Ongoing Corrosion Research Articles

Pit Initiation on Aluminum as a Queueing Process

The pitting corrosion of aluminum is modeled as a queueing process in which chloride ions (customers or units) enter the passive film and are serviced (form an emerging pit) at certain sites (servers) at the oxide/metal interface. X-ray photoelectron spectroscopy (XPS) data show that chloride ions penetrate the passive film on aluminum and are considered to lie in a queue. The servicing (or processing) stage includes chloride-assisted localized dissolution of aluminum, development of local acidity within the emerging pit, and buildup of chloride ions within the developing pit. The arrival rate of chloride ions is determined from quantitative XPS intensity data. The servicing rate has been determined from anodic polarization curves and also from Scully's criterion for stable pit growth. The following queueing characteristic parameters have been calculated: the number of units in the queue, the number of units in the system (queue plus server), the average time a unit spends in the queue, and the average time a unit spends in the system (queue and server). This is done for the following queueing systems: single queue with a single server, single queue with multiple servers, and multiple queues with single or multiple servers. A long time in the system corresponds to a low rate for the ongoing corrosion reaction. The time that a unit spends in the system is maximized for (i) a decrease in the number of servers, (ii) a decrease in the servicing rate μ, (iii) a decrease in the number of queues, or (iv) an increase in the arrival rate (up to ).

An overview of the corrosion aspect of dental implants (titanium and its alloys)

Titanium and its alloys are used in dentistry for implants because of its unique combination of chemical, physical, and biological properties. They are used in dentistry in cast and wrought form. The long term presence of corrosion reaction products and ongoing corrosion lead to fractures of the alloy-abutment interface, abutment, or implant body. The combination of stress, corrosion, and bacteria contribute to implant failure. This article highlights a review of the various aspects of corrosion and biocompatibility of dental titanium implants as well as suprastructures. This knowledge will also be helpful in exploring possible research strategies for probing the biological properties of materials.

In situdetection of bacteria involved in cathodic depolarization and stainless steel surface corrosion using microautoradiography

To examine the activity of bacteria involved in cathodic depolarization and surface corrosion on stainless steel in an in situ model system. The microautoradiographic technique (MAR) was used to evaluate the activity of bacterial populations on stainless steel surfaces with a single cell resolution. Anaerobic uptake and fixation of (14)C-labelled bicarbonate occurred within corrosion sites in the absence of atmospheric hydrogen or other external electron donors, whereas it was taken up and fixed by bacteria at all other stainless steel surfaces in the presence of atmospheric hydrogen. This indicates that the bacteria utilized electrons originating from the corrosion sites due to the ongoing corrosion (cathodic depolarization). Under in situ conditions, bacteria were fixating (14)C-labelled bicarbonate at corrosion sites in the absence of atmospheric hydrogen. This indicates that electrons transferred to the bacteria provided energy for bicarbonate fixation due to cathodic depolarization. Application of the MAR method showed ongoing biocorrosion in the applied in situ model system and allowed in situ examination of bacterial activity on a single cell level directly on a metal surface providing information about potential corrosion mechanisms. Furthermore, application of fluorescence in situ hybridization in combination with MAR allows for identification of the active bacteria.

Measurement of Reinforcement Corrosion Rate Using Transient Galvanostatic Pulse Method

Corrosion rate evaluation of concrete structure steel reinforcement was performed through investigation of a galvanostatic pulse transient response technique. A number of short sections of concrete embedded steel bar were used to conduct measurement of galvanostatic pulse transient measurements. There was a 30 to 180 second variation in applied galvanostatic pulse duration. A typical 1 kHz sampling rate was used to investigate the resulting transient potential response. To obtain separate equivalent electronic components, comprising a capacitance and resistance series, with reinforcing steel corrosion condition dependent values, there was analysis of the electrochemical potential transient response. Separate resistive components summation allowed evaluation of corrosion rate, which was then compared with a conventional linear polarization resistance (LPR) measurement corrosion rate on the same specimens. That the galvanostatic pulse transient technique enables resolution of the separate polarization resistance components, which provides a more conservative ongoing corrosion rate evaluation and offers significant advantages over either the galvanostatic or potentiostatic LPR method, is shown by obtained results.

Production of Wet Natural Gas Containing Corrosive Components: Four Case Histories

Summary In petroleum production, the problem of corrosive media attacking metallic structures is almost ubiquitous. Particularly severe environments are encountered in the production and transport of wet natural gas containing corrosive components, such as hydrogen sulphide and carbon dioxide. When exploring new gas fields, it is therefore a prerequisite to take into account the corrosivity of the respective fluids in all stages of the field development, material selection, field layout, and facilities design. In preparation of the subsequent production phase, reliable corrosion monitoring programs have to be selected, established, and implemented as necessary. Furthermore, the financial aspects always play an important role, thus posing a real challenge for the engineer forced to seek a compromise between economics and design. This paper gives a comprehensive overview of these considerations regarding four different OMV gas fields, two in Austria and two in Pakistan, which were successfully developed and brought onstream between 1967 and 2003. These fields not only vary in their geographical position, but also in their gas compositions, production start, and the location of gas dehydration units. One major aspect dealt with in each of these cases was material selection, including metallic as well as nonmetallic and composite materials. Where the initial decision was made in favor of carbon steel, different methods of corrosion protection, the application of corrosion inhibitors, corrosion monitoring, and intelligent pigging are discussed in the paper. A comparison of the various methods of resolution worked out for all four case histories, as well as the experience gained in more than three decades of production and transportation of wet, corrosive natural gas is presented. Furthermore, results of the ongoing corrosion monitoring measurements in operation in the mature gas fields are discussed under the aspect of the remaining facility lifetimes.

