Corrosion Map Research Articles

Computer modelling for the prediction of the probability of detection of ultrasonic corrosion mapping

The reliability of NDT inspection has traditionally been determined by experimental trials; for example PISC I-III, NORDTEST and RACH. Such trials provide practical measures of the capability of inspection equipment. However, they can be expensive, may have poor statistics and the results obtained are specific to the equipment used as well as the specimens and defects included in the trials. An alternative approach is the use of computer modelling which, if sufficiently realistic, can provide a cost-effective alternative to experimental trials, and can be applied to a broad range of inspection equipment, geometries and defect characteristics. This paper describes a computer model for the prediction of the probability of detection (POD) of the zero degree ultrasonic corrosion mapping technique, which is widely used in the oil and gas industry for the in-service detection and characterisation of corrosion in pipes and vessels. The model has a relatively simple physical/mathematical basis but is believed to be a sufficiently good approximation to take into account the main factors which affect the POD of this inspection technique. The results from the model are compared with those from available experimental POD trials. Results are also given from a sensitivity study to identify and quantify the main parameters which influence POD under different inspection conditions.

Evaluation of Methods for Detecting and Monitoring of Corrosion Damage in Risers

Offshore pipeline failure statistics have been collected for more than 30 years now and illustrate that the riser predominantly fails as a result of corrosion. The consistent wetting and drying in the splash zone combined with defects in the coatings are the usual contributors to the problem. Risers are inspected at some determined frequency and can be done by internal and external methods. Inspecting by either means brings into account caveats and limitations from the technology used as well as human factors. For example, external inspections can be inefficient and inaccurate with some tools missing defects in areas of coating disbondment. In addition, internal inspections sometimes create false positives and can miss defects. These inaccuracies in the technologies or the techniques used may miss defects that eventually lead to failure. On the other hand, using corrosion mapping and fitness-for-service (FFS) assessment from the data collected, along with the inherent conservatism of this data from limited measurement accuracy, may result in the premature replacement of risers. A literature search is being conducted to review existing riser inspection methods and identify candidate nondestructive methods for riser inspection. These methods should be capable of detecting and monitoring general corrosion, localized corrosion pitting, and stress-corrosion cracking (sulfide or hydrogen induced) as external or internal corrosion damage. Thus far, this search has found that assessing the remaining service life of aging risers is largely dependent on the accuracy of analyzing corrosion damage to the riser surface in the atmospheric, splash (tidal), submerged, and buried environmental zones. The accuracy of each technology was analyzed. The capabilities and limitations of each method/technique used for riser inspection are summarized. The investigation is focused on long- and short-range ultrasonic techniques used for initial screening and corrosion mapping. These techniques can be deployed to detect a significant reduction in wall thickness using guided and torsional waves or to map accurately a corrosion damage using single/multiple transducers and phased-array probes in manual or automated mode. A pulsed eddy-current technique that uses a stepped or pulsed input signal for the detection of corrosion areas under insulation (CUI) is also being evaluated. This allows the detection of wall-thinning areas in the riser without removing the outside coatings. In addition, it is found that filmless, real-time, and digital radiography can be used to find internal and external corrosion defects in an insulated splash zone while the riser remains in service. A survey of nondestructive evaluation (NDE) manufacturing companies, NDE inspection companies, and operating companies was completed to collect information about current instrumentation and inspection/operators’ experience for riser inspection. Examples of advanced riser inspection instrumentation and field results are included. The ability of the candidate technologies to be adapted to riser variations, the stage of standardization, and costs are also discussed.

Cumulative damage function model for prediction of uniform corrosion rate of metals in atmospheric corrosive environment

The main focus of the paper is on the development of a unified analytical model for predicting the rate of uniform corrosion for commonly used engineering metals exposed to the atmosphere. A cumulative damage function model is proposed on the presumption that the corrosion is primarily due to the presence of critical corrosive agents in the atmosphere. The model incorporates sensitivity factors to account for the corrosion sensitivity of the metal with respect to the critical corrosive agents and the presence of other corrosive agents. Predictions of the uniform corrosion rate of metallic structures made of iron, mild steel, carbon steel, and zinc are presented. Results predicted using the model are compared with the values expected for mild steel using the data available in the Corrosion Map of India.

