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Caustic embrittlement
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Book Chapter
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
... 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...
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.
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
... 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. Alkalies Caustic...
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.
Image
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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Image
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
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.marine.c9001003
EISBN: 978-1-62708-227-3
... Abstract Gross wastage and embrittlement were observed in plain carbon steel desuperheaters in five new Naval power plants. The gross wastage could be duplicated in laboratory bomb tests using sodium hydroxide solutions and was concluded to be caused by free caustic concentrated by high heat...
Abstract
Gross wastage and embrittlement were observed in plain carbon steel desuperheaters in five new Naval power plants. The gross wastage could be duplicated in laboratory bomb tests using sodium hydroxide solutions and was concluded to be caused by free caustic concentrated by high heat flux. The embrittlement was shown to be caused by the flow of corrosion generated hydrogen which converted the cementite to methane which nucleated voids in the steel. A thermodynamic estimate indicated that a small amount of chromium would stabilize the carbides against decomposition by hydrogen in this temperature range, and laboratory tests with 2-14% Cr steel verified this.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.rail.c9001175
EISBN: 978-1-62708-231-0
... are very corrosive. Therefore this solution is used to test steels for caustic embrittlement 3 . Internal stresses, especially in cold-worked zones are also taken into account. The classic example of an intercrystalline stress corrosion is the well known rivet-hole cracking in steam boilers or brine...
Abstract
A water tube boiler with two headers and 15.5 atm working pressure became leaky in the lower part due to the formation of cracks in the rivet-hole edges. The boiler plate of 20 mm thickness was a rimming steel with 0.05% C, traces of Si, 0.38% Mn, 0.027% P, 0.035% S, and 0.08% Cu. The mean value of the yield point was 24 (24) kg/sq mm, the tensile strength 39 (38) kg/sq mm, the elongation at fracture, d10, 26 (24)%, the necking at fracture 71 (66)% and notch impact value 11.5 (9.4) kgm/sq cm (the values in brackets are for the transverse direction). The specimen from inside surface of the boiler was polished and etched with Fry-solution, which revealed parallel striations formed due to the cold bending of the plate. The zones of slip were concentrated around the rivet holes. The cracks were formed here. The structure examination proved that the cracks had taken an exactly intercrystalline path, which is characteristic for caustic corrosion cracks. It was recommended that the internal stresses be removed through annealing or alternatively lye-resistant steel should be used.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c9001448
EISBN: 978-1-62708-229-7
..., embrittlement of this type was the primary cause of the breaking off of the type rivet heads. Nothing was observed in the course of the examination that suggested caustic cracking. Aging Boiler plate Rivets Rimming steel Brittle fracture When the lagging was removed from the longitudinal seam...
Abstract
Rivets from the longitudinal seam of the terminal shell ring of a 12 year old Lancashire boiler broke off easily during examination. Cleavage fractures indicated a brittle material. Microstructure of a sectioned rivet head was typical of a normal rimming steel except the ferrite crystals contained numerous nitride needles. Their existence indicated an abnormally high nitrogen content. If such a steel is heated for a lengthy period to a temperature of that prevailing in a boiler, precipitation of the nitrides may be expected, with consequent embrittlement. In this case, embrittlement of this type was the primary cause of the breaking off of the type rivet heads. Nothing was observed in the course of the examination that suggested caustic cracking.
Series: ASM Failure Analysis Case Histories
Volume: 1
Publisher: ASM International
Published: 01 December 1992
DOI: 10.31399/asm.fach.v01.c9001061
EISBN: 978-1-62708-214-3
... to be susceptible to IGSCC (caustic embrittlement). The alkaline caustic kraft liquor provided the necessary aggressive environment for IGSCC at the highly stressed weld joints. No material-related deficiencies, such as hardness gradient or unacceptable microstructure, were found. Conclusion and Recommendations...
Abstract
Schedule 80 low-carbon steel pipes used to transfer kraft liquor in a Kamyr continuous pulp digester failed within 18 months after installation. Visual and metallographic examinations established that the cracking initiated on the internal surfaces of the equalizer pipes in the welds and heat-affected zones (HAZs). Fracture/crack morphology was brittle and primarily intergranular and deposits at crack tips were primarily iron oxides with significant amounts of sodium compounds. On these bases, the cracking was characterized as intergranular stress-corrosion cracking (IGSCC). Corrosion-related deterioration was not found, indicating that the material was generally suitable for the intended service. High residual tensile stresses in the welds and HAZS, resulting from field welding under highly constrained conditions using inadequate weld procedures, were the most probable cause of the failures. Minimizing residual stresses through use of welding procedures that include appropriate preweld and interpass temperatures and postweld stress relief heat treatment at 650 deg C (1200 deg F) was recommended to prevent further failures.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.steel.c9001224
EISBN: 978-1-62708-232-7
...×. Etching treatment: ammonia water, 1.5 V + 10 n caustic soda, 1.5 V (etching of carbides and sigma phase). The multiaxial stresses caused by sigma phase formation and the related embrittlement must be viewed as the cause for the fracture of the recuperator. In this case the designer has evidently...
