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Creep fracture/stress rupture
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Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.modes.c9001726
EISBN: 978-1-62708-234-1
... Oxidation Swelling Tubes Carbon steel Creep fracture/stress rupture A carbon steel furnace tube which should have given good service for ten years ruptured after one year. Analysis The tube shows obvious swelling at the point of rupture (see Fig. 1 ), and the bulged surface of the tube has...
Abstract
A carbon steel furnace tube which should have given good service for ten years ruptured after one year. The tube showed obvious swelling at the point of rupture, and the bulged surface of the tube was oxidized at a temperature far above the design temperature. There was little or no loss in wall thickness due to corrosion or scaling, and the tube wall was thinned to a knife edge at the rupture. Metallographic examination showed the condition of the material was satisfactory. The failure was mechanical in nature, typical of short time creep rupture. The localized oxidation indicated improper furnace operation or blockage of the tube. The furnace was checked and found to have a burner tip out of order. After the tip was repaired, localized overheating was minimized and further premature failures did not occur.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c0091028
EISBN: 978-1-62708-229-7
.... Electric power generation Overheating Superheater tubes ASTM A213 grade T22 UNS K21590 Creep fracture/stress rupture Failure occurred in a steel superheater tube in a power plant. The tube was specified as ASTM A 213 grade T 22, and the reported operating conditions were 13 MPa (1900 psi) at 482...
Abstract
Failure occurred in a steel superheater tube in a power plant. The tube was specified as ASTM A 213 grade T 22, and the reported operating conditions were 13 MPa (1900 psi) at 482 deg C (900 deg F). The tube carried superheated steam and was coal fired. Investigation (visual inspection, 2% nital etched 297x images, chemical analysis, and SEM fractographs) supported the conclusion that the superheater tube failed as a result of long-term overheating. Substantial creep damage reduced the strength of the tube to the point that overload failure occurred. No recommendations were made.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c9001000
EISBN: 978-1-62708-229-7
... not be detected. Superheaters Tube bends 1Cr-0.5Mo Creep fracture/stress rupture Rupture occurred at a bend in a superheated steam transfer line between a header and a desuperheater of a boiler producing 230 t/h of steam at 540°C and 118 kPa. The boiler had operated for 77,000 h. The geometry...
Abstract
Rupture occurred at a bend in a superheated steam transfer line between a header and a desuperheater of a boiler producing 230 t/h of steam at 540 deg C and 118 kPa. The boiler had operated for 77,000 h. Rupture occurred along the outer bend radius of the 168 mm diam tube, this being of 1 Cr, 0.5 Mo steel with a wall thickness of 14 mm. The design temperature of this tube was 490 deg C, but there is evidence that it was operating at a temperature much above 500 deg C. Metallographic analysis disclosed an advanced stage of creep damage accumulation in the form of local cracks, microcracks, and aligned damage centers which showed up as voids upon repeated polish-etch cycles. Because of the local nature of creep damage that can occur, any inspection that involves in situ metallography must be conducted at exactly the right or critical position or the presence of damage may not be detected.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c9001011
EISBN: 978-1-62708-229-7
... of creep was not operative throughout the life of the equipment. Outlet tubes Overheating Oxidation Superheaters 2.25Cr-1Mo Creep fracture/stress rupture Thermal fatigue fracture After some 87,000 h of operation, failure took place in the bend of a steam pipe connecting a coil of the third...
Abstract
After some 87,000 h of operation, failure took place in the bend of a steam pipe connecting a coil of the third superheater of a steam generator to the outlet steam collector. The unit operated at 538 deg C and 135 kPa, producing 400 t/h of steam. The 2.25Cr-1Mo steel pipe in which failure took place was 50.8 mm in diam with a nominal wall thickness of 8 mm. It connected to the AISI 321 superheater tube by means of a butt weld and was one of 46 such parallel connecting tubes. The Cr-Mo tubing was situated outside the heat transfer zone of the superheater. The overall sequence of failure involved overheating of the Cr-Mo outlet tubes, heavy oxidation, oxide cracking on thermal cycling, thermal fatigue cracking plus oxidation, creep-controlled crack growth, and rapid plastic deformation and rupture. This failure was indicative of excess temperature of the steam coming from the heat transfer zone of the coil. It showed that many damage mechanisms may combine in the transition from fracture initiation to final failure. The presence of grain boundary sliding as an indication of creep damage was useful in the characterization of the stress level as high and showed that the process of creep was not operative throughout the life of the equipment.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.chem.c9001736
EISBN: 978-1-62708-220-4
... mechanism, namely grain boundary sliding, relating to the periodic nature of the loading, with high residual stresses being present. Grain boundary sliding Petrochemical equipment Transfer piping Welded joints 316 UNS S31600 Creep fracture/stress rupture Leakage was detected at the welds...
