Search Results for iron-base alloys

The thin plates within a type 309 stainless steel chlorinated solvent combustion preheater/heat exchanger designed to process fumes from a solvent coating process showed severe corrosion within 6 months of service. Within a year corrosion had produced holes in the plates, allowing gases to shunt across the preheater/exchanger. Metallographic examination of the plates showed that accelerated internal oxidation had been the cause of failure. Corrosion racks of candidate alloys (types 304, 309, and 316 stainless steels, Inconel 600, Inconel 625, Incoloy 800, Incoloy 825, and Inco alloy C-276) were placed directly in the hot gas stream, containing HCl and Cl2, for in situ testing. Results of this investigation showed that nickel-chromium corrosion-resistant alloys, such as Inconel 600, Inconel 625, and Inco alloy C-276, performed well in this environment. Laboratory testing of the same alloys, along with Inconel alloys 601, 617, and 690 and stainless steel type 347 was also conducted in a simulated waste incinerator nitrogen atmosphere containing 10% Co2, 9% O2, 4% HCl, 130 ppm HBr and 100 ppm SO2 at 595, 705, 815, and 925 deg C (1100, 1300,1500, and 1700 deg F). The tests confirmed the suitability of the nickel-chromium alloys for such an environment. Inconel 625 was selected for fabrication of a new preheater/exchanger.

High-temperature corrosion can occur in numerous environments and is affected by various parameters such as temperature, alloy and protective coating compositions, stress, time, and gas composition. This article discusses the primary mechanisms of high-temperature corrosion, namely oxidation, carburization, metal dusting, nitridation, carbonitridation, sulfidation, and chloridation. Several other potential degradation processes, namely hot corrosion, hydrogen interactions, molten salts, aging, molten sand, erosion-corrosion, and environmental cracking, are discussed under boiler tube failures, molten salts for energy storage, and degradation and failures in gas turbines. The article describes the effects of environment on aero gas turbine engines and provides an overview of aging, diffusion, and interdiffusion phenomena. It also discusses the processes involved in high-temperature coatings that improve performance of superalloy.

This case study demonstrates that Alloy 601 (UNS N06601) is susceptible to strain-age cracking. The observation illustrates the potential importance of post weld heat treatment to the successful utilization of this alloy in certain applications.

This article focuses on the mechanisms of microbially induced or influenced corrosion (MIC) of metallic materials as an introduction to the recognition, management, and prevention of microbiological corrosion failures in piping, tanks, heat exchangers, and cooling towers. It discusses the degradation of various protective systems, such as corrosion inhibitors and lubricants. The article describes the failure analysis of steel, iron, copper, aluminum, and their alloys. It also discusses the probes available to monitor conditions relevant to MIC in industrial systems and the sampling and analysis of conditions usually achieved by the installation of removable coupons in the target system. The article also explains the prevention and control strategies of MIC in industrial systems.

An Incoloy 800H (UNS N08810) transfer line on the outlet of an ethane-cracking furnace failed during decoking of the furnace tubes after nine years in service. A metallographic examination using optical and scanning electron microscopy as well as energy-dispersive x-ray spectroscopy revealed that the failure was due to sulfidation. The source of the sulfur in the furnace effluent was either dimethyl disulfide, injected into the furnace feed to prevent coke formation and carburization of the furnace tubes, or contamination of the feed with sulfur bearing oil.

This article focuses on the mechanisms of microbiologically influenced corrosion as a basis for discussion on the diagnosis, management, and prevention of biological corrosion failures in piping, tanks, heat exchangers, and cooling towers. It begins with an overview of the scope of microbial activity and the corrosion process. Then, various mechanisms that influence corrosion in microorganisms are discussed. The focus is on the incremental activities needed to assess the role played by microorganisms, if any, in the overall scenario. The article presents a case study that illustrates opportunities to improve operating processes and procedures related to the management of system integrity. Industry experience with corrosion-resistant alloys of steel, copper, and aluminum is reviewed. The article ends with a discussion on monitoring and preventing microbiologically influenced corrosion failures.

A steel pot used as crucible in a magnesium alloy foundry developed a leak that resulted in a fire and caused extensive damage. Hypotheses as to the cause of the leak included a defect in the pot, overuse, overheating, and poor foundry practices. Scanning electron microscopy, transmission electron microscopy, optical microscopy, and x-ray microanalysis in conjunction with dimensional analysis, phase diagrams and thermodynamics considerations were employed to evaluate the various hypotheses. All evidence pointed to an oxide mass in the area where the hole developed, likely introduced during the steelmaking process.

