Laboratory Corrosion Research Articles

Atmospheric Corrosion Effects of HNO3: A Comparison of Laboratory and Field Exposed Copper, Zinc, and Carbon Steel

The present trends with decreasing ambient levels and unchanged levels has resulted in an increased interest in as a corrosive pollutant. Despite the fact that ambient levels are still in general much higher than levels, this study shows that plays a significant role for the atmospheric corrosion of copper and zinc but not for carbon steel. A comparison of laboratory and field corrosion effects of on copper, zinc, and carbon steel is presented. The quantitative agreement between extrapolated laboratory results and field results are good for both copper and zinc and the total corrosion effect can be represented by the sum of two contributions; one from and one from remaining corrosion stimulators, including . However, an extrapolation of laboratory results of -induced corrosion of carbon steel resulted in corrosion effects much lower than the total effect observed in the field. The field data used for comparison are from the international projects model for multipollutant impact and assessment of threshold levels for cultural heritage, with 29 sites in Europe, and Regional Air Pollution in Developing Countries with 12 sites in Asia and 4 in Africa.

油井管材料の腐食挙動に及ぼすコンデンセート中の水分率の影響

In order to investigate corrosion behavior of representative Oil Country Tubular Goods (OCTG) materials in environments of gas condensate/water/CO2 or CO2+H2S, laboratory and field corrosion tests were carried out. The laboratory tests were carried out in CO2 or CO2+H2S environments by using an autoclave. Test specimens were set in liquid and gas phases of the autoclave and the water fraction ratio of condensate and water mixture was changed to study the effects of water fraction on corrosion behavior of OCTG materials in oil and gas well environment. In the filed tests, Down hole coupon (DHC) tests were carried out in a sour gas well in the United Arab Emirates. The DHC tests were performed at three different well depths with different water fraction. The laboratory liquid phase test results indicated that corrosion occurs by water wetting on material after emulsion break. The laboratory gas phase test results show that the vapor of condensate acts as corrosion barrier. The comparison between the laboratory and the field tests results indicates that localized corrosion occurred on carbon steel in the field test but did not occur in the laboratory gas phase test, although corrosion rate in the field test was almost the same as that in the laboratory gas phase test. This is because localized water wet condition could not be reproduced in the laboratory gas phase test. From these results, tubing material used for gas well should be selected with taking account of localized water wet conditions, even if a water fraction of bulk fluid is significantly low.

Degradation of heat exchanger materials under biomass co-firing conditions

Co-firing biomass in conventional pulverised coal fired power stations offers a means to rapidly introduce renewable and CO2 neutral biomass fuels into the power generation market. Existing coalfired power stations are both much larger and more efficient than current designs of new biomass combustion systems, so feeding a few percent of biomass feed into an existing large coal fired station will give more biomass derived power than a new dedicated biomass station. Co-firing levels started at ∼2% biomass, but this has increased to ∼5–10% biomass, with higher levels of biomass co-firing being investigated, although supply of biomass becomes an issue with increasing co-firing levels. The lower levels of biomass co-firing (up to ∼5%) can be achieved with relatively minor modifications to existing plants, so avoiding the large capital costs and risks of building new biomass-only fired power systems. However higher levels of co-firing are more difficult to achieve, requiring dedicated biomass supply systems and burners. For existing coal-fired power stations, the co-firing of biomass causes some practical problems, e.g.: the control of co-firing two fuels; changes to bottom/fly ash chemistry; changes to deposition (fouling and slagging) within the boiler; reduced reliability of key high temperature components (e.g. heat exchangers) due to increased corrosion problems relative to those experienced with coal alone.This paper reports the results of assessments carried out to evaluate the potential operating conditions of heat exchangers in combustion systems with biomass (wood or straw) and coal cofiring, as well as laboratory corrosion tests that have been carried out to give an initial assessment of potential effects of biomass-co-firing.The corrosion tests have been carried out using the deposit recoat method in controlled atmosphere furnaces. A series of 1000 hour tests have been carried out at typical superheater and evaporator metal temperatures using simulated deposit compositions and gaseous environments (selected on the basis of plant experience and potential fuel compositions). Five materials were exposed in these tests: 1Cr steel, T22 steel, X20CrMoV121, TP347HFG and alloy 625. In order to produce statistically valid data on the actual metal loss from the materials, the performance of the materials in these tests was determined from dimensional metrology before and after exposure. For each material, these data have been used to determine the sensitivity of the corrosion damage to changes in the exposure conditions (e.g. deposit composition, gas composition) thereby producing initial models of the corrosion performance of the materials. The corrosion data and model outputs have been compared with data available from power plants operating on coal, straw or wood fuels.

