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Steel
ABSTRACT Corrosion monitoring tests were carried out to examine the applicability of electrochemical techniques into corrosion control at a fossil power plant operated with Oxygenated Treatment (OT). A once-through type subcritical pressure boiler was employed to corrosion monitoring tests, and its electric capacity is 125 MW. An autoclave system was installed at the inlet of the economizer. The temperature and pressure in the autoclave were maintained at 215 °C and 7 MPa in the case of the full load operation. The corrosion rate of carbon steel was measured under the oxygenated water condition and All Volatile Treatment (AVT) condition using a modified galvanic couple electrochemical technique and the polarization resistance method. The galvanic current and the polarization resistance were varied with the daily load fluctuations of the plant and were corresponded with the corrosion rate of carbon steel obtained from weight loss measurements. These electrochemical measurement test results suggest that these techniques are applicable to the corrosion monitoring under these conditions, and that the galvanic couple method has advantages compared with the polarization resistance method in respect to the accurate and the instantaneous corrosion rate measurement. INTRODUCTION Carbon steel is widely used for main components of the feedwater and boiler systems in fossil power plants. The OT method as the feedwater treatment has applied for once-through boilers to prevent the corrosion of carbon steel. The OT method was developed in Germany and it has been utilized in Europe as well as Russia since the early 1970s 1~2~. Japanese and United States utilities have been applied this water treatment since the early 1990s3~4( The OT has several benefits compared with the AVT as follows: ? Decrease of iron contents in the feedwater ? Mitigation of the boiler pressure drop ? Suppression of boiler scale formation According to the practical operation experiences, the successful results were reported ~ as mentioned above, but the in-situ data on corrosion rate was not reported, because of difficulties that the conditions of the feedwater system are high temperature (over 150 °C ) and high pressure (over 20 MPa). Therefore, if the information on the corrosion rate of carbon steel in feedwater system was obtained instantaneously, it could be possible to adjust the water treatment to a favorable condition. For the first step of this purpose, this study was conducted to investigate the applicability of electrochemical corrosion measurement techniques such as galvanic current and polarization resistance in feedwater system operated with OT. EXPERIMENTAL PROCEDURE Specimen The material used for the experiments is carbon steel which is used as the boiler and heat exchanger tubes. Table 1 shows the chemical compositions of the specimen. The specimen was cut from the tube to 15mm(width)x50mrn(long)x2mm(thickness). They were polished with emery papers, and then rinsed with acetone. Test facility The corrosion tests and electrochemical measurements were conducted at the inlet of the Economizer of the fossil power plant in Hokkaido Electric Power Company. This unit is a coal-fired once-through boiler and the electric capacity is 125MW. Figure 1 shows the schematic diagram of the test facility. Because of the high temperature (about 230 °C ) and the high pressure (about 23 MPa), the pressure was regulated under than 8 MPa using decompression equipment with capillary system during the test period. Test conditions Table 2 shows the test conditions. The corrosion behavior of carbon steel under the two kinds of water conditions, that is, OT
- Research Report > New Finding (0.49)
- Research Report > Experimental Study (0.34)
- Materials > Metals & Mining > Steel (1.00)
- Energy > Power Industry (1.00)
- Energy > Oil & Gas > Upstream (1.00)
