Search Results for Freezing

Soft-soldered copper pipe joints used in refrigerating plants failed. The solder had not adhered uniformly to the pipe surface. In addition, there were some longitudinal grooves on the pipe surfaces, parts of which were not filled with solder. The unsoldered areas formed cavities within the joints, some of which had been in direct communication with the outsides via the grooves or interconnected cavities. On cooling, moisture condensed on the external surfaces. Some of this was drawn by capillary action into the cavities in open communication with the external surface. On continued cooling to below freezing-point, water that entered the cavities solidified. This was accompanied by a slight increase in volume, which collapsed the pipe walls. In the examples, the pipe ends had not been properly tinned. The solder used was found to be of the tin-antimony type, containing about 5% antimony, which is more difficult to use than the usual tin-lead alloys. The use of this particular type of solder was a contributory factor in the production of unsound joints in the samples examined.

An eddy current survey of the copper evaporator (chiller) tubes in an absorption air-conditioning unit revealed two tubes in the evaporator bundle with indications typical of longitudinal cracks. Significant necking down and grain distortion at the fracture surfaces was revealed by metallographic examination. The fracture features were found to be characteristic of an overload failure in a ductile material. The ruptured tubes were concluded as a result of examination to have failed as a result of excessive internal pressure. The source of the excessive internal pressure was assumed to be a freeze-up of the tube side water that occurred during interruption of the tube side flow or misoperation of the unit.

During the internal fixation, the type 316LR stainless steel cortical bone screw failed. Extensive spiral deformation was revealed by the fracture surface. Dimple structure characteristic of a ductile failure mode was observed with dimples oriented uniformly in the deformation direction. A zone of heavily deformed grains at the fracture edge was revealed by longitudinal metallographic examination. The shearing fractures of a commercially pure titanium screw and a cast cobalt-chromium-molybdenum alloy were discussed for purpose of comparison.

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.

The front wall of a cast iron crankcase cracked at the transition from the comparatively minor wall thickness to the thick bosses for the drilling of the bolt holes. Metallographic examination showed the case was aggravated by the fact that the casting had a ferritic basic structure and the graphite in part showed a granular formation, so that strength of the material was low. In a second crankcase with the same crack formation the structure in the thick-wailed part was better. But it also showed granular graphite in the ferritic matrix in the thin-walled part between the dendrites of the primary solid solution precipitated in the residual melt. A third crankcase had fractures in two places, first at the frontal end wall and second at the thinnest point between two bore holes. In all three cases casting stresses caused by unfavorable construction and rapid cooling were responsible for the crack formation. A fourth crankcase had cracked in the bore-hole of the frontal face. In this case the cause of the fracture was the low strength of a region that was caused by a bad microstructure further weakened by the bore hole.

A sand-cast LM6M aluminum alloy sprocket drive wheel in an all-terrain vehicle failed. Extensive cracking had occurred around each of the six bolt holes in the wheel. Evidence of considerable deformation in this area was also noted. Examination indicated that the part failed because of gross overload. Use of an alloy with a much higher yield strength and improvement in design were recommended.

Accelerated life testing and aging methodologies are increasingly being used to generate engineering data for determining material property degradation and service life (or fitness for purpose) of plastic materials for hostile service conditions. This article presents an overview of accelerated life testing and aging of unreinforced and fiber-reinforced plastic materials for assessing long-term material properties and life expectancy in hostile service environments. It considers various environmental factors, such as temperature, humidity, pressure, weathering, liquid chemicals (i.e., alkalis and acids), ionizing radiation, and biological degradation, along with the combined effects of mechanical stress, temperature, and moisture (including environmental stress corrosion). The article also includes information on the use of accelerated testing for predicting material property degradation and long-term performance.

Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to analyze an automotive polyoxymethylene (POM) sensor housing that was depolymerizing during service. It was found that a combination of heat, oxygen, and sulfuric acid attacked and caused premature failure of the part. POM should not be selected for automotive applications where elevated temperatures and acidic environments can exist. If exposure to acid is suspected, sodium bicarbonate should be applied to neutralize the surrounding environment, followed by copious quantities of water, and repeated until no effervescence is observed.

