CORROSION 2002

ABSTRACT
VCI films based on polyethylene are used in numerous applications. These films are either recycled or disposed of in landfills. Due to a very limited amount of land space, several countries have enacted laws to severely reduce the disposal of plastic materials into landfills. A new generation of VCI film has been developed to address the disposal concerns that some of the polyethylene VCI films have. Corrosion and biodegradation testing demonstrated that these new films not only provide excellent corrosion protection, but also readily degrade when placed in composting conditions. Chronic toxicity testing proved that these films have no detrimental effects on aquatic organisms.

INTRODUCTION
Corrosion is a plight that anyone working with metals faces. Its impact on the United States economy has been documented to be about 4% of the Gross National Product. It was estimated that about one third of the cost of corrosion damage could be avoided. The avoidable costs were related to the failure to use the best corrosion prevention practices available.

There are several ways of combating corrosion. One method that is gaining wider acceptance is the use of vapor phase corrosion inhibitors (VpCIs). These chemical compounds combine their volatility at room temperature with their corrosion?inhibiting properties. VpCI compounds can readily reach inaccessible crevices in metallic structures. Protective vapors disseminate within an enclosed space until equilibrium is reached. This equilibrium is determined by the partial vapor pressure of the VpCI compound.

Vapor phase corrosion inhibitors (VpCIs) were originally developed to protect boilers and piping systems of ships to be mothballed. Their effectiveness and ease of application attracted early users. Over the years, the field of usage has increased to cover electronics1-4, packaging5-7, process industries8,9, coatings10, and metalworking fluids11,12.

VpCI films based on polyethylene are used in numerous applications. These films are either recycled or disposed of in landfills. Due to a very limited amount of land space, several countries have enacted laws to severely reduce the disposal of plastic materials into landfills. An attractive alternative to using polyethylene is biodegradable resins. When placed in the right conditions, these resins will biodegrade into non-toxic compounds.

ABSTRACT
This presentation summarizes the efforts to develop and expand a comprehensive information system for corrosion of metals and alloys in high temperature gases. The current data collection represents about 6.4 million hours of exposure time for about 4,900 tests with 80 alloys. Data are being generated at the rate of about one million exposure hours per year. The system manages/exploits corrosion data from well- defined exposures and determines corrosion product stabilities. New insights in the analysis of thermochemical data for the Fe-Ni-Cr-Co-C-O-S-N system are being compiled. All known phases based upon any combination of the elements are being analyzed to allow the most complete and accurate assessments of corrosion product stabilities. Use of these data will allow prediction of corrosion product stabilities, which can be used to deduce the likely corrosion mechanism. The program has uses in corrosion research, alloy development, failure analysis, lifetime prediction, and process operations. The corrosion mechanisms emphasized are oxidation, sulfidation, sulfidation/oxidation, and carburization.

ABSTRACT
Recently, the application of molecular techniques has greatly improved our knowledge of microbial diversity and distribution in environmental samples. In this paper, we have reviewed the molecular biology techniques that can be used to study microorganisms and biofilms involved in the MIC phenomenon. These techniques include 16S ribosomal DNA (16S rDNA) gene based techniques. In particular, 16S rDNA sequencing, the construction of 16S rDNAs libraries, Fluorescence In Situ Hybridization (FISH), Denaturing Gradient Gel Electrophoresis (DGGE) and Random Amplification of Polymorphic DNA (RAPD) are techniques which can be used to identify and detect bacteria, as well as, to monitor bacteria organized in complex MIC biofilms. In addition to 16S rDNA, the RAPD technique can be applied to obtain probes for detecting bacteria involved in MIC, without any information concerning the bacteria of interest. These techniques can greatly improve our knowledge about MIC.

INTRODUCTION
Many bacteria inhabit oil and gas production and refining facilities. Some of them have a negative effect on the petroleum industry since they are responsible for biofouling and biocorrosion. In particular, biocorrosion or microbiologically influenced corrosion (MIC) is a serious problem, which has a great economical significance in this industry. Offshore water injection systems used for petroleum secondary recovery are particularly vulnerable to MIC since they transport non-sterile seawater that contains a wide variety of microorganisms able to form biofilms, which influence corrosion through a cooperative global metabolism on metallic surfaces 1'

MIC problems are even more relevant in tropical marine environments where the warm water favors a high microbial diversity. In offshore water injection systems, the microorganisms generally involved in MIC are bacteria. Sulfate-reducing bacteria (SRB) have been widely implicated in the anaerobic corrosion of metals and consequently they are the most extensively studied group of bacteria associated with MIC 3. However, aerobic bacteria are also known to participate in MIC 4. Indeed, we previously isolated several aerobic corroding bacteria in an offshore water injection system located in the Gulf of Mexico that were involved in MIC 5' 6.

