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The influence of iron contamination on a stainless steel surface was evaluated based on a novel rust deposition procedure. The main variables that control the corrosion process and the influence of iron contamination on localized corrosion resistance of austenitic and super duplex stainless steel were investigated. Cyclic potentiodynamic polarization tests and environmental exposure with different rust surface contamination degrees were performed. Potentiodynamic polarization curves showed that iron contamination deteriorated the local corrosion resistance of both stainless steels. Environmental salt-spray exposure results indicated that the alloy resistance to rust contamination increased with the materials’ pitting resistance equivalent. Likewise, the extent of localized corrosion decreased with the rust contamination degree. These findings suggested that preferential corrosion from rust contamination was associated with the occluded solution chemistry. Environmentally friendly cleaning methods, including chemical treatments and laser cleaning, were evaluated as alternatives to hazardous pickling based on hydrofluoric-nitric acid. Last, practical recommendations for rust contamination of stainless steel are addressed.

Selective laser melting (SLM) or powder bed fusion is a type of additive manufacturing technology with applications in, e.g., the orthopedics, energy, and aerospace industries. Several studies investigated the localized corrosion behavior of SLM-fabricated Type 316L (UNS S31603) stainless steel. However, little is known about the effects of tribocorrosive conditions on the response of stainless steels fabricated by SLM. In this study, the effects of third-body abrasive particles on the tribo-electrochemical behavior of SLM 316L stainless steel produced by SLM were investigated and compared with wrought counterparts (including UNS S31703, 317W) in 0.6 M NaCl. It was found that the presence of Mo played a more decisive role in the tribocorrosion behavior than the manufacturing method, i.e., 317W revealed the best tribocorrosion behavior vis-a-vis wrought 316L and the SLM-fabricated specimens. The improved tribocorrosion behavior contrasted with the much higher breakdown potential of the SLM-fabricated samples. Nano-scale secondary ion mass spectroscopy was used to investigate the effects of Mo on passivity. The implications of passivity and tribocorrosion behavior are discussed.

The formation of calcareous deposits on thermally sprayed aluminum (TSA)-coated surfaces immersed in natural seawater and connected to a cathodic protection system is a recurring issue. There is at present limited knowledge on the calcareous deposits’ formation kinetics on TSA in natural seawater following prolonged exposure at different temperatures. In this study, bare 25Cr super-duplex stainless steel (SDSS) and TSA-coated SDSS tube coupons (with and without a silicone-based sealer) were exposed to natural seawater under potentiostatic cathodic protection (CP) and open-circuit potential (OCP) conditions at different temperatures (i.e., 20°C, 35°C, 60°C, and 80°C) for 1.5 y. The coupons were extracted at various intervals to construct growth kinetics curves under various test conditions. The deposits were subsequently examined using scanning electron microscopy, energy dispersive spectroscopy, and x-ray diffraction. For all of the specimens, the deposits on the exposed surfaces increased with exposure time. Fewer deposits were seen under CP conditions than OCP at low temperatures (20°C and 35°C), whereas more deposits were observed with CP than those at OCP at high temperatures (60°C and 80°C). Last, a recommended protection potential of −0.90 VSSC (VAg/AgCl) and cathodic current density values of −8 mA/m2 and −15 mA/m2 were obtained based on the findings of this study.

Background: Fretting corrosion at modular junctions contributes to arthroplasty failure. Currently, no evidence-based guidelines are available regarding the acceptable level of trunnion corrosion that can occur in vivo. We aimed to examine the relationship between trunnion corrosion and risk of re-revision to assist surgeons with intraoperative decision making. Method: Grading by 3 independent examiners of revised and re-revised head components was performed using a modified Goldberg corrosion scale. Samples were separated into low-grade (LG) and high-grade (HG) corrosion. Mechanical testing determined the relationship between corrosion severity and pull-off strength at the head-stem junction. Results: 529 retrieved femoral heads were analysed. A positive association was detected between males and HG corrosion (OR 2.07; 95% CI, 1.45–2.94; p Conclusions: A well-fixed stem with corrosion may remain in situ.