Mechanical performance of BStIV grade steel bars with regard to the long-term material degradation due to corrosion damage

The mechanical performance of BStIV grade reinforcing steel bars from four different manufacturers was experimentally investigated and evaluated by exploiting the performance indices concept. The experiments included tensile tests, carried out on uncorroded and pre-corroded steel specimens. To corrode the specimens, accelerated laboratory corrosion tests were involved. The later tests were made to assess the expected degradation of the materials mechanical performance with accumulating corrosion damage during the life of a reinforced structure. For the evaluation of the mechanical performance, index Q D has been introduced. The index Q D considers the combination of tensile strength and tensile ductility in a single quantity by accounting also for scatter in material’s mechanical properties. Index Q D can be applied to assess the materials mechanical performance both in the undamaged and in the corroded conditions. In both cases, the materials were ranked based on the outcome of the evaluation of their mechanical performance. Subjective choice is needed in order to consider the effect of corrosion damage on the material’s mechanical performance.

Reliability of Pb-Free Preplated Leadframe Under Atmosphere and Accelerated Aging Test

Atmospheric corrosion of Pb-free preplated leadframe (PPF) finish, which causes unacceptable appearance due to discoloration, has been meticulously investigated. The discoloration appears particularly on the shoulder, tip, and sidewall of the leadframe, where bare Cu is directly exposed to the given environments. Such Cu exposure is attributed to the forming and trimming process of the PPF. It is found that the geometrical feature of the ragged shear edge on the sidewall of the PPF is dependent on the condition of a cutting tool. There is a porous Ni layer on the Cu substrate. It is also found that the tarnish products consist of cuprous oxide (Cu/sub 2/O) and cuprous sulfide (Cu/sub 2/S). The depth profile reveals a thick Cu oxidation layer over cuprous sulfide, which implies that the integrity of a dual inline package assembled with the PPF is susceptible when exposed to a relatively higher humidity and sulfur-involved environments. To reproduce the atmospheric corrosion, a variety of laboratory aging tests that include the mixed flowing gas (MFG) test was used. Except the MFG test, the laboratory corrosion that yields Cu oxidation only is not identical to the atmospheric corrosion. As results, electronic devices assembled with the PPF must be sealed into a moisture-barrier bag to extend the shelf life during storage, if particularly they are exposed to relatively harsh circumstances, higher humidity in H/sub 2/S atmosphere.

Methods of Evaluating the Corrosion Resistance of Low-Alloy and Carbon Tube Steels under the Service Conditions of Oil and Gas Pipelines

At present, determining the content of corrosion-active nonmetallic inclusions in tube steels is the best way to evaluate these steels' resistance to local corrosion under the service conditions of oil-field tubing in Western Siberia. However, the method needs to be refined or supplemented. Field tests of tube steels are an important means of gauging the corrosion resistance of these materials and pipes when certain conditions are observed. Laboratory corrosion tests should be performed under conditions identical to the corrosion conditions encountered in the field. The rates of the main corrosion processes that take place during the problem-free operation of pipelines may turn out to be significantly higher in the laboratory than in field tests.