Abstract
Leakage was detected at the welds between stiffening plates and the pipe in a transfer line carrying butane and related petrochemical compounds. The line and reinforcing rings were of AISI 316 stainless steel, the pipe being of 508 mm diam and 6.25 mm wall thickness. The design temperature and pressure were 621 deg C and 2.75 kPa, respectively, while the operating conditions were 579 deg C and 1.03 kPa. The line was insulated. Failure occurred after approximately 90,000 h of operation, shutdowns being approximately two per annum. The cracking occurred at the toe of welds between the plates and the pipe. The creep damage failure was attributed to repeated relaxation cycles of very high thermal stresses of resulting from the periodic shutdowns, temperature fluctuations during service, or both. This failure emphasized the information available from an evaluation of the operative creep mechanism, namely grain boundary sliding, relating to the periodic nature of the loading, with high residual stresses being present.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.modes.c0048294
EISBN: 978-1-62708-234-1
... boiler circulation and high furnace temperatures were believed to have caused the prolonged overheating. Heat exchanger tubes Overheating Spheroidizing Superheaters 1.25Cr-0.5Mo ASME SA213-T11 Creep fracture/stress rupture Two instances of superheater rupture occurred about 10 days apart...
Abstract
The tubes of a stationary industrial boiler, 64 mm in diam and made of 1.25Cr-0.5Mo steel (ASME SA-213, grade T-11) failed by two different types of rupture. Noticeable swelling of the tubes in the area of rupture was revealed by visual examination. The tubes with slight longitudinal splits were interpreted to have failed by stress rupture resulting from prolonged overheating at 540 to 650 deg C as the microstructure exhibited extensive spheroidization and coalescence of carbides. The larger ruptures were tensile failures that resulted from rapid overheating to 815 to 870 deg C as a completely martensitic structure was revealed at the edges of the ruptures in these tubes because of rapid quenching by escaping fluid. The prolonged-overheating failures were concluded to have been the primary ruptures and that local loss of circulation had caused rapid overheating in adjacent tubes. Poor boiler circulation and high furnace temperatures were believed to have caused the prolonged overheating.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.modes.c9001688
EISBN: 978-1-62708-234-1
... case. Decarburization Superheaters Tube components ASTM A209 Creep fracture/stress rupture Intergranular corrosion High-temperature corrosion and oxidation The authors have been involved in the examination of many failed superheater components and the two examples given here...
Abstract
Some examples of equipment failures involving high temperature operation are presented. They include some steam generator superheater components and a pump shaft that should not have been at high temperature. Metallographic analysis is used to determine the causes of failure in each case.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c9001737
EISBN: 978-1-62708-229-7
... successfully, it was suggested that the remaining useful life was effectively exhausted and that it should be replaced. Thermal stresses produced during operation would rapidly result in additional cracks. Casings Gas turbines Thermal stresses 321 UNS S32100 Creep fracture/stress rupture Thermal...
Abstract
The hot gas casing of a gas turbine used for peak load power production had developed extensive cracking during operation. The operating time was 18,000 h, and it had been subjected to 1,600 operating cycles. The gas temperature on the hot side was 985 deg C, on the cold side 204 deg C, the material being AISI 321 stainless steel. The purpose of the present study was to determine optimum repair welding procedures on the premise that the material was basically sound and undamaged by creep. The cracking was the result of thermal fatigue, and such cracks can propagate at elevated temperature, with damage ahead of the crack tip occurring by means of very local processes of creep. Metallographic examination disclosed heavy surface layers of carbides, such that the material was extremely brittle when subjected to bending. Accordingly, although it was demonstrated that the casing could be welded successfully, it was suggested that the remaining useful life was effectively exhausted and that it should be replaced. Thermal stresses produced during operation would rapidly result in additional cracks.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.modes.c0048846
EISBN: 978-1-62708-234-1
... Electric power generation Steam lines Welded joints ASME SA335-P22 Intergranular fracture Creep fracture/stress rupture A main steam pipe was found to be leaking during a start-up after a 1-day shutdown. The leak was a large circumferential crack in a pipe-to-fitting weld in one of two steam...
