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ABSTRACT A test apparatus, commonly used in the district heating market, has been successfully adopted to evaluate the functionality of various coating systems for their resistance to soil stress induced in the axial direction due to thermal changes in the pipeline. Coating systems investigated includes 2-layer polyethylene (2LPE), 3-layer polyethylene (3LPE), fusion bonded epoxy (FBE), cold-applied tape, heatshrinkable sleeve with mastic adhesive and heat-shrinkable sleeve with hot melt adhesives. The results showed that the most critical properties of a coating's ability to resist soil stress are the cohesive strength and strong adhesive strength. Coating systems with a softer adhesive component are more sensitive to soil stress, particularly at their exposed edges. However, the study shows that proper selection of the coating system can meet soil stress requirements. INTRODUCTION As the exploration of "energy" continues to expand its limits, so are the requirements for the coatings used in the corrosion protection of pipelines. It is understood that the best method for preventing corrosion on buried pipelines is to prevent the migration of corrosive species to substrate surface with the best available barrier coating. Unfortunately each coating system is a "compromise" of desirable properties and coating stability in soil is one of the many factors to consider in its development. A buried pipeline experiences various types of soil stress and magnitude depending on burial depth, soil type, soil compaction, wet and dry, freeze and thaw cycles, seismic activity, operating temperature, pipe size, etc. These stresses can be classified into four categories [1]: 1) Static load due to the soil and pipe weight. This is particularly troublesome with rocky backfill where coating damage can occur due to penetration; 2) Axial stress due to pipeline expansion and contraction 3) Circumferential stress due to pipeline lateral movement at bends 4) Random direction due to soil swelling and shrinkage caused primarily by clay soil during wet and dry cycles. The magnitude of the stress on the pipeline depends on the stress transfer function between the soil and the coating. When the coating strength is less than the stresses introduced by the soil, the coating will fail and lead to corrosion of the pipeline. One of the major contributors to soil stress is the axial stress induced by variation in pipeline operation temperature that results in pipeline expansions and contractions. Since most coatings are based on organic polymeric materials with temperature dependent mechanical properties, these thermal changes exacerbated the affect of soil stress and necessitated the use of much higher shear resistance products to withstand the mechanical stresses acting on the coating. While it is impossible to simulate the various conditions with a single test, the "soil box" described in this paper can definitely help when dealing with the forces acting exclusively along the longitudinal direction of the pipe caused by thermal expansion and contraction.
- North America > United States (0.47)
- North America > Canada (0.28)
- Materials > Chemicals > Specialty Chemicals (1.00)
- Energy > Oil & Gas (1.00)
- 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 ABSTRACT It is well-known that fiber reinforced composites made from glass-fibers are susceptible to both ageing effects and failure under constant loads (creep-rupture), particularly when exposed to water environments. There are very few experimental studies, however, which have dealt explicitly with the effect of exposure period (ageing) on the resulting creep-rupture response. Understanding this effect is particularly important when dealing with applications which are either delayed in entering full service or are being re-commissioned after some period of dormancy. In the current study, a preliminary examination is made to determine the influence of pre-conditioning period on the resulting time-to-failure curves for a glass-fiber reinforced epoxy system exposed to a water environment. Moisture absorption behavior and resulting failure characteristics are presented. INTRODUCTION Fiber reinforced polymer (FRP) composites are seeing increased application in the infrastructure sector for both new construction and rehabilitation due to their reduced weight and ease of installation. For large structural applications, glass-fiber composites are being considered due to its relative lower cost compared to alternative fiber systems. One of the major issues, however, is understanding and quantifying the durability of these material systems under long-term environmental exposure. While the effect of environment on the mechanical durability of fiber composites has been extensively studied, a number of questions still remain. From the literature, two degradation modes have been identified in glass-fiber composites: 1) ageing [1-3], and 