Precise identification of key microorganisms involved in MIC is essential for the design of novel protective coatings and biocides that provide long-term, efficient protection against corrosion of metals in situ. Our studies indicated that some of the isolated strains could not be identified by classical biochemical tests based on culture-dependent methods. 16S ribosomal DNA gene (16S rDNA) sequencing was performed in order to identify these microorganisms. Novel bacteria can be identified by this method.

ABSTRACT
A state-of-the-art laboratory flow loop has been researched, designed, and developed to study the corrosive effects of sour gas in multiphase flow. This unique system is housed in an environmentally isolated, explosion-proof area providing a safe location where an operator can study the effects of a single parametric change on corrosion. This report describes the fluid pumping system, the flow monitoring system, the corrosion monitoring methods, and safety systems associated with the new experimental loop. Initial baseline testing of the entire system consisted of slug flow and full-pipe flow regimes in seawater and the resulting effect on corrosion rates under partial pressures of CO2.

INTRODUCTION
CO2 and H2S content in produced fluids constitute a very corrosive environment that has been studied extensively in glass cells and autoclaves since the early 1970?s, but little research work has been completed to model corrosion in slug flow of a sour system. Under various multiphase conditions, the slug flow regime has been shown to increase the corrosion damage to pipelines1,2. High velocity slugs are very turbulent with the existence of pulses of entrained bubbles in the mixing zone behind the front of the slug. These pulses of bubbles impact the pipe wall and collapse causing a cavitation-type effect, leading to increased corrosion rates in slug flow3.

H2S-related corrosion is a topic of great concern due to the increased oil and gas production technology that allows deeper wells producing more corrosive fluids and longer transmission lines. Longer transmission lines of multiphase fluids over various terrains provide opportune environments for slug flow regimes. In the presence of H2S, acidity of the corrosive media is a parameter known to play a determining role in the cracking phenomena (SWC, SSC, SCC) of low alloy steels as well as stainless steel and must be accurately evaluated4. Corrosion in the presence of H2S has resulted in the formation of an iron sulfide film that decelerated the corrosion rate at temperatures between 20ºC and 60ºC5. A similar film was seen at low concentrations of H2S in a brine containing CO2 and acted as a corrosion film that greatly decreased the corrosion rates in 2-liter glass cells6. The addition of hydrogen sulfide to a corrosive system contained in a bubble cell or other small volume test apparatus provides information necessary for characterizing the reactions and by-products of the corrosion process. However, this information fails to show the mechanical action of the flow regime on the scale or corrosion product film. Sour gas corrosion research has been limited to small-scale studies, which do not provide an adequate environment for the simulation of corrosion in multiphase slug flow.


Current laboratory research associated with sour gas is conducted in autoclaves because of the ability to reproduce the wellhead temperature and pressure conditions; some even have circulatory pumps to achieve better mass transfer in the corrosion process. Srinivansan7 describes an autoclave system developed to simulate fluid flow induced corrosion in CO2/H2S systems. This small-scale system provides an adequate environment for reproducing the corrosive constituents and wall shear stress effects, but lacks the size for development of certain flow regimes. Studies such as Pargeter8 have provided valuable information on maximum permissible hardness levels for welded steels at risk of sulfide stress corrosion cracking, but he did have some concerns that the 16:1 solution volume to sample surface area was small and resulted in a higher contamination of the aqueous environment not seen in a production environment.

ABSTRACT
Microbiologically influenced corrosion (MIC) of stainless steels in some plant failure cases were often observed at welded joints. It is important to understand the MIC mechanism for stainless steel welds. Experiments were performed to investigate the effect of the shape of the weld bead on the bacterial adhesion and pitting corrosion. Type 304 stainless steel coupon with the weld bead (308 filler filled by TIG) were exposed in culture medium with bacteria (Methylobacterium sp. or Bacillus sp.). After a fixed period of incubation, bacteria adhered on the surface of the specimen were stained with AO (Acridine Orange), and observed by epifluorescence microscopy. With shaking during the incubation, bacteria adhered to the HAZ and the toe region than the base metal or top of the weld region. After 60 days of incubation, SEM observation of the specimens surface was conducted. Pitting corrosion was observed at the toe region where some bacterial adhesion was seen. The austenite phase was preferentially attacked and the 6-ferrite phase was retained like a skeleton. Bacterial adhesion corresponded with the occurrence of pitting corrosion. Therefore the weld bead shape is considered to have significant influence on bacterial adhesion and MIC occurrence in stainless steel.

