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Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.design.c0048819
EISBN: 978-1-62708-233-4
... Abstract A large pressure vessel that had been in service as a hydrogen sulfide (H2S) absorber developed cracks and began leaking at a nozzle. The vessel contained a 20% aqueous solution of potassium hydroxide (KOH), potassium carbonate (K2CO3), and arsenic. The vessel wall was manufactured...
Abstract
A large pressure vessel that had been in service as a hydrogen sulfide (H2S) absorber developed cracks and began leaking at a nozzle. The vessel contained a 20% aqueous solution of potassium hydroxide (KOH), potassium carbonate (K2CO3), and arsenic. The vessel wall was manufactured of ASTM A516, grade 70, low-carbon steel plate. A steel angle had been formed into a ring was continuously welded to the inside wall of the vessel. The groove formed by the junction of the lower tray-support weld and the top part of the weld around the nozzle was found to have a crack. Pits and scale near the crack origin were revealed by microscopic examination and cracking was found to be transgranular. Periods of corrosion alternated with sudden instances of cleavage, under a tensile load, along preferred slip planes were interpreted during examination with a microscope. It was concluded that the combination of the residual plus operating stresses and the amount of KOH present would have caused stress corrosion as a result of caustic embrittlement. It was recommended that the tray support should be installed higher on the vessel wall to prevent coincidence of the lower tray-support weld with the nozzle weld.
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Published: 15 January 2021
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Published: 15 January 2021
×. (d) Potassium hydroxide etching confirms the presence of sigma phase at grain boundaries in the core microstructure. Original magnification: 500×
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Published: 01 January 2002
Fig. 21 Large enclosed cylindrical pressure vessel that failed by SCC because of caustic embrittlement by potassium hydroxide. (a) View of vessel before failure and details of nozzle and tray support. Dimensions given in inches. (b) Micrograph showing corrosion pits at edge of fracture surface
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in Failures of Pressure Vessels and Process Piping
> Analysis and Prevention of Component and Equipment Failures
Published: 30 August 2021
Fig. 85 Large enclosed cylindrical pressure vessel that failed by stress-corrosion cracking because of caustic embrittlement by potassium hydroxide. (a) View of vessel before failure and details of nozzle and tray support (dimensions given in inches). (b) Corrosion pits at edge of fracture
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in Failure of a Low-Carbon Steel Pressure Vessel From Caustic Embrittlement by Potassium Hydroxide
> ASM Failure Analysis Case Histories: Design Flaws
Published: 01 June 2019
Fig. 1 Large enclosed cylindrical pressure vessel that failed by SCC because of caustic embrittlement by potassium hydroxide. (a) View of vessel before failure and details of nozzle and tray support. Dimensions given in inches. (b) Micrograph showing corrosion pits at edge of fracture surface
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Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001324
EISBN: 978-1-62708-215-0
... Abstract A type 430Ti stainless steel flue gas expansion joint cracked because of caustic-induced stress-corrosion cracking. Energy-dispersive X-ray spectroscope analysis of the fracture surface deposits revealed the presence of sodium and potassium—caustics in hydroxide form. Primary fracture...
Abstract
A type 430Ti stainless steel flue gas expansion joint cracked because of caustic-induced stress-corrosion cracking. Energy-dispersive X-ray spectroscope analysis of the fracture surface deposits revealed the presence of sodium and potassium—caustics in hydroxide form. Primary fracture surfaces were all similar in appearance, and a primary crack origin could not be identified. A secondary crack brought to fracture in the laboratory showed brittle, cleavage features rather than classic, tensile overload features. This suggested that the material was embrittled.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.chem.c9001525
EISBN: 978-1-62708-220-4
... that experienced the same service conditions developed no corrosion. Corrosion was linked to forming defects that provided sites for localized corrosion, and to lack of steam drying after cleaning, which increased susceptibility to general corrosion. Corrosion products Hydroxides Potassium compounds Steam...
Abstract
Welded steel storage vessels used to hold mildly alkaline solution were produced in exactly the same manner from deep-drawn aluminum-killed SAE 1006 low-carbon steel sheet. After the cylindrical shell was drawn, a top low-carbon steel closure was welded to the inside diameter. The containers were then filled with the slightly alkaline solution, pressurized, and allowed to stand under ambient conditions. A small number, less than 1%, were returned because they began to leak in service. Inspection revealed general corrosion and pitting on the inner surfaces. However, other tanks that experienced the same service conditions developed no corrosion. Corrosion was linked to forming defects that provided sites for localized corrosion, and to lack of steam drying after cleaning, which increased susceptibility to general corrosion.
Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001387
EISBN: 978-1-62708-215-0
...) The operating parameters were: Electrolyte composition 5 to 10 wt % potassium hydroxide in the feedwater Cell voltage 2.5 to 3.5 V dc Current 5000 A Temperature Electrolyte side: 50 °C (120 °F) Cooling water side: 45 °C (110 °F) Specimen Selection Several specimens from...