ABSTRACT The purpose of the present study was to develop the optimum processing condition to improve sulfide stress corrosion cracking (SSCC) resistance for line pipe steels. The effects of alloying, slab reheating temperature, water cooling pattern and coiling temperature on microstructure, hydrogen induced cracking (HIC) and SSCC sensitivities, and mechanical properties were analyzed. The mechanism of SSCC was studied by a dead weight tensile test as well as a constant elongation rate test method. The maximum contents of Mn and P showed the best relationship with the HIC sensitivity, and the mean contents of P and S were the secondary factor. The HIC and SSCC sensitivity of Nb-V-Ti added steels were better than those of Nb-V added steel. However, the addition of Cu and Ni that has been used to HIC resistant steels in the weak acidic solution (pH=4.8-5.4) was not helpful in the strong acidic solution (pH=2.5-3.8). The HIC sensitivity was increased as slab-reheating temperature (SRT) was decreased from 1250°C to 1150°C. The HIC sensitivity was increased due to the formation of coarse ferrite grains as the cooling rate was reduced. Anodic or cathodic polarization at about +100mV resulted in reducing the SSCC resistance, which was explained by a model related to anodic dissolution and hydrogen embrittlement. The SSCC mode could be classified into stress corrosion cracking (SCC) and stress oriented hydrogen induced cracking (SOHIC) and the former that was formed in the lower strength steels showed lesser threshold strength level. The reason of SCC formation was attributed to the mixed grain structure and grain boundary film cementite. The SSCC resistance was superior when the acicular ferrite structure was formed. HSLA steel, Line pipe steel, Hot strips, H2S gas, HIC, SSCC, CLT, SSRT, Hot rolling Conditions INTRODUCTION In recent years, requirements for line pipe have become progressively more sophisticated in order to cope with severe environments such as arctic weather and offshore conditions J. Together with UOE and seamless varieties, high frequency electric resistance welded (ERW) line pipe has been used increasingly in natural gas and petroleum service. Hot strips for ERW line pipe are required to have not only high strength but also excellent resistance to HIC and superior field weldability. In particular, the steel must resist both HIC and SSCC. These forms of corrosion damage can lead to the ultimate failure of the pipeline and to the subsequent release of poisonous hydrogen sulfide gas into the environment. To prevent the failure of a pipeline by either HIC or SSCC, oil and gas companies must exercise considerable care in the selection of materials for sour service. Consequently, steelmakers must produce skelp with low sulfur levels and with minimum centerline segregation and microstructural banding. In addition, they must utilize inclusion shape control techniques to promote spheroidization of nonmetallic inclusions. Pipemakers need to employ strict quality and process controls to ensure product integrity. This paper describes the improvement of the technology of manufacturing hot strips for ERW line pipe with high strength and high resistance to HIC and SSCC, which has been confirmed by laboratory tests. Typical production results of line pipes for sour gas environments are also presented. EXPERIMENTAL PROCEDURE Materials Preparation Some of the steels used in this investigation (No. A, B, and C) were prepared by vacuum induction melting and were casted as 50 kg ingots and the others were produced as continuous catsted slabs by mill trials. The detailed chemical compositions of the steels used are shown in Table 1. Steel No. A, B, and C are hot-rolled
- Materials > Metals & Mining > Steel (1.00)
- Energy > Oil & Gas > Upstream (1.00)
ABSTRACT Crack tip opening displacement (CTOD, 8) tests were carried out in buffer solutions, sand and clay to evaluate initiation of hydrogen stress cracking (HSC) at surface defects in buried pipelines under cathodic protection. Four series of line pipe steels and seam welds showed a similar tendency in cathodic current density (i) versus the critical CTOD ( 8 c ) curves, irrespective of types, pH and water content of the soils; 8c showed a minimum ( 8nsc ) when i>i~h (i,,-~1 mA/cm ~) in all the testing conditions. The critical CTOD with cathodic protection, 8use,, increased with increasing the critical CTOD in air, 8c. HSC could initiate at surface defects in pipelines only when i>i,h and 8 ~ 8use. INTRODUCTION Cathodic protection (CP) is one of the important factors in the behavior of buried gas transmission pipelines. When the cathodic current density for CP is considerably large (so-called "cathodic overprotection"), hydrogen atoms are generated electrochemically on coating defects ("holidays") in pipelines. The pipelines absorb a part of the hydrogen atoms generated at the holidays. The absorbed hydrogen atoms could cause hydrogen stress cracking (HSC) if a sufficiently large tensile stress is applied to the pipelines. HSC is, therefore, one of the major concerns in the maintenance of buried gas transmission pipelines. Groenveld reported that mechanical (static tensile stress), environmental (cathodic overprotection) and material (hardness) conditions were necessary for HSC