2) creep-rupture (CR) [4-6]. Both are associated with a decrease in mechanical strength over time with exposure to a given environment. The former occurs without the application of applied stress to the material (ageing), while the latter is associated with damage under constant loads (CR). For both damage modes, the level of degradation is a function of the specific composite material system (matrix and fiber), the fiber interfacial properties, and the exposure environment (chemistry and temperature). Ageing of composite materials is most often evaluated by performing simple tensile tests (monotonic loading conditions) on samples which have been pre-exposed to particular service environments. While this method is simple, inexpensive and provides a direct measure of residual strength with exposure time, it is unclear whether the results are a sufficient measure of long-term durability. For applications where the material is also subjected to sustained loading conditions (in conjunction with exposure), creep-rupture testing is most commonly employed. The main disadvantage with these tests is increased cost and complexity. In general, strength loss in glass-fiber reinforced polymers is increased by exposure to aqueous solutions and elevated temperatures [1-6]. Under immersion conditions, most glassfiber composites will absorb water leading to degradation of the polymer matrix or to the fibermatrix interface. When superimposed loads are applied during immersion, further degradation of mechanical strength occurs due to stress corrosion cracking of the glass fibers [4-6]. The interaction between these two degradation mechanisms, however, is not fully understood. The objective of this study is to investigate the effect of moisture pre-conditioning (ageing) on the resulting creep-rupture behavior of a glass-fiber polyester composite system.
ABSTRACT It is today well known that low temperature creep or relaxation plays an impoftant role in the failure mechanism for hydrogen embrittlement of duplex stainless steel subject to cathodic protection. Avoiding low temperature creep or relaxation during service has been one important principle in recent design recommendations in order to avoid hydrogen embrittlement. Low temperature creep and relaxation experiments at room temperature have been performed for stainless steels at relevant stress levels for hydrogen ernbrittlement. The creep experiments were performed with dead weight creep test equipment normally used for testing at high temperatures. For the same materials relaxation was also investigated at lower load levels. The results may indicate that there is a difference in ranking of the alloys between the influence of low temperature creep and relaxation. The austenite spacing in the duplex microstructure seems to be an important parameter for the resistance against hydrogen embrittlernent of duplex stainless. The fine grained materials with smaller austenite spacing have better resistance. The low temperature creep behavior is different between fine grained duplex and coarser material. For the investigated bar material with larger austenite spacing, the low temperature creep is present a lower load levels than for the extruded tube material with smaller austenite spacing. The results indicate that straining i.e. due to low temperature creep is needed in order to promote HISC. However, even if creep is present HISC does not need to be initiated. One explanation could be that enough stress concentration is needed, which is probably an influence by size of the ferrite areas. INTRODUCTION Some failures due to hydrogen embrittlement during the last years have resulted in two documents with new recommendationsfor design in order to avoid hydrogen embrittlement on duplex stainless steels when subject to cathodic protection in seawater. In those documents a prime factor is to avoid low temperature creep b designing the load conditions to stress or strain levels where low temperature creep is not present . These levels are based on experiences from the industry. In a guideline it is stated that duplex stainless steel experiences "cold creep" at stresses below the yield strength of the material .To the knowled e of the author there is only a few publications on low temperature creep and duplex stainless steels . Linder et al, made a study at 100°C, Woolin with coworkers during a constant load tests and Festen et al. made experiments with duration of 12 hours. These studies show that duplex stainless steels can be subject to low temperatures creep. The study of Festen et al. showed the low temperature creep behavior is different for diierent load levels. Low temperature creep occurs when a material is subject to a constant load that results in that the material will deform plastically during time and thus expand. A linked process is relaxation where a material is subject to a constant strain. Also for relaxation of duplex stainless steel there is limited data available.