A Metallurgical Approach to Metal Dusting of Nickel-Base Alloys

Preliminary laboratory corrosion tests of two conventional Ni-base alloys were conducted at 650°C for 200 h in various CO–H2–CO2–H2O gas mixtures. For gas mixtures of high ac and CO content, alloy 600 (75 mass %Ni–15%Cr) specimens lost its mass due to metal dusting and deposition of coke was heavy on the surface of the specimen. Meanwhile, any pit formation was not occurred on the alloy 690 (60%Ni–30%Cr) specimens. Microscopic observation indicated that for the corroded Ni-base alloy specimens, inward diffusion of carbon presumably at cracks and flaws in the oxide scale was prominent. Carbon in the diffusion zone reacted with chromium to precipitate carbides in the matrix, followed by the “direct” formation of graphite platelets with a lamellar structure at the revealed metal surface. This direct precipitation of graphite platelets can be considered by a eutectoid reaction, which is similar to the pearlite transformation observed in Fe–C system. In the lamellar structure, the γ matrix thinned with the growth of graphite plates, and small metal particles of Ni and Fe which may catalyze the coke deposition reaction were crumbled and detached from the lamella.

南長岡ガス田における１３％Ｃｒ鋼チュービングの二酸化炭素腐食に対する酢酸の影響

Localized corrosion was found on inner surfaces of 13 %Cr steel tubing at shallow depths in deep, hot corrosive Minami-Nagaoka gas wells. Judging from the high penetration rates of corrosion pits, factors other than high temperature and carbon dioxide (CO2) are expected to exist. The chemical analyses on produced fluids revealed that acetic acid of 250∼300 ppm existed in the produced condensed water. Laboratory corrosion test results showed that acetic acid in the condensed water saturated with CO2 markedly affected the passivity of 13 %Cr steel due to low pH. The existence of acetic acid can be a cause of the localized corrosion of 13 %Cr steel tubing in Minami-Nagaoka wells.

Electrochemical evaluation of a corrosion fatigue failure mechanism in a duplex stainless steel

M.R. STOUDT and R.E. RICKER Laboratory corrosion fatigue studies on smooth and precracked samples indicated that two duplex stainless steels would have similar service lives in a paper-processing environment; but, in service, one of these alloys has exhibited premature failures. Since corrosion fatigue experiments had proven unable to detect this failure mechanism, electrochemical measurements and slow strain rate tensile tests were used to evaluate four alloy composition-dependent failure mechanism hypotheses. No significant differences were found in the dissolution rates or hydrogen fugacities produced when mechanical processes expose bare surface, and slow strain rate tensile tests found no indication of a difference in cracking susceptibility for the same hydrogen fugacity. Electrochemical experiments found that pits nucleate in one phase of the duplex microstructure at lower potentials in the failure prone alloy, but do not propagate beyond the microscopic dimensions of this phase. These microstructurally limited “micropits” were found to nucleate fracture in slow strain rate tensile tests, and examination of a service failure confirmed the presence of microscopic pits at crack initiation sites. The premature failures are attributed to the lower pitting resistance of the failure prone alloy, and the failure of laboratory experiments to predict this behavior is attributed to the slow kinetics of pit nucleation in these experiments. A laboratory testing methodology is suggested that will ensure detection of similar susceptibilities in future corrosion fatigue testing programs.

