Abstracts of papers to be presented at the Congress Bratislava 2023

Complex Impedance Measurements on a pipeline section to localise corrosion sites

  • Lucio Di Biase, Scientific Consultant (Past President CEOCOR 2009 – 2015) – Italy
  • Edoardo Proverbio – Full Professor at University of Messina – Italy
  • Osvaldo Fumei Technical Director of SOLARIA – Route d’Ajaccio Lieu-dit-Croccichia – 20260 CALVI – France

The measurements of the Complex Impedance on a buried pipeline is an above–ground technique which enables the localisation of corrosions on the steel of a pipeline, even under disbonded coatings. This technique is not simple to be used in the real field as it needs the installation of special equipment to feed an a.c. signal and particularly sophisticated equipment to detect and to record the relevant signal response over the pipeline.

The Complex Impedance Measurements technique over a buried pipeline allows the identification of low/very-low values of the Rp (Polarisation Resistance). This information, together with the D.C. Current requirements and the IR Drop values over a specific section of the pipeline, allows to localise areas where the coating is disbonded, where this disbondment corresponds to corrosions on the steel pipeline or where the coating is missing and corrosion is taking place.

In this paper the results of some tests performed on a real, corroded pipeline are reported. The main limitation of the technique is certainly the fact that, as the portion that can be investigated is in the order of some hundred metres, in order to investigate other sections, the whole installation and equipment (temporary Groundbed, A.C. Feeder, Potentiostat, Galvanostat, Frequency Response Analyser) must be moved along the pipeline, over suspected sections.

Anyhow, it could be of great support in solving doubt cases when the pipeline/coating laying conditions and soil characteristics suggest corrosion likelihood on a specific section of the pipeline.


Degradation of grounding conductors for ac mitigation: influence of backfill composition and ac current level

Julien Duboscq, Nada Marzouq, Keltouma Zmoug, Ahmed Fakhry, Romuald Bouaffre.

Buried pipelines protected against corrosion by CP systems can be influenced by alternative current flowing from different sources. These influences can lead to important corrosion phenomena. In order to reduce corrosion risk, GRTgaz installs grounding systems such as galvanized steel to mitigate ac effects and discharge induced current in the ground. After a few years, GRTgaz found some grounding conductors with a premature degradation. RICE (Research and Innovation Center for Energy – GRTgaz) has conducted laboratory tests to investigate the impact of ac current level on the degradation of galvanized steel, with different backfill material: sand, bentonite and coke breeze. In the chosen conditions, the higher the ac current, the greater the degradation. The aging of a conductor placed half in sand and half in bentonite or coke breeze does not induce a greater degradation, compared to aging in simple backfill materials (only bentonite or coke breeze). Finally, these tests showed that bentonite allows for a longer protection of steel by zinc, contrary to coke breeze that accelerates the degradation of the conductor.

Julien Duboscq, RICE – GRTgaz  PhD – Corrosion Engineer

Ductile iron corrosion influenced by acid-producing bacteria

Fumio Kajiyama, Dr.

Tokyo Gas Network Co., Ltd., 1-5-20, Kaigan, Minato-ku, Tokyo 105-8527, Japan

The author noted that a natural gas 200 mm diameter ductile iron pipeline corrosion as high as 0,405 mm/y in acid soil with pH 3,82 containing iron-oxidizing bacteria (IOB) which oxidize Fe2+ to Fe3+ in aerobic H2SO4 environments. IOB are classified as acid-producing chemoautotrophic bacteria. The pipeline had been in service of 17 years. Field and laboratory studies were performed to understand the phenomenon using statistical analyses, scanning vibrating electrode technique (SVET) together with fluorescent microscope and electrochemical measurements. It has been demonstrated that there is direct correlation between numbers of IOB and the extent of corrosion. IOB utilize energy produced by the reactions involving dissolved Fe2+, H2SO4 in soil solution, and O2 at the Fe/electrolyte interface. IOB’s habitat is anodic area, leading to have an influence on corrosion.

Influence of overprotection on AC corrosion.
Analysis of a real case.


Automa S.r.l. – Via Casine di Paterno, 122/A – 60131 Ancona – Italia

The risk of AC corrosion has always been linked in particular to the parallelisms of underground pipelines with HVAC lines, especially in those geographical areas where the morphology of the territory creates obligatory so-called “technological corridors”, and therefore forces the coexistence of different services over long distances.

More recently, the greater diffusion of AC-powered railway networks has further increased the AC interfering sources, while the use of more performing coatings on underground pipelines has on the one hand increased their insulation from the surrounding soil, and on the other has increased the risk of overprotection compared to old, less performing, or more degraded coatings.

This paper, starting from a real case found in a gas distribution network in a European capital, will present the normative criteria to be used to keep the AC corrosion risk under control, and will highlight how precisely the simultaneous presence of cathodic overprotection may result in an autocatalytic cycle leading to accelerated AC corrosion, in which monitoring becomes essential in order to be able to carry out on time the appropriate corrective actions.

Remote synchronized CP off-potential measurements of test-posts. 