in pipelines ~. By means of slow strain rate testing (SSRT) with tensile bar specimens, Kasahara and lsowaki clarified the effect of hardness on HSC; line pipe steels had high HSC susceptibility when their hardness was larger than a critical hardness". They concluded that HSC could hardly initiate in the pipelines free from hard zones which had smooth surfaces. Based on this conclusion, they recommended the maximum allowable hardness for pipelines to prevent initiation of HSC. Leaks attributed to HSC occurred in regions of mechanical damage in pipelines in service, as the result of hydrogen atoms generated by cathodic overprotection. A failure analysis showed that the regions of these leaks was free from hard zones. These leaks indicated that the effects of mechanical damage on HSC in pipeline should be clarified. To evaluate the effects of defects on the integrity of steel structures quantitatively, fracture mechanics is generally employed. Although sustained load tests were carried out using notched bar specimens ' previously, a fracture mechanics-based study was yet to be conducted for HSC in regions of mechanical damage in pipelines. The objective of the present research program was to study initiation of HSC in regions of mechanical damage, in particular, surface defects in pipelines under CP by means of fracture mechanics. The present program employed crack tip opening displacement (CTOD) testing 4 , one of the elastic-plastic fracture mechanics (EPFM) techniques. In this program, Hagiwara and Oguchi reported the following results of CTOD testing for four series of base metals of X65 line pipes under CP in buffer solutionsS-6; 1)Initiation of HSC at surface defects could be evaluated with a critical CTOD, 8c. 2) Under cathodic overprotection, 8 c was dependent on the CTOD testing rate, that is, the strain rate; a" c decreased with decreasing CTOD testing rate. When the CTOD testing rate was equal to or less than 0.01 ram/rain, o"c depended less on the testing rate. From this result, it was inferred that quasi-static stress due to internal pressure and ground subsidence could cause HSC but that dynamic stress due to earthquakes and ground liquefaction could hardly cause HSC. 3) 8 c was d
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (0.54)
- Energy > Oil & Gas > Midstream (0.94)
- Materials > Metals & Mining > Steel (0.91)
A Comparison Between Simultaneously Performed Measurements of Electrochemical Noise and Mechanical Parameters on Tensile Test Specimens During SRLT Tests
Leban, Mirjam (University of Maribor) | Dolecek, Valter (University of Maribor) | Legat, Andraz (Slovenian National Building) | Kuhar, Viljem (National Building & Civil Institute)
INTRODUCTION ABSTRACT The main aim of this study was to characterize EN measured during cracking processes, and to compare it with simultaneously measured mechanical changes. Electrochemical noise (EN) measurements have been performed using three electrodes made from the same piece of AISI 304 stainless steel, in one case of the sensitized and in the other case of the non-sensitized type. One of the electrodes, which was subjected to a constant, slowly increasing load (the SRLT test) acted as a working electrode. Measurements of the extension of a tensile test specimen were performed simultaneously with the EN measurements. The experiments were carried out in a diluted solution of sodium thiocyanate, under open circuit potential conditions, at room temperature. After the yield point was reached, current and voltage spikes, as well as extension "jumps", were detected, all of them appearing at the same time. This is clear proof that cracking processes can be detected reliably by means of the EN method. The time series of the rate of tensile test specimen extension (so-called crack velocity) were calculated by means of a simple differential equation from the extension time series. The crack velocity maximums, which coincide with the characteristic EN fluctuations, were then compared with the amplitudes of these fluctuations. The results of the comparison indicated that the amplitudes of the electrochemical noise spikes are linearly dependent upon crack velocity. Stress-corrosion cracking (SCC) is well-known as an unpredictable corrosion process, which causes delayed failures of structures and their components. From the initiation of the crack to final failure a long time, known as the propagation period, can elapse. In many cases, cracks grow without the appearance of any outward visible damage. In recent years, much research work has been directed towards the development of a system