Search Results for steam-injected cleaning

A steam accumulator, constructed with 10.3 mm thick SA515-70 steel heads and an 8 mm thick SA455A steel shell, ruptured after about three years of service. The accumulator was used in plastic molding operations. An extensive lack of weld penetration in this the head-to-shell girth weld was revealed by laboratory examination. Some misalignment of the head to the shell because of radial displacement of the shell and head centerlines was observed which was found to result in excessive clearances between the two parts and a slight difference in the thicknesses of the parts. Transgranular fracture with occasional secondary branching was revealed. It was interpreted by stress analysis that a small amount of misalignment added to lack of penetration increased the stresses to near the tensile strength of the material. The failure was judged to be a short-cycle high-stress notch-fatigue failure.

This article explains the main types and characteristic causes of failures in boilers and other equipment in stationary and marine power plants that use steam as the working fluid with examples. It focuses on the distinctive features of each type that enable the failure analyst to determine the cause and suggest corrective action. The causes of failures include tube rupture, corrosion or scaling, fatigue, erosion, and stress-corrosion cracking. The article also describes the procedures for conducting a failure analysis.

Failures in boilers and other equipment taking place in power plants that use steam as the working fluid are discussed in this article. The discussion is mainly concerned with failures in Rankine cycle systems that use fossil fuels as the primary heat source. The general procedure and techniques followed in failure investigation of boilers and related equipment are discussed. The article is framed with an objective to provide systematic information on various damage mechanisms leading to the failure of boiler tubes, headers, and drums, supplemented by representative case studies for a greater understanding of the respective damage mechanism.

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.

Heat exchangers are devices used to transfer thermal energy between two or more fluids, between a solid surface and a fluid, or between a solid particulate and a fluid at different temperatures. This article first addresses the causes of failures in heat exchangers. It then provides a description of heat-transfer surface area, discussing the design of the tubular heat exchanger. Next, the article discusses the processes involved in the examination of failed parts. Finally, it describes the most important types of corrosion, including uniform, galvanic, pitting, stress, and erosion corrosion.

Stress-corrosion cracking (SCC) is a form of corrosion and produces wastage in that the stress-corrosion cracks penetrate the cross-sectional thickness of a component over time and deteriorate its mechanical strength. Although there are factors common among the different forms of environmentally induced cracking, this article deals only with SCC of metallic components. It begins by presenting terminology and background of SCC. Then, the general characteristics of SCC and the development of conditions for SCC as well as the stages of SCC are covered. The article provides a brief overview of proposed SCC propagation mechanisms. It discusses the processes involved in diagnosing SCC and the prevention and mitigation of SCC. Several engineering alloys are discussed with respect to their susceptibility to SCC. This includes a description of some of the environmental and metallurgical conditions commonly associated with the development of SCC, although not all, and numerous case studies.

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 discusses the effect of using unsuitable alloys, metallurgical discontinuities, fabrication practices, and stress raisers on the failure of a pressure vessel. It provides information on pressure vessels made of composite materials and their welding practices. The article explains the failure of pressure vessels with emphasis on stress-corrosion cracking, hydrogen embrittlement, brittle and ductile fractures, creep and stress rupture, and fatigue with examples.

This article commences with a discussion on the characteristics of stress-corrosion cracking (SCC) and describes crack initiation and propagation during SCC. It reviews the various mechanisms of SCC and addresses electrochemical and stress-sorption theories. The article explains the SCC, which occurs due to welding, metalworking process, and stress concentration, including options for investigation and corrective measures. It describes the sources of stresses in service and the effect of composition and metal structure on the susceptibility of SCC. The article provides information on specific ions and substances, service environments, and preservice environments responsible for SCC. It details the analysis of SCC failures, which include on-site examination, sampling, observation of fracture surface characteristics, macroscopic examination, microscopic examination, chemical analysis, metallographic analysis, and simulated-service tests. It provides case studies for the analysis of SCC service failures and their occurrence in steels, stainless steels, and commercial alloys of aluminum, copper, magnesium, and titanium.

This article focuses on common failures of the components associated with the flow path of industrial gas turbines. Examples of steam turbine blade failures are also discussed, because these components share some similarities with gas turbine blading. Some of the analytical methods used in the laboratory portion of the failure investigation are mentioned in the failure examples. The topics covered are creep, localized overheating, thermal-mechanical fatigue, high-cycle fatigue, fretting wear, erosive wear, high-temperature oxidation, hot corrosion, liquid metal embrittlement, and manufacturing and repair deficiencies.