The pit stability product—defined as the product of pit depth and dissolution current density (x·i)—was first introduced by Galvele as the criterion indicating the conditions that sustain a critically acidic solution within the pit. The one-dimensional (1D) electrode is the most commonly used experimental configuration for determining the pit solution chemistry and pit stability product. In our current works, a ‘sandwich’ like 1D pit electrode was developed, which enabled the in-situ and ex-situ visualization of pit depth. A methodology that avoids lacy cover formation was proposed to pre-dissolve a Type 316L stainless steel (SS) 1D electrode to specific depths. Based on the new methodology and mathematical models, it was found that 1D Fick’s law of diffusion could not be used to estimate the pit stability product under a salt film because electro-migration had a measurable contribution (i.e., 67%) to the dissolution current. Although the diffusion coefficient of metal cations decreased with an increasing concentration inside the pit, it could be replaced by a constant diffusion coefficient to estimate the pit stability product, defined as an equivalent diffusion coefficient in our work. Later, a more comprehensive mathematical model, which included hydrolysis reactions and activity, was built to predict the local chemistry within the pit cavity. Recently, a galvanostatic method was developed to estimate the critical pit stability product of Type 316L SS, which was between 0.8 and 0.9 A/m in 0.6 M NaCl at 25°C, findings that were also confirmed by mass transport modelling. Here, we will present the proposed improved theoretical framework and discuss the next steps in modelling the propagation of pits in stainless steels.

In this work, a galvanostatic method based on the one-dimensional pit electrode technique was developed to identify the critical pit stability product of 316 L stainless steel (SS). The critical pit stability product of 316 L SS in 0.6 M NaCl at 25 °C was between 0.8 and 0.9 A m−1, which was confirmed by mass transport modelling and potentiodynamic polarization results in pit-like solutions. The critical concentration of metal cations at the pit base was between 70 and 82% of the saturation concentration. The implications of these findings are discussed in detail.

The use of methyldiethanolamine (MDEA) as a pH stabilizer in natural gas pipelines utilizing monoethylene glycol (MEG) injection is an attractive option in systems with high carbon dioxide (CO2) pa...

Tribo-electrochemical behavior of a high chromium white cast iron (high-Cr WCI) used in, e.g., slurry pumps in mining and mineral processing applications, was investigated using a combination of electrochemical techniques, including zero resistance amperometry as well as potentiostatic and potentiodynamic polarisation. The effects of third body particles angularity on the localised tribocorrosion response of the cast alloy was studied during and post abrasion-corrosion by round ceramic beads and semi-angular silica sand particles. Advanced characterization methods such as electron backscatter diffraction and focused-ion beam cross-sectioning of affected areas were also employed to understand the wear and corrosion interactive actions. It was found that in chloride-free solutions, the behavior of high-Cr WCI resembled that of the austenitic 316 SS studied before. In contrast, in chloride-containing electrolytes, the semi-angular silica sand particles increased interfacial (carbide/matrix) localised corrosion susceptibility during and post-abrasion as indicated by the stark increase in anodic current and the morphology of the attack. Semi-angular silica sand abrasives had a greater adverse impact on post-abrasion interfacial corrosion vulnerability, compared to round ceramic beads. The complex behavior observed indicates that any material developed for tribocorrosive conditions must account for the particles angularity and their subsequent effects on localised corrosion.

A comprehensive mathematical model, including electrode kinetics, hydrolysis and complexation reactions, salt film precipitation and pit interface movement, was developed to investigate pit growth of 316L stainless steel under a salt film. The new mathematical framework incorporates activity coefficients into the hydrolysis and complexation reaction calculations for the first time, using experimental results to parametrize the electrode kinetics in a saturated pit solution. The model was validated by 1D pit experiments and results documented in the literature. It can successfully estimate the transition potentials, salt film thickness, pit stability product, saturated pit concentration, and the pH at the pit base during pit propagation under the presence of a salt film. Moreover, the model can predict the Cr enrichment and Fe depletion in the saturated solution at the pit base, attributed to the higher diffusion coefficient of Fe and the lower Cr diffusivity.