INTRODUCTION
Microorganisms and their metabolites have been utilized in many fields, such as fermentation, water treatment and medical supplies. However, harmful influences by microorganisms have been reported (i.e., the degradation of plastics, the corrosion of metals under the influence of microorganisms as Microbiologically Influenced Corrosion (MIC) in industrial plants have been reporteda-4). MIC on stainless steels has been observed in mild environments (fresh water environment). Corrosion damage to stainless steels by MIC have been observed in welded joints 5' 6. Walsh et al. 7 reported that the initial microbial attachment was random, but within 4 to 12 hours microbial consortia on the HAZ or on the weld were growing much more rapidly. Sreekumari et al. 8 reported that the adhesion of Bacillus sp. on base metal, HAZ and weld metal of 304L and 316L stainless steels was influenced not only by the surface roughness but also by the microstructure and that the preferential adhesion of bacteria could be considered as one of the factors causing preferential MIC attack on welds.

The welded portion of stainless steels generally has higher susceptibility to corrosion than the base metal. The mechanism of the lower corrosion resistance in welds can be explained by; (1) the effect of the non-homogeneous distribution of the elements like Cr and Mo, which contribute to the corrosion resistance, (2) the solidified microstructure in welds, and (3) by the effect of the defective passive film as a result of the oxide, which forms on the surface of the metal during the welding process 9, ~0. However, this higher susceptibility to corrosion in welds has not been fully understood in relation to the preferential MIC occurrence in welds of stainless steels. In this study, the adhesion behavior of bacteria near the weld was examined, especially the effect of the shape of the weld bead on bacterial adhesion. The correlation between bacterial adhesion and corrosion will be discussed.

ABSTRACT
Imidazolines have been used in the area of corrosion inhibition since at least the mid 1940?s when it was shown that long chain organic compounds with polar functional groups had corrosion inhibition properties when applied to oil-field environments. Many fundamental studies involving imidazoline-type compounds have been conducted and reported but although many acknowledge that conventional imidazoline contains multiple species, i.e., imidazoline, amide precursor etc., none have endeavoured to separate/isolate the various components. Therefore, the extent to which each of the components in an imidazoline mixture contributes to observed properties, i.e., corrosion inhibition performance, toxicity, biodegradation and bioaccumulation are not quantitatively known.

This paper reports the synthesis, separation/isolation and performance characteristics of various imidazoline species synthesised from oleic acid (OA) and diethylenetriamine (DETA). Also reported, are initial investigations into the inhibitory performance characteristics of each of these isolated species.


INTRODUCTION
Imidazolines have been used in the area of corrosion inhibition since at least the mid 1940?s when it was shown that long chain organic compounds with polar functional groups had corrosion inhibition properties when applied to oil-field environments.

The pathway to the use of imidazolines is not clear but it is probable that early workers found that certain long chain Fatty Acids (FA?s) and Amines could be used as oil field corrosion inhibitors at low concentrations. From there it would be an intuitive step to blend mixtures of these chemicals in order to obtain the most cost effective products. Such mixtures are salts and although they provide good inhibition properties they are often highly viscous liquids which are difficult to work with and formulate products from.

For a chemist the obvious answer would be to try to react these components together. Heating to moderate temperatures (~160ºC) produces an ?amide? whilst further heating to higher temperature (~230ºC) produces an ?imidazoline?. Both of these species provide corrosion inhibition properties although their manufacture adds significant cost due to the chemical facilities and energy required. Despite this the imidazolines have proved astonishingly successful commercially. This is because they are liquids at ambient conditions with relatively low viscosities. This makes them easy to formulate into products for use in a wide range of applications and climatic conditions.

Many fundamental studies involving imidazoline type compounds have been conducted and reported 1,2,3,4. Although some of these studies acknowledged that a conventional imidazoline probably contains multiple species, i.e., imidazoline, amide precursor, diamide and imidazoline amide, none have endeavoured to fully separate or isolate the various components. In efforts to further understand the ?mechanism? of inhibition afforded by conventional imidazoline mixtures, an understanding of the characteristics of each component is required.