Raman and Rayleigh mapping of corrosion and mechanical aging in SiC fibres

SiC fibres are a complex system of heterogeneous nanophases. We used Raman microspectrometry to monitor the chemical changes of carbon phases and SiC nanocrystals in such fibres submitted to an alkali and oxidant environment (modelled by molten NaNO 3). Specific study of Nicalon-NLM ®, Tyranno SA3 ® and Sylramic ® fibres allowed to evidence that surface and volume properties are different. Chemical and/or strain gradients change during corrosion. The important reactivity of the fibre’s core is supposed to be linked to the easy intercalation of Na + ions, which accelerates the oxidant species diffusion. Singular areas that were hardly strained during microindentation tests on SCS-6 ® fibres (a model for composites with self-healing interfaces like (SiC/C/BN)), were analysed using Rayleigh microspectrometry to determine the surface geometry.

An experimental comparison of three wire beam electrode based methods for determining corrosion rates and patterns

Laboratory experiments have been carried out to examine the advantages and limitations of three wire beam electrode (WBE) based techniques, including the noise resistance R n-WBE method, the overpotential–galvanic current method, and the galvanic current method, in determining corrosion rates and patterns. These techniques have been applied simultaneously to several selected corrosion systems of different characteristics. It has been found that the R n-WBE method has advantages over other WBE based methods when applying to WBE surfaces under uniform corrosion. However, the R n-WBE method has been found to be unsuitable for low noise level corrosion systems. It has also been found that both R n-WBE and overpotential–galvanic current methods are similarly applicable to WBE surfaces under nonuniform corrosion. However, the galvanic current method has been found to be suitable only for WBE surfaces under highly localised corrosion. Some related issues regarding R n calculation such as trend removal and its effects on corrosion mapping have also been discussed.

Impact angle effects on the erosion–corrosion of superlattice CrN/NbN PVD coatings

Wastage due to the combined effects of erosion and corrosion is a serious issue in a wide range of industrial environments. The extent of wastage is dependent on a range of parameters relating to properties of the particle, target and the environment. In such cases, surface engineering (through providing a protective coating) may be used to avoid the deleterious effects of both processes. In recent years, there has been an increasing interest in the potential of CrN/NbN superlattice PVD coatings to provide resistance to erosion–corrosion in such conditions. Initial studies on the effects of velocity have shown that they significantly outperform conventional coatings, although the behaviour depends on the conditions. There is however, poor understanding on the effects of many important tribological variables, such as particle size and impact angle, on the performance of such coatings. In this work, the effect of impact angle on the erosion–corrosion of a range of CrN/NbN superlattice coatings was assessed at a range of applied potentials in a carbonate/bicarbonate solution. The mechanisms of erosion–corrosion of the coatings, as a function of impact angle and applied potential, showed significant differences when these parameters were varied. Erosion–corrosion maps were constructed based on these results showing the change in mechanisms and wastage rates as a function of impact angle and applied potential. Possible reasons for the differences in erosion–corrosion regimes for coated and uncoated specimens are described in this paper.

Nondestructive Mapping of Corrosion of Steel beneath Paint Coating by Synchrotron X-Ray Absorption Spectroscopy

Nondestructive Mapping of Corrosion of Steel beneath Paint Coating by Synchrotron X-Ray Absorption Spectroscopy

Modelling particulate erosion–corrosion in aqueous slurries: some views on the construction of erosion–corrosion maps for a range of pure metals