 Paul Mignot

One of the challenges for implementing a remote monitoring strategy for CP is when off-potential measurements are required on the structure. To solve this a remote monitoring solution has been developed that remotely switches the Rectifier and simultaneously identifies the connected test posts and measures the CP at 100ms intervals. In this way the depolarization curve of each test post is recorded. From this curve the off potential value is then automatically identified. The benefit is that a 100% remote monitoring maintenance strategy is now possible when off potentials measurements are required of the structure. This case will be presented in cooperation with DSO Stedin  A secondary use case will be presented where the off potential value is calculated from microvolt measurements along a 30-50m fixed length pipe. This will be presented in cooperation with DSO name to be confirmed 

Stray current corrosion of pipelines: An assessment of critical conditions

David Joos, Markus Büchler and Michael Gerhard
SGK Zurich, Switzerland

The concepts associated with stray current interference are well understood and described in EN ISO 21857. DC interference represents a possible risk for the integrity of buried infrastructure and assessing potentially critical conditions is of highest relevance. In order to understand the limiting influencing factors, laboratory investigations have been performed under extreme soil and interference conditions. These include very low soil resistivity, increased chloride content and anodic current densities of up to 100 A/m2. These represent extreme conditions that may indeed be encountered in field applications. The associated results are presented and the possible implications with respect to the integrity of pipelines and mitigation methods are discussed.

Corrosion of steel in soil: A discussion of relevant influencing factors

Markus Büchler
SGK Zurich, Switzerland

Experience shows that corrosion occurs on steel in contact with soil. Without protective measures, such as cathodic corrosion protection, the service life of these installations is often limited and damage cannot usually be ruled out. Nevertheless, numerous infrastructure installations, such as water transport pipelines, low-pressure gas pipelines or penstocks are often buried underground and are operated over extended periods of time. In many cases, the corrosion protection is limited to a coating of comparatively poor quality. The corresponding empirical values regarding the occurrence of damage, the metrological effects as well as the influence of soil parameters and the earthing situation are presented and discussed.

Cathodic protection shielding of buried pipeline coatings

Abdelkader Meroufel, Andrew Gordon, Dominique Thierry
RISE Research Institutes of Sweden

During the 2000s, the concept of cathodic protection (CP) shielding was first raised in open literature and remains debated between coatings professionals. The mechanism of CP shielding, and its understanding continue to be studied for different coatings with different approaches and using various techniques. From the CP shielding factors to the assessment methods, published scientist’s efforts merit a deep analysis to capture the established knowledge and identify the research gaps for complete control of the phenomenon for the reliability of structures. A holistic approach to this topic seems necessary where materials, corrosion, electrochemistry, and transport processes should be considered. In the first part of the present review the recent works related to the understanding of CP were considered to discuss the mechanisms involved underneath coatings. Transport phenomena and their relationship with coating structure are tackled in the second part. Finally, CP shielding assessment methods and modelling works are presented and discussed from different perspectives.

Title: Effects of electrical interference on Microbiologically Influenced Corrosion (MIC)

 S. Jansen, J. Gerritse (Deltares), G.H. Horstink (Gasunie)

Abstract: Several forms of AC and DC stray currents can lead to interference with cathodic protection, and thus to corrosion. ISO DIS 21857 E:2019 describes criteria for the assessment and monitoring of possible effects of electrical interference, including the practical Q-test. It is unknown whether these criteria are valid for Microbiologically Influenced Corrosion (MIC). This was tested using laboratory experiments with Electrical Resistivity (ER) probes covered with an active MIC biofilm under controlled sulphate-reducing conditions with cathodic protection (-1200 mV vs Cu/CuSO4) in combination with electrical interference. Three exemplary forms of electrical interference were simulated: 1) stray current from a solar park (12 hours interference with +500 mV, 12 hours no interference); 2) interference from passing trains (3 V sinus with a duration and frequency comparable to a representative Dutch railway track); 3) 50 Hz AC interference (1 V and 3 V). The results demonstrate that the timing of interference is important for the effects: in case of 50 Hz interference and interference by trains, no corrosion occurred, whereas in the case of 12 hr interference (simulation of stray current from a solar park), corrosion was stimulated. This might be related to the fact that kinetics is important: for interference, the building up/breaking down of pH gradients is needed, and the increase of microbial activity requires time.

In-situ photometric reflectance measurements of passive film on carbon steel in alkaline electrolyte

Federico Martinelli-Orlando and Ueli Angst
Institute for Building Materials, ETH Zurich, Zurich

The passive film formation on carbon steel has been extensively characterized in the last decades. However, the formation and growth of passive film in presence of cathodic current density, e.g., during application of cathodic protection, is still under debate. The aim of this work is to study the influence of the applied current densities on the passive film formation and growth on carbon steel samples. The formation and growth of the passive film was monitored with in-situ spectroscopy measurements in alkaline electrolyte (pH 13) as a function of the applied potential and as a function of the experimental time. The results showed that the passive film can be formed in presence of both anodic and cathodic current densities. Moreover, the results also showed that the thickness of the passive film increases with the application of less negative potentials and with increasing the experimental time for all the potentiostatic conditions considered. The results obtained in this study are of main interest for cathodic protection conditions of carbon steel in soil.