An injection-molded PVC water-filter housing fractured in service. 75x views and visual inspection supported the conclusion that failure occurred due to fatigue crack propagation, as indicated by the presence of discontinuous crack-growth bands and their evolution. However, an initial fissure was believed to have started first due to residual stresses developed during injection molding. No recommendations were made.

A component of a water filtration unit failed while being used in service for approximately eight months. The filter system had been installed in a commercial laboratory, where it was stated to have been used exclusively in conjunction with deionized water. The failed part had been injection molded from a 30% glass-fiber and mineral-reinforced nylon 12 resin. Investigation, including visual inspection, 118x SEM images, 9x micrographs, energy-dispersive x-ray spectroscopy, micro-FTIR in the ATR mode, and TGA, supported the conclusion that the filter component failed as a result of molecular degradation caused by the service conditions. Specifically, the part material had undergone severe chemical attack, including oxidation and hydrolysis, through contact with silver chloride. The source of the silver chloride was not established, but one potential source was photographic silver recovery.

River water was pumped into a brine plant by a battery of vertical pumps, each operating at 3600 rpm and at a discharge pressure of 827 kPa (120 psi). The pumps were lubricated by means of controlled leakage. The 3.8 cm (1 in.) OD pump sleeves were made of an austenitic stainless steel and were hard faced with a fused nickel-base hardfacing alloy (approximately 58 HRC). Packing for the pumps consisted of a braided PTFE-asbestos material. After several weeks of operation, the pumps began to leak and to spray water over the platforms on which they were mounted at the edge of the river. Analysis supported the conclusions that the leaks were caused by excessive sleeve wear that resulted from the presence of fine, abrasive silt in the river water. The silt, which contained hard particles of silica, could not be filtered out of the inlet water effectively.

Tube sheets (found to be copper alloy C46400, or naval brass, and 5 cm (2 in.) thick) of an air compressor aftercooler were found to be cracked and leaking approximately 12 to 14 months after they had been retubed. Most of the tube sheets had been retubed several times previously because of unrelated tube failures. Sanitary (chlorinated) well water was generally used in the system, although filtered process make-up water (river water) containing ammonia was occasionally used. Investigation (visual inspection, chemical analysis, mercurous nitrate testing, unetched 5X micrographs, and 250X micrographs etched in 10% ammonium persulfate solution) supported the conclusion that the tube sheets failed by SCC as a result of the combined action of internal stresses and a corrosive environment. The internal stresses had been induced by retubing operations, and the environment had become corrosive when ammonia was introduced into the system by the occasional use of process make-up water. Recommendations included making a standard procedure to stress relieve tube sheets before each retubing operation. The stress relieving should be done by heating at 275 deg C (525 deg F) for 30 min and slowly cooling for 3 h to room temperature.

One of three valves in a dry automatic sprinkler system tripped accidentally, thus activating the sprinklers. Maintenance records showed that the three valves had been in service less than two years. The valve consisted of a cast copper alloy clapper plate that was held closed by a pivoted malleable iron latch. The latch and top surface of the clapper plate were usually in a sanitary-water environment (stabilized, chlorinated well water with a pH of 7.3) under stagnant conditions. Process make-up water that had been clarified, filtered, softened, and chlorinated and had a pH of 9.8 was occasionally used in the system. Analysis (visual inspection and 250x micrograph) supported the conclusions that failure of the latch was caused by plastic deformation from extensive loss of metal by galvanic corrosion and the sudden loading related to the tripping of the valve. Failure in some regions of the contact area was by ductile (transgranular) fracture. Recommendations included changing the latch material from malleable iron to silicon bronze (C87300). The use of silicon bronze prevents corrosion or galvanic attack and proper adjustment of the latch maintains an adequate contact area.

This article presents a general overview of outdoor weather aging factors, their effects on the performance of polymeric materials, and the accelerated test methods that can be used to investigate those effects. These test methods are used to characterize material performance when subjected to specific, often controlled, and well-defined factors. The article also presents an overview of weathering instrument types that simulate outdoor stress factors.

