Abstract

The dual function of leaf extract of Fig (Ficus carica L.) as antiscalant and corrosion inhibitor for steel were studied employing electrochemical impedance spectroscopy (EIS), potentiostatic and potentiodynamic polarization techniques. The obtained results showed that the plant extract inhibits the corrosion of steel under the tested conditions. Polarization curves indicated that the extract of Fig leaf acts as an anodic inhibitor, reducing metal dissolution. Mineral scales were deposited in the scaling solution experimentally by subjecting the metallic surface to cathodic polarization at -900 mV (ve SCE). A significant increase of steel electrode impedance has occurred after the electrode was exposed to the scaling environment at different intervals up to 20 hours. Potentiostatic current-time curves showed that concentration of 75 ppm of the extract is sufficient to inhibit the scale formation Evaluation study was made between the performance of the commercial antiscalant polyacrylic acid, PAA and the novel tested Fig. extract. The anti-scale action of 30 ppm PAA shows similar trend as that obtained by the 75 ppm of Fig extract; EIS plots for scaling environment in the  absence and the presence of Fig leaf extract indicated that it can be used safely as antiscalant and corrosion inhibitor.

Keywords: corrosion, steel, anti-scale, extract, Fig, EIS.

Abstract

The hazards of chrome plating have been under investigation for many years and the U.S. federal government will issue new guidelines soon that  will further restrict the use of chrome plate.

In anticipation of this increased control, industry has been seeking alternatives for traditional chrome plate. Many alternative surface engineering technologies such as plasma spray and physical vapor deposition (PVD) have been evaluated and are in use.

This paper will review the status of chrome plating regulations and alternative technologies; particularly PVD coating technology. PVD technology has grown rapidly during the last 20 years in a wide range of tooling and component applications. The role of PVD in corrosion control and replacement of traditional chrome plate will be documented.

Abstract

It is relatively straight forward to model the thrmodynamics and transport of compounds undergoing stoichiometric vaporization of deposition reactions at elevated temperatures where the kinetics are rate limited by gaseous transport. Such systems, thermodynamic properties change significantly as a function of time due to phenomena such as changing stoichiometry and other compositional influences associated with impurities in either the gas or solid. In this presentation we will discuss how to deal with changing stoichiometry in systems which remain single phase. For the purpose of illustration we will use the group 4 and 5 transition metal carbides to illustrate the application of several models that combine both solid state and gaseous diffusion in order to assess both steady state and non-steady state behavior. The group 4 and 5 transition metal carbides rank among the most refractory compounds that exist, having melting points approaching 2000-4000 K. Thus, they are suitable for a variety of high temperature applications, particularly where the oxygen partial pressure is low, such an in pure hydrogen propellants. A primary life limiting phenomena for these materials at extreme temperatures in direct vaporization or gaseous corrosion. During vaporization or corrosion of these metal carbides the surface composition changes with time, due to incongruent loss of metal and carbon atoms, eventually approaching a congruently vaporizing composition (CVC). At the CVC, metal and carbon atoms are removed in a ratio equal to that present on the solid surface. This paper describes an approach  for calculating or modeling the incongruent vaporization process with emphasis on determining time dependent surface composition. It will be shown that while the diffusion of carbon establishes the surface carbon concentration at any instant in time, the rate of vaporization is controlled by gaseous diffusion.

Abstract

Failure investigation due to the internal severe corrosion in desal unit no.5 vacuum system have been carried out on repete failed SS spoole piece, which connect the second stage ejectors (A&B) to the after condencer. Detalled follow up visual inspection, NDT & DT have been executed on five failed spoole piece (2^nd stage ejector discharge section tube) Photographs of the failed spoole pieces and ejectors have been performed and presented. Material of the failed parts have been tested, by using of both alloy analyzer and atomicabsorption techniques, and the results are presented. The corrosion products were conducted, chemically analysed and presented. Field fluid lab analysis, has been performed on both vapor and liquid phases. Operation failure histories parameters, design documents have been reviewed and presented. Disscussion with both operation and process engineering point of views for the main causes of corrosion problem was concluded and the recommendation to overcome the future problem are presented.

Abstract

The aim of the present study was evaluated the corrosion behavior of Teflon coating on anodized Al alloy. For approaching purpose, first of all, few samples of Al alloy were selected and anodized, then, after surface preparation of anodized Al, Teflon coated substrates. The evaluation of Teflon coating was done by scanning electron microscopy (SEM) and energy dispersive X-ray (EDAX). The corrosion behaviors of coated and uncoated samples were compared in 3/5% NaCl at room temperature by polarization test. The results of these experiments show considerable and positive effect of Teflon coating on reducing current density of substrate and improvement of its surface propery and corrosion behavior.