ABSTRACT
This paper describes a new probe for potential monitoring of cathodically protected structures. Features of the probe are: elimination of copper sulfate solution, elimination of interliquid potential contribution, elimination of ohmic drop contribution, reliable measurement in presence of stray currents, and high durability. The probe is composed of a steel coupon and a reference electrode, both embedded in an alkaline mortar, simulating a coating defect. Different types of internal reference electrodes were tested, like Mixed Metal Oxide (MMO) titanium activated and AISI 304 stainless steel. The different probes were tested using different types of mortar; alkaline mortar (obtained from portland cement and sand), chloride containing mortar and carbonated mortar. Laboratory tests were carried out to verify the electrode durability under cathodic polarization and in presence of variable interfering electric field, simulating the presence of stray current. The results of two year laboratory test and a first field test are reported and discussed. The MMO reference electrode was more stable and more reliable than stainless steel when strong electric fields were present. Alkaline probes seemed to be more stable than other mortar type.

INTRODUCTION
Cathodic protection (CP) conditions are verified by checking that the structure potential matches the protection criteria. The potential measurement is easy to carry out, but its interpretation may present some concerns when stray currents cause huge ohmic drop contributions which may lead to misinterpretation.

ABSTRACT
The efficacy of a "self-healing" corrosion protection coating system for use on steel enclosures for outdoor equipment has been investigated. Urea formaldehyde microcapsules (60-150 microns in diameter) that contained several types of film forming compounds (healants) and corrosion inlaibitors were mixed into commercially available coatings systems. Laboratory tests showed that when the coating system was damaged by abrasion, the mierocapsules broke open and released their film forming and corrosion inhibiting compounds, thus initiating the self-healing process, in which the damaged area of the coating is covered and repaired, and corrosion of the substrate is inhibited. Steel substrates coated with these self-healing systems were scribed and laboratory tested according to ASTM D 5894, in which the specimens are alternately subjected to salt spray and ultraviolet exposure. The coated test specimens were evaluated with respect to undercutting at the scribe in accordance with ASTM D 1654. The undercutting was reduced from 2.12 mm to 0.46 mm at the scribe by using microcapsules containing phenolic varnish, a long chain polyester diluent, a second carrier/diluent based on high molecular weight hydrocarbons and a corrosion inhibitor. Electrochemical impedance spectroscopy (EIS) tests showed that the incorporation of self-healing mierocapsules resulted in significantly higher impedances for exposed coatings than for similar coatings containing no microcapsules.

INTRODUCTION
The efficacy of a "self-healing" corrosion inhibiting coating system for use on outdoor steel cabinet enclosures for electrical equipment is being investigated. Microcapsules in the form of microscopic spheres on the order of 50 to 150 microns in diameter containing corrosion-inhibiting compounds and coating "healants," or "coating repairing" compounds were investigated as the means of effecting the self-healing mechanism. These microcapsules can be manufactured so that they can be dispersed into various paint formulations in order to release their corrosion inhibiting/self healing constituents when mechanically ruptured, which wilt occur when the coating is damaged by impact or abrasion. These corrosion-inhibiting microeapsules can be used in paint systems to minimize the damage caused by scratches or abrasions to that system by the release of specially formulated chemicals that flow into the damaged areas and form thin films that provide corrosion protection. Self-healing coatings were developed by adding microcapsules to commonly used primers. The microeapsules release healing liquids when the coating system is damaged in laboratory experiments. Laboratory studies eonf'wmed that urea formaldehyde (UF) microeapsules 50 to 150 microns in diameter can be added to primers, (0.004 inches thick) to increase the coating service life by healing the damaged area. Accelerated corrosion testing was conducted on conventional coating systems using ASTM D 5894 (Standard Practice for Cyclic Salt Fog/UV Exposure of Painted Metal (Alternating Exposures in a Fog/Dry Cabinet and a UV Condensation CabineO land Electrochemical Impedance Spectroscopy 2'3 in the laboratory.