Problems with materials compatibility were encountered in pyrotechnically driven devices used in a number of ordnance applications requiring rapid mechanical actuation. A fine bridgewire is located in contact with the chemical pyrotechnic, and the charge is ignited by electrical heating of the bridgewire. Evidence of severe corrosion was revealed on examination of the nickel-chromium-iron alloy bridgewire and the nickel-iron alloy pins. Metallic elements in the pin or bridgewire and substantial amounts of chlorine were detected from the x-ray spectra. Morphological changes indicative of decomposition and dissolution were revealed to have occurred in regions of the pyrotechnic that had been in contact with the bridgewire and pin surfaces by examination of the titanium-potassium perchlorate (Ti-K-Cl-O4) pyrotechnic. Substantial amounts of water were revealed to be associated with the surfaces of the titanium particles in the pyrotechnic by nuclear magnetic resonance. It was proposed that the chlorine-containing residue combined with the water from the pyrotechnic to form a thin aqueous film corroding the bridgewire and pins. A new cleaning procedure was implemented for the glass headers to eliminate the chloride contamination and a vacuum drying procedure was instituted for the pyrotechnic.

High temperature corrosion may occur in numerous environments and is affected by factors such as temperature, alloy or protective coating composition, time, and gas composition. This article explains a number of potential degradation processes, namely, oxidation, carburization and metal dusting, sulfidation, hot corrosion, chloridation, hydrogen interactions, molten metals, molten salts, and aging reactions including sensitization, stress-corrosion cracking, and corrosion fatigue. It concludes with a discussion on various protective coatings, such as aluminide coatings, overlay coatings, thermal barrier coatings, and ceramic coatings.

This paper describes an investigation on the failure of a large leaded bronze bearing that supports a nine-ton roller of a plastic calendering machine. At the end of the normal service life of a good bearing, which lasted for seven years, a new bearing was installed. However the new one failed catastrophically within a few days, generating a huge amount of metallic wear debris and causing pitting on the surface of the cast iron roller. Following the failure, samples were collected from both good and failed bearings. The samples were analyzed chemically and their microstructures examined. Both samples were subjected to accelerated wear tests in a laboratory type pin-on-disk apparatus. During the tests, the bearing materials acted as pins, which were pressed against a rotating cast iron disk. The wear behaviors of both bearing materials were studied using weight loss measurement. The worn surfaces of samples and the wear debris were examined by light optical microscope, SEM, and energy-dispersive x-ray microanalyzer. It was found that the laboratory pin-on-disk wear data correlated well with the plant experience. It is suggested that the higher lead content ~18%) of the good bearing compared with 7% lead of the failed bearing helped to establish a protective transfer layer on the worn surface. This transfer layer reduced metal-to-metal contact between the bearing and the roller and resulted in a lower wear rate. The lower lead content of the failed bearing does not allow the establishment of a well-protected transfer layer and leads to rapid wear.

A segment of a stainless steel clad bottom cone of an acid sulfite pulping batch digester failed from severe corrosion loss. The digester was fabricated of 19 mm ( 3 4 in.) low-carbon steel with 3.8 mm (0.15 in.) type 317L stainless steel cladding. The manufacturing method for the cladding was unknown. Visual and metallographic analyses indicated that the failure was from transgranular stress-corrosion cracking (TGSCC), which caused extensive cracking and spalling of the cladding and was localized in a segment of the bottom cone. The remainder of the digester cladding was unaffected. The TGSCC was attributed to high, locked-in residual stresses from the cladding process. It was recommended that the bottom cone replacement segment be stress relieved prior to installation.

The information provided in this article is intended for those individuals who want to determine why a casting component failed to perform its intended purpose. It is also intended to provide insights for potential casting applications so that the likelihood of failure to perform the intended function is decreased. The article addresses factors that may cause failures in castings for each metal type, starting with gray iron and progressing to ductile iron, steel, aluminum, and copper-base alloys. It describes the general root causes of failure attributed to the casting material, production method, and/or design. The article also addresses conditions related to the casting process but not specific to any metal group, including misruns, pour shorts, broken cores, and foundry expertise. The discussion in each casting metal group includes factors concerning defects that can occur specific to the metal group and progress from melting to solidification, casting processing, and finally how the removal of the mold material can affect performance.