Abstract
A recuperator for blast heating of a cupola furnace became unserviceable because of the brittle fracture of several finned tubes made of heat resistant cast steel containing 1.4C, 2.3Si and 28Cr. The service temperature was reported as 850 deg C. This led to the suspicion that the fracturing had something to do with the precipitation of sigma phase. Metallographic examination showed that the multiaxial stresses caused by sigma phase formation and the related embrittlement was the cause for the fracture of the recuperator. A steel of lower chromium content with no or little tendency for sigma phase formation would have had adequate corrosion resistance at the relatively low service temperature.
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
... the earliest forms of SCC (season cracking and caustic embrittlement) predate the term itself. It was during investigations into early SCC failures that the three required elements of SCC were discovered: a susceptible metal/alloy, a specific environment, and the presence of tensile stress. Season Cracking...
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.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c0048158
EISBN: 978-1-62708-229-7
... cracking by caustic penetration. Conclusions The springs fractured by intergranular stress-corrosion cracking during service. The cracks were promoted by the action of liquid zinc and tin in combination with static and torsional stresses on the spring wire. Stress-corrosion cracking by caustic...
Abstract
Several of the springs, made of 1.1 mm diam Inconel X-750 wire and used for tightening the interstage packing ring in a high-pressure turbine, were found broken after approximately seven years of operation. Intergranular cracks about 1.3 mm in depth and oriented at an angle of 45 deg to the axis of the wire were revealed by metallographic examination. A light-gray phase, which had the appearance of liquid-metal corrosion, was observed to have penetrated the grains on the fracture surfaces. The spring wires were found to fracture in a brittle manner characteristic of fracture from torsional loading (along a plane 45 deg to the wire axis). Liquid-metal embrittlement was expected to have been caused by metals (Sn, Zn, Pb) which melt much below maximum service temperature of the turbine. The springs were concluded to have fractured by intergranular stress-corrosion cracking promoted by the action of liquid zinc and tin in combination with static and torsional stresses on the spring wire. As a corrective measure, Na, Sn, and Zn which were present in pigmented oil used as a lubricant during spring winding was cleaned thoroughly by the spring manufacturer before shipment to remove all contaminants.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.steel.c9001225
EISBN: 978-1-62708-232-7
... with ammonia water ( Fig. 5 ), but was discolored brown by caustic soda solution ( Fig. 6 ). Therefore it did not consist of chromium carbide but of σ-phase 1 . The fracture followed along the σ-precipitates at the grain boundaries ( Fig. 7 ). The cracking of the disks therefore was caused or favored by σ...
Abstract
Three radially-cracked disks that circulated the protective gases in a bell-type annealing furnace were examined. During service they had been heated in cycles of 48 h to 720 deg C for 3 h each time, then were kept at temperature for 15 h followed by cooling to 40 deg C in 30 h, while rotating at 1750 rpm. Two disks were cracked at the inner face of the sheet metal rim while the rim of the third was completely cracked through. An analysis of the sheet metal rim of one of the disks showed the following composition: 0.06C, 1.98Si, 25.8Cr, and 35.8Ni. A steel of such high chromium content was susceptible to s-phase formation when annealed under 800 deg C. The material selected was therefore unsuitable for the stress to be anticipated. In view of the required oxidation resistance, a chromium-silicon or chromium-aluminum steel with 6 or 13% Cr would have been adequate. If the high temperature strength of these steels proved inadequate, an alloy lower in chromium would have been preferable.
Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001354
EISBN: 978-1-62708-215-0
... of sodium on crack surfaces, which is indicative of NaOH-induced stress-corrosion cracking. Failure was attributed to superheater problems that resulted in caustic carryover from the boiler. Two options for disk repair, installing a shrink-fit disk or applying weld buildup, were recommended. Weld repair...