50 and 80 wt.% monoethylene glycol (MEG)/water mixtures at pH 4 and 6 were tested under different hydrodynamic conditions to investigate the MEG effects on CO2 corrosion of carbon steel. At pH 4, the presence of MEG resulted in a lower and less flow-dependent corrosion current density ( i corr ) than those of aqueous solutions. Since MEG changed the physical properties of the solution, it evidently led to a hindered transport of H+ ions to the steel surface and the decreased corrosion kinetics. At pH 6, i corr was slightly increased with shear stress in water-only and 50 wt.% MEG solutions, while it was decreased at 80 wt.% MEG concentration. It was found that at pH 6, MEG predominantly inhibited corrosion by anodic adsorption on the active sites and blocking the ionic transport.

Today, there is a large number of accepted tests to study crevice corrosion phenomena. The different methodologies can be used for comparing and ranking alloys, quality control, assessing the effects of changes in manufacturing routes and alloy composition on crevice corrosion resistance, as well as in evaluations to determine critical temperatures and potentials and induction times.The goal of the chapter is to describe the various standard test methods available to the corrosion specialist as well as adaptations to study specific crevice corrosion parameters. The focus is on test methods developed by the ASTM Committee G-1 on corrosion of metals, but other procedures are also included. While the test principles have been applied to many alloy systems, the scope of the chapter is on stainless steels and nickel-based alloys.

In this work, the methods used for the pre-dissolving step in one-dimensional (1D) pit experiments have been investigated in combination with a “sandwich” like 1D pit electrode, which enabled the in situ and ex situ visualization of pit depth. The proposed methodology avoided lacy cover formation during the pre-dissolving step for a Type 316L stainless steel 1D electrode placed upright. In contrast, it was challenging to avoid lacy cover formation with the proposed method when the 1D pit electrode was placed facing down, plausibly caused by accelerated convection effects inside the pits.

This study investigates the effects of particle angularity on the tribo-electrochemical behaviour of 316L stainless steel under low-stress three-body abrasion–corrosion conditions. Different angularity particles were delivered to the interface between the samples and a rotating rubber counterface, while changes in current with time were potentiostatically monitored. Based on a linear relationship existed between tribological factors (load and speed) and the average current evolved, an empirical correlation is proposed and possible underlying mechanisms are discussed. The effects of particle angularity on the surface and sub-surface damage are also demonstrated. It was found that increasing particle angularity improved their depassivation efficiency.

Jacketing or a weather barrier is usually installed in insulated piping systems and pressure vessels to prevent water ingress and protect the insulation. In the event of water penetration and accumulation resulting from poor design and/or aging of the jacketing, drain holes are proposed to accelerate the water dry-out process. This study investigated the influence of jacketing and drain holes on corrosion under insulation of carbon steel. In an enclosed system without the drain holes, where the water dry-out process is reduced, the underlying steel remains exposed to the corrosive environment for a longer period of time. Severe pitting corrosion was observed, which could be a result of limited oxygen diffusion into the insulation creating differential aeration environments favorable for pitting corrosion. The presence of drain holes promoted the water dry-out rate and oxygen diffusion into the insulation. As a result, the average corrosion rate increased in short-term exposure tests, but over a longer term the average corrosion rate, as well as the pitting rate, decreased.

Tribo-electrochemical behaviour of 316L stainless steel was studied using three contact configurations: two-body ceramic counterface (2B-CC), three-body rubber counterface (3B-RC) and three-body ceramic counterface (3B-CC). Electrochemical methods were employed to investigate the effects of tangential speed and wear mechanism on the tribo-electrochemical characteristics of the 316L samples at each contact configuration. In both 2B-CC and 3B-RC contacts increasing the tangential speed resulted in higher current measured while in the 3B-CC contact the current was an increasing function of time even at a constant rotational speed. After the abrasion-corrosion tests different repassivation kinetics was found for each contact configuration.

