Xinming Hu

Characterization of chemically bonded composite sol–gel based alumina coatings on steel substrates

Abstract Phosphate-bonded sol–gel composite alumina coatings were prepared on stainless steel substrates at processing temperatures of 300, 400 and 500°C. Mechanical property and electrochemical characterisation has been carried out and relationships sought between both processing temperature and coating microstructure. Coating corrosion and electrochemical behaviour is largely controlled by the degree of cracking and porosity in the coatings, which is minimum in those processed at the lowest temperature. Little correlation was found between coating processing or microstructure and coating mechanical properties (micro and scratch hardness, elastic modulus) or residual stresses but the interface toughness, as measured by a high load indentation method, increased with process temperature on coatings deposited on sand-blasted substrate surfaces.

Inhibition of Flow-Induced Corrosion and Erosion-Corrosion for Carbon Steel Pipe Work from an Offshore Oil and Gas Facility

A flow-induced corrosion and erosion-corrosion investigation was conducted to determine the degradation rates and mechanisms that had been experienced in service in the pipe work of an offshore facility. The investigation reviewed the flow-induced corrosion and erosion-corrosion performance of the carbon steel parent metal of the pipe work in comparison to the heat-affected zone (HAZ) and the nickel-molybdenum weld material. The program of experiments assessed the potential of two corrosion inhibitors to control adequately the material degradation caused by static corrosion, flow-induced corrosion, and erosion-corrosion on the three regions. Static corrosion tests were performed using linear polarization in carbon dioxide (CO2)-saturated conditions. Flow-induced corrosion and erosion-corrosion experiments were conducted using a submerged impinging jet (SIJ) in CO2-saturated conditions at a fluid velocity of 7 m/s with sand loadings of 0 mg/L and 100 mg/L. The effects of flow-induced corrosion and erosion-...

Assessment of Preferential Weld Corrosion of Carbon Steel Pipework in CO2-Saturated Flow-Induced Corrosion Environments

Preferential weld corrosion (PWC) has posed a problem to the oil and gas industry for a number of years. The general consensus from authors is that environmental effects take precedence over the we...

Assessment of electrochemical response from high alloy stainless steels during slurry impingement and single impacts to improve understanding of erosion-corrosion

Abstract Erosion-corrosion by liquid-solid impact results in damage on high alloy stainless steels where slurries are transported through pipes, valves, and pumps. It is well recognised that this damage is caused by a complex combination of mechanical (impact) and electrochemical (corrosion) processes. The synergy between erosion and corrosion is significant and depends on the nature of the materials and the aqueous environment. As part of a wider study investigating the mechanisms or erosion-corrosion of high alloy stainless steels, a series of electrochemical tests under multiple particle erosion-corrosion conditions and single impact conditions have been performed. In this paper the electrochemical behaviour under slurry erosion-corrosion and the transient electrochemical response under single impact of three stainless steels (UNS S31254, UNS S32654, and UNS S32750) is assessed. The depassivation and repassivation characteristics of the surface are characterised and these results are discussed in relation to the overall performance of the materials under erosion-corrosion conditions.

Empirical prediction of carbon-steel degradation rates on an offshore oil and gas facility: predicting CO2 erosion-corrosion pipeline failures before they occur

Various sections of carbon steel pipework removed from an offshore facility were found to have experienced severe degradation, partly attributed to an insufficient inhibitor dose rate, as discussed in a previous case study (Hu et al., 2011b). An investigation was conducted to compare the predictive capability of an empirical model generated using data from submerged impinging jet laboratory apparatus. The model was assessed in its ability to determine the rate of thickness loss for carbon steel pipework subjected to a CO2-containing erosion-corrosion environment, reviewing to what extent the prediction agrees with inspection data. The investigation considers whether the developed tool could have predicted pipework failures on the facility, comparing it to the degradation rate calculated from a leak which occurred within the past 2 years. The program of experiments set out to create a means of prediction using the material loss data from submerged impinging jet tests over a range of conditions replicating those within the line. Information pertaining to the temperature, production rate and sand loading was collated for the offshore facility. This data was used along with mass loss results to predict the degradation rate on the asset as a function of time over a 5 year period. This in turn was used to predict the total thickness loss of the pipework wall as a function of time. Consideration was also given to the current use of inhibition (10 ppm Inhibitor A) as well as the predicted thickness losses as a function of time had a candidate inhibitor been used instead (50 ppm Inhibitor B). Limitations of the model are presented, along with suggestions for ways to develop the model further.

Crevice corrosion of biomedical alloys: A novel method of assessing the effects of bone cement and its chemistry†‡

In this study, five commercially available poly(methyl methacrylate) PMMA bone cements were tested to investigate the effects of antibiotics on the severity of crevice corrosion. Bone cements with varying chemistry were also tested. A test method was developed in part reference to ASTM F746-04. Cylindrical specimens were fitted with a bone cement tapered collar, creating consistent crevice conditions. Crevice corrosion was then studied using potentiodynamic polarization techniques in 0.9% NaCl solution (pH7.4) at 37°C. Surface analyses using a light microscope and scanning electron microscopy were also conducted to investigate the surface morphology after accelerated electrochemical testing. Initial testing of commercially available bone cements indicated that different PMMA bone cements can affect the initiation and propagation mechanism of crevice corrosion. Further studies, utilising electrochemical and mass spectroscopy techniques, have identified that the addition of radiopaque agent and antibiotics affect the initiation mechanisms of 316L stainless steel, whilst significantly increasing the extent of propagation in CoCrMo alloys.

Evaluating Inhibitor Performance in CO2-Saturated Erosion-Corrosion Environments

Over the last decade, significant advances in chemical inhibi- tion have enabled operators to use carbon steel pipework in oil and gas facilities where sand production is a concern. The ability of these inhibitors to reduce both the electrochemical corrosion reactions and the mechanical damage attributed to particle impingement is well documented, but the underlying mechanisms have been the subject of less attention. This pa- per presents a review of three commercially available oilfield corrosion inhibitors (two standard corrosion inhibitors and one high shear-resistant inhibitor) in an effort to establish their performance in erosion-corrosion environments. Experiments were conducted at 45°C using a submerged impinging jet in carbon dioxide (CO2)-saturated conditions with a fluid velocity of 14 m/s and sand loading of 500 mg/L. A combination of gravimetric measurements, in situ electrochemistry, and sur- face profilometry allowed the inhibitors to be assessed based on a number of different parameters (i.e., mass loss, in situ corrosion behavior, and total penetration depth). The results demonstrate the importance of surface analysis techniques when evaluating the performance of inhibitors in erosion- corrosion environments, indicating that mass loss and in situ electrochemical techniques alone can sometimes provide misleading information in relation to their performance. The inhibitors are evaluated in erosion-corrosion environments where no semi-protective corrosion product formation occurs. Electrochemical impedance spectroscopy measurements are incorporated into the analysis to assist in interpreting inhibi- tion mechanisms and to help determine how inhibitors may be capable of reducing both the erosion and corrosion compo- nents of material loss.

Tribocorrosion reactions between metal-on-metal and metal-on-polymer surfaces for total hip replacement

The open circuit potential and linear polarisation resistance were measured during pin-on-plate tribometer tests for three different total hip replacement bearing material combinations in 0.35% NaCl and bovine serum solutions. In addition, surface analysis was performed using laser interferometry and focused ion beam scanning electron microscopy. It was found that the level of tribologically enhanced corrosion taking place at the bearing surface was substantially higher for metal-on-metal tribocouples than metal-on-polymer ones. Tribological depassivation may be reduced by the presence of organic boundary lubricants.