Abstract
Nickel anodes failed in several electrolysis cells in a heavy-water upgrading plant. Dismantling of a cell revealed gouging and the presence of loosely attached black porous masses on the anode. The carbon steel top, plate was severely corroded. An appreciable quantity of black powder was also present on the bottom or the cell. SEM/EDX studies of the outer and inner surfaces of the gouged anode showed the presence of iron globules at the interface between the gouged and the unattacked anode. The chemical composition of the black powder was determined to be primarily iron. Cell malfunction was attributed to the accelerated dissolution of the carbon steel anode top, dislodgment of grains from the material, and subsequent closing of the small annular space between the anode and the cathode by debris from the anode top. Cladding of the carbon steel top with a corrosion-resistant material, such as nickel, nickel-base alloy, or stainless steel, was recommended.
Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001323
EISBN: 978-1-62708-215-0
... of the gouge shown in Fig. 6 . The results show the presence of sodium, aluminum, silicon, phosphorus, sulfur, potassium, calcium, titanium, and iron. Sodium in the form of sodium hydroxide caused the gouging, and the attack was probably aggravated by the presence of silicon and sulfur (silicates and sulfur...
Abstract
Original carbon steel and subsequent replacement austenitic stainless steel superheater tube U-bend failures occurred in a waste heat boiler. The carbon steel tubes had experienced metal wastage in the form of caustic corrosion gouging, while the stainless steel tubes failed by caustic-induced stress-corrosion cracking. Sodium was detected by EDS in the internal deposits and the base of a gouge in a carbon steel tube and in the internal deposits of the stainless steel tube. The sodium probably formed sodium hydroxide with carryover moisture and caused the gouging, which was further aggravated by the presence of silicon and sulfur (silicates and sulfates). It was recommended that the tubes be replaced with Inconel 600 or 601, as a practical option until the carryover problem could be solved.
Series: ASM Handbook
Volume: 11
Publisher: ASM International
Published: 15 January 2021
DOI: 10.31399/asm.hb.v11.a0006760
EISBN: 978-1-62708-295-2
... and austenitic stainless steels after extensive exposure to temperatures ranging from 650 to 900 °C (1200 to 1650 °F). It forms more rapidly from ferrite than from austenite. Electrolytic etching with potassium hydroxide (KOH) reveals a sigma phase ( Fig. 26 ). Fig. 26 Duplex stainless steel etched...
Abstract
Visual examination, using the unaided eye or a low-power optical magnifier, is typically one of the first steps in a failure investigation. This article presents the guidelines for selecting samples for scanning electron microscope examination and optical metallography and for cleaning fracture surfaces. It discusses damage characterization of metals, covering various factors that influence the damage, namely stress, aggressive environment, temperature, and discontinuities.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.modes.c9001177
EISBN: 978-1-62708-234-1
... are chlorides such as calcium and magnesium chloride, but also highly concentrated alkali solutions such as potassium or sodium hydroxide. The process takes place very slowly at room temperature, but is strongly accelerated by raising the temperature, Stresses are effective even if they lie far below the yield...
Abstract
A solution containing 50 to 70% calcium chloride (pH 7.5 to 8.5) was concentrated by evaporation in a brick-lined vessel by passing steam at a pressure of 15 atmospheres through a system of heating coils made of austenitic stainless steel X 10 Cr-Ni-Mo-Ti 18 12 (Material No. 1.4573). After five months one of the coils, which consisted of tubes having a wall thickness of 3.4 mm, developed a leak. Tightly closed cracks were seen on the outer surface of the tube. Further tests with color penetration process revealed multiple branched cracks. Longitudinal section showed that the cracks had started from the outside surface of the tube. Electrolytic etching further showed that they had propagated mainly across the grains. It was concluded that this was a typical case of transcrystalline stress corrosion.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.usage.c9001660
EISBN: 978-1-62708-236-5
... unit employing Kroll's etch and a rare earth polishing compound. Application of a duplex etching treatment consisting of Kroll's solution followed by a hydrogen peroxide-potassium hydroxide mixture, combined with interference microscopy, was needed to delineate the shear bands. The threads were...
Abstract
Failure analysis was performed on threaded Ti-6Al-4V fasteners that had fractured in the threads during installation. Scanning electron microscopy (SEM) and optical metallography revealed that the fractures initiated in circumferential shear bands present at the thread roots. The fractures propagated by microvoid coalescence typical of that observed in notched tensile specimen fractures of the same material. For comparison, Ti-6Al-4V fasteners from various commercial sources were tested to failure in uniaxial tension and examined in the SEM. In all cases, the fracture appearances were similar to that exhibited by the fasteners that failed during installation. In addition, results of optical microscopy indicated that the geometry and extent of the shear bands appeared to depend on the fabrication process employed by the individual manufacturers. Causes of shear band formation are discussed along with potential methods to eliminate these microstructural in homogeneities.
