Search Results for corrosion performance

A nozzle in a wastewater vaporizer began leaking after approximately three years of service with acetic and formic acid wastewaters at 105 deg C (225 deg F) and 414 kPa (60 psig). The shell of the vessel was weld fabricated from 6.4 mm (0.25 in.) E-Brite stainless steel plate and measured 1.5 m (58 in.) in diameter and 8.5 m (28 ft) in length. Investigation (visual inspection, chemical analysis, radiography, dye-penetrant inspection, and hydrostatic testing of all E-Brite welds, 4x images, 100x/200x images electrolytically etched with 10% oxalic acid, and V-notch Charpy testing) supported the conclusion that failure of the nozzle weld was the result of intergranular corrosion caused by the pickup of interstitial elements and subsequent precipitation of chromium carbides and nitrides. Carbon pickup was believed to have been caused by inadequate joint cleaning prior to welding. The increase in the weld nitrogen level was a direct result of inadequate argon gas shielding of the molten weld puddle. Two areas of inadequate shielding were identified: improper gas flow rate for a 19 mm (0.75 in.) diam gas lens nozzle, and contamination of the manifold gas system. Recommendations included changes in the cleaning and welding process.

Post-service destructive evaluation was performed on two commercially pure zirconium pump impellers. One impeller failed after short service in an aqueous hydrochloric acid environment. Its exposed surfaces are bright and shiny, covered with pockmarks, and peppered with pitting. Uniform corrosion is evident and two deep linear defects are present on impeller blade tips. In contrast, the undamaged impeller surfaces are covered with a dark oxide film. This and many other impellers in seemingly identical service conditions survive long lives with little or no apparent damage. No material or manufacturing defects were found to explain the different service performance of the two impellers. Microstructure, microhardness and material chemistry are consistent with the specified material. Examination reveals the damage mechanism to be corrosion-enhanced cavitation erosion, the most severe form of erosion corrosion. Cavitation damage to the protective oxide film caused the zirconium to lose its normally outstanding corrosion resistance. The root cause of the impeller failure is most likely the introduction of excessive air into the pump due to low liquid level, a bad seal or inadequate head. Corrosion pitting, crevice corrosion, and solidification cracks (casting defect) also contributed to the failure.

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.

Corrosion is the deterioration of a material by a reaction of that material with its environment. The realization that corrosion control can be profitable has been acknowledged repeatedly by industry, typically following costly business interruptions. This article describes the electrochemical nature of corrosion and provides the typical analysis of environmental- and corrosion-related failures. It presents common methods of testing of laboratory corrosion and discusses the processes involved in the prevention of environmental- and corrosion-related failures of metals and nonmetals.

Eddy-current inspection was performed on a leaking absorber bundle in an absorption air-conditioning unit. The inspection revealed crack-like indications in approximately 50% of the tubes. The tube material was phosphorus-deoxidized copper. Investigation (visual inspection, chemical analysis, 0.75x images, 2x macrographs after light acid cleaning to remove corrosion product, and 75x micrographs) supported the conclusion that the absorber tubes failed by SCC initiated by ammonia contamination in the lithium bromide solution. No recommendations were made.

Several type 304 stainless steel fire truck water tanks developed through-wall leaks after being in service for approximately two years. One representative tank underwent a comprehensive laboratory analysis, which included metallographic examinations and chemical analyses. The examinations revealed a classic case of microbiologically influenced corrosion (MIC), which preferentially attacked the heat affected zones of the tank welds, resulting in the leaks.

This article provides an overview of the electrochemical nature of corrosion and analyzes corrosion-related failures. It describes corrosion failure analysis and discusses corrective and preventive approaches to mitigate corrosion-related failures of metals. These include: change in the environment; change in the alloy or heat treatment; change in design; use of galvanic protection; use of inhibitors; use of nonmetallic coatings and liners; application of metallic coatings; use of surface treatments, thermal spray, or other surface modifications; corrosion monitoring; and preventive maintenance.

A 5000-gal (20,000-L) hot-water holding tank fractured at a large automotive manufacturing plant. The tank was made from Type 304 austenitic stainless steel. The inner diameter of the tank displayed a macroscopic, web-like network of cracks that deceptively suggested intergranular stress-corrosion cracking. The problem, however, originated on the outside surface of the tank where a tensile stress (due to low applied stress and fabrication-induced residual stresses) accelerated the growth of numerous stress corrosion cracks that eventually broke through to the inner surface, causing leakage and ultimately failure.

Military aircraft use a cartridge ignition system for emergency engine starts. Analysis of premature failures of steel (AISI 4340) breech chambers in which the solid propellant cartridges were burned identified corrosion as one problem with an indication that stress-corrosion cracking may have occurred. A study was made for stress-corrosion cracking susceptibility of 4340 steel in a paste made of the residues collected from used breech chambers. The constant extension rate test (CERT) technique was employed and SCC susceptibility was demonstrated. The residues, which contained both combustion products from the cartridges and corrosion products from the chamber, were analyzed using elemental analysis and x-ray diffraction techniques. Electrochemical polarization techniques were also utilized to estimate corrosion rates.

An E-Brite /Ferralium explosively bonded tube sheet in a nitric acid condenser was removed from service because of corrosion. Visual and metallographic examination of tube sheet samples revealed severe cracking in the heat-affected zone between the outer tubes and the weld joining the tube sheet to the floating skirt. Cracks penetrated deep into the tube sheet, and occasionally into the tube walls. The microstructures of both alloys and of the weld appeared normal. Intergranular corrosion characteristic of end-grain attack was apparent. A low dead spot at the skirt / tube sheet joint allowed the Nox to condense and subsequently reboil. This, coupled with repeated repair welding in the area, reduced resistance to acid attack. Intergranular corrosion continued until failure. Recommendations included changing operating parameter inlet to prevent HNO3 condensation outside the inlet and replacement of the floating skirt with virgin material (i.e., material unaffected by weld repairs).