which would be able to detect stress corrosion cracks at an early stage in their propagation, and thus help to predict the life-time of metal structures. Standardized electrochemical methods (e.g. potentiodynamic polarization reactivation) and mechanical methods (e.g. various modifications of the Slow- Strain-Rate-Test - SSRT test) can be used to determine the basic characteristics of the materials being investigated, e.g. susceptibility to SCC, and the time to final failure. They cannot, however, be used to detect the initiation and/or propagation of stress-corrosion cracks ~' 2). Over the last two decades electrochemical noise measurement (EN) <3) has proved to be one of the most promising methods for detecting uniform and localized types of corrosion (metastable pitting, pitting corrosion, crevice corrosion) (4m. Since EN measurements can be performed in a freely corroding system without the application of an external electrical source, the corrosion processes are not accelerated as they are during the application of other commonly used electrochemical methods (e.g. potentiodynamic polarization, electrochemical impedance spectroscopy - EIS). Because of this, the spontaneous evolution of corrosion processes can be satisfactorily monitored. Among the various types of corrosion, the detection of SCC by means of EN measurements has received considerable attention °°lg~, although these studies are still relatively rare. In the middle of the 1980's, Newman and Sieradzki °°" ~) were the first to detect simultaneous fluctuations of electrochemical current noise and discrete acoustic emission events during SCC processes, which were consistent for experiments performed on cA-brass specimens, and not so consistent for experiments performed on stainless steel specimens. In the same period Cottis and Loto published two pap
- Materials > Metals & Mining > Steel (0.66)
- Energy > Oil & Gas > Upstream (0.55)
ABSTRACT Fireside corrosion in kraft recovery boilers is a continuing problem in the pulp and paper industry, especially in the boilers using carbon steel tubes in lower furnace areas. Certain areas in the lower furnace of kraft recovery boilers consistently have higher corrosion rates than the nearby areas. As the tube material in these areas is the same, differences in the corrosion rate suggest that the local environmental conditions in the two areas are different. Corrosive environments were characterized in a kraft recovery boiler, which had well-defined areas with high corrosion rates and low corrosion rates. Three important variables, tube surface temperature, gas composition at the waterwall surface, and smelt composition were monitored in the selected areas. Recovery boiler gases were analyzed using an on-line gas chromatograph. Waterwall temperature and smelt did not have any effect on differences in the corrosion rate in the two areas. Gas compositions were found to play a predominant role in corrosion behavior differences in the lower furnace of kraft recovery boilers. Results from this work have shown that the local environments can be very different at the waterwall surfaces in a given general area leading to differences in the local corrosion rates. INTRODUCTION During kraft pulping process, wood chips are cooked in sodium sulfide containing caustic solution, called white liquor. In this process the lignin is fragmented into smaller segments whose sodium salts are soluble in the cooking liquor, leaving cellulose and hemicellulose in the form of intact fibers needed for papermaking (1). Resultant liquor with dissolved organics is called black liquor due to its color. The black liquor is concentrated and fed into the kraft recovery boiler through liquor guns. Burning of organic constituents of the black liquor produces heat in the boiler. In the process oxidized sulfur is reduced to sulfide and the inorganic chemicals are recovered to be used in pulping cycle. Heat energy is recovered through heat transfer and steam generation through waterwall tubes. The lower furnace of the boiler, below tertiary air-ports, has a reducing-sulfidizing environment. Carbon steel is generally used for waterwall tubes in the low-pressure boilers with saturated steam temperatures around 260oC or lower. However, the waterwalls in the lower furnace area of high-pressure boilers are now constructed with 304L stainless steel/carbon steel composite tubes. Stainless steel (304L) outer layer provides better corrosion resistance under high temperature reducingsulfidizing conditions compared to the carbon steel. Although sulfidation problems in the lower furnace