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- North America > United States (0.29)
ABSTRACT ABSTRACT During the last 10 years, failures have occurred in duplex stainless steels in subsea applications. When the duplex stainless steels are cathodic protected, the hydrogen concentration on the surface increases significantly and when combined with stress, failures and cracks can occur due to hydrogen embrittlement. This study is a part of a larger test program covering hydrogen embrittlement in different duplex stainless steel grades and different product forms. So far, it has focused on UNS S32750. Materials have been tested using a constant load with dead weight, a potential of -1050 mV (SCE) and a low temperature, 4°C. The different product forms included in the test program were small and large diameter bar, extruded and welded tubes. In addition to investigate the different product forms, the objective was also to further investigate how the phase size in different product forms affects susceptibility to hydrogen embrittlement. Different loads were applied, relating to the material?s yield strength (Rp0.2) at 4°C. The results showed that the small diameter bar achieved a load of at least 120% of the Rp0.2(4°C). The large diameter bar managed 84% but failed at 93%. The extruded tube achieved at least 130% and the welded tube 120%. No crack initiations were observed, except in the failed specimens of large diameter bar. The difference in austenite spacing between the small bar and large diameter bar is a good indication of the test results achieved. The small bar material had an austenite spacing of 15 µm and the larger bar 32-51 µm. The fracture surface indicated brittle behavior and transgranular cleavage in the ferrite phase, which is observed typically in Hydrogen Induced Stress Cracking (HISC). It was also clear that the cracks are arrested in the ferrite/austenite boundaries and how important the microstructure and austenite spacing are to the susceptibility to HISC and its mechanism. Further studies are in progress for UNS S32205, UNS S32906 and newer super duplex stainless steel and they will be investigated using the same methodology. INTRODUCTION Duplex stainless steels have been used for over 20 years in subsea equipment exposed to cathodic protection. Failures, due to hydrogen embrittlement, have occurred during the last 10 years, which has prompted discussion about whether duplex stainless steels are suitable for this application. New guidelines have been drawn up to avoid future problems. Three conditions have to be fulfilled for hydrogen embrittlement to occur; there has to be a hydrogen source, tensile stress must be present and the material has to be susceptible to hydrogen. The failures that have occurred have been caused by one or a combination of the following - very high loads, large grain sizes, intermetallic phases and/or high ferrite content in a weld. In subsea applications, duplex stainless steels are under cathodic protection (typically -1000 to -1100 mVSCE) because they are connected to carbon and low alloy steel structures. As a result, water reduction increases and atomic hydrogen is generated on the steel surface. Hydrogen on the surface can diffuse into the material and cause embrittlement, especially when combined with stress, so called HISC.
ABSTRACT Elastomeric vinyl esters have been available for many years to bond corrosion resistant composites and to manufacture resilient parts such as kayaks. These polymers normally have an elongation from 7% to 20%. A fire retardant, elastomeric bisphenol A vinyl ester resin has been developed for similar types of applications and also for military vehicles, etc. Liquid and cast resin properties plus fire retardant test results will be presented. INTRODUCTION The main thrust for the development of a fire retardant elastomeric, bisphenol A, vinyl ester (FREBA) resin was military vehicles. It was also thought that an elastomeric composite would have better resistance to ballistic damage but this paper will focus on the mechanical properties of a casting, composite and fire retardant properties. The fire retardant test that was performed was ASTM E 84 since it is a standard test and widely recognized. ASTM E 84 requires that the composite be a minimum of 45.7 cm (18 inches) wide by 7.3 meters (24 feet) long. ASTM E 84 values are compared in burning characteristics to a mineral fiber cement board, which is rated 0, and a red oak board that is rated 100. To meet an ASTM E 84 class I rating, the laminate in question must have an ASTM E 84 rating of 25 or less. EXPERIMENTAL The new fire retardant elastomeric bisphenol A vinyl ester resin was formulated to a low viscosity and a long gel time in order to infuse large parts for military vehicles. Liquid properties were tested with standard equipment and methods that are typically used in the industry. Mechanical testing was completed on a casting, three plies of 450 grams per square meter (1.5 ounce per square foot) chopped strand mat composite and another made with 2 plies of 569 grams per square meter (24 ounce per square yard) woven roving with 225 grams per square meter (0.75 ounce per square meter) chopped strand mat between the two woven roving plies. The composite tested according to ASTM E 84 was made with 2 plies of 24 ounce woven roving with 225 grams per square meter (0.75 ounce per square meter) chopped strand mat between the two woven roving plies. Composites were post-cured at 82°C for four hours and shipped to an outside laboratory for ASTM E 84 testing. See Table A for liquid properties details, Table B for cast preparation method, and Table C for cast mechanical properties, Table D for composite mechanical properties and Table E for ASTM E 84 results. FREBA has been in production for three years and shelf stability of the resin has been monitored. RESULTS AND DISCUSSION 1) Resin liquid properties are typical of other vinyl ester resins formulated to a long gel time. 2) Casting mechanical properties indicate that the elongation is 12% and the heat distortion is 216°F/102°C, which is unusual.Normally resins with 12% elongation have a much lower heat distortion.