            Keyword : Aluminum alloy, Anodizing process, Teflon coating, Corrosion behavior, Polarization test, Morphology.  

Abstract

Corrosion reactions of metals and alloys have been studied mostly employing traditional electrochemical techniques such as dynamic polarization, chronoampersometric, impedance, and other measurements. Results of these studies provide a rather phenomenological understanding, as well as kinetic and thermodynamic parameters, for the reactions. We have been studying corrosion reactions of a few metals and alloys by using nontraditional techniques such as spectroelectrochemical, electrochemical quartz crystal microbalance (EQCM), and scanning probe microscopic experiments. In this presentation, we will review how the nontraditional electrochemical techniques help understand mechanisms of the reactions on molecular and/or atomic levels. Examples  include spectroelectrochemical studies of the corrosion reactions of the zinc, stainless steel and brass specimens, EQCM measurements of the corrosion of zinc over the iron substrates, and in situ scanning tunneling microscopy experiments on organic corrosion inhibitor molecules adscorbed on the iron surface. With these experiments along with the traditional electrochemical measurements, one can obtain not only the kinetic and thermodynamic information but also an understanding of the corrosion reactions on molecular and/or atomic levels.  

Abstract

The range of applications for magnesium alloys is still limited due to their relatively poor corrosion behavior. In recent years, various new magnesium alloys were developed, some of these also with improved corrosion properties, thus opening new fields of application. However, the number of alloying elements for the use in conventional cast processes is limited due to their interaction with liquid magnesium or large differences in the melting temperatures. The possibilities for grain refinement by post-processing are also restricted. Therefore, PVD techniques, i.e. ion beam and magnetron sputtering were used to produce substrates. The corrosion properties of these layers consisting of both, supersatured Mg-Al and Mg-Al-X and unconventional Mg-Ti and Mg-Ti-X alloying systems, were compared to ascast alloys and pure magnesium.  

Abstract

This study investigates the surface modification of different substrates, including Al₂O₃-TiC and Si, using So-incorporated hydrogenated amorphous carbon coatings (Si-aC:H) synthesized by radio frequency plasma enhanced chemical vapor deposition (PECVD). The precursor gas was a mixture of C₂H₂/Ar plasma and tetramethylsilane (TMS). A number of characterization techniques such as highresolution x-ray reflectometry, XRR, heavy-ion elastic recoil detection, ERD, x-ray photoemission spectroscopy, XPS, Raman spectroscopy, atomic force microscopy, and surface profiler have been employed to investigate the role of microstructure and composition on the electrochemical properties of the Si-aC:H coatings. We have demonstrated that TMS-incorporation causes a massive reduction in the established by ERDA technique, which was used to directly estimate the hydrogen content in the films.  The increased hydrogen concentration associated with the TMS precursor was responsible for a rise in density of voids and an associated reduction in the connectivity and stress release of the carbon network. In contradiction to the dramatic reduction in density and increase density of voids in the films, TMS-incorporation also led to significant improvements in the corrosion resistance of Al₂O₃-TiC substrates. The electrochemical impedance spectroscopy (EIS) showed an increase in the charge transfer resistance and reduction in the anodic current of the polarization curves. The improvements in corrosion resistance are thought to be related to formation of a passivation layer, which fills the increased number of pores present in the films .

Abstract

The influence of the microstructure on the corrosion behaviour of AXJ530 magnesium alloy in 3.5% NaCl solution at 25^oC and pH 7.25 hsa been investigated. Cut specimens of AXJ 530 alloy were obtained either directly from ingots, or from permanent mould cast billets with or without electromagnetically stirring, or from box-lime components produced by high pressure die casting or thixocasting. The experimental procedures consist of constant immersion technique and potentiodynamic polarization measurements. Surface of specimens, phase composition, and corrosion products morphology were analysed. Potentiodynamic polarization studies have shown that among all the tested specimens, thixocast specimens and ingot specimens have the highest and the lowest corrosion resistance, respectively. The corrosion resistance of die cast specimens was found to be higher than that of the billets specimens. These behaviours can be attributed to (1) the volume fraction of secondary phases, especially (Mg, Al)₂Ca phase, and (2) the aluminium concentration in the primary phase. Additional tests have been made with die cast AZ9lD specimens to compare and interpret the obtained results.

