A corrosion inhibition study of steel grinding balls in an oxygen and alkaline environment

The corrosion of steel grinding balls is a major recurrent cost for mill operators concerned with the production gold. Subsequently, the use of corrosion inhibitors in production fluids, which is typically at pH >9, is an attractive and economical option. This study reports on the corrosion wear of steel grinding balls under alkaline/oxygen conditions and in presence of cyanide. A fundamental study on the influence of several inorganic-based inhibitors (i.e., nitrite, chromate, silicate, hexametaphosphate) on the corrosion rate of carbon steel was undertaken. Subsequently, the corrosion performances of various inhibitors were evaluated in stirred vessels. Corrosion rates were determined via mass loss and electrochemical methods (i.e., linear polarisation, Tafel). It was observed that inhibitors based upon chromate provide superior protection under the conditions investigated in this study. In lime treated, high chloride waters, chromate gave over 80% protection at levels of 10 100 ppm with no evidence of pitting.

Corrosion monitoring under disbonded coatings

Localized corrosion can occur under disbonded coatings threatening the safe operation of industry infrastructures such as underground oil and gas pipelines. Currently the assessment of localised corrosion under coating defects is a major technical challenge. The application of corrosion probes to monitor corrosion under disbonded coating also remains a difficulty. This paper presents a new corrosion sensor concept capable of electrochemically measuring corrosion rates under disbonded coatings on cathodically protected structures such as energy pipelines. Examples of its capabilities are illustrated with experimental data obtained in low conductivity aqueous solutions.

Understanding the effects of electrical interference signals and the environment on the effectiveness of cathodic protection

Cathodic protection (CP) failure due to excursions from safe CP levels is a challenge for the protection and maintenance of buried energy pipelines. Although research shows that stray current is a major factor contributing to CP failure, there is little consensus on how 'big' the excursions (either in magnitude, length or frequency) need to be in order to cause pipeline corrosion problems. This uncertainty has caused difficulties in selecting suitable parameters in relevant industry standards. This paper provides a brief review of past research on different factors affecting CP efficiency. Preliminary results from new electrochemical cells designed to develop an understanding of how CP excursions away from the 'safe' level can lead to corrosion problems are also presented.

A review of techniques for the monitoring of cathodic shielding and corrosion under disbonded coatings

The mitigation of external corrosion of energy pipelines by a combination of barrier coatings and Cathodic Protection (CP) is not always effective. Even when design specifications are properly met, the shielding of cathodic protection current from reaching steel surface by disbonded barrier coatings, often referred to as cathodic shielding, may lead to severe corrosion problems such as deep pitting, high and near neutral pH Stress Corrosion Cracking (SCC) and Microbiologically Induced Corrosion (MIC). Unfortunately, current indirect assessment methods used in the pipeline industry have serious difficulties in detecting such corrosion problems. This paper provides a brief review of current techniques and their limitations when being applied under complex buried pipeline environmental conditions. The main purpose is to identify potential methods that could be utilised in the design of new monitoring probes specific for the monitoring of cathodic shielding and corrosion of disbonded coatings in the pipeline industry.

An overview of methods for simulating and evaluating pipeline corrosion

Steel pipelines, buried under the soil and protected by the combination of protective coatings and cathodic protection (CP), are used for oil and gas transportation. These pipelines are one of the critical infrastructures for energy transportation and therefore became lifelines of modern society. The deterioration of the external surfaces of transmission pipelines is a serious problem and is caused mainly by coating and/or CP failure leading to the loss of integrity of pipelines. To avoid such damage, there is a need of techniques which are able to locate active corrosion sites, monitor corrosion, and evaluate corrosion damage. Fundamental understanding of such processes occurring on coated pipelines (with various types of defects in coatings as well as pipe) in complex soil environment is necessary for the development of such techniques. Numerous laboratory techniques, i.e., electrochemical impedance spectroscopy based, polarisation measurements based, mathematical simulations, direct observation etc. have been used to develop fundamental understanding, simulate and evaluate corrosion occurring in oil and gas pipelines under various operating conditions. Given the complex nature of the pipeline corrosion, application of these laboratory techniques in field measurements as well as in understanding the corrosion mechanisms is lacking. This paper presents an overview of investigations, based on electrochemical techniques, for simulation and evaluation of pipeline corrosion in laboratory.

A novel approach for monitoring pipeline corrosion under disbonded coatings

Underground pipeline corrosion monitoring is a complex technical challenge. Currently there is no corrosion monitoring probe that is able to provide in situ information on corrosion under disbonded coatings. This paper presents a proof of concept of a novel corrosion monitoring probe intended to simulate corrosion under disbonded pipeline coatings and monitor its rate under Cathodic Protection (CP). The probe's capabilities to measure corrosion rates and simulate disbonded coating conditions are illustrated by a typical experiment that involved testing of the probe in 0.1M NaCl at -850mVCSE. Estimated metal thickness losses based on results measured by the probe were compared against corrosion patterns and profilometry measurements of control specimens exposed to the same conditions.