High-level radioactive wastes generated during the processing of nuclear materials are kept in large underground storage tanks made of low-carbon steel. The wastes consist primarily of concentrated solutions of sodium nitrate and sodium hydroxide. Each of the tanks is equipped with a purge ventilation system designed to continuously remove hydrogen gas and vapors without letting radionuclides escape. Several intergranular cracks were discovered in the vent pipe of one such system. The pipe, made of galvanized steel sheet, connects to an exhaust fan downstream of high-efficiency particulate air filters. The failure analysis investigation concluded that nitrate-induced stress-corrosion cracking was the cause of the failure.

A residential subdivision near Tampa, FL was constructed in 1984 through 1985. Several sections of copper pipe were removed from one residence that had reported severe leaking. Visual examination revealed extensive pitting corrosion throughout the ID surfaces of the sample. Microscopic evaluation of a cross section of a copper pipe revealed extensive pitting corrosion throughout the inner diametral surfaces of the pipe. Some pits had penetrated through the wall thickness, causing the pin hole leaks. Analysis of a sample of water obtained from the subdivision revealed relatively high hardness levels (210 mg/l), high levels of sulfate ions (55 mg/l), a pH of 7.6 and a sulfate-to-chloride ratio of 3:1. Analysis of corrosion product removed from the ID surfaces of the pipe section revealed that an environment rich in carbonates existed inside the pipe, a result of the hard water supply. It was concluded that pitting corrosion was a result of the corrosive waters supplied by the local water utility. Waters could be rendered non-pitting by increasing their pH to 8 or higher and neutralizing the free carbon dioxide.

Six cases of failure attributed to microbiologically influenced corrosion (MIC) were analyzed to determine if any of the failures could have been avoided or at least predicted. The failures represent a diversity of applications involving typical materials, primarily stainless steel and copper alloys, in contact with a variety of liquids, chemistries, and substances. Analytical techniques employed include stereoscopic examination, energy dispersive x-ray spectroscopy (EDS), temperature and pH testing, and metallographic analysis. The findings indicate that MIC is frequently the result of poor operations or improper materials selection, and thus often preventable.

A failure analysis was conducted on brass alloy 270 heat exchanger tubes that were pulled from a unit used to cool oil for the speed regulators and thrust bearings of a hydroelectric power plant. The tubes began to leak after approximately 5.5 years of service. Macrophotography and scanning electron microscopy were used to examine samples from the tubes. An energy-dispersive electron microprobe analysis was carried out to evaluate the zinc distribution. Results showed that the failure was due to dezincification. Replacement of the tubes with new tubes fabricated from a dezincification-resistant alloy was recommended.

Two hot water reheat coil valves from a heating/ventilating/air-conditioning system failed in service. The values, a 353 copper alloy 19 mm (3/4 in.) valve and a 360 copper alloy 13 mm (1/2 in.) valve, had been failing at an increasing rate. The failures were confined to the stems and seats. Visual examination revealed severe localized metal loss in the form of deep grooves with smooth and wavy surfaces. Metallographic analysis of the grooved areas revealed uniform metal loss. No evidence of intergranular or selective attack indicating erosion-corrosion was observed, Recommendations included use of a higher-copper brass, cupronickel, or Monel for the valve seats and stems and operation of the valves in either the fully opened or closed position.

A large number of electropolished copper parts showed evidence of discoloration (tinting) after electropolishing. Because these parts are used in a high-vacuum application, even trace amounts of organic materials would be problematic. Scanning electron microscopy of nondiscolored and discolored areas both showed trace amounts of residue in the form of adherent deposits. EDS, FTIR spectroscopy, XPS, and secondary ion mass spectroscopy (SIMS) analyses indicated that the discoloration to the copper components was due to the development of CuO at localized regions. It was recommended that process changes be made to completely remove residual processing fluids from the part surfaces before electropolishing. The use of more aggressive detergents was suggested, and it was recommended also that a filtering and recirculating system be considered for use in the cleaning and electropolishing tanks.

