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.

The wires used in a wet precipitator for cleaning the gases coming off a basic oxygen furnace failed. The system consisted of six precipitators, three separate dual units, each composed of four zones. Each zone contained rows of wires (cold drawn AISI 1008 carbon steel) suspended between parallel collector plates. It was determined that the 1008 wires failed because of corrosion fatigue. It was decided to replace all of the wires in the two zones with the highest rates of failure with cold-drawn type 304 austenitic stainless steel wire. These expensive wires, however, failed after a week by transgranular SCC. Annealed type 430 ferritic stainless steel was subsequently suggested to prevent further failures.

The bolt in a bolt and thimble assembly used to connect a wire rope to a crane hanger bracket was worn excessively. Two worn bolts, one new bolt, and a new thimble were examined. Specifications required the bolts to be made of 4140 steel heat treated to a hardness of 277 to 321 HRB. Thimbles were to be made of cast 8625 steel, but no heat treatment or hardness were specified. Analysis (visual inspection, hardness testing, and metallographic examination) supported the conclusion that the wear was due to strikingly difference hardness measurements in the bolt and thimble. Recommendations included hardening and tempering the bolts to the hardness range of 375 to 430 HRB. The thimbles should be heat treated to a similar microstructure and the same hardness range as those of the bolt. Molybdenum disulfide lubricant can be liberally applied during the initial installation of the bolts. A maintenance lubrication program was not suggested, but galling could be reduced by periodic application of a solid lubricant.

The failure during use of a seat on a heavy-duty swing set at an elementary school was investigated. The seat contained a perforated reinforcing sheet metal (galvanized type 430 stainless steel) insert covered by an elastomeric material. Specimens of the reinforcing sheet from the failed seat were examined using SEM fractography, tensile and ductility tests, and spectrographic chemical analysis. The test results showed that the steel used did not meet the manufacturer's specifications for ductility (elongation). In addition, the small-diameter punched holes caused a stress concentration factor that aggravated the brittleness of the steel.

An ASTM A391 steel chain link of an over head hoist failed catastrophically, causing damage to both property and personnel. Macrofractography identified the sequence of fractures within the chain link. The first fracture occurred at the welded joint, a second occurred opposite the weld. SEM fractography and metallography indicated that the link failed in a ductile manner because of tensile overload, which occurred when the hoist hook contacted the hoist's housing and prevented uptake of the chain. It was recommended that a load-sensing device be installed to prevent future occurrences and that a dye penetrant inspection be performed on the renwinder of the chain.

Turbine buckets in a 37.5-MW gas turbine made of Udimet 500 superalloy failed in service. The power plant was located 1 km (0.6 miles) from the Pacific Ocean and operated on No. 2 diesel fuel, which was supplied by tanker ship. Turbine bucket failures occurred on three units after 2500 to 6400 h of operation. Investigation (visual inspection, metallographic examination, and stress analysis) supported the conclusion that the differing microstructure of the airfoil resulted in changes in mechanical properties. Because normal operation includes cycling of loads and temperatures, the shroud tip fractured due to thermomechanical fatigue in its degraded state. Recommendations included special chromium or silicon-rich coating to minimize corrosion in gas turbines operating in a marine environment with operating temperatures in the range of type 2 corrosion (650 to 750 deg C, or 1200 to 1380 deg F). Additionally, it was suggested that fuel delivery, handling, and treatment be high quality, to maintain fuel contamination within design limits, and inlet air filtration must be designed for the coastal site. Also, changing the bucket tip by increasing its thickness and changing the casting technique would reduce the stress and make the design more tolerant of corrosion.

Graphitization, the formation of graphite nodules in carbon and low alloy steels, contributes to many failures in high-temperature environments. Three such failures in power-generating systems were analyzed to demonstrate the unpredictable nature of this failure mechanism and its effect on material properties and structures. In general, the more randomly distributed the nodules, the less effect they have on structural integrity. In the cases examined, the nodules were found to be organized in planar arrays, indicating they might have an effect on material properties. Closer inspection, however, revealed that the magnitude of the effect depends on the relative orientation of the planar arrangement and principle tensile stress. For normal orientation, the effect of embrittlement tends to be most severe. Conversely, when the orientation is parallel, the nodules have little or no effect. The cases examined show that knowledge is incomplete in regard to graphitization, and the prediction of its occurrence is not yet possible.

The right front spring hanger on a dual rear axle of the tractor of a tractor-trailer combination failed, causing the vehicle to roll-over. The hanger was made from malleable cast iron that had been heat treated to produce a decarburized surface layer and a pearlitic transition layer. It had been repair welded after breaking into two pieces longitudinally in a prior incident, using cast iron as weld metal. The repair weld bead on both surfaces missed the fracture over 15 to 20% of their lengths. The incomplete repair weld and brittleness of the weld metal and heat-affected zones led to the failure.

A deformed steel tube was received for failure analysis after buckling during a heat-treat operation. The tube was subjected to various metallurgical tests as well as nondestructive testing to confirm the presence of residual stresses. The microstructure of the tube was found to be homogenous and had no banded structure. However, x-ray diffraction analysis confirmed the presence of up to 6% retained austenite which likely caused the tube to buckle during the 910 °C heat treating procedure.

Type 347 stainless steel moderator circuit branch piping in a pressurized hot water reactor was experiencing frequent leakage. Investigation of the problem involved failure analysis of leaking pipe specimens, analytical stress analysis, and determination of “leak-before-break” conditions using fracture mechanics and thermal fatigue simulation tests. Failure analysis indicated that cracking had been initiated by thermal fatigue. Data from the analysis were used in making the leak-before-break predictions. It was determined that the cracks could grow to two-thirds of the circumferential length of the pipe without catastrophic failure. A thin stainless steel sleeve was inserted in the branch pipe to resolve the problem.

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.

This article outlines the basic steps to be followed and the range of techniques available for failure analysis, namely, background data assembling, visual examination, microfractography, chemical analysis, metallographic examination, electron microscopy, electron microprobe analysis, X-ray techniques, and simulations. It also describes the steps for analyzing the data, preparing the report, preservation of evidence, and follow-up on recommendations.

This article presents tools, techniques, and procedures that engineers and material scientists can use to investigate plastic part failures. It also provides a brief survey of polymer systems and the key properties that need to be measured during failure analysis. It describes the characterization of plastics by infrared and nuclear magnetic resonance spectroscopy, differential scanning calorimetry, differential thermal analysis, thermogravimetric analysis, thermomechanical analysis, and dynamic mechanical analysis. The article also discusses the use of X-ray diffraction for analyzing crystal phases and structures in solid materials.