Nuclear power plants typically experience two or three high-cycle fatigue failures of stainless steel socket-welded connections in small bore piping during each plant-year of operation. This paper discusses fatigue-induced failure in socket-welded joints and the strategy Texas Utilities Electric Company (TU Electric) has implemented in response to these failures. High-cycle fatigue is invisible to proven commercial nondestructive evaluation (NDE) methods during crack initiation and the initial phases of crack growth. Under a constant applied stress, cracks grow at accelerating rates, which means cracks extend from a detectable size to a through-wall crack in a relatively short time. When fatigue cracks grow large enough to be visible to NDE, it is likely that the component is near the end of its useful life. TU Electric has determined that an inspection program designed to detect a crack prior to the component leaking would involve frequent inspections at a given location and that the cost of the inspection program would far exceed the benefits of avoiding a leak. Instead, TU Electric locates these cracks by visually monitoring for leaks. Field experience with fatigue-induced cracks in socket-welded joints has confirmed that visual monitoring does detect cracks in a timely manner, that these cracks do not result in catastrophic failures, and that the plant can be safely shut down in spite of a leaking socket-welded joint in a small bore pipe. Historical data from TU Electric and Southwest Research Institute are presented regarding the frequency of failures, failure locations, and the potential causes. The topics addressed include 1) metallurgical and fractographic features of fatigue cracks at the weld toe and weld root; 2) factors that are associated with fatigue, such as mechanical vibration, internal pulsation, joint design, and welding workmanship; and 3) implications of a leaking crack on plant safety. TU Electric has implemented the use of modified welding techniques for the fabrication of socket-welded joints that are expected to improve their ability to tolerate fatigue.

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.

Corrosion is the electrochemical reaction of a material and its environment. This article addresses those forms of corrosion that contribute directly to the failure of metal parts or that render them susceptible to failure by some other mechanism. Various forms of corrosion covered are galvanic corrosion, uniform corrosion, pitting, crevice corrosion, intergranular corrosion, selective leaching, and velocity-affected corrosion. In particular, mechanisms of corrosive attack for specific forms of corrosion, as well as evaluation and factors contributing to these forms, are described. These reviews of corrosion forms and mechanisms are intended to assist the reader in developing an understanding of the underlying principles of corrosion; acquiring such an understanding is the first step in recognizing and analyzing corrosion-related failures and in formulating preventive measures.

This article addresses the forms of corrosion that contribute directly to the failure of metal parts or that render them susceptible to failure by some other mechanism. It describes the mechanisms of corrosive attack for specific forms of corrosion such as galvanic corrosion, uniform corrosion, pitting and crevice corrosion, intergranular corrosion, and velocity-affected corrosion. The article contains a table that lists combinations of alloys and environments subjected to selective leaching and the elements removed by leaching.

This introductory article describes the various aspects of chemical structure that are important to an understanding of polymer properties and thus their eventual effect on the end-use performance of engineering plastics. The polymers covered include hydrocarbon polymers, carbon-chain polymers, heterochain polymers, and polymers containing aromatic rings. The article also includes some general information on the classification and naming of polymers and plastics. The most important properties of polymers, namely, thermal, mechanical, chemical, electrical, and optical properties, and the most significant influences of structure on those properties are then discussed. A variety of engineering thermoplastics, including some that are regarded as high-performance thermoplastics, are covered in this article. In addition, a few examples of commodity thermoplastics and biodegradable thermoplastics are presented for comparison. Finally, the properties and applications of six common thermosets are briefly considered.

A mechanical part, which supports the moving part, is termed a mechanical bearing and can be classified into rolling (ball or roller) bearings and sliding bearings. This article discusses the failures of sliding bearings. It first describes the geometry of sliding bearings, next provides an overview of bearing materials, and then presents the various lubrication mechanisms: hydrostatic, hydrodynamic, boundary lubrication, elastohydrodynamic, and squeeze-film lubrication. The article describes the effect of debris and contaminant particles in bearings. The steps involved in failure analysis of sliding bearings are also covered. Finally, the article discusses wear-damage mechanisms from the standpoint of bearing design.

This article describes some of the welding discontinuities and flaws characterized by nondestructive examinations. It focuses on nondestructive inspection methods used in the welding industry. The sources of weld discontinuities and defects as they relate to service failures or rejection in new construction inspection are also discussed. The article discusses the types of base metal cracks and metallurgical weld cracking. The article discusses the processes involved in the analysis of in-service weld failures. It briefly reviews the general types of process-related discontinuities of arc welds. Mechanical and environmental failure origins related to other types of welding processes are also described. The article explains the cause and effects of process-related discontinuities including weld porosity, inclusions, incomplete fusion, and incomplete penetration. Different fitness-for-service assessment methodologies for calculating allowable or critical flaw sizes are also discussed.

This article focuses on the mechanisms of microbiologically influenced corrosion as a basis for discussion on the diagnosis, management, and prevention of biological corrosion failures in piping, tanks, heat exchangers, and cooling towers. It begins with an overview of the scope of microbial activity and the corrosion process. Then, various mechanisms that influence corrosion in microorganisms are discussed. The focus is on the incremental activities needed to assess the role played by microorganisms, if any, in the overall scenario. The article presents a case study that illustrates opportunities to improve operating processes and procedures related to the management of system integrity. Industry experience with corrosion-resistant alloys of steel, copper, and aluminum is reviewed. The article ends with a discussion on monitoring and preventing microbiologically influenced corrosion failures.

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 focuses on the mechanisms of microbially induced or influenced corrosion (MIC) of metallic materials as an introduction to the recognition, management, and prevention of microbiological corrosion failures in piping, tanks, heat exchangers, and cooling towers. It discusses the degradation of various protective systems, such as corrosion inhibitors and lubricants. The article describes the failure analysis of steel, iron, copper, aluminum, and their alloys. It also discusses the probes available to monitor conditions relevant to MIC in industrial systems and the sampling and analysis of conditions usually achieved by the installation of removable coupons in the target system. The article also explains the prevention and control strategies of MIC in industrial systems.