Three ASME SA106 grade B carbon steel feed water piping reducers from a pressurized water reactor showed indications of flaws near welds during ultrasonic testing. Further examination and testing indicated that the cracks resulted from a low-cycle corrosion fatigue phenomenon.

A carbon steel (ASTM A515 grade 70) pressure vessel failed by brittle fracture while being hydro tested in the fabricating shop. The fracture origin was a small crack at a welding arc strike associated with the toe of a nozzle weld. A fracture mechanics calculation indicated that this imperfection, although small, initiated fracture because of the local geometry and stress conditions and the low toughness of the steel. It was recommended that (1) the probability of flaws be reduced by welding over or grinding out arc strikes, (2) the local stresses be lowered by post weld stress relief and improved weld toe geometry, and (3) toughness be improved by specifying fine-grain steel and/ or by normalizing.

An unusual type of defect was discovered during hydraulic testing of a water-tube boiler after repairs to the superheater tubes following erosion from soot-blowers. When the pressure reached 700 psi, slight leakage was found to be taking place from one of the superheater tubes in a region where there appeared to be a split, approximately 8 in. long. What was thought to be a split was actually a pronounced fold. Microscopic examination showed that a corrosion-fatigue fissure had developed from one of the inside corners of the fold, presumably as a result of the fluctuating bending stresses to which this portion of the tube would be subjected because of the discontinuity in the tube wall. It was from this fissure that the leakage occurred. It was evident that the defect developed during the manufacture of the tube, probably in the course of a drawing or rolling operation without an internal plug. The diam of this portion of the tube was reduced by local collapse and folding of the section rather than by longitudinal extension of the tube itself.

Piping and structural components used in space launch facilities such as NASA's Kennedy Space Center and the Air Force's Cape Canaveral Air Station face extreme operating conditions. Launch effluent and residue from solid rocket boosters react with moisture to form hydrochloric acid that settles on exposed surfaces as they are being subjected to severe mechanical loads imparted during lift-off. Failure analyses were performed on 304 stainless steel tubing that ruptured under such conditions, while carrying various gases, including nitrogen, oxygen, and breathing air. Hydrostatic testing indicated a burst strength of 13,500 psi for the intact sections of tubing. Scanning electron microscopy and metallographic examination revealed that the tubing failed due to corrosion pitting exacerbated by stress-corrosion cracking (SCC). The pitting originated on the outer surface of the tube and ranged from superficial to severe, with some pits extending through 75% of the tube's wall thickness. The SCC emanated from the pits and further reduced the service strength of the component until it could no longer sustain the operating pressure and final catastrophic fracture occurred. Corrosion-resistant coatings added after the investigation have proven effective in preventing subsequent such failures.

This article considers two mechanisms of cavitation failure: those for ductile materials and those for brittle materials. It examines the different stages of cavitation erosion. The article explains various cavitation failures including cavitation in bearings, centrifugal pumps, and gearboxes. It provides information on the cavitation resistance of materials and other prevention parameters. The article describes two American Society for Testing and Materials (ASTM) standards for the evaluation of erosion and cavitation, namely, ASTM Standard G 32 and ASTM Standard G 73. It concludes with a discussion on correlations between laboratory results and service.

One of five underground drain lines intended to carry a highly acidic effluent from a chemical-processing plant to distant holding tanks failed in just a few months. Each line was made of 304L stainless steel pipe 73 mm (2 in.) in diam with a 5 mm (0.203 in.) wall thickness. Lengths of pipe were joined by shielded metal arc welding. Soundness of the welded joints was determined by water back-pressure testing after several lengths of pipe had been installed and joined. Before completion of the pipeline, a pressure drop was observed during back-pressure testing. An extreme depression in the backfill revealed the site of failure. Analysis (visual inspection, electrical conductivity, and soil analysis) supported the conclusions that the failure had resulted from galvanic corrosion at a point where the corrosivity of the soil was substantially greater than the average, resulting in a voltage decrease near the point of failure of about 1.3 to 1.7 V. Recommendations included that the pipelines be asphalt coated and enclosed in a concrete trough with a concrete cover. Also, magnesium anodes, connected electrically to each line, should be installed at periodic intervals along their entire length to provide cathodic protection.