In studies of erosion–corrosion by solid particles in aqueous conditions, there have been various attempts in recent years to model the process. In particular, predictive models have been developed for steels to chart transitions between erosion–corrosion regimes. Such regimes identify whether the erosion–corrosion process is affected by active dissolution or passivation processes in the aqueous environment. A very important development in the study of aqueous corrosion of pure metals has been the concept of the corrosion map, developed by Pourbaix in the last century. Such maps identify regimes of corrosion, ranging from immunity to active dissolution and to passivation, as a function of pH and electrochemical potential. The position of the boundaries, as a function of the latter variables, may differ significantly for various pure metals. This paper models the erosion–corrosion behaviour for a range of pure metals, i.e. Ni, Al, and Cu (metals which have not been addressed to date using such an approach) and compares the results with a reference metal, Fe. Erosion–corrosion mechanism and wastage maps are constructed based on the results. In addition, materials selection maps are developed based on the results, showing how erosion–corrosion resistance for the materials may be optimised in such conditions.

Improved plant availability by advanced condition based inspections

An industrial plant has to operate safely, reliably and efficiently at the lowest possible cost. Plant availability plays an important role regarding economic life optimisation. Industrial installations that are under pressure and are operating at high temperatures have a limited life due to creep and fatigue. It is, therefore, of critical importance to know the location of any possible weak spots in the installation. To avoid safety risks, unplanned plant shutdown and, as a consequence, high costs for unavailability, cycling and repair, periodic inspections and strain measurements are recommended. A Speckle Image Correlation Analysis (SPICA) system enables on-stream measurement of deformation due to creep in critical areas like the heat-affected zone in welds. Plant management and operators use the strain measurements to take action when necessary and, consequently, prevent failures. In those plants that have been provided with SPICA-technology for some years plant availability has improved significantly as a result. Another important development for yielding improved availability concerns steam drums. During some 20 years, KEMA has been performing automated ultrasonic steam drum inspections from outside. The Dutch authorities accepted this methodology in this period as an alternative (rather than an addition) after several pilot projects. An advantage of this inspection methodology is the possibility to record of the inspection results and possibility of thus trending these data. The resulting reduction of through time appeared a major benefit for plant owners. Since the authorities adopted the RBI approach during the last 10 years, another advantage of the inspection methodology became apparent: complete scanning and recording of the inspection data of circumferential and longitudinal (butt and fillet) welds, inspection of nozzle welds and inner radius as well as corrosion mapping has been covering all higher risk areas in these drums. This enhanced inspection programme together with improved monitoring of operation parameters during operation has resulted in dramatic inspection interval extension. This attractive method for inspection interval extension has been applied at several Dutch power plants.

Low carbon steel corrosion damage prediction in rural and urban environments

This paper presents an Artificial Neural Network (ANN) model for the damage function of carbon steel, expressed in μm of corrosion penetration as a function of environmental variables. Working in the context of the Iberoamerican Atmospheric Corrosion Map Project, the experimental data comes as result of the corrosion of low alloy steel subtracts in three test sites in Uruguay, South America. In addition, we included experimental values obtained from short time kinetics studies, corresponding to special series from one of the sites. The ANN numerical model shows attractive results regarding goodness of fit and residual distributions. It achieves a RMSE value of 0.5 μm while a classical regression model lies in the range of 4.1 μm. Furthermore, a properly adjusted ANN model can be useful in the prediction of corrosion damage under different climatological and pollution conditions, while linear models cannot.

Erosion–corrosion mapping of Fe in aqueous slurries: some views on a new rationale for defining the erosion–corrosion interaction

In studies of erosion–corrosion of materials in aqueous conditions, there have been various attempts to define regimes of interaction. Such regimes indicate whether erosion or corrosion may dominate the wastage mechanism. However, intermediate regimes in which corrosion and erosion interact with each other may lead to situations where the wastage is far greater than the sum of the processes acting separately. A common method of defining erosion–corrosion interactions has been to distinguish between the regime in which erosion enhances the corrosion rate (the so called “additive effect” because the corrosion contribution can be measured electrochemically and thus added to the erosion contribution to assess the overall wastage rate) and the regime where corrosion enhances erosion (the so-called “synergistic” effect). However, regimes of erosion–corrosion, where corrosion impedes the erosion are also of great importance mechanistically, and usually these are termed as exhibiting “negative synergism”. Defining the conditions in which a transition from “positive” to “negative synergism” occurs, is useful in order to optimize the parameters to minimize the wastage rate. This paper reviews the rationale that has been used to define erosion–corrosion regimes in aqueous conditions as part of a study of the erosion–corrosion of Fe at various pHs. The mathematical definitions are discussed in relation to practical erosion–corrosion problems. In addition, a new “antagonistic” erosion–corrosion regime is proposed to properly define the concept of “negative synergism”.