An overview of new progresses in understanding pipeline corrosion

An approach to achieving the ambitious goal of cost effectively extending the safe operation life of energy pipeline to 100 years is the application of health monitoring and life prediction tools that are able to provide both long-term remnant pipeline life prediction and in-situ pipeline condition monitoring. A critical step is the enhancement of technological capabilities that are required for understanding and quantifying the effects of key factors influencing buried steel pipeline corrosion and environmentally assisted materials degradation, and the development of condition monitoring technologies that are able to provide in-situ monitoring and site-specific warning of pipeline damage. This paper provides an overview of our current research aimed at developing new sensors and electrochemical cells for monitoring, categorising and quantifying the level and nature of external pipeline and coating damages under the combined effects of various inter-related variables and processes such as localised corrosion, coating cracking and disbondment, cathodic shielding, transit loss of cathodic protection.

Monitoring cathodic shielding and corrosion under disbonded coatings

This work presents a novel corrosion monitoring probe designed for simulating the conditions developed under disbonded coatings and for measuring current densities and their distribution over a simulated pipeline surface. The probe’s concept was experimentally evaluated via immersion tests under Cathodic Protection (CP) in high resistivity aqueous solution. Under the disbonded area, anodic currents as well as cathodic currents were both measured. Anodic current densities were used to calculate metal losses by means of Faraday’s law. Calculated corrosion patterns were compared with corrosion damage observed at the probe’s surface after a period of test. The probe’s working principles are explained in terms of simple electrochemistry.

Investigation of corrosion inhibition mechanisms of rare-earth mercaptoacetate inhibitors on AA2024-T3

 Corrosion inhibition mechanisms on the aerospace alloy, AA2024-T3, was investigated for the inhibitor combination of rare earth metals and mercaptoacetate. The inhibitor demonstrated synergistic protection for AA2024-T3 from localised corrosion. It is intended to be a more environmentally friendly alternative to toxic chromate-based inhibitors.

Synergistic effects of sodium lauroyl sarcosinate and glutamic acid in inhibition assembly against copper corrosion in acidic solution

© 2015 Elsevier B.V. All rights reserved. A self-assembled multilayer (SAM) from sodium lauroyl sarcosinate (SLS) and glutamic acid (GLU) is formed on copper surface. Its inhibition ability against copper corrosion is examined by electrochemical analysis and weight loss test. In comparison to SAM formed by just SLS or GLU, a synergistic effect is observed when the coexistence of SLS and GLU in SAM. The SLS/GLU SAM has an acicular multilayer structure, and SAM prepared under the condition of 5 mM SLS and 1 mM GLU shows the best protection efficiency. PM6 calculation reveals that the synergistic effect stems from interactions between SLS, GLU and cupric ions.

Electrochemically monitoring localized corrosion patterns and CP effectiveness under disbonded coatings

© 2015 by Nace International. This paper presents new experimental evidences on the capability of a novel electrochemical corrosion monitoring sensor, which was recently conceived, for measuring localized corrosion under disbonded pipeline coatings. The sensor's design includes an artificial crevice for simulating the conditions developed under disbonded coatings and an electrode array for measuring current density distribution over its surface. The sensor capabilities were further evaluated by studying the dependency of corrosion patterns and current density distribution on the Cathodic Protection (CP) potential applied upon immersion in an aqueous environment. At the less negative CP potential, a good correlation was found between the inhomogeneous corrosion distribution under the disbonded coating as measured by the sensor and actual metal loss and corrosion attack observed on its surface at the end of the test. At more negative CP potentials no corrosion was detected or observed on the sensor's surface. In addition, characteristic changes in the cathodic current distribution at different CP potentials illustrated the possibility of employing the sensor to obtain valuable feedback on the performance of a given CP setup, without requiring its interruption or compensation of IR-drops. Furthermore, the sensor's capability to detect some of the effects of overprotection were shown at the most negative CP potential applied.

Quantifying the effects of major factors affecting the effectiveness of cathodic protection of pipelines

electrical interference signals on CP and steel corrosion using newly designed electrochemical corrosion cells; as well as to monitoring cathodic disbondment of coatings using electrochemical impedance spectroscopy. Typical results from using these new techniques for measuring stray current corrosion and for probing the cathodic disbondment of pipeline coatings have been briefly discussed.

Evaluation of WC-17Co and WC-10Co-4Cr thermal spray coatings by HVOF on the fatigue and corrosion strength of AISI 4340 steel

It is known that chromium electroplating is related to the reduction in the fatigue strength of base metal. However, chromium results in protection against wear and corrosion combined with chemical resistance and good lubricity. Environmental requirements are an important point to be considered in the search for possible alternatives to hard chrome plating. Aircraft landing gear manufactures are considering WC thermal spray coating applied by the high-velocity oxygen-fuel (HVOF) process an alternative candidate, which shows performance at least comparable to results, obtained for hard chrome plating. The aim of this study is to compare the influence of WC-17Co and WC-10Co-4Cr coatings applied by HVOF process and hard chromium electroplating on the fatigue strength of AISI 4340 steel, with and without shot peening. S-N curves were obtained in axial fatigue test for base material, chromium plated and tungsten carbide coated specimens. Tungsten carbide thermal spray coating results in higher fatigue strength when compared to hard chromium electroplated. Shot peening prior to thermal spraying showed to be an excellent alternative to increase fatigue strength of AISI 4340 steel. Experimental data showed higher axial fatigue and corrosion resistance in salt fog exposure for samples WC-10Co-4Cr HVOF coated when compared with WC-17Co. Fracture surface analysis by scanning electron microscopy (SEM) indicated the existence of a uniform coverage of nearly all substrates. (C) 2004 Elsevier B.V. All rights reserved.