Stator vanes (cast from a Cu-Mn-Al alloy) in a hydraulic dynamometer used in a steam-turbine test facility were severely eroded. The dynamometer was designed to absorb up to 51 MW (69,000 hp) at 3670 rpm, and constituted an extrapolation of previous design practices and experience. Its stator was subject to severe erosion after relatively short operating times and initially required replacement after each test program. Although up to 60 cu cm (3.7 cu in.) of material was being lost from each vane, it only reduced the power-absorption capacity by a small amount. Analysis supported the conclusion that the damage was due to liquid erosion, but it could not be firmly established whether it was caused by cavitation or by liquid impact. Recommendations included making a material substitution (to Mo-13Cr-4Ni stainless steel) and doing a redesign to reduce susceptibility to erosion as well as erosion-producing conditions.

A spherical carbon steel fixed-catalyst bed reactor, fabricated from French steel A42C-3S, approximately equivalent to ASTM A201 grade B, failed after 20 years of service while in a standby condition. The unit was found to contain primarily hydrogen at the time of failure. The vessel had a type 304 stainless steel shroud around the catalyst bed as protection against the overheating that was possible if the gas bypassed the bed through the refractory material. The failure was observed to have begun at the toe of the shroud-support ring weld. The ring was found to have a number of small cracks at the root of the weld. The cleavage mode of fracture was confirmed by SEM. The presence of extensive secondary cracking and twinning (Neumann bands) where the fracture followed the line of the shroud-support ring was revealed by metallography. It was revealed by refinery maintenance records that the ring had been removed for hydrotest and welded without any postweld heat treatment. The final cause of failure was concluded to be cracking that developed during the installation of the new shroud ring. Stress-relief heat treatments were recommended to be performed to reduce residual-stress levels after welding.

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.

A recurring piston shaft failure problem on the billet-loading tray of an extrusion press was investigated. Two shafts fractured within a period of 10 days. The shaft was machined from normalized EN3 (AISI C1022) steel stock without further treatment. Visual, microstructural, chemical, and mechanical (hardness and tensile properties) analyses of failed shaft specimens were conducted. The examinations showed that the shafts had failed by fatigue. It was recommended that a low-alloy steel (e.g., 3% Ni-Cr) in the hardened and tempered condition and subjected to shot-peening surface-hardening treatment be used. The provision of a stop to reduce bending stresses was also recommended.

Vibration analysis can be used in solving both rotating and nonrotating equipment problems. This paper presents case histories that, over a span of approximately 25 years, used vibration analysis to troubleshoot a wide range of problems.

A detailed investigative failure analysis was conducted on an autoclave which blew apart in a furnace for no apparent reason. Bolt failure resulted in separation of the autoclave lid and subsequent destruction of the furnace. Analysis using metallography, fractography, mechanical testing and exemplar tests were performed on the bolt material. Mechanical engineering analysis and leak-before-break criteria were extensively analyzed. Results led to only one possible conclusion: that an explosion occurred within the autoclave. Suggestions for autoclave design are presented as a result of the analysis.

The repeated failure of a welded ASTM A283 grade D pipe that was part of a 6 km (4 mi) line drawing and conducting river water to a water treatment plant was investigated. Failure analysis was conducted on sections of pipe from the third failure. Visual, macrofractographic, SEM fractographic, metallographic, chemical, and mechanical property (tension and impact toughness) analyses were conducted. On the basis of the tests and observations, it was concluded that the failure was the combined result of poor notch toughness (impact) properties of the steel, high stresses in the joint area, a possible stress raiser at the intersection of the spiral weld and girth weld, and sudden impact loading, probably due to water hammer. Use of a semi- or fully killed steel with a minimum Charpy V-notch impact value of 20 J (15 ft·lbf) at 0 deg C (32 deg F) was recommended for future water lines. Certified test results from the steel mill, procedure qualification tests of the welding, and design changes to reduce water hammer were also recommended.