Some of the admiralty brass tubes were failing in a heat exchanger. The heat exchanger cooled air by passing river water through the inside of the tubes. The wall thickness of all tubes ranged between 1.19 to 1.27 mm (0.047 to 0.050 in.). General intergranular corrosion occurred at the inside surfaces of the tubes. Transgranular stress-corrosion cracking, probably the result of sulphates under basic conditions, and dezincification occurred also as the result of galvanic corrosion under the deposits in the tubes. Recommendations were to use a closed-loop water system to eliminate sulphates, ammonia, etc., and to run trials on one unit with tubes of other alloys such as 80-20 Cu-Ni or 70-30 Cu-Ni to evaluate their performance prior to any large scale retubing operations.

A bent Ni-Cu Monel 400 alloy tube, which operated as part of a pipeline in a petrochemical distillery, failed by through-thickness cracking. The pipeline was used to carry a stream of gaseous hydrocarbons containing hydrochloric acid (HCl) into a reaction tower. The tower provided a caustic solution (NaOH) to remove HCl from the stream, before the latter was directed to a burner. Metallographic examination showed that the cracks were intergranular and were frequently branched. Although nominal chemical composition of the component was found within the specified range, energy dispersive x-ray analysis (EDXA) indicated significant segregation of sulfur and chlorine along the grain boundaries. Failure was attributed to hypochlorous-acid (HClO)-induced stress-corrosion cracking (SCC). The HClO was formed by the reaction of HCl with atmospheric O 2 that entered the tube during shutdowns and startups. Residual stresses, originating from in situ bend forming of the tube during assembly of the line, provided a driving force for crack growth, and the segregation of sulfur on grain boundaries made the material more susceptible to cracking.

A pair of steam generators operating at a pressurized water reactor site were found to be leaking near a closure weld. The generators were the vertical U-tube type, constructed from ASTM A302 grade B steel. The shell material exhibited high hardness values prior to confirmatory heat treatment, indicating high residual stresses in the area of the weld. All cracks were transgranular and were associated with pits on the inside surfaces of the vessels. It was concluded that the cracking was caused by a low-cycle corrosion fatigue phenomenon, with cracks initiating at areas of localized corrosion and propagating by fatigue. The cause of the pitting/cracking was related to the unit's copper species in solution.

Inhibited admiralty brass (UNS C44300) condenser tubes used in a natural-gas-fired cogeneration plant failed during testing. Two samples, one from a leaking tube and the other from an on leaking tube, were examined. Chemical analyses were conducted on the tubes and corrosion deposits. Stress-corrosion cracking was shown to have caused the failure. The most probable corrosive was ammonia or an ammonium compound in the presence of oxygen and water. All of the tubes were replaced.

An 1100 aluminum alloy connector of a high-tension aluminum conductor steel-reinforced (ACSR) transmission cable failed after more than 20 years in service, in a region of consider able industrial pollution. The steel core was spliced with a galvanized 1020 carbon steel sheath. Visual examination showed that the connector had undergone considerable plastic deformation and necking before fracture. The steel sheath was severely corroded, and the steel splice was pressed off-center in the axial direction inside the connector. Examination of the fracture surface and micro-structural analysis indicated that the failure was caused by mechanical overload, which occurred because of weakening of the steel support cable by corrosion inside the fitting. The corrosion was ascribed to defective assembly of the connector which allowed moisture penetration.

Eddy current inspection was performed on a vertical evaporator unit (that contained 180 tubes) used in a chemical processing plant. It was advised that the tube material was type 316 stainless steel. The shell-side fluid was condensate and gaseous methylene chloride, while the tube-side fluid was contaminated liquid methylene chloride. More than 100 tubes exhibiting severe outer surface pitting and cracklike indications near each tube sheet were revealed during eddy current inspection. It was observed that the indications correlated with rust-stained, pitted, and cracked areas on the outer surfaces. The cracking was revealed by metallographic examination to have initiated from the outer surface, frequently at pits, and penetrated the tube wall in a transgranular, branching fashion. The crack features were characteristic of chloride stress-corrosion cracking. A change in tube material was recommended to avoid future failures and loss of service.

Corrosive wear is defined as surface damage caused by wear in a corrosive environment, involving combined attacks from wear and corrosion. This article begins with a discussion on several typical forms of corrosive wear encountered in industry, followed by a discussion on mechanisms for corrosive wear. Next, the article explains testing methods and characterization of corrosive wear. Various factors that influence corrosive wear are then covered. The article concludes with general guidelines for material selection against corrosive wear.

Two suction rolls at the first press section of a 25 ft. wide paper machine developed cracks within two years of service. The rolls were austenitic stainless steel castings made of ASTM A 351 Grade CF8M alloy containing molybdenum. The rolls were exposed to slightly acidic white water (pH approximately 4.7) containing chlorides (45 ppm). Visual and liquid penetrant inspections of the rolls revealed extensive cracking at the roll inside surface. The cracks penetrated more than 30 percent of the wall thickness and a few cracks were several inches long. The cracks were preferentially oriented along the roll length and primarily at the roll inside surface. Field metallographic examination showed significant grain boundary chromium-carbide precipitation and intergranular corrosion. The roll failures were attributed to chromium depletion along the grain boundaries (sensitization) resulting from slow cooling of the casting to avoid large residual stresses. The roll manufacturer recommended a proprietary ferritic/austenitic stainless steel as the replacement material for the rolls.