Search Results for unit conversion tables

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.

Mechanical testing is an evaluative tool used by the failure analyst to collect data regarding the macro- and micromechanical properties of the materials being examined. This article provides information on a few important considerations regarding mechanical testing that the failure analyst must keep in mind. These considerations include the test location and orientation, the use of raw material certifications, the certifications potentially not representing the hardware, and the determination of valid test results. The article introduces the concepts of various mechanical testing techniques and discusses the advantages and limitations of each technique when used in failure analysis. The focus is on various types of static load testing, hardness testing, and impact testing. The testing types covered include uniaxial tension testing, uniaxial compression testing, bend testing, hardness testing, macroindentation hardness, microindentation hardness, and the impact toughness test.

Bending fatigue caused crack propagation and catastrophic failures at several locations near the welds on the low-carbon steel tubular cargo box frame of police three-wheel motorcycles. ANSYS finite element analysis revealed that bending stresses in some of the frame members were aggravated by poor detail design between vertical and horizontal tubes. Stresses observed in the ANSYS analysis were not sufficient to cause the onset of fatigue. However when compounded by stress concentration factors and in-service dynamic loading, the frame could have been regularly subjected to stresses over the fatigue limit of the material. A strain gage static loading test verified FEM results, and finite element techniques were applied in the design of reinforcing members to renovate the frames. Material properties were determined and welding procedures specified for the reinforcing members. Inspection intervals were devised to avoid future problems.

This article discusses the most common thermal analysis methods for thermosetting resins. These include differential scanning calorimetry, thermomechanical analysis, thermogravimetric analysis, and dynamic mechanical analysis. The article also discusses the characterization of uncured thermosetting resins as well as the curing process. Then, the techniques to characterize the physical properties of cured thermosets and composites are presented. Several examples of stress-strain curves are shown for thermosets and thermoplastic polymers.

Grate bars in the traveling grate indurators in several taconite processing units suffered excessive corrosion following a conversion from acid to fluxed pellet production procedures. The campaign life of the HH grade cast stainless steel bars was reduced from more than 7 years to approximately 9 months. Several corroded grate bars were examined metallographically and by electron microscopy to determine the causes of the accelerated corrosion. Chemical and X-ray diffraction analyses were also conducted, along with simulation tests to assess the role of alkali chlorides in the corrosion process. The basic cause of degradation was found to be hot corrosion caused by the deposition of alkali sulfates and chlorides. However this degradation may have been aggravated by thermal cycling and abrasion. The source of the salt was impurities in the flux. Two potential solutions were proposed: modification of the processing parameters to reduce the salt deposition and / or change of bar materials to a more resistant alloy.

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.

To samples of helical compression springs were returned to the manufacturer after failing in service well short of the component design life. Spring design specifications required conformance to SAE J157, “Oil Tempered Chromium Silicon Alloy Steel Wire and Springs.” Each spring was installed in a separate heavy truck engine in an application in which spring failure can cause total engine destruction. The springs were composed of chromium-silicon steel, with a hardness ranging from 50 to 54 HRC. Chemical composition and hardness were substantially within specification. Failure initiated from the spring inside coil surface. Examination of the fracture surface using scanning electron microscopy showed no evidence of fatigue. Final fracture occurred in torsion. X-ray diffraction analysis revealed high inner-diameter residual stresses, indicating inadequate stress relief from spring winding. It was concluded that failure initiation was caused by residual stress-driven stress-corrosion cracking, and it was recommended that the vendor provide more effective stress relief.

X-ray spectroscopy is generally accepted as the most useful ancillary technique that can be added to any scanning electron microscope (SEM), even to the point of being considered a necessity by most operators. While “stand-alone” x-ray detection systems are used less frequently in failure analysis than the more exact instrumentation employed in SEMs, the technology is advancing and is worthy of note due to its capability for nondestructive analysis and application in the field. This article begins with information on the basis of the x-ray signal. This is followed by information on the operating principles and applications of detectors for x-ray spectroscopy, namely energy-dispersive spectrometers, wavelength-dispersive spectrometers, and handheld x-ray fluorescence systems. The processes involved in x-ray analysis in the SEM and handheld x-ray fluorescence analysis are then covered. The article ends with a discussion on the applications of x-ray spectroscopy in failure analysis.

This article describes the characteristics of tubing of heat exchangers with respect to general corrosion, stress-corrosion cracking, selective leaching, and oxygen-cell attack, with examples. It illustrates the examination of failed parts of heat exchangers by using sample selection, visual examination, microscopic examination, chemical analysis, and mechanical tests. The article explains corrosion fatigue of tubing of heat exchangers caused by aggressive environment and cyclic stress. It also discusses the effects of design, welding practices, and elevated temperatures on the failures of heat exchangers.