Some thoughts on modelling the effects of oxygen and particle concentration on the erosion–corrosion of steels in aqueous slurries

Advances in the understanding of slurry erosion–corrosion has gained momentum in recent years, due to the wide range of laboratory studies carried out in such environments. There are now new insights into the causes of “synergistic” effects in such environments for many particle/target/environment combinations. However, identifying such effects is difficult because in aqueous conditions, the corrosion and erosion variables are not independent of each other. In this work, some new developments on the modelling of slurry erosion–corrosion processes are described for steels. The effects of increases in flow velocity, and oxygen and particle concentration are considered. Theoretical erosion–corrosion maps are constructed showing the differences between the erosion–corrosion mechanisms as a function of these variables.

Mapping sliding wear of steels in aqueous conditions

In studies of sliding wear in dry environments, there have been many attempts at mapping the processes. For steels, the classical “wear map” has been developed and various other studies have extended the approach to composites, ceramics and coated materials. Despite this work, there have been few attempts to extend the methodology to wet conditions, where the wear process interacts with solutions that are defined by pH and electrochemical potential. The object of this work was to study the sliding wear–corrosion behaviour of steels in a pin-on-disc apparatus in aqueous conditions. The effects of applied load and velocity were evaluated at various electrochemical potentials in carbonate/bicarbonate solution pH 9.8). The results were analysed using weight loss and scanning electron microscopy techniques. Wear mechanisms were identified in the various environments and a method of identifying the wear–corrosion transitions, in aqueous conditions, was proposed in the work. These regimes were superimposed on wear–corrosion maps, where the change in wear–corrosion regime was identified as a function of velocity and electrochemical potential. Possible reasons for the differences in the boundaries of the map at various applied loads are discussed in this paper.

Mapping climate conditions with materials corrosion

The world's first comprehensive materials corrosion mapping system can predict the effects that climatic conditions have on the life cycle of products ranging from automobiles to bridges, according to Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the Australian Industrial Galvanizers Corporation. Both jointly announced the system on 14 November.The mapping system, which incorporates conditions such as moisture, salinity pollution, and prevailing winds, can predict the corrosion of materials in any part of Australia, they said. Ivan Cole of CSIRO Materials Engineering said the mapping system even takes into account durability factors impacting on greenhouse gas contributions and soil conditions, making it a unique tool for Australian industry.

Particulate erosion–corrosion of Al in aqueous conditions: some perspectives on pH effects on the erosion–corrosion map

In the nomenclature to describe erosion–corrosion behaviour in aqueous conditions, there has been considerable confusion in relation to the terminology used to describe the various interactions. One such description has been to separate the effects into two main divisions, the effects (”synergistic”) of corrosion on the erosion rate (i.e. the change in mechanical response of the material due to corrosion) and the effects (”additive”) of erosion on the corrosion rate (the change in corrosion of the material due to mechanical action). In addition, there is confusion on why some materials exhibit high “synergistic” effects whereas others tend to lose material mainly through “additive” effects. This paper describes a programme of work carried out in an impinging jet apparatus, in which the erosion–corrosion response of Al was investigated at three pH values. The effects of applied potential and velocity were also assessed in these conditions. The results showed that the erosion–corrosion response very much depended on the pH and the potential. For Al, at pH∼13, the erosion–corrosion response was dominated by dissolution. However, at pH values of 4 and 7, the response differed due to the adherent passive film formed on Al in these conditions. Erosion–corrosion maps were constructed for Al in the various environments based on these results.