The discrete depth characteristics of thin passive oxide films were investigated using high-resolution electron microprobe and nanoscale secondary ion mass spectrometry (NanoSIMS). A novel NanoSIMS method involving a Cs layer deposition before Cs + sputtering was employed for the first time to determine the elemental distribution at different sub-layers of a passive film. The film was formed in air on the surface of a multi-phase microstructure of high-chromium cast iron (HCCI). It was found that the film composition and thickness varied according to the underlying microstructure phase. Based on the microprobe and NanoSIMS results, the influence of the HCCI passive film thickness and composition on the localized passivity breakdown has been proposed.

Two high-chromium cast irons (HCCIs) with different microstructure and Cr:C ratio of 9 and 6 were tested using a new three-body abrasion–corrosion rig incorporating electrochemical techniques. Coarse garnet particles acted as abrasive grits and the effect of mechanical parameters (i.e. load, sliding distance) was investigated. Electrolytes with different pH, neutral and alkaline were used and the effects of chloride ions and elevated temperature were also tested. SEM and optical profilometry were used to analyse the extent of abrasion–corrosion damage and the surface morphology. In the corrosion-only tests it was found that the corrosion rate increased with increasing pH, and both the chloride ions and elevated temperature had a detrimental effect. Increasing alkalinity has shifted the anodic behaviour from the matrix to the carbides. The influence of key alloying elements on the corrosion behaviour is also addressed. Electrochemical measurements revealed that the concurrent three-body abrasion had accelerated corrosion for both HCCIs in most environments tested. The following abrasion–corrosion mechanism for HCCIs in highly alkaline solutions is proposed: (i) removal of a thin oxidized layer from the carbide phase; (ii) plastic deformation and extrusion of the Fe–Cr matrix over the carbide-depleted regions. SEM images revealed repeated plastic deformation with the wear morphology similar to the three-body abrasion of ductile materials, and carbides were not visible. In neutral environments the carbide/matrix interface was the most vulnerable to corrosion initiation, with the matrix dissolving preferentially and the unsupported carbides fracturing. The influence of materials characteristics on the abrasion–corrosion synergistic action is also described in this paper.

A new tribometer to investigate a conjoint effect of three-body abrasion and corrosion has been developed. In this design, a flat wear sample is loaded against a rotating cylindrical disc counterface and the abrasive slurry is delivered to the contact interface. Capabilities of the newly developed tribometer have been assessed through conducting abrasion–corrosion tests involving simultaneous electrochemical measurements. In this work, the stability of the passive layer on stainless steel under three-body abrasive wear in a near neutral electrolyte was investigated using potentiodynamic polarization tests. 316L Stainless Steel wear samples were abraded by coarse garnet particles in an aerated sodium sulphate electrolyte. The effects of load and speed on the polarization curves and passivity of 316L steel were determined. It was found that under abrasion–corrosion conditions 316L steel became more thermodynamically active and the passive corrosion rate has increased. Increasing the contact load resulted in a small increase in the passive corrosion current, while increasing the rotating speed had the opposite effect of decreasing the current. Linear polarization resistance method was used to analyse corrosion current changes with time during abrasion–corrosion testing. The existence of three distinct stages was explained by the third-body effect on the corrosion potential and current. First stage was revealed by continuous decrease of corrosion potential. Then, the potential reached a plateau for the second and third stages. In the first and second stages, particle constraint in the contact zone plays the major role and a linear rise in corrosion current with time has been recorded. After a certain amount of surface roughening, no further increase in particles entrapment is expected. Therefore, in the third stage steady-state corrosion current values are anticipated. The rig developed can also be used to simulate two-body abrasion–corrosion. The capabilities of the new rig have been compared against other experimental set-ups used in studies of combined abrasion–corrosion behaviour.

