One inch diam Type 304 stainless steel piping was designed to carry containment atmosphere samples to an analyzer to monitor hydrogen and oxygen levels during operational and the design basis accident conditions that are postulated to occur in a boiling water reactor. Only one of six lines in the system had thru-wall cracks. Shallow incipient cracks were detected at the lowest elevations of one other line. The balance of the system had no signs of SCC attack. Chlorides and corrosion deposits in varying amounts were found throughout the system. The failure mechanism was transgranular, chloride, stress-corrosion cracking. Replacement decisions were based on the presence of SCC attack or heavy corrosion deposits indicative of extended exposure time to chloride-contaminated water. The existing uncracked pipe, about 75 percent of the piping in the system, was retained despite the presence of low level surface chlorides. Controls were implemented to insure that temperatures are kept below 150 deg F, or, walls of the pipe are moisture-free or the cumulative wetted period will never exceed 30 h.

Alloy 430 stainless steel tube-to-header welds failed in a heat recovery steam generator (HRSG) within one year of commissioning. The HRSG was in a combined cycle, gas-fired, combustion turbine electric power plant. Alloy 430, a 17% Cr ferritic stainless steel, was selected because of its resistance to chloride and sulfuric acid dewpoint corrosion under conditions potentially present in the HRSG low-pressure feedwater economizer. Intergranular corrosion and cracking were found in the weld metal and heat-affected zones. The hardness in these regions was up to 35 HRC, and the weld had received a postweld heat treatment (PWHT). Metallographic examination revealed that the corroded areas contained undertempered martensite. Fully tempered weld areas with a hardness of 93 HRB were not attacked. No evidence of corrosion fatigue was found. Uneven temperature control during PWHT was the most likely cause of failure.

Two leaks were discovered at a sulfur recovery unit in a refinery. The leaks were at pipe-to-elbow welds in a 152 mm (6 in.) (NPS 6) diam line, operating in lean amine service at 50 deg C (120 deg F) and 2.9 MPa (425 psig). Thickness measurements indicated negligible loss of metal, and the leaks were clamped. A year later, 15 additional leaks were discovered, again at pipe-to-elbow welds in lean amine lines. Further nondestructive testing located other cracks, giving a total of 35. These lines had been in service for approximately eight years. Investigation (visual inspection, hardness testing, and micrographic cross-sections) supported the conclusion that the failure was caused by lean amine SCC. It was considered unlikely that these pipe welds had received such a postweld heat treatment, although it is industry practice to postweld stress relieve piping and pressure vessels in lean amine service if the temperature is expected to be above 95 deg C (200 deg F). Recommendations included inspecting all welds using shear wave ultrasonic testing and postweld heat treating all welds in lean amine service.

After ten years of satisfactory operation, economizer-tube failures occurred in a large black liquor recovery boiler for a paper mill. The economizer contained 1320 finned tubes. Two fins ran longitudinally for most of the tube length and were attached by fillet welding on one side. The economizer tube leaks occurred at the end of the fin near the bottom of the economizer. A sample from a tube that had not failed showed heavy pitting attack on the inside of the tube, probably due to excess oxygen in the feedwater. Penetrant testing revealed numerous longitudinal cracks on the inside in the area of the fin tip. Cracking at the end of the fin-to-tube fillet weld was noted. The results indicate the failures were due to corrosion fatigue whose stresses were primarily thermally induced. A temporary solution included inspecting all tubes with shear-wave ultrasonics. Tubes with the most severe cracking were ground and repair welded. The square corners of the fins were trimmed back with a gradual taper so that expansion strains would be more gradually transferred to the tube surface. Water chemistry was closely evaluated and monitored, especially with regard to oxygen content.

A falling film black liquor evaporator consisted of flat twin plate heat exchangers and was used to increase black liquor solids content prior to its burning in the recovery boiler. Several plate heat exchangers were fabricated of AISI type 316L stainless steel by electric resistance welding. Cracks initiated at the inside surface of the welded areas and penetrated through the wall thickness. In several locations, the weld fractured and the plates separated with significant spring back, indicative of high residual stresses attributed to fabrication and weld procedures. The cracks had extended radially from the electric resistant weld into the base metal. Metallographic examination revealed the cracks were transgranular and branching, characteristic of SCC in austenitic stainless steels. The fracture surfaces had a brittle cleavage-like appearance, typical of SCC in austenitic stainless steels. Chlorides in the service environment were a contributory factor. The primary factor causing SCC localized at the electric resistant welds was substantial residual stresses as a result of fabrication procedures. It was recommended that the heat exchanger plates be subjected to stress-relief heat treatment following fabrication and welding.