The drive-shaft hanger bearings failed after 300 to 400 h in service. The shaft, supported by labyrinth-sealed single row radial ball bearings of ABEC-1 tolerances, was made of aluminum 2024-T3 tubing (2.5 cm diam and 1.2 mm wall thickness). The bearings were lubricated with a paste-type mineral-oil lubricant (containing molybdenum disulfide and polytetrafluoroethylene particles) or grease conforming to MIL-G-81322 (containing thickening agent and synthetic hydrocarbons) and had two-piece spot-welded retainers. On visual examination, the balls were observed to be embedded in the inner-ring raceway which had been softened by the elevated temperatures reached during the failure. Broken retainers and worn and bent out of shape seals were found. Penetration of gritty particles, water and other corrosive agents and leakage of lubricant out of the bearing permitted by the worn seals was observed. It was concluded that overheating was caused by lubricant flow was permitted by wear of the labyrinth seals. Positive rubbing seals and MIL-G-81322 grease lubricant were found to have longer life than those with the labyrinth seals and mineral-oil-paste lubricant on testing under simulated environmental conditions and were installed as a corrective measure. Importance of dirt free supply and drainage of oil was discussed.

The first-stage nozzles of a high-pressure turbine section of an industrial gas turbine exhibited leading and trailing-edge deterioration. The nozzles were made of X-40, a cobalt-base alloy, and were aluminide coated. Failure analysis determined that the deterioration was the result of hot corrosion caused by a combination of contaminants, cooling-hole blockage, and coating loss.

Several hundred leaks were reported in the type 304 stainless steel pipelines, vessels, and tanks of a chemical plant at a tropical location within a few weeks after startup. Investigation of the failure involved a site visit, metallographic examination and analysis of the material, analysis of hydrotest waters, and microbiological examination of slime that had formed in certain pipework sections. It was determined that the failure resulted from microbially induced corrosion promoted by the use of poor-quality hydrotest water and uncontrolled hydrotesting practice. Use of appropriate hydrotesting procedures was recommended to prevent similar failures.

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.

An austenitic stainless steel (type 316/316L stainless steel, schedule 40, 64 mm (2.5 in.) diam and larger) piping network used in the fire-sprinkler system in a large saltwater passenger and car ferry failed by rapid leaking. Operating conditions involved stagnant seawater at ambient temperatures. The pipe was in service for four weeks when three leaks appeared. Investigation (visual inspection and photographic images) supported the conclusion that the failure was caused by attack and corrosion damage of Cl ions in conditions that were ideal for three modes of highly accelerated pitting of austenitic stainless steel: the bottom surface, weld or HAZ pits, and crevices. Recommendations included proper material selection for piping, flanges, and weld rods with greater corrosion resistance. Proper filtering to prevent entrained abrasives and timely breakdown inspections were also advised.

Corrosion in a closed-loop cooling water system constructed of austenitic stainless steel occurred during an extended lay up of the system with biologically contaminated water. The characteristics of the failure were those of microbiologically influenced corrosion (MIC). The corrosion occurred at welds and consisted of large subsurface void formations with pinhole penetrations of the surfaces. Corrosive attack initiated in the heat affected zones of the welds, usually immediately adjacent to fusion lines. Stepwise grinding, polishing, and etching through the affected areas revealed that voids generally grew in the wrought material by uniform general corrosion. Tunneling or worm-holing was also observed, whereby void extension occurred by initiating daughter voids probably at flaws or other inhomogeneities. Selective attack occurred within the fusion zone, i.e., within the cast two-phase structure of the weld filler itself. The result was a void wall which consisted of a rough and porous ferritic material, a consequence of preferential attack of the austenitic phase and slightly lower rate of corrosive attack of the ferrite phase. The three-dimensional spongy surface was studied optically and with the scanning electron microscope.

This article describes the processes involved in photochemical aging and weathering of polymeric materials. It explains how solar radiation, especially in the UV range, combines with atmospheric oxygen, driving photooxidation and the development of unstable photoproducts that cause various types of damage when they decompose, including the scission of carbon bonds and polymer chains. The article illustrates some of the degradation reactions that occur in different polymers and presents an overview of the strategies used to prevent such reactions or otherwise mitigate their effects.