Abstract
A main steam pipe was found to be leaking due to a large circumferential crack in a pipe-to-fitting weld in one of two steam leads between the superheater outlet nozzles and the turbine stop valves (a line made of SA335-P22 material). The main crack surface was found to be rough, oriented about normal to the outside surface, and had a dark oxidized appearance. The cracking was found to be predominantly intergranular. Distinct shiny bands that etched slower than the remainder of the sample at the top of each individual weld bead were revealed by microscopic examination. These bands were found contain small cracks and microvoids. A mechanism of intergranular creep rupture at elevated temperature was identified as a result of a series of stress-rupture and tensile tests. It was revealed by the crack shape that cracking initiated on the pipe exterior, then propagated inward and in the circumferential direction in response to a bending moment load. It was concluded that the primary cause of failure was the occurrence of bending stresses that exceeded the stress levels predicted by design calculations and that were higher than the maximum allowable primary membrane stress.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.aero.c0047720
EISBN: 978-1-62708-217-4
...-related failures Creep fracture/stress rupture Airfoil-shape impingement cooling tubes were fabricated of 0.25-mm (0.010-in.) thick Hastelloy X sheet stock, then pulsed laser beam butt welded to cast Hastelloy X base plugs. Each weldment was then inserted through the base of a hollow cast turbine...
Abstract
Airfoil-shape impingement cooling tubes were fabricated of 0.25 mm (0.010 in.) thick Hastelloy X sheet stock, then pulse-laser-beam butt welded to cast Hastelloy X base plugs. Each weldment was then inserted through the base of a hollow cast turbine blade for a jet engine. The weldments were finally secured to the bases of the turbine blades by a brazing operation. One of the laser beam attachment welds broke after a 28-h engine test run. Exposure of the fracture surface for study under the electron microscope revealed the joint had broken in stress rupture. Failure was caused by tensile overload from stress concentration at the root of the laser beam weld, which was caused by the sharp notch created by the lack of full weld penetration. Radiographic inspection of all cooling-tube weldments was made mandatory, with rejection stipulated for joints containing subsurface weld-root notches. In addition, all turbine blades containing cooling-tube weldments were reprocessed by back-brazing. Back brazed turbine blades were reinstalled in the engine and withstood the full 150-h model test run without incident.
Series: ASM Failure Analysis Case Histories
Volume: 1
Publisher: ASM International
Published: 01 December 1992
DOI: 10.31399/asm.fach.v01.c9001128
EISBN: 978-1-62708-214-3
... behavior was the prime failure mechanism of seam-welded steam pipes. Creep (materials) ASTM A155-66 class 1 2.25Cr-1Mo Creep fracture/stress rupture Background Creep crack growth and fracture toughness tests were performed using test material machined from a seam-welded steam pipe that had...
Abstract
Creep crack growth and fracture toughness tests were performed using test material machined from a seam welded ASTM A-155-66 class 1 (2.25Cr-1Mo) steel steam pipe that had been in service for 15 years. The fracture morphology was examined using SEM fractography. Dimpled fracture was found to be characteristic of fracture toughness specimens. Creep crack growth generally followed the fusion line region and was characterized as dimpled fracture mixed with cavities. These fracture morphologies were similar to those of an actual steam pipe. It was concluded that creep crack growth behavior was the prime failure mechanism of seam-welded steam pipes.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c0048299
EISBN: 978-1-62708-229-7
... to find the circuits with the greatest accumulation of debris and replacing them as necessary was recommended on an annual basis. Exfoliation Scale (corrosion) 1.25Cr-0.5Mo ASME SA213-T11 High-temperature corrosion and oxidation Creep fracture/stress rupture This particular pendant-style...
Abstract
Pendant-style reheater, constructed of ASME SA-213, grade T-11, steel ruptured. A set of four tubes, specified to be 64 mm OD x 3.4 mm minimum wall thickness was examined. A small quantity of loose debris was removed from the inside of one of the tubes. The major constituent was revealed by EDS analysis of the debris to be iron with traces of phosphorus, manganese, sodium, calcium, copper, zinc, potassium, silicon, chromium, and molybdenum. Thus the debris was interpreted to be the scale from ID of the tube with boiler feedwater chemicals from the attemperation spray. The likely cause of failure was concluded to be exfoliation of the scale from the ID surface of the tube. Creep failures were interpreted to be caused by localized temperatures higher than the maximum service temperature. Replacement of the affected tubes was recommended. Inspection of the tubes by radiography to find the circuits with the greatest accumulation of debris and replacing them as necessary was recommended on an annual basis.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c9001711
EISBN: 978-1-62708-229-7
..., as a function of oxidation thickness, temperature and time, confirming the creep failure diagnostic. Boiler pipes Electric power generation Steam 10CrMo9-10 X20MoV12-1 Creep fracture/stress rupture Introduction Carbon steels are not adequate for boiler pipes, which must work for long times...