Mobility and Criticality of Plutonium in a Repository

In an underground repository for spent fuel, criticality is excluded initially by compliance with the disposal conditions. In the long term, critical accumulations of fissile material can be formed only by mobilization of uranium and plutonium from the waste forms and subsequent precipitation or sorption of these elements. This paper presents an overview of mechanisms relevant for mobilization and possible accumulation of U and Pu from disposed mixed-oxide fuel elements. Concentrations of fissile materials observed in laboratory corrosion experiments together with model approaches are applied to determine the degree of fissile material accumulation and the risk of a sustained nuclear chain reaction. A prerequisite of criticality in a repository is an accumulation of fissile materials. Since geometry, moderation, and neutron absorption properties cannot be forecast, the neutron multiplication factor kinf is used (instead of keff) as a measure of the incidence of criticality. The factor kinf is derived for several scenarios. Required critical masses and critical volumes are evaluated.The accumulation of Pu onto solids is considered, and it is shown how selective enrichment of Pu and U may affect the risk of criticality. It is also shown that the criterion for criticality would be met only in the unrealistic case of selective sorption of 239Pu. Realistic sorption densities are too low to provide sufficient accumulation of fissile materials for criticality. This is particularly true if high Cl concentrations are present.

Hydrocarbon-Soluble VNKh Inhibitors of Corrosion of Ferrous and Nonferrous Metals

An approach to selection of starting reagents for the synthesis of corrosion inhibitors was proposed. The approach is based on thermodynamic analysis of criteria of the adsorbability of surfactants at a metal from a dilute aqueous solution, as well as on estimation of the metal affinity of a starting reagent from its electronic structure. The results of laboratory and industrial corrosion tests of the VNKh inhibitors are presented.

The Corrosion Rate of Copper in a Test Parcel at the Äspö Hard Rock Laboratory

ABSTRACTCylindrical copper electrodes have been installed in a test parcel at the Äspö Hard Rock Laboratory and real-time corrosion monitoring was initiated in May 2001. The test parcel was emplaced on October 29, 1999, and will be retrieved in 2004. The three electrodes, each of about 100 cm2 surface area, are installed in bentonite block 36, where the temperature is about 24°C.The corrosion monitoring is performed with linear polarization resistance (LPR), harmonic distortion analysis (HDA) and electrochemical noise techniques. A value on the Stern-Geary coefficient is required to calculate the corrosion rate from the measured LPR data. A default value of 10.3 mV has been used, but an actual value can in fact be obtained from the HDA. The corrosion rate will be overestimated if the frequency of the voltage perturbation for the LPR measurements is not low enough. Electrode impedance measurements have been performed to verify this.Two and a half year after emplacement the recorded corrosion rate of copper in the above bentonite block amounts to about 2.2 μm per year (using a default value of 10.3 mV for the Stern-Geary coefficient and a 0.01 Hz voltage perturbation frequency). The actual corrosion rate is estimated to less than 0.7 μm per year (considering a measured Stern-Geary coefficient of 6.5 mV and the findings from the electrode impedance measurements).

Development of dense corrosion resistant coatings by an improved HVOF spraying process

For 6 years, we have developed corrosion resistant coatings to protect steel structures in the marine environment by using a thermal spray technique. This paper summarizes the major developments and results obtained. Such a coating requires primarily impermeability and secondarily homogenous and clean microstructure. In order to make denser and highly corrosion resistant coatings, we selected spray materials and improved fabrication processes. HastelloyC was a suitable material for High Velocity Oxy-Fuel (HVOF) spraying to form corrosion resistant coatings because of its high resistance against thermal oxidation as well as seawater corrosion, especially crevice and pitting corrosion. An inert gas shroud system was attached with a commercial HVOF apparatus and this attachment increased the in-flight velocity of spray particles over 750 m s−1 and simultaneously suppressed oxidation significantly. In addition, some new methods were designed to evaluate the sprayed particle’s state and the coating properties with high accuracy and sensitivity. Thermal energy of in-flight spray particles was revealed by molten fraction of spray particles, determined by quantitative analysis of melted and unmelted particles captured in an agar gel. Through-porosity of the coatings with open porosity below 0.1% was determined by using Inductively Coupled Plasma analysis of dissolved substance from substrate through the penetrating path of the coatings. The coating of HastelloyC nickel base alloy by the HVOF spraying with the gas shroud attachment had zero through-porosity and 0.2 mass% of oxygen content. The laboratory corrosion tests showed that the on-shroud HastelloyC coating was comparable to the bulk material of HastelloyC in terms of corrosion resistance. This coating, formed on steel, demonstrated an excellent protective performance over 10 months in the marine exposure test.