- Materials > Chemicals > Specialty Chemicals (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.78)
ABSTRACT Low C - 13%Cr martensitic stainless steels have been widely used in the oil and gas industries because of their high strength and excellent corrosion res istance in corrosive conditions. Recently, higher strength(over 110 ksi grade ) corrosion resistant alloys have been requested from users. Nb addition is consider ed to be one of the most appropriate strengthening methods. In this paper, the strengthening of low C - 13%Cr martensitic stainless steel is examined. The e ffect of Nb addition on mechanical properties and corrosion resistance of low C - 13%Cr martensitic stainless steel i s discussed. An optimized chemical composition i s also studied. INTRODUCTION Martensitic stainless steels have been widely used for OCTG (oil country tubular goods) because they have high strength and excellent corrosion resistance in CO2 gas wells[1-13]. Recently, much attention has been paid for application of these steels in light sour environments as a partial substitute for 22%Cr duplex stainless steels . Lower C and higher Ni and Mo compared to Type AISI 420 (13%Cr - 0.2%C) steels are the basic modified points , and these grades are called super 13%Cr martensitic stainless steels. Lower C and higher Ni contents lead to high toughness. Therefore, it was possible to achieve high strength steels. Super 13%Cr martensitic stainless steel, whose h ardness and yield strength were HRC27 and 730MPa maximum respectively, has been registered in NACE MR0175. Super 13%Cr martensitic stainless steels showed no significant effect of strength on SSC resistance . These reported studies were limited to its strength up to 110 ksi grade( 758 -861MPa YS ). In this paper, higher strength steel than existing steels was focused. Nb addition combined with high tempering temperature was examined for development of 125 ksi grade( 861-965MPa YS ). Optimization of chemical composition was also studi ed. EXPERIMENTAL PROCEDURE Tests were conducted to clarify the following objectives; to examine the effect of Nb on ability to reach the required strength with a high tempering temperature, to see how the stee ls with high tempering temperature behave in SSC tests, to see how combination of Nb and C contents affects the strength achieved with the higher tempering temperature. Materials. : First melt was conducted to confirm effect of Nb addit ion on mechanical properties and corrosion resistance. Six kinds of laboratory melted alloy with changing Nb content from 0 to 0.09% were used. Chemical composition range of laboratory melted alloy s is listed in Table 1. Quenching temperature was 920 degree C. Tempering temperature was 525 - 700 degree C. : Second melt was conducted to optimize chemical composition of the developed steel. Six kinds of laboratory melted alloy with changing Nb content from 0 .02 to 0.03% and C content from 0.01 to 0.05% were used. Chemical composition range of the second laboratory melted alloy s is listed in Table 2. Quenching temperature was 920 degree C. Tempering temperature was 525 - 700 degree C.