have largely been controlled with the use of composite tubes, the 304L composite tubes have other corrosion problems, which will not be addressed in this paper. The most important factor concerning corrosion and integrity of waterwall tubes is that water leakage into the char-bed, at the bottom of the boiler, can lead to potentially destructive explosions. Therefore, fireside corrosion in the lower furnace region is a safety concern for the pulp and paper industry. New materials for waterwall or protective coating matrials can be effectively identified and applied to mitigate the corrosion if the factors causing this corrosion are understood. Previous work, reviewed by different authors (2-5), has shown that fireside corrosion of waterwall tubes in the lower furnace region is primarily due to reactions of tube material with hot sulfurbearing gases. Generally, the rate of corrosion for the carbon steel in the lower furnace area of recovery boilers is around 0.05 mm per year or lower, but corrosion rates of carbon steel tubes have been repo
- Materials > Paper & Forest Products (1.00)
- Materials > Metals & Mining > Steel (1.00)
- Energy > Oil & Gas > Upstream (1.00)
ABSTRACT Soil stress and cathodic protection shielding problems of tape coatings have been two of the most discussed problems in the pipeline industry. The challenge to develop a tape coating system that helps mitigate these problems was taken by one company approximately ten years ago. This particular tape coating system has a woven geotextile fabric backing (soil side) over a compound composed of a rubber modified bitumen. This tape system is cold applied by wrapping over a properly prepared and primed pipe surface and has been successful in overcoming many of the problems associated with soil stress and CP shielding. INTRODUCTION The failures associated with tape products have caused many pipeline companies to stop using any cold applied tape products for coatings. One company has developed and continues to test, improve and further develop a tape product that helps to eliminate many of the problems associated with tape coatings. This product has been on the market for ten years and has been successful in field use. Tape coatings have been used for approximately 50 years to protect pipelines from external corrosion. They are usually more economical than other coating systems and are easy to apply in plant and field applications. There have been a wide variety of tapes used for pipeline coatings. Most cold applied tapes are composed of a solid film backed polyolefin laminated with an adhesive compound to adhere the backing to the pipe surface. Some tapes are manufactured with a separator sheet between tape layers to prevent the compound bonding to the backing during manufacturing and storage. Those tape products that do not have a separator sheet between layers require the "memory" properties of the stretchable film carrier as the primary agent for overlap adhesion. If this type tape is not properly applied the overlap adhesion may not be sufficient. In conditions where soil stress, loss of adhesive compound or disbondment occurs, many tape coatings have failed to properly protect the pipe. DISBONDED COATING AND CATHODIC PROTECTION SHIELDING Many of the external corrosion problems on pipelines are caused from coatings that have disbonded (lost adhesion to the steel) allowing water to penetrate between the coating and the pipe steel. If the coating shields the cathodic protection currents, corrosion can become a serious problem. Disbonded coating provides an electrical shield, limits the current distribution to the exposed metal surface, and harbors a corrosion environment different from that at the holidays i. If a holiday is present in the coating, cathodic protection currents can provide some protection to the steel where it is exposed at the holiday. In low resistant electrolytes or where the coating damage is large, some protection can be provided under the disbonded coating. Many times coating disbondments have very few holidays or openings for CP to enter and provide protection, but many times water can penetrate these shielded areas. Corrosion can occur despite apparently adequate pipe-to-soil potentials". Solid film polyolefin backed tape, shrink sleeves and some other coatings that have disbonded are subject to this condition. Electrical resistance of PE (polyethylene) coatings and their susceptibility for an unbonded installation creates a serious problem on pipelines, iii A basic rule is to assume that cathodic protection can only protect what it can "see". If the steel is exposed to the same electrolyte as the CP anode and the protection level is adequate the steel will be protected. There are several reasons why tape coatings (and many others) disbond. Among these are: Soil stress Improper application Improper surface preparation