Abstract

Stress Corrosion Cracking Mechanism : Stress corrosion cracking (SCC) has been observed on the soil side of buried, natural gas pipelines since the early 1960s. Transgranular SCC has caused service as well as hydrotest failures, and cracks have been found associated with gouges and cracks have been found associated with gouges and dents. Transgranular cracking occurs in environments with pH about 6.5, and is referred to as near-neutral pH cracking, as opposed to high pH cracking, which is intergranular in nature.

The stress corrosion cracking (SCC) results from multiple metallurgical, mechanical, and environmental factors. Chemical composition of the steel, residual stress in the steel as well as applied stress, water chemistry in the field, including CO₂, oxygen, and ionic concentrations in the groundwater near the pipe surface, may all have an effect on crack initiation and propagation .

Stress corrosion cracking in pipelines involves several steps: (i) The coating applied to the pipeline during installation becomes degraded, an electrolyte comes into contact with the surface, and the environment that causes SCC to develop; (ii) The initiation and growth of multiple cracks that form colonies; (iii) These cracks may continue to grow and coalesce, and (iv) In the final step, a dominant crack reaches a critical size for rapid growth to failure, producing either a leak or a rupture. The time to failure depends on a number of factors, including the pipe material, stress history, environment, and crack distribution.

Nearly all studies of SCC have been carried out without distinguishing the characteristics of initiation from those of propagation. Many of the studies on propagation have focused on growth of long cracks in pre-cracked specimens.Initiation of SCC is,however, studied using specimens that are not pre-cracked. The definition of an initiated crack is not well defined, and there is no clear mechanistic interpretation of the events that lead to initiation.

SCC has been observed to initiate from the base of localized corrosion sites (i,e. pits, crevices) for a variety of metal-environment combinations. There remains debate on whether the stress intensification at the base of the pit or the enhanced electrochemical conditions within the pit is the controlling factor in SCC. Several investigators believe it is the localized environment that plays the biggest role in crack initiation and not necessarily the stress concentration provided by the localized corrosion site, whereas others believe that crack initiation in smooth samples requires the presence of a stress raiser. The most common way to establish such a stress raiser is either through corrosion or mechanical damage.

Compexities in SCC Phenomena : SCC in steels for oil and gas pipelines is a very complex and challenging phenomenon. The complexity of SCC is reflected in the changes, with time, of the diverse parameters influencing the cracking phenomena, whereas the biggest challenge is in obtaining field-relevant reproducible laboratory data. SCC encompasses major effects from metallurgical, mechanical, and environmental parameters, all of which can be dominant under specific conditions. Adding to the complexity are the loading conditions in operating pipelines that define the mode of failure as SCC or corrosion fatigue (CF). While SCC and CF are sometimes regarded as different modes of failure, the distinctions between them in mechanistic or engineering terms are becoming less sharply defined.

Abstract

Leak or rupture of carbon steel linepipe caused by hydrogen-assisted cracking (HAC) in near-ambient temperature of wet sour hydrocarbon services could lead to catastrophic consequences ranging from loss of lives to heavy financial impact. This paper discusses lines of defense to be implemented during the plate and pipe manufacturing and testing and field application in order to avoid occurrence of HAC failures including hydrogen-induced cracking (HIC), stress-oriented HIC (SOHIC) and sulfide stress cracking (SSC). These lines of defense include the following measures : 1) Quality control of plate (raw product) manufacturing process and testing requirements, 2) Quality control of pipe (finished product) manufacturing process and testing requirements, and 3) pipe selection criteria and field application quality control. Implementation of these requirements will result in increased safety/ reliability, reduced maintenance/ inspection costs and unnecessary usage of corrosion mitigation methods such as coating applications or inhibition systems.

Keywords: sour service, hydrogen assisted cracking (HAC), hydrogen induced cracking (HIC, stress oriented HIC (SOHIC), sulfide stress cracking (SSC), quality control plate procurement, pipe procurement, pipe selection.

Abstract

Corrosion behavior of dental alloys in artificial saliva was studied using different chemical and electrochemical techniques. The order of corrosion rate for the three investigated alloys is: wironit < wirolloy < wiron99. This order agrees with the results of chemical studies for determining the cumulative ions concentration using ICP/MS. The open-circuit potential of wirolloy is more positive than wiron99. The higher corrosion rate of wiron99 compared to wirolloy is due to presence of high concentration of Mo. Increasing casting number leads to decrease R_cl value and increasing C_cl.

The effect of hydrogen peroxide carbamide peroxide and fluoride solution on the  corrosion behavior of