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.

The cross bars of conveyor belt links that served to transport glass containers through a stress relief furnace fractured in many cases. They consisted of wires of 5 mm diam made of low-carbon Siemens-Martin steel, while the interwoven longitudinal bars were made of strip steel of 4 x 2 sq mm. The furnace temperature was said to be 500 deg C. In addition to the fractures they also showed many more or less advanced cracks. These occurred in the circumferential grooves that recurred at regular intervals. The fractures were abraded and oxidized. They could have been fatigue fractures. The fracture probably was induced by the pressing-in or abrading of the sharp steel band edges into the surface of the cross bars. Torsion fatigue fractures may have started from these notches. Relaxation then contributed positively through recovery and recrystallization. Such damage occurs less frequently in round wire conveyor belt links because the round wire neither impresses so sharply nor abrades against the cross bars, and it also exerts less torsion than the flat wire.

Rheology is defined as the study of the flow and deformation of matter. This article begins with an examination of flow behavior. It describes the geometries and methods employed for rheological testing of polymers in their molten state. It also discusses materials that are predominantly in the solid state and the methods employed for solids testing. Examples of unidirectional and dynamic oscillatory testing are provided for different mechanical behaviors.

Several 304H stainless steel superheater tubes fractured in stressed areas within hours of a severe caustic upset in the boiler feedwater system. Tests performed on a longitudinal weld joint, which connected two adjacent tubes in the tertiary superheater bank, confirmed caustic-induced stress-corrosion cracking, promoted by the presence of residual welding stresses. Improved maintenance of check valves and routine inspection of critical monitoring systems (conductivity alarms, sodium analyzers, etc.) were recommended to help avoid future occurrences of severe boiler feedwater contamination. Additional recommendations were to eliminate these short longitudinal weld joints by using a bracket assembly joint between the tubes, use a post-weld heat treatment to relieve residual welding stress or select a more stress-corrosion cracking resistant alloy for this particular application.

Engineering plastics, as a general class of materials, are prone to the development of internal stresses which arise during processing or during servicing when parts are exposed to environments that impose deformation and/or temperature extremes. Thermal stresses are largely a consequence of high coefficients of thermal expansion and low thermal diffusivities. Although time-consuming techniques can be used to analyze thermal stresses, several useful qualitative tests are described in this article. The classification of internal stresses in plastic parts is covered. The article describes the effects of low thermal diffusivity and high thermal expansion properties, and the variation of mechanical properties with temperature. It discusses the combined effects of thermal stresses and orientation that result from processing conditions. The article also describes the effect of aging on properties of plastics. It explains the use of high-modulus graphite fibers in amorphous polymers.

Metallographic studies found that steel used to fabricate the U.S.S. Arizona battleship during original construction, 1913-1915 and reconstruction, 1929-1931 were consistent with the best materials available during each time period. Due to the force of the forward magazine detonation, the best steel available today would not have had any impact on the outcome. Heavy banding in steels from both periods could adversely affect the corrosion resistance under anaerobic conditions that prevail during a corrosion cycle that has developed under hard biofouling layers for over 58 years. Banding would have no effect on corrosion rate under aerobic conditions that may occur in local areas on the hull. In the part of the ship from which samples for this report were obtained, high temperatures above 1340 deg F did not occur. Hull plate samples from the submerged wreckage are not yet available. These samples will be important to confirm findings to this time and determine the remaining thickness of the hull plate and, indirectly, the integrity of the fuel oil tanks.

Flow forming technology has emerged as a promising, economical metal forming technology due to its ability to provide high strength, high precision, thin walled tubes with excellent surface finish. This paper presents experimental observations of defects developed during flow forming of high strength SAE 4130 steel tubes. The major defects observed are fish scaling, premature burst, diametral growth, microcracks, and macrocracks. This paper analyzes the defects and arrives at the causative factors contributing to the various failure modes.

This article reviews the applied aspects of creep and stress-rupture failures. It discusses the microstructural changes and bulk mechanical behavior of classical and nonclassical creep behavior. The article provides a description of microstructural changes and damage from creep deformation, including stress-rupture fractures. It also describes metallurgical instabilities, such as aging and carbide reactions, and evaluates the complex effects of creep-fatigue interaction. The article concludes with a discussion on thermal fatigue and creep fatigue failures.