Abstract
An A-470 steel rotor disk was removed from the high-pressure portion of a steam turbine-powered compressor after nondestructive testing revealed cracks in the shoulder of the disk during a scheduled outage. Samples containing cracks were examined using various methods. Multiple cracks, primarily intergranular were found on the inlet and outlet faces along prior-austenite grain boundaries. The cracks initiated at the surface and propagated inward. Multiple crack branching was observed. Many of the cracks were filled with iron oxide. X-ray photoelectron spectroscopy indicated the presence of sodium on crack surfaces, which is indicative of NaOH-induced stress-corrosion cracking. Failure was attributed to superheater problems that resulted in caustic carryover from the boiler. Two options for disk repair, installing a shrink-fit disk or applying weld buildup, were recommended. Weld repair was chosen, and the rotor was returned to service; it has performed for more than 1 year without further incident.
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
... instances, on-load corrosion resulting in embrittlement of certain tubes of a boiler has been associated with a less intensive form of corrosion in other regions, being more reminiscent of attack by concentrated caustic, as for example, that shown in Fig. 13 . In addition, the fact that the material...
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 Handbook Archive
Volume: 11
Publisher: ASM International
Published: 01 January 2002
DOI: 10.31399/asm.hb.v11.a0001818
EISBN: 978-1-62708-180-1
... 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. brittle fracture composite creep rupture ductile fracture fabrication failure analysis fatigue...
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
Volume: 3
Publisher: ASM International
Published: 01 December 2019
DOI: 10.31399/asm.fach.v03.c9001832
EISBN: 978-1-62708-241-9
... Stress-Corrosion Cracking Caustic Stress-Corrosion Cracking (CSCC) Nitrate Stress-Corrosion Cracking (NSCC) Conclusions It is concluded that the observations and findings during the failure investigation are consistent with nitrate-induced stress-corrosion cracking. The low-carbon steel...
Abstract
High-level radioactive wastes generated during the processing of nuclear materials are kept in large underground storage tanks made of low-carbon steel. The wastes consist primarily of concentrated solutions of sodium nitrate and sodium hydroxide. Each of the tanks is equipped with a purge ventilation system designed to continuously remove hydrogen gas and vapors without letting radionuclides escape. Several intergranular cracks were discovered in the vent pipe of one such system. The pipe, made of galvanized steel sheet, connects to an exhaust fan downstream of high-efficiency particulate air filters. The failure analysis investigation concluded that nitrate-induced stress-corrosion cracking was the cause of the failure.
Series: ASM Handbook
Volume: 11A
Publisher: ASM International
Published: 30 August 2021
DOI: 10.31399/asm.hb.v11A.a0006812
EISBN: 978-1-62708-329-4
... occurred and the resulting consequences. Examples of damage mechanisms include high-temperature creep, hydrogen embrittlement, stress-corrosion cracking, and sulfidation. A damage mechanism describes how damage came to be present. This definition of failure mechanism also should not be confused...
Abstract
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.
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
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.a0003540
EISBN: 978-1-62708-180-1
..., as shown in Fig. 10(b) . Optical metallography revealed IGA under ridgelike deposits, shown in Fig. 10(c) . Deposit analysis indicated a slightly alkaline to a very alkaline (caustic) environment. Environmental impurities consisting of sulfate, sulfide, sodium, lead, and copper were also detected...
Abstract
This article briefly reviews the various metallurgical or environmental factors that cause a weakening of the grain boundaries and, in turn, influence the occurrence of intergranular (IG) fractures. It discusses the mechanisms of IG fractures, including the dimpled IG fracture, the IG brittle fracture, and the IG fatigue fracture. The article describes some typical embrittlement mechanisms that cause the IG fracture of steels.
Series: ASM Failure Analysis Case Histories
Volume: 1
Publisher: ASM International
Published: 01 December 1992
DOI: 10.31399/asm.fach.v01.c9001117
EISBN: 978-1-62708-214-3
... in transgranular attack in steel. The “rock candy” fracture appearance seen in the failed samples would be more indicative of a caustic attack. Because the material has been used successfully for many years in this environment and because there were no known abnormal stresses or aggressive environments...
Abstract
Several tin plated, low-alloy steel couplings designed to connect sections of 180 mm (7 in.) diam casing for application in a gas well fractured under normal operating conditions. The couplings were purchased to American Petroleum Institute (API) specifications for P-110 material. Chemical analysis and mechanical testing of the failed couplings showed that they had been manufactured to the API specification for Q-125, more stringent specification than P-110, and met all requirements of the application. Fractographic examination showed that the point of initiation was an embrittled region approximately 25 mm (1 in.) from the end of the coupling. The source of the embrittlement was determined to be hydrogen charging during tin plating. Changes in the plating process were recommended.
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