PurposeThe aim of this paper is to obtain optimal corrosion resistance of certain differently treated samples by investigation of their electrochemical properties.Design/methodology/approachNanocrystalline plasma electrolytic carbonitriding (PEC/N) treatments were applied on the surface of commercially pure titanium in a glycerol bath with different additives. The carbonitriding process was performed in a glycerol bath with different additives such as carbamide, natrium nitrate and triethanolamine. The effects of electrolyte composition on chemical composition and corrosion resistance of the PEC/N films were examined by means of X‐ray diffraction, scanning electron microscopy, potentiodynamic polarization and electrochemical impedance spectroscopy in a Ringer solution.FindingsThe results showed that the PEC/N films obtained in solutions with triethanolamine (T‐film) had better corrosion resistance. All coated samples had a better electrochemical behaviour compared with the untreated substrate. Different nano‐structures and morphologies were obtained by different additives in electrolyte.Practical implicationsThe results obtained in this research into nanocrystalline PEC/N can be used wherever good corrosion and wear resistance with the highest efficiency is required.Originality/valueThe speed of treatment by this technique makes this method very suitable for the industrial surface treatment of different components.

Very few studies have focused on the optimisation of the nanocrystalline pulsed plasma electrolytic carbonitriding process parameters. A design of experiment technique, the Taguchi method, has been used to optimise the nanocrystalline pulsed plasma electrolytic carbonitriding. The experimental design consisted of four factors (triethanolamine concentration, electrical conductivity of electrolyte, applied voltage and duration of process), each containing three levels. All experiments were carried out under optimum constant frequency and duty cycle of rectangular shape pulse current method. Abrasive wear measurements were carried out to determine the wear resistance of the coated samples. The optimised coating parameters for wear resistance are 1020 g L–1 for triethanolamine concentration, 360 ms cm–1 for electrical conductivity of electrolyte, 400 V for applied voltage, 30 min for treatment time. The results showed that the applied voltage is the most significant factor affecting the wear resistanc...

Electrical conductivities and densities of acidic zinc, cadmium and manganese sulphate solutions were measured. Empirical equations have been derived to represent the measured values with high accuracy. Electrical conductivity of solutions has been shown to be expressed as a logarithmic function of temperature, a second order polynomial function of sulphuric acid concentration and a linear function of metal ion concentration. It can be deduced that the density of solution can be described as a linear function of metal ion concentration, temperature and sulphuric acid concentration. These equations could be used to improve the electrowinning or electrorefining process conditions.

Electrochemical behaviour of sodium silicate and 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) on carbon steel corrosion control in neutral and aerated soft water solutions have been investigated using electrochemical impedance spectroscopy and Tafel polarization techniques. The impedance and polarization results revealed that inhibitors mixtures have shown synergistic effects at lower value of HEDP. At 15 ppm silicate and 10 ppm HEDP showed optimum enhanced inhibition compared to their individual effects. The co-addition of 15 ppm HEDP and 15 ppm silicate has shown antagonistic behaviour. These observations have been supported by scanning electron microscopy (SEM) images, illustrating that the surface homogeneity increases in case of inhibitors mixture application and this provides good protection to carbon steel against corrosion in soft water solution.

PurposeTo study and compare the inhibition effects of eco‐friendly inhibitors of sodium silicate and 1‐hydroxyethylidene 1,1 diphosphonic acid (HEDP) in corrosion control and prevention of soft water discolouration (red water) in carbon steel pipelines.Design/methodology/approachElectrochemical impedance and Tafel polarization measurements were used to study corrosion inhibition properties. The experiments were carried out under different concentration ratios of inhibitors. Different hydrodynamic conditions were applied to simulate pipeline fluid flow. Scanning electron microscopy (SEM) and EDAX analysis were used for surface studies.FindingsIt was observed that corrosion inhibitor combinations under static conditions showed synergistic effects at low concentrations. The inhibition efficiency and synergistic behaviours of inhibitors were enhanced as the electrolyte turbulence was increased. In addition, the inhibitor concentration value required to reach maximum inhibition decreased. It was found that at 20 ppm sodium silicate and 5 ppm HEDP, co‐inhibition efficiencies increased significantly to more than 90 per cent and the corrosion rate decreased far below 1 mpy as the electrode rotational speed was increased. Surface studies using SEM revealed the formation of a compact and uniform film of co‐inhibitors.Practical implicationsThe results of this paper can be used for the development of effective, non‐toxic and economically attractive corrosion inhibitor formulations for soft water transmission pipelines.Originality/valueThe observed synergistic behaviour can be due to the incorporation of the silicate gel‐like network through organic phosphorous bonds. The hydrodynamic condition of the electrolyte leads to enhancement of inhibition efficiency, which indicates that the corrosion inhibition was mass transfer controlled.