Cavitation damage of diesel engine cylinder liners is due to vibration of the cylinder wall, initiated by slap of the piston under the combined forces of inertia and firing pressure as it passes top dead center. The occurrence on the anti-thrust side may possibly result from bouncing of the piston. The exact mechanism of cavitation damage is not entirely clear. Two schools of thought have developed, one supporting an essentially erosive, and the other an essentially corrosive, mechanism. Measures to prevent, or reduce, cavitation damage should be considered firstly from the aspect of design, attention being given to methods of reducing the amplitude of the liner vibration. Attempts have been made to reduce the severity of attack by attention to the environment. Inhibitors, such as chromates, benzoate/nitrite mixtures, and emulsified oils, have been tried with varying success. Attempts have been made to reduce or prevent cavitation damage by the application of cathodic protection, and this has been found to be effective in certain instances of trouble on propellers.

The information provided in this article is intended for those individuals who want to determine why a casting component failed to perform its intended purpose. It is also intended to provide insights for potential casting applications so that the likelihood of failure to perform the intended function is decreased. The article addresses factors that may cause failures in castings for each metal type, starting with gray iron and progressing to ductile iron, steel, aluminum, and copper-base alloys. It describes the general root causes of failure attributed to the casting material, production method, and/or design. The article also addresses conditions related to the casting process but not specific to any metal group, including misruns, pour shorts, broken cores, and foundry expertise. The discussion in each casting metal group includes factors concerning defects that can occur specific to the metal group and progress from melting to solidification, casting processing, and finally how the removal of the mold material can affect performance.

The metallurgical condition of a cylindrical induction melter (CIM) vessel was evaluated after approximately 375 h of operation over a two-year span at temperatures between 1400 to 1500 deg C. Wall thinning and significant grain growth was observed in the lower portion of the conical section and the drain tube. No through-wall penetrations were found in the cylindrical and conical sections of the CIM vessel and only one leak site was identified in the drain tube. Failure of the drain tube was associated with localized overheating and creep. The observed degradation resulted from cumulative service at elevated temperature. A recommendation was made to implement a support for the conical section of the CIM and to increase the wall thickness of the drain tube. Thus, the possibility of drain tube misalignment in the induction coils and localized over heating will be minimized. In addition, the use of grain stabilized Pt/Rh alloy should be evaluated as a method to prevent grain growth.

This article focuses on the general root causes of failure attributed to the casting process, casting material, and design with examples. The casting processes discussed include gravity die casting, pressure die casting, semisolid casting, squeeze casting, and centrifugal casting. Cast iron, gray cast iron, malleable irons, ductile iron, low-alloy steel castings, austenitic steels, corrosion-resistant castings, and cast aluminum alloys are the materials discussed. The article describes the general types of discontinuities or imperfections for traditional casting with sand molds. It presents the international classification of common casting defects in a tabular form.

The primary purpose of this article is to describe general root causes of failure that are associated with wrought metals and metalworking. This includes a brief review of the discontinuities or imperfections that may be common sources of failure-inducing defects in the bulk working of wrought products. The article addresses the types of flaws or defects that can be introduced during the steel forging process itself, including defects originating in the ingot-casting process. Defects found in nonferrous forgings—titanium, aluminum, and copper and copper alloys—also are covered.

This article briefly reviews the general causes of weldment failures, which may arise from rejection after inspection or failure to pass mechanical testing as well as loss of function in service. It focuses on the general discontinuities observed in welds, and shows how some imperfections may be tolerable and how the other may be root-cause defects in service failures. The article explains the effects of joint design on weldment integrity. It outlines the origins of failure associated with the inherent discontinuity of welds and the imperfections that might be introduced from arc welding processes. The article also describes failure origins in other welding processes, such as electroslag welds, electrogas welds, flash welds, upset butt welds, flash welds, electron and laser beam weld, and high-frequency induction welds.

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.

Corrosion is the deterioration of a material by a reaction of that material with its environment. The realization that corrosion control can be profitable has been acknowledged repeatedly by industry, typically following costly business interruptions. This article describes the electrochemical nature of corrosion and provides the typical analysis of environmental- and corrosion-related failures. It presents common methods of testing of laboratory corrosion and discusses the processes involved in the prevention of environmental- and corrosion-related failures of metals and nonmetals.