Search Results for Sulfur recovery units

Two leaks were discovered at a sulfur recovery unit in a refinery. The leaks were at pipe-to-elbow welds in a 152 mm (6 in.) (NPS 6) diam line, operating in lean amine service at 50 deg C (120 deg F) and 2.9 MPa (425 psig). Thickness measurements indicated negligible loss of metal, and the leaks were clamped. A year later, 15 additional leaks were discovered, again at pipe-to-elbow welds in lean amine lines. Further nondestructive testing located other cracks, giving a total of 35. These lines had been in service for approximately eight years. Investigation (visual inspection, hardness testing, and micrographic cross-sections) supported the conclusion that the failure was caused by lean amine SCC. It was considered unlikely that these pipe welds had received such a postweld heat treatment, although it is industry practice to postweld stress relieve piping and pressure vessels in lean amine service if the temperature is expected to be above 95 deg C (200 deg F). Recommendations included inspecting all welds using shear wave ultrasonic testing and postweld heat treating all welds in lean amine service.

A component of a water filtration unit failed while being used in service for approximately eight months. The filter system had been installed in a commercial laboratory, where it was stated to have been used exclusively in conjunction with deionized water. The failed part had been injection molded from a 30% glass-fiber and mineral-reinforced nylon 12 resin. Investigation, including visual inspection, 118x SEM images, 9x micrographs, energy-dispersive x-ray spectroscopy, micro-FTIR in the ATR mode, and TGA, supported the conclusion that the filter component failed as a result of molecular degradation caused by the service conditions. Specifically, the part material had undergone severe chemical attack, including oxidation and hydrolysis, through contact with silver chloride. The source of the silver chloride was not established, but one potential source was photographic silver recovery.

Several 304H stainless steel superheater tubes fractured in stressed areas within hours of a severe caustic upset in the boiler feedwater system. Tests performed on a longitudinal weld joint, which connected two adjacent tubes in the tertiary superheater bank, confirmed caustic-induced stress-corrosion cracking, promoted by the presence of residual welding stresses. Improved maintenance of check valves and routine inspection of critical monitoring systems (conductivity alarms, sodium analyzers, etc.) were recommended to help avoid future occurrences of severe boiler feedwater contamination. Additional recommendations were to eliminate these short longitudinal weld joints by using a bracket assembly joint between the tubes, use a post-weld heat treatment to relieve residual welding stress or select a more stress-corrosion cracking resistant alloy for this particular application.

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.

Metallographic studies found that steel used to fabricate the U.S.S. Arizona battleship during original construction, 1913-1915 and reconstruction, 1929-1931 were consistent with the best materials available during each time period. Due to the force of the forward magazine detonation, the best steel available today would not have had any impact on the outcome. Heavy banding in steels from both periods could adversely affect the corrosion resistance under anaerobic conditions that prevail during a corrosion cycle that has developed under hard biofouling layers for over 58 years. Banding would have no effect on corrosion rate under aerobic conditions that may occur in local areas on the hull. In the part of the ship from which samples for this report were obtained, high temperatures above 1340 deg F did not occur. Hull plate samples from the submerged wreckage are not yet available. These samples will be important to confirm findings to this time and determine the remaining thickness of the hull plate and, indirectly, the integrity of the fuel oil tanks.

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.

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 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 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.

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.

This article describes the general aspects of creep, stress relaxation, and yielding for homogeneous polymers. It then presents creep failure mechanisms in polymers. The article discusses extrapolative methods for the prediction of long-term creep failure in polymer materials. Then, the widely used models to simulate the service life of polymers are highlighted. These include the Burgers power-law model, the Findley power-law model, the time-temperature superposition (or equivalence) principle (TTSP), and the time-stress superposition principle (TSSP). The Larson-Miller parametric method, one of the most common to describe the material deformation and rupture time, is also discussed.

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 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.

This article provides practical information and data on property development in engineering plastics. It discusses the effects of composition on submolecular and higher-order structure and the influence of plasticizers, additives, and blowing agents. It examines stress-strain curves corresponding to soft-and-weak, soft-and-tough, hard-and-brittle, and hard-and-tough plastics and temperature-modulus plots representative of polymers with different degrees of crystallinity, cross-linking, and polarity. It explains how viscosity varies with shear rate in polymer melts and how processes align with various regions of the viscosity curve. It discusses the concept of shear sensitivity, the nature of viscoelastic properties, and the electrical, chemical, and optical properties of different plastics. It also reviews plastic processing operations, including extrusion, injection molding, and thermoforming, and addresses related considerations such as melt viscosity and melt strength, crystallization, orientation, die swell, melt fracture, shrinkage, molded-in stress, and polymer degradation.

Polymer materials are key building blocks of the modern world, commonly used in packaging, automobiles, building materials, electronics, telecommunications, and many other industries. These commercial applications of polymeric materials would not be possible without the use of additives. This article is divided into five sections: mechanical property modifiers, physical property modifiers, biological function modifiers, processing aids, and colorants. It describes three classes of additives that are used to inhibit biological activity, six classes of mechanical property modifiers, three classes of physical property modifiers, and two classes of both colorants and processing aids.

This article reviews the analytical techniques most commonly used in plastic component failure analysis. These include the Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, thermomechanical analysis, and dynamic mechanical analysis. The descriptions of the analytical techniques are supplemented by a series of case studies that include pertinent visual examination results and the corresponding images that aid in the characterization of the failures. The article describes the methods used for determining the molecular weight of a plastic resin. It explains the use of mechanical testing in failure analysis and also describes the considerations in the selection and use of test methods.

This article aims to identify and illustrate the types of overload failures, which are categorized as failures due to insufficient material strength and underdesign, failures due to stress concentration and material defects, and failures due to material alteration. It describes the general aspects of fracture modes and mechanisms. The article briefly reviews some mechanistic aspects of ductile and brittle crack propagation, including discussion on mixed-mode cracking. Factors associated with overload failures are discussed, and, where appropriate, preventive steps for reducing the likelihood of overload fractures are included. The article focuses primarily on the contribution of embrittlement to overload failure. The embrittling phenomena are described and differentiated by their causes, effects, and remedial methods, so that failure characteristics can be directly compared during practical failure investigation. The article describes the effects of mechanical loading on a part in service and provides information on laboratory fracture examination.

The types of metal components used in lifting equipment include gears, shafts, drums and sheaves, brakes, brake wheels, couplings, bearings, wheels, electrical switchgear, chains, wire rope, and hooks. This article primarily deals with many of these metal components of lifting equipment in three categories: cranes and bridges, attachments used for direct lifting, and built-in members of lifting equipment. It first reviews the mechanisms, origins, and investigation of failures. Then the article describes the materials used for lifting equipment, followed by a section explaining the failure analysis of wire ropes and the failure of wire ropes due to corrosion, a common cause of wire-rope failure. Further, it reviews the characteristics of shock loading, abrasive wear, and stress-corrosion cracking of a wire rope. Then, the article provides information on the failure analysis of chains, hooks, shafts, and cranes and related members.

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.