Nickel anodes failed in several electrolysis cells in a heavy-water upgrading plant. Dismantling of a cell revealed gouging and the presence of loosely attached black porous masses on the anode. The carbon steel top, plate was severely corroded. An appreciable quantity of black powder was also present on the bottom or the cell. SEM/EDX studies of the outer and inner surfaces of the gouged anode showed the presence of iron globules at the interface between the gouged and the unattacked anode. The chemical composition of the black powder was determined to be primarily iron. Cell malfunction was attributed to the accelerated dissolution of the carbon steel anode top, dislodgment of grains from the material, and subsequent closing of the small annular space between the anode and the cathode by debris from the anode top. Cladding of the carbon steel top with a corrosion-resistant material, such as nickel, nickel-base alloy, or stainless steel, was recommended.

This article describes some of the common elemental composition analysis methods and explains the concept of referee and economy test methods in failure analysis. It discusses different types of microchemical analyses, including backscattered electron imaging, energy-dispersive spectrometry, and wavelength-dispersive spectrometry. The article concludes with information on specimen handling.

An investigation was conducted to determine why 16 out of 139 pipe bends cracked during hot induction bending. The pipe conformed to API 5L X65 PSL2 line pipe standards and measured 1016 mm (40 in.) in diam with a wall thickness of 18.5 mm. A metallurgical cross section was removed along a crack on the extrados to document the crack morphology using optical microscopy. In addition to cracking, golden-yellow streaks were visible at the extrados, and the composition was examined using scanning electron microscopy with energy dispersive spectroscopy. Based on the results, investigators concluded the pipe was contaminated with copper at the mill were it was produced.

A shotgun barrel fabricated from 1138 steel deformed when test firing alternative nontoxic ammunition. The test shells contained soft iron shot, which at 72 HB, is much harder than traditional lead shot (typically 30 to 40 HB). An investigation based on ID and OD profiling supported the conclusion that the iron shot increased stresses in the choke zone of the barrel, causing it to deform. Variations in the amount of bulging were attributed to a lack of uniformity in wall thickness. Recommendations included making the barrel from steel with a higher yield strength, making the barrel walls thicker and more uniform, and/or developing an alternative nontoxic metal shot with a hardness in the range of 30 to 40 HB.

This article addresses the forms of corrosion that contribute directly to the failure of metal parts or that render them susceptible to failure by some other mechanism. It describes the mechanisms of corrosive attack for specific forms of corrosion such as galvanic corrosion, uniform corrosion, pitting and crevice corrosion, intergranular corrosion, and velocity-affected corrosion. The article contains a table that lists combinations of alloys and environments subjected to selective leaching and the elements removed by leaching.

Nineteen out of 26 bolts in a multistage water pump corroded and cracked after a short time in a severe working environment containing saline water, CO 2 , and H 2 S. The failed bolts and intact nuts were to be made from a special type of stainless steel as per ASTM A 193 B8S and A 194. However, the investigation (which included visual, macroscopic, metallographic, SEM, and chemical analysis) showed that austenitic stainless steel and a nickel-base alloy were used instead. The unspecified materials are more prone to corrosion, particularly galvanic corrosion, which proved to be the primary failure mechanism in the areas of the bolts directly exposed to the working environment. Corrosion damage on surfaces facing away from the work environment was caused primarily by chloride stress-corrosion cracking, aided by loose fitting threads. Thread gaps constitute a crevice where an aggressive chemistry is allowed to develop and attack local surfaces.

Leakage was detected in a malleable iron elbow (ASTM A 47, grade 35018) after only three months in service. Life expectancy for the elbow was 12 to 24 months. The piping alternately supplied steam and cooling water to a tire-curing press. The supply line and elbow were subjected to 14 heating and cooling cycles per hour for at least 16 h/day, or a minimum of 224 cycles/day. Steam and water pressure were 1035 kPa (150 psi) and 895 kPa (130 psi) respectively, and water-flow rate was estimated to be 1325 L/min (350 gal/min) based on pump capacity. Water-inlet temperature was 10 to 15 deg C (50 to 60 deg F) and outlet temperature was 50 to 60 deg C (120 to 140 deg F). The pH of the water was 6.9. Investigation (visual inspection, chemical analysis, and 67x nital etched micrographs) supported the conclusion that the elbows had been given the usual annealing and normalizing treatment for ferritizing malleable iron. This resulted in lower resistance to erosion and corrosion than pearlitic malleable iron. Recommendations included replacing the elbows with heat-treated fittings with a pearlitic malleable microstructure.