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- Asia > Middle East > Saudi Arabia (0.47)
- Materials > Metals & Mining > Steel (1.00)
- Energy > Oil & Gas (1.00)
ABSTRACT This paper describes a new method for the non-destructive detection of graphitization corrosion in gray iron pipe, based on magnetic flux density measurements. Graphitization corrosion is unique to gray cast iron, which comprises much of the municipal water distribution infrastructure in the United States. Graphitic corrosion is particularly insidious in that graphitized pipe may appear perfectly sound upon visual inspection, despite being embrittled and prone to premature failure under load. INTRODUCTION Graphitic corrosion, or graphitization, occurs when the metallic constituents of gray iron are selectively removed or converted into corrosion products. This process leaves behind the graphite matrix of the gray iron, in the shape of the original casting. While pipes undergoing graphitization may appear sound and may conduct water adequately, the metallic portion of the pipe wall may, in places, be significantly thinner than the apparent thickness of the wall. Graphitized regions of pipe wall will be brittle and subject to failure under load as the result of temperature variation, heavy traffic, or shock. Water main failures are very expensive for municipalities. Not only do they incur expenses in terms of repair, flooding damage, and loss of revenue to affected businesses, but water main failures can potentially interrupt the operation of vital services including medical care and fire fighting operations. Currently, millions of dollars are spent annually by industry and municipalities on the repair of failed gray iron pipe. The rate of failure will only increase in the future as the existing gray iron infrastructure continues to age. Therefore, it is important to develop a sensing technique that will allow for the non-destructive detection of graphitization before failures occur. This will enable repair of graphitized pipe to be undertaken before failure, and so minimize the expense incurred due to corrosion in the water distribution infrastructure. BACKGROUND Gray Iron Metallurgy Krause1 has discussed the metallurgy of gray iron in detail. The most important elements in gray cast iron, aside from iron, are carbon and silicon. The silicon content affects the carbon distribution in the metal. Unlike the carbon in ductile iron and steel, which is disbursed as graphite spheroids and pearlite, respectively, the carbon in gray iron is present in flake form. These flakes form in the eutectic cell boundaries during cooling of the cast metal. As a result, the graphite flakes form a continuous matrix throughout the gray iron. Increasing the silicon content decreases the amount of carbon present in the eutectic, causing more carbon to take the form of pearlite and less to be present in the graphite matrix, in flake form. This lowering of the flake graphite content of the iron results in increased tensile strength. Graphitic Corrosion Graphitic corrosion is one example of the dealloying of a metal. During dealloying, one component of an alloy is selectively dissolved, leaving other components behind. In the case of gray iron, the preferential attack on iron results from graphite's highly noble, or corrosion resistant, position in the galvanic activity series. The relative position of two metals in the galvanic activity series determines which will most readily participate in electrochemical reactions, such as corrosion.
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (0.67)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (0.67)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (0.55)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (0.48)
ABSTRACT ABSTRACT SCC studies in stainless steels and nickel alloys reveal that all grades and conditions are susceptible to SCC in high temperature water, whether deaerated or aerated, high H2 or low, theoretical purity water or buffered I contaminated, lower temperature or higher. However, the kinetics of SCC growth vary enormously with stress intensity, yield strength, sensitization, water chemistry, irradiation, temperature, etc. The role of yield strength is especially important because it changes with surface cold work, bulk cold work, weld shrinkage strain, and irradiation hardening; the role of metallurgical strengthening mechanisms, e.g., nitrogen additions or precipitation hardening, may have a similar effect. SCC growth rate measurements were performed in high temperature water on unsensitized stainless steels (and alloy 600) of various grades and compositions. Little effect of grade / heat of stainless steel, martensite content or HI hgacity / permeation rate was observed, while large