The corrosion of potlining refractories: A unified approach

The study of corrosion chemistry of aluminosilicate refractories in potlinings has historically focused on a single corrosive agent: either molten sodium fluoride or metallic sodium. Each approach can explain only a fraction of in-field observations. This article presents a unified approach, taking into account the effect of both corrosion agents on aluminosilicates. Along with the model, mathematical tools have been developed to help interpret experimental results as well as to make predictions of in-service behaviors. Those predictions are based on the use of corrosion maps, which vary according to the sodium ratio [RNa=NNa(M)/(NNaF+NNa(M))], as well as other parameters. Predictions made with the model match almost perfectly with the results obtained in a wide range of corrosion conditions. Depending on the quantity of fluorides that a lining lets percolate and the amount of metallic sodium diffusing, cells can be divided into two distinct groups: wet or dry. This article discusses the wet/dry distinction, including industrial aspects.

Mapping non-uniform corrosion using the wire beam electrode method. II. Crevice corrosion and crevice corrosion exemption

A wire beam electrode (WBE) was used to study corrosion of steel (UNS no. G10350) under carbon dioxide and oxygen environments with the presence of an artificial crevice. Local electrochemical parameters were measured directly from crevice areas and were used to calculate local corrosion rates and their distributions. Electrochemically calculated corrosion maps were found to be quantitatively comparable with microscopic observation of corroded electrode surface. It was also found that the WBE– R n method has a limitation when applied to oxygen corrosion in a stagnant electrolyte. An alternative method, which is based on galvanic currents, was employed for corrosion rate calculation. Under oxygen environment, localised corrosion was found to concentrate on crevice areas, while under carbon dioxide environment, crevice corrosion was not observed. This work confirms the applicability of the WBE method in crevice corrosion studies.

Evaluation of Deterioration and Specification of Defect of RC Structure by Natural Potential and External Impact-Acoustic Methods

It is a worldwide problem to build safer reinforced concrete (under-mentioned RC) structures on reflection of the great Hanshin earthquake disaster in 1995, Japan. The researches on the durability and the earthquake proof have advanced and the various countermeasures for these have been proposed. This paper deals with the specification of deterioration zones and its reliance, by using an external impact-acoustic detector, newly developed, which enables us to examine nondestructively the corrosive state of the inside of a concrete structure, and furthermore the verification with the natural potential method. The main experimental results concerning the building used in common are as follows:(1) The macroscopical corrosive degree of the RC structure can be evaluated by measuring the natural potential by means of the CuCuSO4 half cell and the effectiveness of the corrosion map. (2) “The external impact-acoustic method” can specify precisely the corrosive parts of reinforcement without the least damage on the RC structure, although the judgment of the corrosive grade is difficult; so, this disadvantage must be covered by using the natural potential method at the same time. (3)The relationship between the natural potential method and the external impact-acoustic one is quantitatively analyzed concerning an existing building.

Corrosion behaviour and characterisation of iron in hot flowing Bayer liquors

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Artificial neural network modeling of atmospheric corrosion in the MICAT project

This paper presents an Artificial Neural Network(ANN)-based solution methodology for modeling atmospheric corrosion processes from observed experimental values, and an ANN model developed using the cited methodology for the prediction of the corrosion rate of carbon steel in the context of the Iberoamerican Corrosion Map (MICAT) Project, which includes seventy-two test sites in fourteen countries throughout Iberoamerica. The ANN model exhibited superior performance in terms of goodness of fit (sum of square errors) and residual distributions when compared against a classical regression model also developed in the context of this study, and is expected to provide reasonable corrosion rates for a variety of climatological and pollution conditions. Furthermore, the proposed methodology holds promise to be an effective and efficient tool for the construction of analytical models associated with corrosion processes of other metals in the context of the MICAT project, and, in general, in the modeling of corrosion phenomena from experimental data.