Investigation on Accelerated Laboratory Corrosion Test of Oil Storage Tank Baseplate

Investigation on Accelerated Laboratory Corrosion Test of Oil Storage Tank Baseplate

The effect of deposits on waterwall corrosion in fossil fueled boilers

Corrosion of water walls in fossil fueled boilers and gasifiers has traditionally been considered the result of gaseous corrodants, such as H2S and HC1, reacting with the heat exchanger tube surfaces. Under reducing conditions these corrodants prevent the formation of a protective oxide scale, leading to increased metal loss. Recent field experience in boilers, using staged combustion systems, has shown much greater corrosion rates than predicted by simple gas/solid corrosion processes. The presence of large quantities of unoxidized iron sulfide in deposits in areas where high corrosion rates were found, suggests that deposits play a role as well. Subsequent laboratory corrosion studies found that the presence of FeS can indeed lead to very high corrosion rates, but only under oxidizing conditions. Since FeS usually deposits only where reducing conditions are present, the accelerated corrosion observed requires alternating reducing and oxidizing conditions. These are usually found in load following boilers. It is also shown that chlorine corrosion may be caused or at least accelerated by chloride containing deposits in fossil fueled boilers, similar to waste incinerators, where the role of chloride rich deposits has been well established. Due to the relatively high sulfur content of fossil fuels, chloride deposits most likely form under reducing conditions only. However, once formed they can be highly corrosive under oxidizing conditions.

On the Corrosion State of Structures of the Kama Water-Power System

Laboratory and field corrosion investigations carried out over many years in the Kama hydrotechnical structures are reviewed. The main reasons, character, and kinetics of intense pitting corrosion of structural steels are discussed and compared with those in other river basins. An unusually high corrosivity of the Kama water was explained. Effective versions of polymer coatings were developed for the specific conditions of the Kama basin. The preshipping period of corrosion protection was extended by using polymeric materials highly resistant to negative temperatures.

Cemented carbide and cermet tooling for film-perforating

The tools used to perforate a particular photographic film started to wear at an unacceptable rate when the film base was changed from cellulose triacetate to polyester (PET). A laboratory investigation was initiated to screen candidate tool materials and identify ones with potential for 10 times life improvement over cemented carbide (WC/10% Co).The screening tests started with abrasion and corrosion tests on various grades of cemented carbide, cermets and selected ceramics. Concurrent production trials indicated that the laboratory corrosion tests were not correlating with production results. To address this problem, a “nibbler” test was developed which simulates perforating and material removal on a punch after 106 perforations (nibbles) became the screening test metric.It was determined that abrasion tests do not accurately predict tool material behavior when chemicals are present on or in the materials being perforated. Static corrosion tests do not predict tool response under production conditions. The rubbing of the film on the tool surfaces removes protective films and there can be a significant corrosion component in tool erosion. The nibbler simulates real tool conditions because erosion is produced by actual cutting of coated webs. Nibbler tests in this study indicated that alumina/zirconia resisted film erosion better than cemented carbide, even cemented carbide with PVD coatings. The nibbler tests also indicated that leaving recast layers from electrical discharge machining on cemented carbide greatly increases erosion rates. It should be removed.Production tests conducted since completion of these laboratory studies suggests that nibbler results correlate with production results. Coated cemented carbides are providing 3 times the service life of uncoated cemented carbides as predicted by the nibbler test.

