminum corrosion in highly concentrated sodium chloride solutions with and without solid deposits show that the method is useful in simulating and studying corrosion especially localized corrosion in pipelines.