Abstract
Failures of 10Cr-Mo9-10 and X 20Cr-Mo-V12-1 superheated pipes during service in steam power generation plants are described. Through micrographic and fractographic analysis, creep and overheating were identified as the cause of failure. The Larson-Miller parameter is computed, as a function of oxidation thickness, temperature and time, confirming the creep failure diagnostic.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.usage.c0048303
EISBN: 978-1-62708-236-5
... increased the actual operating stress. Tube wastage and high operating temperatures hastened the failure. A better understanding of the material condition of this superheater was recommended to verify all the suspect hot tubes. Overheating 2.25Cr-1Mo Creep fracture/stress rupture This example...
Abstract
A tube in a radiant superheater, the boiler of which is coal fired, failed by creep after 17 years of service. The failed tube was specified to be made of ASME SA-213, grade T-22. Measurable swelling of the tube diameter by about 2.4 mm and tube wastage caused by corrosion or erosion were observed. Log stress versus Larson-Miller Parameter (LMP) plots were produced to assess the remaining life of the superheater. It was revealed that the estimated operating temperature of 1060 deg F was higher than the estimated design temperature of 1000 deg F and that the tube wastage had increased the actual operating stress. Tube wastage and high operating temperatures hastened the failure. A better understanding of the material condition of this superheater was recommended to verify all the suspect hot tubes.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.chem.c9001735
EISBN: 978-1-62708-220-4
... showed the welds to be inadequate, and to have a strength and creep resistance below those of the base metal. Reformer furnaces Tubine Welded joints HK-40 UNS J94224 Creep fracture/stress rupture A sample tube was removed from a reformer furnace for life assessment after 69,000 h...
Abstract
A sample tube was removed from a reformer furnace for life assessment after 69,000 h of service. Sections were cut from the tube, which was a spindle cast A297 Grade HK 40 (25 Cr, 20 Ni, 0.4 C) austenitic steel of 122.5 mm OD and 10.5 mm nominal wall thickness. They were examined metallographically on transverse sections and on longitudinal sections through the butt welds joining the separate cast segments of the tube. Creep damage was mainly concentrated within the inner one third of the wall thickness. The use of damage assessment parameters in evaluating the reformer tube remaining life showed the welds to be inadequate, and to have a strength and creep resistance below those of the base metal.
Series: ASM Failure Analysis Case Histories
Volume: 1
Publisher: ASM International
Published: 01 December 1992
DOI: 10.31399/asm.fach.v01.c9001132
EISBN: 978-1-62708-214-3
... environment. On this basis, it was concluded that creep of the solder alloy was the most probable cause of failure. Creep (materials) Fire protection Soldered joints Solders Solder alloy Creep fracture/stress rupture Background A sprinkler head unit that was installed in a smoking lounge...
Abstract
A sprinkler head unit that was installed in a smoking lounge of a multi story office building in 1975 failed, causing substantial water damage. There was no fire in the building. A set of four sprinkler heads -- three that had been installed in 1975 (the failed unit, an unfailed unit from the same room, and an unfailed unit from another room) and an unused 1991 unit -- were examined. casting revealed no material defects or mechanical damage. Because of several environmental factors, it was suspected that the failed unit was exposed to temperatures much above the normal office environment. On this basis, it was concluded that creep of the solder alloy was the most probable cause of failure.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c0048845
EISBN: 978-1-62708-229-7
... inspection. The unit was operated under reduced-temperature conditions and with less load cycling than previously until a redesigned SA335-P22 header was installed. Boilers Piping Pressure vessels Superheaters ASME SA335-P11 Creep fracture/stress rupture It is generally not possible...