Series: ASM Handbook
Volume: 11A
Publisher: ASM International
Published: 30 August 2021
DOI: 10.31399/asm.hb.v11A.a0006825
EISBN: 978-1-62708-329-4
... hydroxide). Below 570 °C (1060 °F), the main constituent of the scale formed on carbon and low-alloy steel is magnetite (Fe 3 O 4 ), whereas above 570 °C (1060 °F), it is wustite (FeO). The scale formed on T91 steel, which has special significance as a tube material for supercritical boilers, is somewhat...
Abstract
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.
Series: ASM Handbook Archive
Volume: 11
Publisher: ASM International
Published: 01 January 2002
DOI: 10.31399/asm.hb.v11.a0001818
EISBN: 978-1-62708-180-1
... location, traces of potassium and titanium were found. Analyses of other areas did not disclose definitive evidence of contaminants to support SCC as the failure mechanism. Fig. 10 Fracture surface of mechanical test specimen from piping cross. Fracture is intergranular. The coarse grain size...
Abstract
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.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c9001396
EISBN: 978-1-62708-229-7
... may be defeated by the phenomenon known as “hide out”, a term used to describe local concentration of chemicals, e.g. phosphates and alkali, which can occur within a boiler thereby leading to anomalous conclusions when interpreting the results of water analyses. Potassium salts, instead of sodium...
Abstract
The phenomenon of on-load corrosion is directly associated with the production of magnetite on the water-side surface of boiler tubes. On-load corrosion may first be manifested by the sudden, violent rupture of a boiler tube, such failures being found to occur predominantly on the fire-side surface of tubes situated in zones exposed to radiant heat where high rates of heat transfer pertain. In most instances, a large number of adjacent tubes are found to have suffered, the affected zone frequently extending in a horizontal band across the boiler. In some instances, pronounced local attack has taken place at butt welds in water-wall tubes, particularly those situated in zones of high heat flux. To prevent on-load corrosion an adequate flow of water must occur within the tubes in the susceptible regions of a boiler. Corrosion products and suspended matter from the pre-boiler equipment should be prevented from entering the boiler itself. Also, it is good practice to reduce as far as possible the intrusion of weld flash and other impedances to smooth flow within the boiler tubes.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c9001143
EISBN: 978-1-62708-229-7
... and potassium chloride. As the steam expands through the turbine, the solubility of the corrosive chemicals decreases. When the solubility limit is reached the chemicals precipitate into droplets of concentrated solutions which are in equilibrium with the steam. Chemicals such as sodium hydroxide are in a class...
Abstract
The assignment of financial liability for turbine blade failures in steam turbines rests on the ability to determine the damage mechanism or mechanisms responsible for the failure. A discussion is presented outlining various items to look for in a post-turbine blade failure investigation. The discussion centers around the question of how to determine whether the failure was a fatigue induced failure, occurring in accordance with normal life cycle estimates, or whether outside influences could have initiated or hastened the failure.
Series: ASM Handbook
Volume: 11
Publisher: ASM International
Published: 15 January 2021
DOI: 10.31399/asm.hb.v11.a0006785
EISBN: 978-1-62708-295-2
... Engineering Experiment Station concluded, “The results which have been obtained justify the opinion which has prevailed in the United States that mild steel is embrittled by sodium hydroxide… Stress and chemical attack now appear to be the predominating factors, neither of which can produce embrittlement...
Abstract
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.
Series: ASM Handbook Archive
Volume: 11
Publisher: ASM International
Published: 01 January 2002
DOI: 10.31399/asm.hb.v11.a0003555
EISBN: 978-1-62708-180-1
... by internal sulfidation above 800 °C (1470 °F); alloy depletion is generally associated with the corrosion front. This attack involves molten ash and deposits containing sodium sulfate and/or potassium sulfate salts. Very small amounts of sulfur and sodium or potassium can produce sufficient Na 2 SO 4...
Abstract
High temperature corrosion may occur in numerous environments and is affected by factors such as temperature, alloy or protective coating composition, time, and gas composition. This article explains a number of potential degradation processes, namely, oxidation, carburization and metal dusting, sulfidation, hot corrosion, chloridation, hydrogen interactions, molten metals, molten salts, and aging reactions including sensitization, stress-corrosion cracking, and corrosion fatigue. It concludes with a discussion on various protective coatings, such as aluminide coatings, overlay coatings, thermal barrier coatings, and ceramic coatings.
Series: ASM Handbook Archive
Volume: 11
Publisher: ASM International
Published: 01 January 2002
DOI: 10.31399/asm.hb.v11.a0003553
EISBN: 978-1-62708-180-1
Abstract
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.
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