This article addresses some established protocols for characterizing thermoplastics and whether they are homogeneous resins, alloyed, or blended compositions or highly modified thermoplastic composites. It begins with a discussion on characterizing mechanical, rheological, and thermal properties of polymer. This is followed by a section describing molecular weight determination using viscosity measurements. Next, the article discusses the use of cone and plate and parallel plate geometries in melt rheology. It then reviews the processes involved in the analysis of thermoplastic resins by chromatography. Finally, the article covers three operations of thermoanalysis, namely differential scanning calorimetry, thermogravimetric analysis, and thermomechanical testing.

A precipitation-hardened stainless steel poppet valve assembly used to shut off the flow of hydrazine fuel to an auxiliary power unit was found to leak. SEM and optical micrographs revealed that the final heat treatment designed for the AM-350 bellows material rendered the AM-355 poppet susceptible to intergranular corrosive attack (IGA) from a decontaminant containing hydroxy-acetic acid. This attack provided pathways for which fluid could leak across the sealing surface in the closed condition. It was concluded that the current design is flight worthy if the poppet valve assembly passes a preflight helium pressure test. However a future design should use the same material for the poppet and bellows so that the final heat treatment will produce an assembly not susceptible to IGA.

Corrosion failure occurred in a titanium clad tubesheet because of a corrosive tube-side gas-liquid mixture leaking through fatigue cracks in the seal welds at tube-to-tubesheet joints. The tubesheet was a carbon steel plate clad with titanium on the tube side face. The seal weld cracks were initiated by cyclic stress imposed by exchanger tubes. The gas-liquid mixture passed through cracks under tube-side pressure, resulting in severe corrosion of the steel backing plate. The failure started with the loosening of the expanded tube-to-tubesheet joints. Loose joints allowed the exchanger tubes to impose load on seal welds and the shell side cooling water entered the crevice between the tubesheet and the tubes. The cooling water in the crevice caused galvanic reaction and embrittlement of seal welds. Brittle crack opening and crack propagation in seal welds occurred due to the cyclic stress imposed by the tubes. The cyclic stress arised from the thermal cycling of the heat exchanger. The possible effects of material properties on the failure of the tubesheet are discussed.

On 13 Dec 1994, two massive detonations leveled portions of an ammonium nitrate plant near Sioux City, IA. The primary explosion allegedly occurred in defectively-designed titanium sparger piping inside the neutralizer vessel. Investigation however, revealed the explosion occurred because of unsafe plant operations and poor maintenance procedures. Specifically, the ammonium nitrate within the 18,000 gal capacity neutralizer vessel had become contaminated and made highly acidic. The operators then injected superheated steam directly into the ammonium nitrate in the neutralizer vessel.

The operator of an electric transit system purchased a large number of tin-plated copper connectors, putting some in service and others in reserve. Later, when some of the reserve connectors were inspected, the metal surfaces were covered with spots consisting of an ash-like powder and the plating material had separated from the substrate in many areas. Several connectors, including some that had been in service, were examined to determine what caused the change. The order stated that the connectors were to be coated with a layer of tin-bismuth (2% Bi) to guard against tin pest, a type of degradation that occurs at low temperatures. Based on the results of the investigation, which included SEM/EDS analysis, inductively coupled plasma spectroscopy, and x-ray diffraction, the metal surfaces contained less than 0.1% Bi and thus were not adequately protected against tin pest, which was confirmed as the failure mechanism in the investigation.

The principal types of elevated-temperature mechanical failure are creep and stress rupture, stress relaxation, low- and high-cycle fatigue, thermal fatigue, tension overload, and combinations of these, as modified by environment. This article briefly reviews the applied aspects of creep-related failures, where the mechanical strength of a material becomes limited by creep rather than by its elastic limit. The majority of information provided is applicable to metallic materials, and only general information regarding creep-related failures of polymeric materials is given. The article also reviews various factors related to creep behavior and associated failures of materials used in high-temperature applications. The complex effects of creep-fatigue interaction, microstructural changes during classical creep, and nondestructive creep damage assessment of metallic materials are also discussed. The article describes the fracture characteristics of stress rupture. Information on various metallurgical instabilities is also provided. The article presents a description of thermal-fatigue cracks, as distinguished from creep-rupture cracks.