Abstract
The maximum life of base-loaded headers and piping is not possible to be predicted until they develop microcracking. The typical elements of a periodic inspection program after the occurrence of the crack was described extensively. Cracks caused by creep swelling in the stub-to-header welds in the secondary superheater outlet headers (constructed of SA335-P11 material) of a major boiler were described as an example. The OD of the header was measured to detect the amount of swelling and found to have increased 1.6% since its installation. Ligament cracks extending from tube seat to tube seat were revealed by surface inspection. Cracks were found to originate from inside the header, extend axially in the tube penetrations and radially from those holes into the ligaments. Cracks in 94 locations, ranging from small radial cracks to full 360Ý cracks were revealed by dye-penetrant inspection. The unit was operated under reduced-temperature conditions and with less load cycling than previously until a redesigned SA335-P22 header was installed.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.modes.c0060144
EISBN: 978-1-62708-234-1
... caused by third-stage creep in tubes because of the cost involved in removing the catalysts. Cracking (fractoring) Radiography Reformer furnaces Tubes HK-40 UNS J94204 Creep fracture/stress rupture ( Ref 1 ). About 1 year after start-up, two steam-methane reformer furnaces were subjected...
Abstract
Two steam-methane reformer furnaces were subjected to short-time heat excursions because of a power outage, which resulted in creep bulging in the Incoloy 800 outlet pigtails, requiring complete replacement. Each furnace had three cells, consisting of 112 vertical tubes per cell, each filled with a nickel catalyst. The tubes were centrifugally cast from ASTM A297, grade HK-40 (Fe-25Cr-20Ni-0.40C), heat-resistant alloy. The tube was concluded after metallurgical inspection to have failed from creep rupture (i.e., stress rupture). A project for detecting midwall creep fissuring was instigated as a result of the failure. It was concluded after laboratory radiography and macroexamination that if the fissure were large enough to show on a radiograph, either with or without the catalyst, the tube could be expected to fail within one year. The set up for in-service radiograph examination was described. The tubes of the furnace were radiographed during shut down and twenty-four tubes in the first furnace and 53 in the second furnace showed significant fissuring. Although, radiography was concluded to be a practical technique to provide advance information, it was limited to detecting fissures caused by third-stage creep in tubes because of the cost involved in removing the catalysts.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.chem.c0090454
EISBN: 978-1-62708-220-4
... resistance of the material and accelerated the failure. Chemical analysis Creep resistance Molding resins Residual stresses Shrinkage Solvents Storage vessels High-density polyethylene Creep fracture/stress rupture Brittle fracture A chemical storage vessel failed while in service...
Abstract
A chemical storage vessel failed while in service. The failure occurred as cracking through the vessel wall, resulting in leakage of the fluid. The tank had been molded from a high-density polyethylene (HDPE) resin. The material held within the vessel was an aromatic hydrocarbon-based solvent. Investigation (visual inspection, stereomicroscopic examination, 20x/100x SEM images, micro-FTIR in the ATR mode, and analysis using DSC and TGA) supported the conclusion that the chemical storage vessel failed via a creep mechanism associated with the exertion of relatively low stresses. The source of the stress was thought to be molded-in residual stresses associated with uneven shrinkage. This was suggested by obvious distortion evident on cutting the vessel. Relatively high specific gravity and the elevated heat of fusion indicated that the material had a high level of crystallinity. In general, increased levels of crystallinity result in higher levels of molded-in stress and the corresponding warpage. The significant reduction in the modulus of the HDPE material, which accompanied the saturation of the resin with the aromatic hydrocarbon-based solvent, substantially decreased the creep resistance of the material and accelerated the failure.
Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001279
EISBN: 978-1-62708-215-0
... outage. Boiler tubes Graphitization Mechanical properties ASME SA219-T1A UNS K12023 High-temperature corrosion and oxidation Creep fracture/stress rupture Background Applications The superheater tubes were from a utility boiler, a base-loaded unit that had been in service for 13...
Abstract
Tube 3 from a utility boiler in service for 13 years under operating conditions of 540 deg C (1005 deg F), 13.7 MPa (1990 psi) and 1,189,320 kg/h (2,662,000 lb/h) incurred a longitudinal rupture near its 90 deg bend while Tube 4 from the same boiler exhibited deformation near its bend. Metallographic examination revealed creep voids near the rupture in addition to graphite nodules. Exposure of the SA209 Grade T1A steel tubing to a calculated mean operating temperature of 530 deg C (983 deg F) for the 13 years resulted in graphitization and subsequent creep failure in Tube 3. The deformation in Tube 4 was likely the result of steam washing from the Tube 3 failure. Graphitization observed remote from the rupture in Tube 3 and in Tube 4 indicated that adjacent tubing also was susceptible to creep failure. In-situ metallography identified other graphitized tubes to be replaced during a scheduled outage.
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