Stability of protective oxide films in waste incineration environment—solubility measurement of oxides in molten chlorides

Solubility measurements of several oxides in molten NaCl–KCl and NaCl–KCl–Na 2SO 4–K 2SO 4 were conducted in three different levels of basicity. The dissolution behavior of the oxides showed almost the same tendency as that shown by the dissolution behavior of the oxides in molten Na 2SO 4 in literature. In a waste incineration environment, a protective Cr 2O 3 film easily dissolves in molten chlorides as CrO 4 2− because pO 2− of the molten chlorides tends to have a small value due to the effect of water vapor contained in the combustion gas. From the result of the solubility measurement, the addition of molybdenum and/or silicon was expected to improve the corrosion resistance of alloys. Laboratory corrosion tests confirmed this expectation. However, the scale analysis suggested that the effect of molybdenum could not be explained completely by only the mechanism derived from the result of the solubility measurement.

Corrosion behavior of nickel alloys in wet hydrofluoric acid

Hydrofluoric acid is a water solution of hydrogen fluoride (HF). Hydrofluoric acid is used widely in diverse types of industrial applications; traditionally, it is used in pickling solutions in the metal industry, in the fabrication of chlorofluorocarbon compounds, as an alkylation agent for gasoline and as an etching agent in the industry of glass. In recent years, hydrofluoric acid has extensively been used in the manufacture of semiconductors and microelectronics during the wet chemical cleaning of silicon wafers. Hydrofluoric acid can be considered a reducing acid and although it is chemically classified as weaker than, for example, sulfuric or hydrochloric acids, it is extremely corrosive. This acid is also particularly toxic and poses greater health hazard than most other acids. The corrosion behavior of metals in hydrofluoric acid has not been as systematic studied in the laboratory as for other common inorganic acids. This is largely because tests using hydrofluoric acid cannot be run in standard equipment and because of the toxic nature of this acid. Moreover, short-term weight loss laboratory corrosion tests in hydrofluoric acid can be frustrating since the results are not as highly reproducible as in the case of other acids such as sulfuric or hydrochloric. Onemore » of the reasons is because hydrofluoric acid commonly attacks the coupons used for testing in a non-uniform manner. That is, the corrosive power of this acid is not aimed to uniform thinning but mostly to localized penetration below the skin of the metal in the form of thin cracks, voids, pits, trenches and sometimes intergranular attack. Figure 1 shows the cross section of a coupon of Alloy 600 (N06600) exposed for 336 h to the vapor phase of a solution of 20% HF at 93 C. In cases where internal penetration occurs such as in Figure 1, it may not be recommended to use corrosion rates based on weight loss for material selection.« less

Design of accelerated corrosion tests for electronic components in automotive applications

Two new accelerated laboratory corrosion tests for electronic components in automotive applications have been developed, based on the use of metallic copper as a meter for corrosivity. The accelerated tests are designed so that they reproduce the same kind of corrosion effects as observed with exposure of copper in real vehicle environments. The test cycle that best simulates the corrosion characteristics of an engine compartment is composed of the following steps: a) exposure to neutral salt spray for 2 h; b) drying at 23/spl deg/C and 50% RH for 22 h; c) exposure to a test atmosphere of 1.5 ppm NO/sub 2/ and 0.5 ppm SO/sub 2/ at 25/spl deg/C and 95% RH for five days; d) drying at 23/spl deg/C and 50% RH for one day. The predominating corrosion products of copper, formed both during service exposure and in the accelerated test, are Cu/sub 2/O and Cu/sub 2/Cl(OH)/sub 3/, with a small amount of sulphur-containing corrosion products in the form of sulphates. In terms of corrosivity of copper, a test duration of six weeks corresponds to 7.5 years of exposure in the reference engine compartment selected for this study. The test cycle designed for the passenger compartment contains the steps: a) exposure for five days to a test atmosphere of 10 ppm NO/sub 2/ and 95% RH at 35/spl deg/C, followed by b) drying at 23/spl deg/C and 50% RH for two days. In this case, Cu/sub 2/O is the predominating corrosion product. In terms of corrosivity of copper, a test duration of four weeks corresponds to 7.5 years of exposure in the reference passenger compartment of this study.