- North America > United States (0.28)
- North America > Canada (0.28)
- Energy > Oil & Gas > Upstream (0.90)
- Materials > Metals & Mining > Steel (0.55)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
ABSTRACT Electrochemical Impedance Spectroscopy (EIS) is a good tool to investigate the deterioration of coating on a metal. For gas pipelines, the equivalent circuit parameters in presence of disbonded coatings can be found in literature. Models parameters are coating thickness, and the area under disbonded coating. A coated pipeline can be modelled as a sequence of simple equivalent circuits, which can be handled using standard theory to yield the observed impedance in terms of the values for circuit elements in the line. The proposed model has been tested to verify its applicability for detecting corrosion sites in buried pipelines. The effect of a few geometrical and physical parameters has been investigated, and results have been compared with the output of laboratory and field measurements. In some cases, the adjustment of literature parameters has been enough to obtain a good correspondence; modification of the equivalent circuit have been however found necessary. Future work in this field is possible and promising, provided that the circuital model is modified following the results of the present study. INTRODUCTION Electrochemical Impedance Spectroscopy (EIS) is a well known technique to evaluate modifications in coated metals, when in contact with aggressive environments [1-4]. EIS has a great power in investigating corrosion processes occurring at the interface metal-environment [5]. EIS utilises a small alternate signal between the test electrode and the counter electrode, allowing the measure of the system response as Bode diagrams, Nyqist diagrams and/or phase diagrams. Results can be analysed modelling the pipe with an equivalent circuit and evaluating the single elements of the equivalent circuit. A typical use of EIS [6] is in investigating and/or monitoring the deterioration of coating on a metal. For low alloy steel coated with polyethylene, as in the case of gas pipeline, the equivalent circuit parameters in presence of disbonded coatings have been studied in laboratory and in field (limiting the experimental work to buried samples) [7-9]. EIS parameters give indications on the coating thickness, and on the ratio of the area under disbonded coatings with respect to the total sample area. The method gives information on the coating characteristics, and can follow the evolution of the coating properties during time. A buried pipeline can be modelled using a sequence of simple equivalent circuits, taking into account the presence of an inductive component, due to the length and shape of the pipe [ 10]. With this approach the equivalent circuit can be readily handled using standard circuit theory to yield the observed impedance in terms of the values for circuit elements in the line. On the other hand, the parameters which have an influence on the shape of the Bode diagram are more numerous in field than in laboratory; they change with time and with the distance travelled by the stimulus signal along the pipe. To obtain a feasibility study for a complete research program aimed at detecting and localising corrosion sites in buried pipelines via EIS [11], a simple circuital model dividing the pipe in sections has been used [12]. The proposed model has been tested with reference to the values of parameters of interest [ 13], to verify the effect of: ? dimension of the pipe (total section considered, and partial sections) ? nature of the coating (polyethylene and/or bituminous) ? distance and dimension of the damaged section ? nature of the damage (defect/disbonding) ? interferences due to: alternating currents and/or earth electrodes ? presence of rectifiers and/or insulating joints. Results of the model have been compared with the output of a few
- Energy > Oil & Gas > Midstream (0.54)
- Materials > Metals & Mining > Steel (0.34)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Piping design and simulation (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