effects were observed for yield strength (cold work), stress intensity factor, corrosion potential, and temperature. A model "stainless steel" containing 5% Si (and elevated Ni and reduced Cr) showed high growth rates and little effect of corrosion potential or stress intensity factor. INTRODUCTION Stress corrosion cracking (SCC) in stainless steels and nickel alloys has occurred in various unimdiated and irradiated components in light water reactors. Despite many observations and common characteristics, SCC is ofien compartmentalized into small, unique modes with individualized mechanisms and dependencies [I-71. It is now acknowledged [I-81 that the crack tip is deaerated and at low potential in all cases, the environmental conditions under which crack advance occurs in light water reactor systems are vely similar [1,2,4-71. Primary differences are associated with: coolant additives that shift the pH at temperature from 5.6 to ? 7.0; H2 fugacity (? 50 vs 3000 ppb H2); and temperature (274 ° C vs. 323 ° C - or higher in the pressurizer). Of these differentiating factors, temperature is the most important in stainless steels; temperature and H2 are both important in nickel alloys. B/Li or NH3 in the PHT range ~5.5 to 8.0 has little effect on SCC growth rates in deareated water, unlike their effect in aerated water [9]. The existence of surface cold work, weld shrinkage strains, bulk cold work and irradiation hardening elevate the importance of understanding the mechanism and kinetics associated with cold work or, more fundamentally, yield strength. Cold work increases the SCC growth rate under all conditions - high and low corrosion potential, temperature, sensitization, stress intensity factor, etc. EXPERIMENTAL PROCEDURES Stainless steels were typically solution annealed at 1050 ° C (1100 ° C for alloy 600) for 30 minutes followed by a water quench. Deformation was typically introduced by heating the plate material to +I40 ° C (or cooling to -55 ° C; alloy 600 was rolled at 25 ° C) and rolling about half of the total reduction in each direction. Rolling at +I40 ° C (termed "cool work" in this paper) produces much less deformation-induced martensite in these stainless steels than rolling at -55 ° C (termed "cold work"). Some materials were worked by forging. No deformationinduced martensite forms in alloy 600.
- Materials > Metals & Mining > Steel (1.00)
- Energy > Power Industry > Utilities > Nuclear (1.00)
Electrochemical And Scc Behavior Of Highly Alloyed Austenitic Stainless Steels In Different Chloride Containing Media
Holzleitner, S. (Materials Center Leoben GmbH) | Mori, G. (Department for General, Analytical and Physical Chemistry, University of Leoben) | Falk, H. (Department for General, Analytical and Physical Chemistry, University of Leoben) | Eglsaeer, S. (Boehler Edelstahl GmbH)
ABSTRACT Potentiodynamic measurements, Slow Strain Rate Tests (SSRT) and Constant Load Tests (CLT) were executed on austenitic stainless steels to investigate chloride induced stress corrosion cracking (CISCC). Tests were conducted in boiling 43 wt% calcium chloride (CaCl2) and 45 wt% magnesium chloride (MgCl2) solutions. For the tests one CrNiMo and five CrMnN were chosen. To get mechanical reference values glycerin was used at SSR test as inert medium. Additionally influences of chloride concentration and temperature were investigated in potentiodynamic measurements and slow strain rate tests on the highly alloyed CrNiMo steel. All tests were conducted under atmosphere conditions. The variation of nickel content among the CrMnN steels showed no influence in time to failure. The comparison between manganese and nickel austenitic steels in time to failure showed, that Ni-stabilized austenitic steels do have a 10 to 100 times higher time to failure than Mn-stabilized steels if CISCC is induced. INTRODUCTION Nonmagnetic austenitic stainless steels are used in many applications where CISCC plays a major role. The aim of this investigation is to study comparative material resistance against Chloride Induced Stress Corrosion Cracking (CISCC) on highly alloyed austenitic stainless steels, in this case chromiummanganese- nitrogen (CrMnN) and chromium-nickel-molybdenum (CrNiMo) steels, under atmosphere conditions. To gain results in appropriate times without additional acidification or applied pressure hot or even boiling, concentrated salt solutions in connection with Slow Strain Rate Tests (SSRT) or Constant Load Tests (CLT) are used due to their high boiling points and high chloride contents. Critical chloride concentration and temperature raise with the alloying content of steels. Boiling MgCl2 solutions with different chloride content are one of the most popular media in which CISCC on highly alloyed austenitic stainless steels is