Several glass wool insulation sections from a heat-treat furnace showed visible, but only cosmetic discoloration. EDS showed the presence of silicon, aluminum, and oxygen in the nondiscolored region, and these elements are consistent with glass wool. Relatively high levels of chromium and nickel were detected in the discolored area, along with lower amounts of iron, manganese, sodium, calcium, cobalt, and sulfur, in addition to the surrounding glass wool elements. Results of this limited evaluation showed the discoloration was caused by the presence of elevated levels of chromium, nickel, and aluminum. The visual appearance, along with the EDS findings, suggested these elements were present in the form of oxides. These oxides were likely deposited from adjacent structural components of the furnace, which had oxidized during operation.

A 680,000 kg (750 ton) per day ammonia unit was shut down following a fire near the outlet of the waste heat exchanger. The fire had resulted from leakage of ammonia from the type 316 stainless steel outlet piping. The outlet piping immediately downstream from the waste heat exchanger consisted of a flange made from a casting, and a reducing cone, a short length of pipe, and a 90 deg elbow, all made of 13 mm thick plate. A liner wrapped with insulation was welded to the smaller end of the reducing cone. All of the piping up to the flange was wrapped with insulation. Investigation (visual inspection, 10x unetched images, liquid-penetrant inspection, and chemical analysis of the insulation) supported the conclusion that the failure occurred in the area of the flange-to-cone weld by SCC as the result of aqueous chlorides leached from the insulation around the liner by condensate. Recommendations included eliminating the chlorides from the system, maintaining the temperature of the outlet stream above the dewpoint at all times, or that replacing the type 316 stainless steel with an alloy such as Incoloy 800 that is more resistant to chloride attack.

Field metallography and replication were performed on a type 316 stainless steel column in diglycol amine vacuum service to determine the cause of visible OD pitting on the column in several areas above the insulation support rings. The examination revealed transgranular stress-corrosion cracking beneath the pitted areas on the OD. The likely cause of the cracking was chloride stress corrosion, with chlorides deriving from the marine atmosphere and concentrating under the insulation around the support rings. A complete insulation evaluation, including repair or replacement, was recommended to prevent chloride buildup. Painting of the steel surface with an epoxy-phenolic or epoxy-coal tar was also suggested.

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.

A forged 4130 steel cylindrical permanent mold, used for centrifugal casting of gray- and ductile-iron pipe, was examined after pulling of the pipe became increasingly difficult. In operation, the mold rotated at a predetermined speed in a centrifugal casting machine while the molten metal, flowing through a trough, was poured into the mold beginning at the bell end and ending with the spigot end being poured last. After the pipe had cooled, it was pulled out from the bell end of the mold, and the procedure was repeated. Investigation supported the conclusion that failure of the mold surface was the result of localized overheating caused by splashing of molten metal on the bore surface near the spigot end. In addition, the mold-wash compound (a bentonite mixture) near the spigot end was too thin to provide the proper degree of insulation and to prevent molten metal from sticking to the bore surface. Recommendations included reducing the pouring temperatures of the molten metal and spraying a thicker insulating coating onto the mold surface.

This article addresses electrical testing and characterization of plastics and presents a number of techniques for evaluating the electrical properties of insulating materials, with a special focus on plastics, accompanied by a list of the electrical properties of different types of plastics. It provides the reader with sufficient information to select the appropriate electrical test(s) for a specific application. The tests covered in this article are widely used in industry to determine the electrical properties of insulating materials, particularly plastics. The article lists and defines terms used in connection with testing and specification of plastics for electrical applications.

Two silica phenolic nozzle liners cracked during proof testing. The test consisted of pressuring the nozzles to 14.1 MPa (2050 psia) for 5 to 20 s. It was concluded that the failure was due to longitudinal cracking in the convergent exhaust-nozzle insulators, stemming from the use of silica phenolic tape produced from flawed materials that went undetected by the quality control tests, which at the time, assessed tape strength properties in the warp rather than the bias direction. Once the nozzle manufacturer and its suppliers identified the problem, they changed their quality control procedures and resumed production of nozzle liners with more tightly controlled fiber/fabric materials.

The small cable (drop wire) providing service for individual subscribers from the aerial plant is held in place by a clamp made of a tin-coated brass body (attached to the cable) and a copper tail wire loop (attached to a galvanized steel hook or to a porcelain insulator). The tail wire is 2.6 mm (0.102 in.) diam annealed copper, and the clamp assembly must withstand a 2470 N (555 lb) load without breaking or slipping. A number of these clamps, located a few hundred feet from the ocean, have failed. The sharply broken wire indicated to weakening by abrasion. The copper tail wire failures had characteristics generally associated with corrosion fatigue. The broken wires showed multiple transgranular cracks near the failure, originating at the bases of pits. It was diagnosed that the copper tail wire failures were due to corrosion fatigue. The solution to this problem was to change the tail wire material for direct seashore exposure from annealed copper to annealed Monel.

Within about one month, several knuckle pins (AMS 6470 steel failed, and required to have a minimum case hardness of 92 h15N, a case depth of 0.4 to 0.5 mm (0.017 to 0.022 in.), and a core hardness of 285 to 341 HRB) used in engines failed over a range of 218 to 463 h in operation. Visual examination revealed beach marks typical of fatigue cracks that had nucleated at the base of the longitudinal oil hole. Micrographs of sections revealed a remelt zone and an area of untempered martensite within the region of the cracks. However, review of inspection procedures disclosed the pins had been magnetic-particle inspected by inserting a probe into the longitudinal hole. Evidence found supports the conclusions that the knuckle pins failed by fatigue fracture. The circular cracks at the longitudinal holes were the result of improper technique in magnetic-particle inspection. Thermal transformation of the metal also causes a stress concentration that may lead to fatigue failure. Recommendations included insulating the conductor to prevent arc burning at the base of the longitudinal oil hole. Also, a borescope or metal monitor could be used to inspect the hole for evidence of arc burning from magnetic-particle inspection.