ABSTRACT Six different heats were chosen from an archival data base of X52 pipeline steel using a statistical test design to evaluate the microstructure/microchemistry effects of S, P, and C. Crack growth measurements were carried out on compact tension specimens in the carbonate/bicarbonate environment at 75°C and potential control to evaluate the stage 2 crack growth rates and K~sc~. In general, the microstructure/microchemistry had a small effect on the SCC behavior. INTRODUCTION High pH stress corrosion cracking 1'2 in the pipeline industry follows an intergranular path in carbon steels. The environmental conditions that lead to cracking are a carbonate/bicarbonate environment (pH ~ 10 ), elevated temperatures ( ~ 75°C), and an electrochemical l~otential range of-0.60 to -.75 volts (vs ambient temperature calomel reference electrode). Bubenik et al. propose that all carbon steels are thought to be susceptible to SCC to some degree in this environment. Parkins 2'3'4 has made major contributions to understanding SCC processes in the pipeline industry. Most of his crack growth rate results have been by slow strain rate or tapered specimens, and he has defined the standard high pH test environment to be 1 N sodium carbonate + 1 N sodium bicarbonate at 75°C and a controlled potential of-0.65 volts (SCE). Parkins measures a crack growth rate in this environment of approximately 1E-7 crn/s. In one paper, Parkins et al. 4, examined a number of pipeline steel heats but did not extend their observations to the effects of the microstructure/microchemistry on the SCC process. Hunt 5 was the first to examine the effects of the carbon steel microstructure/microchemistry in the 1 N sodium carbonate + 1 N sodium bicarbonate (75°C) environment. He used a high purity 0.15% C steel that was doped with three levels of P, S, Sn, Cu or Ni. The high purity baseline case was 0.82% Mn, 0.004% P and 0.003% S. One of his heat treatments was 500°C for 48 hours to segregate impurities to the grain boundaries (GBs). The steels were evaluated for SCC performance by time to failure (ratioed to the baseline steel) using the slow strain rate technique (strain rate = 1E-6 s -l) . The specimens were polarized to the active-passive transition region determined by a potentiodynamic scan--the authors' reference electrode system was a silver, silver chloride system at 75°C which makes it different from that of others. The author reports that all the impurities were beneficial; that is, increased the time to failure. Hunt makes the observation that C decreases the resistance to SCC, but his experimental data does not confirm this observation since he did not change the carbon level. The author attempted to fracture the steels in the AUGER spectrometer in order to measure the level of segregation to the GBs, and in all cases, except the very high P steels, failed to get intergranular fracture. Asahi et al. 6 in a recent paper studied the effect of microstructure of modern steels (higher strength, lower carbon) in the standard 1 N sodium carbonate + 1 N sodium bicarbonate test environment. The studied materials involved line pipe steels including one X52, three X65 grades, and one X80 grade. Several laboratory manufactured steels with 0.02, 0.05, and 0.08% C (all 1.55% Mn) were also examined. Through controlled rolling, thermomechanical-controlled processing (TMCP) or quench and tempering, high strength microstructures were created for these steels. A tapered specimen was subjected to a triangular cyclic load (~lE-3 Hz, R = 0.7) where the maximum stress was at 100% of yield. After a certain number of cycles, the specimen was cross sectioned and the number and depth of the cracks determined as a function of the locati
- Well Drilling > Drilling Fluids and Materials > Drilling fluid selection and formulation (chemistry, properties) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (0.88)
- (2 more...)
ABSTRACT The objective of the research described in this paper was to evaluate the influence of the composition of the sparging gas on the electrochemical corrosion kinetics, hydrogen permeation, and crack growth behavior of a line pipe steel in a simulated near-neutral-pH cracking electrolyte. A series of potentiodynamic polarization experiments, Devanathan/Stachurski type hydrogen permeation experiments, and cyclic loading tests were performed with varying levels of O2 and CO2. Tests revealed that increasing the level of CO2 increased the corrosion rate at the free corrosion potential, increased hydrogen permeation, and accelerated crack growth during cyclic growth tests. Increasing the level of O2 had little effect on the corrosion rate at the free corrosion potential, decreased the rate of hydrogen permeation, and increased the crack growth rate in crack growth tests.