investigated. Ambient conditions as chloride concentration, temperature, pH-value, cation species, pressure and time are strongly influencing CISCC. Alloying and metallurgical factors have an enormous influence on CISCC susceptibility as well The major prediction one can make out of these tests is whether the material is resistant to CISCC in this kind of solution or not. Streicher and Speidel et al. interpret this conditions as dry out situations, when water is evaporated and a high concentrated salt solution remains. Our testing was established under controlled variation of electrolyte parameters like chloride content and temperature to show their influences on electrochemical and CISCC behavior of the tested stainless steels. The pH value has not been changed due to difficulties in measuring pH in such hot and high concentrated salt solutions. An approach has been proved, to what extent electrochemical measurements can give a first indication whether the tested steel is susceptible to stress corrosion cracking in a defined medium. CISCC initiation and propagation are linked closely to the shape of the potentiodynamically measured i- E plots. These are basically influenced by temperature, chloride concentration and pH value of the solution. Temperature plays a major role, resulting first in accelerated reactions and second in a decrease of mechanical properties of the tested materials. MATERIALS Six highly alloyed stainless steels have been investigated. Material W1 to W5 are CrMnN steels and material W6 is a superaustenitic CrNiMo steel.
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- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Reservoir Description and Dynamics (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 ABSTRACT This paper presents several material problems experienced with rotary lime kiln operation, along with approaches to mitigate them Some of the problems discussed are fatigue, high temperature sulfidic corrosion, creep and impact damage, and their effects on burner nozzles, shell, and lump breakers. The information is based upon field experiences during scheduled and non-scheduled maintenance operations in several North American paper mills. INTRODUCTION Lime kilns are part of the chemical recovery system in pulp mills where lime mud (CaCO3) is converted to quick lime (CaO), a process called calcination. Quick lime is used in the causticizing process, which regenerates the sodium salts needed for kraft pulping. To complete the reaction, the lime mud is heated (¿) to 925°C (1700°F) to produce quick lime and CO2 in accordance with the chemical reaction [1]: (available in full paper) The traditional rotary lime kiln remains the most popular method for calcination (Figure 1). Most of the kiln is lined with insulating refractory bricks (in the hot end) and castable refractory (towards the cold end) to prevent overheating of the carbon steel kiln shell, which is typically AISI 1020 or ASTM A 36 plate material. During operation, the kiln rotates at approximately 1 rpm to mix the lime mud with the hot gases from the burner and to convey the lime from the inlet (cold) to the discharge (hot) end. The kiln is a cylinder, nominally 90 meters long (300 ft) and 3 meters (10 ft) in diameter, which is slightly raised at the cold (inlet) end. The kiln is supported by two to five tires (one per pedestal) that roll over support trunnions (Figure 2). Each tire is made from a thick ring of forged steel, typically AISI 1045 carbon steel, to minimize distortion as it rides over the trunnion. Wet lime mud is fed into the high end of the kiln and the solid phase moves countercurrent to the flow of the hot gases as the kiln rotates. The transfer of heat into the mud at the cold end is optimized by providing an extended surface area by means of steel chains that are attached to the kiln shell and hang in the hot gases (Figure 1). The hot end is typically maintained at 1150-1250°C (2100-2300°F) while the cold end is about 290-300°C (550-575°F). The hot end of the kiln will have one or more burners to supply heat through combustion of a choice of different fuels. Most kilns are set up to burn natural gas. However, current energy market conditions have forced many mills to search for less expensive fuels such as residual oil No. 6, or "Bunker C" oil, and atomized petroleum coke. In many instances, lime kilns also burn non-condensable gases (NCG's) in a separate burner (Figure 1). The discharge (hot) end of the kiln typically has high temperature alloy castings shaped as "alligator heads" or "grizzly paws", known as lump breaker bars, that pick up large lime lumps, as the rotating action of the kiln releases the large lumps from up above, causing them to fall and subsequently brake into smaller lime particles.