This article discusses technologies focused on processing plastic materials or producing direct tools used in plastics processing. The article focuses on extrusion and injection molding, covering applications, materials and their properties, equipment, processing details, part design guidelines, and special processes. It also covers the functions of the extruder, webline handling, mixing and compounding operations, and process troubleshooting. Thermoforming and mold design are covered. Various other technologies for polymer processing covered in this article are blow molding, rotational molding, compression molding, transfer molding, hand lay-up process, casting, and additive manufacturing.

There are many reasons why plastic materials should not be considered for an application. It is the responsibility of the design/materials engineer to recognize when the expected demands are outside of what the plastic can provide during the expected life-time of the product. This article reviews the numerous considerations that are equally important to help ensure that part failure does not occur. It provides a quick review of thermoplastic and thermoset plastics. The article focuses primarily on thermoset materials that at room temperature are below their glass transition temperature. It describes the motivation for material selection and the goal of the material selection process. The use of material datasheets for material selection as well as the processes involved in plastic material selection and post material selection is also covered.

During testing of compressors under start/stop conditions, several helical suspension springs failed. The ensuing failure investigation showed that the springs failed due to fatigue. The analysis showed that during start/stop testing the springs would undergo both a lateral and axial deflection, greatly increasing the torsional stresses on the spring. To understand the fatigue limits under these test conditions, a bench test was used to establish the fatigue strength of the springs. The bench tests showed that the failed springs had an unacceptable surface texture that reduced the fatigue life. Based on an understanding of the compressor motion, a Monte Carlo model was developed based on a linear damage theory to predict the fatigue life of the springs during start/stop conditions. The results of this model were compared to actual test data. The model showed that the design was marginal even for springs with acceptable surface texture. The model was then used to predict the fatigue life requirements on the bench test such that the reliability goals for the start/stop testing would be met, thus reducing the risk in qualifying the compressor.

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.

This article discusses the thermal properties of engineering plastics and elastomers with respect to chemical composition, chain configuration, and base polymer conformation as determined by thermal analysis. It describes the processing of base polymers with or without additives and their response to chemical, physical, and mechanical stresses whether as an unfilled, shaped article or as a component of a composite structure. It summarizes the basic thermal properties of thermoplastics and thermosets, including thermal conductivity, temperature resistance, thermal expansion, specific heat, and glass transition temperature. It also provides information on polyimide and bismaleimide resin systems. Representative examples of different types of engineering thermoplastics are discussed primarily in terms of structure and thermal properties.

Wear, a form of surface deterioration, is a factor in a majority of component failures. This article is primarily concerned with abrasive wear mechanisms such as plastic deformation, cutting, and fragmentation which, at their core, stem from a difference in hardness between contacting surfaces. Adhesive wear, the type of wear that occurs between two mutually soluble materials, is also discussed, as is erosive wear, liquid impingement, and cavitation wear. The article also presents a procedure for failure analysis and provides a number of detailed examples, including jaw-type rock crusher wear, electronic circuit board drill wear, grinding plate wear failure analysis, impact wear of disk cutters, and identification of abrasive wear modes in martensitic steels.

Engineered components fail predominantly in four major ways: fracture, corrosion, wear, and undesirable deformation (i.e., distortion). Typical fracture mechanisms feature rapid crack growth by ductile or brittle cracking; more progressive (subcritical) forms involve crack growth by fatigue, creep, or environmentally-assisted cracking. Corrosion and wear are another form of progressive material alteration or removal that can lead to failure or obsolescence. This article primarily covers the topic of abrasive wear failures, covering the general classification of wear. It also discusses methods that may apply to any form of wear mechanism, because it is important to identify all mechanisms or combinations of wear mechanisms during failure analysis. The article concludes by presenting several examples of abrasive wear.

A liquid hydrogen main fuel control valve for a rocket engine failed by fracture of the Ti-5Al-2.5Sn body during the last of a series of static engine test firings. Fractographic, metallurgical, and stress analyses determined that a combination of fatigue and unexpected aqueous stress-corrosion cracking initiated and propagated the crack which caused failure. The failure analysis approach and its results are described to illustrate how fractography and fracture mechanics, together with a knowledge of the crack initiation and propagation mechanisms of the valve material under various stress states and environments, helped investigators to trace the cause of failure.

This article reviews analytical techniques that are most often used in plastic component failure analysis. The description of the techniques is intended to familiarize the reader with the general principles and benefits of the methodologies, namely Fourier transform infrared spectroscopy, energy-dispersive x-ray spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical analysis. The article describes the methods for molecular weight assessment and mechanical testing to evaluate plastics and polymers. The descriptions of the analytical techniques are supplemented by a series of case studies to illustrate the significance of each method. The case studies also include pertinent visual examination results and the corresponding images that aided in the characterization of the failures.