A case of continual product refinement stimulated by product failures was described. Brittle fracture of gas transmission line pipe steels occurred demonstrating a poor combination of materials, environment, manufacturing and installation problems, and loads. Initial efforts were concentrated towards decreasing the Charpy ductile-to-brittle transition temperature to avoid brittle fracture. It was subsequently revealed that the absorbed energy on the upper shelf of the Charpy energy-temperature curve was critical for arresting a moving crack. Both fracture initiation and fracture propagation were needed be controlled. It was concluded that improved steel processing procedures, chiefly hot-working temperature and deformation control, were also required to optimize microstructure and properties.

Tribology is the study of contacting materials in relative motion and more specifically the study of friction, wear, and lubrication. This article discusses the classification and the mechanisms of friction, wear, and lubrication of polymers. It describes the tribological applications of polymers and the tribometers and instrumentation used to measure the tribological properties of polymers. The article discusses the processes involved in calculating the wear rate of polymers and the methods of characterization of the sliding interface. It provides information on the pressure and velocity limit of polymer composites and polymer testing best practices.

The boom lift equalizer hose on an excavator failed and the resultant release of high-pressure hydraulic fluid damaged the operator cabin. The hose was a heavy duty, high-impulse, multiple-spiral wire-reinforced, rubber covered hydraulic hose equivalent to 100R13 specifications as set in AS3791-1991. It had a maximum operating pressure of 34.5 MPa (5000 psi). The failure occurred adjacent to one of the couplings, although some of the wire strands had not broken. The two outer layers of reinforcement wire on the failed end had experienced extensive corrosion, corroding away completely in most areas. This corrosion was fairly uniform around the circumference of the hose. The loss of two spirals/layers of wire reinforcement effectively reduced the pressure carrying capacity of the hose to below that of the maximum operational pressure experienced. Either the hose (or assembly) was already corroded prior to being fitted, or, the hose experienced aggressive conditions causing rapid corrosion of the exposed wire strands.

An unacceptable degree of porosity was identified in several closure welds on stainless steel containers for plutonium-bearing materials. The pores developed in the weld tie-in region due to gas trapped by the weld pool during the closure process. This paper describes the efforts to trace the root cause of the porosity to the geometric conditions of the weld joint and establish corrective actions to minimize such porosity.

This article discusses pressure vessels, piping, and associated pressure-boundary items of the types used in nuclear and conventional power plants, refineries, and chemical-processing plants. It begins by explaining the necessity of conducting a failure analysis, followed by the objectives of a failure analysis. Then, the article discusses the processes involved in failure analysis, including codes and standards. Next, fabrication flaws that can develop into failures of in-service pressure vessels and piping are covered. This is followed by sections discussing in-service mechanical and metallurgical failures, environment-assisted cracking failures, and other damage mechanisms that induce cracking failures. Finally, the article provides information on inspection practices.

This article provides some new developments in elevated-temperature and life assessments. It is aimed at providing an overview of the damage mechanisms of concern, with a focus on creep, and the methodologies for design and in-service assessment of components operating at elevated temperatures. The article describes the stages of the creep curve, discusses processes involved in the extrapolation of creep data, and summarizes notable creep constitutive models and continuum damage mechanics models. It demonstrates the effects of stress relaxation and redistribution on the remaining life and discusses the Monkman-Grant relationship and multiaxiality. The article further provides information on high-temperature metallurgical changes and high-temperature hydrogen attack and the steps involved in the remaining-life prediction of high-temperature components. It presents case studies on heater tube creep testing and remaining-life assessment, and pressure vessel time-dependent stress analysis showing the effect of stress relaxation at hot spots.

The repeated failure of rubber-covered rotors and volute liners in a flue gas desulfurization system after conversion from lime slurry reagent to limestone slurry reagent was investigated. The pump was a horizontal 50 x 65 mm (2 x 2.5 in.) Galiger pump with a split cast iron case and open rotor (impeller). Both the case and the ductile iron rotor core were covered by natural rubber. Analyses conducted included surface examination of wear patterns, chemical analysis of materials, measurement of mechanical properties, and in-place flow tests. It was determined that the proximate cause of failure was cavitation and vortexing between the rotor and the lining. The root cause of the failure was the conversion from lime to limestone slurry without appropriate modification of the pump. Conversion to the limestone slurry resulted in fluid dynamics outside the operational limits of the pump. The recommended remedial action was replacement with a pump appropriately sized for the desired pressures and flow rates for limestone slurry.