High-Cr white cast irons (WCIs) are multiphase alloys commonly used in aqueous industrial environments in applications that require both high abrasion and high corrosion resistance. Various electrochemical techniques can be useful in elucidating tribocorrosion characteristics of metallic materials undergoing wear in a corrosive environment. This study is focused on the interpretation of electrochemical measurements applied to three-body abrasion corrosion contacts of high-Cr WCIs. Particular attention has been paid to determine whether tribo-electrochemical data can pick up any effects that the multiphase microstructure of WCIs may have on the tribocorrosion characteristics, especially in environments containing chloride ions. Since both wear and corrosion of multiphase alloys are usually not uniform, their tribocorrosion behaviour is difficult to study and is still poorly understood. The experimental results are discussed in terms of benefits and limitations of tribo-electrochemical techniques such as polarization (potentiostatic, potentiodynamic) and electrochemical noise (galvanic coupling, potentiostatic) in studying abrasion corrosion behaviour of high-Cr WCIs. The application of high-resolution surface analysis techniques (microprobe, NanoSIMS, C-AFM and SKPFM), used in support of the electrochemical data interpretation, is also demonstrated.

The transportation of wet gas fluid in carbon steel pipelines for onshore processing offers an economically attractive strategy. Although a substantial saving in capital cost can be realised, the risks of hydrate formation and corrosion damage are two of the main issues with such an approach. The standard industrial practice is to apply chemical solutions to reduce the risks. A thermodynamic hydrate inhibitor, such as monoethylene glycol (MEG) and corrosion inhibitors are commonly utilized to provide hydrate and corrosion control, respectively. Other production chemicals, such as an oxygen scavenger, may also be deployed as part of the risk management process. Consequently, the main challenge to the corrosion inhibitor is to provide corrosion protection throughout the production and processing facility while subjected to high temperatures in the MEG regeneration process and exposure to other production chemicals. Thermal stability and performance assessments should be an important aspect of the qualification process in the selection of corrosion inhibitors. This paper presents data from laboratory corrosion inhibitor evaluation programs, using thermally stressed MEG/chemicals under simulated wet gas pipeline operating conditions, which resulted in the successful qualification of a corrosion inhibitor for the production facility. In addition, the performance of oxygen scavengers for use in MEG systems is reviewed, including details of an oxygen scavenger that performs in lean MEG.

Polypyrrole (PPy) and polypyrrole-phosphate (PPyP) coatings were electropolymerised onto carbon steel electrodes in aqueous oxalic acid solution using the cyclic voltammetry technique. The electropolymerisation of PPyP was carried out with addition of trisodium phosphate to the supporting electrolyte. Prepared coatings were characterised using scanning electron microscopy. In addition, the ability of the coatings to control the corrosion of carbon steel was studied with the help of a variety of electrochemical methods: open circuit potential monitoring, potentiodynamic polarisation and electrochemical impedance spectroscopy all in 3·5% NaCl solution. All the results have consistently indicated that carbon steel is better protected by the PPyP coating than by the PPy coating.

Summary This study investigates the oxygen-scavenging behavior of bisulfite ions in monoethylene glycol (MEG)/water mixtures at concentrations commonly found in gas-transportation pipelines. Temperatures and pH values were varied. The influence of transition-metal (TM) ions to catalyze the bisulfite oxygen scavenging was studied. Experimental results indicate that MEG significantly inhibits bisulfite oxygen removal, which is hindered at low pH values and, to some extent, temperature. TMs can accelerate the oxygen-scavenging reaction in pH-unadjusted solutions, although the rate was still lower than that of the pH-adjusted solutions. The possible mechanism for such behavior and industrial implications are discussed.