BACKGROUND
External stress corrosion cracking (SCC) continues to be an integrity concern for the natural gas pipeline industry. Two forms of cracking have been identified; namely high-pH SCC (also referred to as classical SCC) and near-neutral-pH SCC (also referred to as low-pH SCC). A characteristic of both forms of SCC is the presence of colonies of up to hundreds of longitudinal surface cracks in the body of the pipe that link up to form long shallow flaws. The fracture faces are covered with black magnetite or iron carbonate films. In the case of high-pH SCC, the cracking is intergranular and there is usually little evidence of general corrosion associated with the cracking. A concentrated carbonate-bicarbonate solution was identified as the most probable environment responsible for this form of cracking.(1, 2)
Near-neutral-pH SCC is transgranular and is associated with corrosion of the crack faces and, in some cases, with corrosion of the external surface of the pipe as well. This form of cracking occurs in near-neutral-pH (6
- Materials > Metals & Mining > Steel (1.00)
- Energy > Oil & Gas > Midstream (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.34)
ABSTRACT Biofilm monitoring on carbon and different stainless steel types was performed using a mobile mini-plant as bypass to an industrial water system in a 10 month experiment. Biofilms were analyzed for cell counts of MIC-relevant bacteria from the sulfur-/iron-/manganese-/nitrogen-cycle, microbial activity, and the content of corrosive elements (chloride, sulfur, manganese). Biofilms on carbon steel exhibited a higher microbial diversity, higher cell counts, and a higher microbial activity as on stainless steels. Chemoorganotrophic bacteria were the dominant group in the biofilm-biocoenosis. Although MIC-relevant bacteria like nitric and sulfuric acid producing bacteria, SRB, and manganese(II)ion oxidizing bacteria colonized the materials, steel samples were not affected by biocorrosion. The corrosion rates of all stainless steel types were below 0.01 mm/year. INTRODUCTION Almost every material can be colonized by bacteria. Microbial adhesion leads to biofilm formation resulting in biocorrosion of the material or biofouling. This causes a decrease in technical functionality of e.g. heat exchangers. Yearly costs for combating biocorrosion and biofouling are estimated to be 60 billions US $ for the USA and 20 billions US $ for Germany ~). Especially the chemical and the oil industry suffer from biocorrosion and biofouling problems. Several german companies of the chemical industry reported in the last decade failure problems with stainless steels which were thought to be resistant against MIC. In one case, stainless steel tubes (material: AISI 316 Ti), which were used in a cooling system with river water, showed after 3 month of commencement leackages at the welding site. The free corrosion potential increased for more than 600 mV (vs. H-electrode) and the pitting penetration rate was estimated to be 20 mm/year (21. The free corrosion potential decreased quickly after heating up the water to over 55 °C or after biocide addition. Nevertheless, the microorganisms which were responsible for the corrosion were not identifed. In a second case, nitrifiying bacteria were identified to be responsible for corrosion of steel (material: carbon steel, AISI 304, and AISI 316 Ti), which was used in a waste water purification plant. It was modernized by addition of a microbiological nitrification/denitrification unit. Failures and leackages were detected 6 month later ~3). The same problems with biocorrosion, especially of stainless steel, were reported from another chemical plant (4). The reports demonstrate the obvious need for testing and selecting steel types, which are resistant to biocorrosion and biofouling in order to reduce the costs for manufacters and operators. For this purpose different types of steels, which are commonly used in Germany, were tested in a research project between microbiologists of the University of Hamburg and corrosion engineers of the BAYER AG, Germany. The aim of the study was to investigate various steel types in industrial water systems for biofilm development and their susceptibility to biocorrosion and biofouling. For this a recently described mini-plant was used ~5) It can be connected as a bypass to water systems to monitor biofilm development and MIC on different metallic surfaces under identical conditions. This paper contains the first results on the composition of the biofilm community with relation to steel types and the suscebtibility against microbial attack. MATERIALS AND METHODS Materials Beside a common carbon steel a ferritic-austenitic and several austenitic stainlees steels were tested (TABLE 1). The stainless steel grades covered wide spread used material like AISI 304 and 316 types and high alloyed materials, which are considered to be co
- Europe > Germany (0.76)
- North America > United States > Texas (0.30)
- Water & Waste Management > Water Management > Water Supplies & Services (1.00)
- Materials > Metals & Mining > Steel (1.00)
- Materials > Chemicals (1.00)