On the Mechanism of Cathodic Protection and Its Implications on Criteria Including AC and DC Interference Conditions

To provide a reference for the evaluation of corrosion rate under dynamic metro stray current, both simulated experiments in laboratory and coupon tests in the field were conducted to explore the corrosion behavior and the relationship between corrosion rates and dynamic DC interference parameters of buried pipelines. The results show that the dynamic period has a significant influence on the corrosion rate and the ratio of actual corrosion rate to the theoretical corrosion rate. The statistical data of pipe to soil potentials or current densities of coupons electrically connected to pipelines obtained from the field in many cities of China show that the dynamic fluctuation periods under metro stray current are within the range of 0–300 s, among which the majority of fluctuation periods distribute from 50 to 200 s. The dynamic fluctuation of pipe to soil potentials and current densities of coupons exhibits symmetric or asymmetric characteristics. Under the situation of symmetric positive and negative current density, the ratio of the actual corrosion rate to the theoretical corrosion rate ranges from about 4% to 22% under the typical dynamic periods range from 50 to 200 s based on the simulated experiments results in the laboratory. Besides, two corrosion rate assessment methods, including the positive shifting and time ratios of off‐potentials and symmetrical or asymmetric characteristics of DC current density of coupons were proposed. In addition, the evaluation of the on‐potential criteria to assess the corrosion risk of time‐variant anodic interference was also discussed in the paper.

Section: Resultsmentioning

confidence: 99%

Research on corrosion rate assessment of buried pipelines under dynamic metro stray current

Qin

Liu³

et al. 2021

“…The Pourbaix diagram is, therefore, in no way a state space that fully describes the state of the steel surface/ electrolyte system, as suggested in Figure 8 in a recent publication. [3] This cannot be expected from a diagram that is only defined along the thermodynamic equilibrium lines.…”

Section: The Pourbaix Diagrams In Connection With the Corrosion Promentioning

confidence: 99%

“…A representation of the cathodic polarization process of steel including the indication of protection potentials (circles) in a Pourbaix diagram, as described in Reference [3] [Color figure can be viewed at wileyonlinelibrary.com]…”

Section: The Pourbaix Diagrams In Connection With the Corrosion Protementioning

confidence: 99%

“…"A fairly detailed study of these phenomena has suggested, quite recently, that one should distinguish between passivation phenomena, corresponding to an increase of resistance to ionic exchange reactions between a metal and a solution due to their separation by a surface layer, and states of passivity in which this resistance is sufficient to reduce the rates of these reactions below limits at which they are appreciable in spite of there being an affinity for the conversion of the metal into its corrosion products." F I G U R E 8 A representation of the cathodic polarization process of steel including the indication of protection potentials (circles) in a Pourbaix diagram, as described in Reference [3] [Color figure can be viewed at wileyonlinelibrary.com]…”

Section: The Pourbaix Diagrams In Connection With the Corrosion Promentioning

confidence: 99%

See 1 more Smart Citation

The limits of the Pourbaix diagram in the interpretation of the kinetics of corrosion and cathodic protection of underground pipelines

Barthel¹,

Deiss

2020

This article deals with the basics of corrosion and corrosion protection, with the focus on equilibrium thermodynamics. Particular attention is paid to the easy‐to‐understand creation of Pourbaix diagrams, their uses, and limitations of this tool. In addition, the basics of electrochemical kinetics are dealt with to provide an overview of the possibilities and the interaction of both methods. Finally, it is argued that the globally recognized and practice‐proven protection potential criteria remain valid.

“…Ghanbari and Lillard, [ 30 ] Eichler and Isecke, [ 31 ] and Andrea et al [ 32 ] considered the influence of AC and DC stray current corrosion and analyzed the cathodic protection effect of various parameters on steel structures. Büchler [ 33 ] introduced the effectiveness of cathodic protection on the steel surface, based on the increasing pH value and passivation conditions. Xiong et al [ 34 ] developed an imaging technology to monitor real‐time images of carbon steel and evaluated long‐term photocathodic protection performance.…”

Section: Introductionmentioning

confidence: 99%

Assessment of cathodic protection effect on long‐distance gas transportation pipelines based on buried steel specimens

Han

Liao

et al. 2020

Different severe corrosions are found at the damaged point of anticorrosive coating on natural gas pipelines, even though the cathodic protection (CP) potential is between −0.85 and −1.15 V. Therefore, there are totally 168 buried steel specimens (BSSs) and 28 soil samples at 28 buried points that are taken out in situ and then analyzed in the lab to assess the CP effectiveness. First, the CP status is simulated by BSSs at the damaged points, and the corrosion products on BSSs are analyzed microscopically. Second, the corrosion rates of the testing BSSs are calculated by the weight‐loss method to perform the quantitative assessment. Third, the specific reasons for external corrosion are explored via analyzing the CP potential attenuation tendency and the corrosiveness of soil. The corrosion growth trend is also investigated by comparing the test results among three test cycles within 8 years. Finally, the control measures for external corrosion of pipelines are put forward. The study is beneficial to evaluate the CP system and determine the causes of external corrosion of pipelines, thereby formulating corresponding protective measures.