ABSTRACT
Corrosion resistance of surface-modified T22 steel intended for use as superheater tubes in waste incinerators was examined by laboratory and field corrosion tests. An alloy of 40%Ni-30%Cr- 20%Mo-10%Nb (wt.%, referred to alloy 4321) was used as a coating and applied to T22 steel by either HVOF metal spray or weld overlay. A thin film of alloy 4321 approximately 10gm thick, generated by unbalanced-magnetron (UBM) sputtering of target metals and subsequently ion-plated on either a metal spray or weld overlay coating of alloy 625 was prepared and tested as well. According to a laboratory corrosion test conducted by coating the samples with a synthetic ash and exposure to gas mixture of 1000ppmHC1-50ppmSO2-10%O2-10%CO2- 20%H20-bal.N2 at 550°C for 100h, alloy 4321 coatings showed considerably better corrosion resistance than alloy 625. However, field corrosion testing in a stoker type furnace exposed at 500-550°C for 3100 h showed the corrosion resistance of alloy 4321 coatings was similar or even worse than alloy 625. Thus, Nb additions between 3.5% to 10% and Mo additions between 9% to 20% to Ni-base alloys are considered not effective in combating corrosion in the present environments.

INTRODUCTION
Fireside corrosion of superheater tubes in waste incinerators has been an important issue when considering high efficiency waste-to-energy (WTE) plants. Higher steam conditions have been favored for advanced WTE plants in various countries ~'2, but selection of corrosion resistant alloys (CRAs) and mitigation for boiler tube corrosion do not seem to have been established yet, presumably due to the harsh and complicated corrosive environments. Among high-temperature steels and alloys, high- molybdenum alloys such as alloy 625 are reported to perform relatively well in the literature ~. However, the corrosion thickness loss of alloy 625 tested at a superheater location in a Japanese high- efficiency WTE demonstration plant (steam conditions of 500°C, 100 atm, 13800 h duration) were as high as 1.9 mm in a corrosion-dominated section and 3.0 mm in an erosion-dominated section 3. These values are indeed too high for practical application of such alloys in real systems. Hence, an ultimate CRA system, including coating, is needed to combat this harsh environment.

Studies have shown that the corrosion of superheater tubes in WTE plants results from fuel slag deposits on the fireside surface of boiler tubes 4. Sulfate and chloride salts concentrate at the deposit/scale interface, and become partially fused since these deposits contain alkali metals (Na, K) and heavy metals such as Pb and Zn, which can form low melting-point salts at the operating metal temperatures 5. The corrosion can be interpreted as hot corrosion 6 caused predominantly by low melting-point fused salts in the slag deposits.

ABSTRACT
The effect of ennoblement on chemistry of passive films on 316L stainless steel (SS) was quantified using surface-sensitive analytical techniques. Under well-defined laboratory conditions, SS coupons were ennobled to ~ +350mVsCE by biofilms of manganese-oxidizing bacterium Leptothrix discophora SP-6. Ennobled coupons were analyzed by x-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (TofSIMS). From the XPS depth profiles of Fe, Cr, O, Ni, C and Mn, we evaluated thickness of the passive layers before and after ennoblement, while the TofSIMS depth profiles were used to evaluate spatial distribution of Mn, Cr, Fe and Ni on the surface. Because the ennobled coupons were covered with biomineralized deposits, sputtering was used to remove these deposits under ultrahigh vacuum (UHV) conditions before probing the chemistry of the underlying passive layers. The main conclusion of the paper is that oxide layers on the ennobled coupons are significantly thinner than those on the pre-ennobled coupons, which may, hypothetically, contribute to their susceptibility to localized corrosion.

Corresponding author: Zbigniew Lewandowski. E-mail: ZL@erc.montana.edu

INTRODUCTION
Numerous studies have reported increases from -200 mVscE to +350 mVscE in the open circuit potentials (OCP) of stainless steels immersed in natural waters; this is known as ennoblement. Ennoblement facilitates pitting corrosion in the presence of low amount of aggressive ions, such as C1-, which is ordinarily not enough to cause pitting by itself.

Several mechanisms have been proposed for ennoblement: Some models include depolarization of the oxygen reduction reaction caused by enzymes 1'2, strong acidification of the surface from biofilm activity 3'4, combined effects of increased H202 concentrations and decreased pH from biological origin 5, and reduction of MnO2 formed by the activity of manganese-oxidizing bacteria. This last mechanism of ennoblement by reduction of biologically produced MnO2 is the only model that has been proved experimentally in the laboratory as well as in the field 6'7'8'9. In this model, the reduction of MnO2 produced by the activity of manganese-oxidizing bacteria (MOB) to MnOOH, reaction (1), and the further reduction of MnOOH to Mn 2+, reaction (2), are responsible for the elevated potentials on stainless steel. Reactions (1) and (2) have the same formal electrode potential (E') values as the observed ennoblement potentials in the laboratory and in the field.