On-Site Measurements on Corrosion Rate of Steel in Reinforced Concrete

The corrosion of steel in reinforced concrete is a dynamic process strongly influenced by the environmental exposure conditions. Thus, there can be difficulties in assessing the ongoing corrosion problem for reinforced concrete structures in the field due to fluctuating ambient conditions. A number of laboratory electrochemical techniques have been developed to directly measure the corrosion rate of steel in reinforced concrete. These techniques are still not extensively used, however, although some have now been developed sufficiently to enable the measurement of corrosion rate in the field. The focus of this study is the accuracy of using the linear polarization resistance (LPR) method for field assessment of the corrosion rate of steel in reinforced concrete structures. In this paper, the influences of climatic parameters on LPR corrosion rate measurements are discussed. Measurements of the polarization resistance of reinforcing steel were made on reinforced concrete specimens exposed to urban marine weather conditions in the UK. The results obtained show that the concrete resistance and, as a result, the corrosion rate, was significantly influenced by the ambient temperature and rainfall. Guidelines are suggested for using the linear polarization resistance technique to assess the corrosion of steel reinforcement of in-place concrete structures.

Combined photoelectrochemical conditioning and surface analysis of InP photocathodes: II. Photoelectron spectroscopy

The photoelectrochemical modification of p-InP(111) surfaces in HCl and H 2SO 4 is investigated. In 0.5 M HCl a photoreduction/oxidation procedure via cyclic voltammetry leads to a solar energy conversion efficiency of the p-InP/vanadium 2+,3+—4 M HCl/C photoelectrochemical solar cell (PECS) of η=11.6% in natural sunlight. The optimisation procedures are followed by surface analysis methods performed ex-situ at the modified InP electrodes after cathodic and after anodic polarisation in the supporting acidic electrolytes and in the redox solution. X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and low energy electron diffraction (LEED) are used. At cathodic polarisation in H 2SO 4, XPS shows formation of indium metal and In x (SO 4) y compounds, whereas in HCl a stable interfacial film consisting of indium monochloride to a smaller extent of indium oxides is formed. This film is optimised by cycling in HCl having a thickness of 10±3 Å. Cyclic polarisation in the vanadium redox electrolyte changes the composition and thickness. Whereas in HCl, the optimised interphase consists of 0.7 parts InCl and 0.3 parts In(PO 3) 3, phosphates are absent after optimisation in V 2+/3+ and more indium oxide is found. The film thickness is reduced to 6±2 Å for the InCl component and about 0.6 monolayers of indium oxide are found. UPS measurements are mainly used to derive an energy band diagram of the semiconductor/film/electrolyte junction. The results show in that the stabilisation of the film in chloride containing electrolytes can be explained by the relative conduction band positions of p-InP with respect to cathodic decomposition energies. Since the electron affinity increases with surface phase formation in HCl, whereas it stays low in sulphuric acid, the ongoing corrosion in the latter solution can be understood, the LEED data show that the surface phase is ordered with lattice constants close to InP, indicating the formation of a hitherto unknown InOCl phase. According to the results we propose reaction mechanisms for dissolution and stabilisation and present schematic energy band diagrams which explain the corrosion processes in H 2SO 4 and the passivation phenomenon in HCl. The influence of the properties of the interfacial film on the functioning of the solar cell is outlined.

Measurement of Concrete Resistivity for Assessment of Corrosion Severity of Steel Using Wenner Technique

The Wenner technique is becoming increasingly popular for measuring resistivity of reinforced concrete to assess the rate of corrosion of the steel reinforcement once it becomes depassivated by chloride attack or carbonation. This paper summarizes work carried out over several years in assessing the efficiency of this technique. Several sources of measurement error are identified, and recommendations are put forward to enable engineers to obtain more accurate results when using this technique in practical situations to evaluate the severity of ongoing corrosion problems.

Monitoring Cathodically Protected Steel in Concrete Structures with Electrochemical Impedance Techniques

Abstract The effectiveness of cathodic protection (CP) in mitigating corrosion on buried carbon steel structures is limited by the inability to (1) detect ongoing corrosion and (2) determine the level of CP in the presence of voltage (IR) drop in the environment. In this study, the feasibility was established for using electrochemical impedance spectroscopy (EIS) as a monitoring tool for detecting corrosion on cathodically protected carbon steel structures in soil and concrete.