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Book Chapter
Series: ASM Failure Analysis Case Histories
Volume: 3
Publisher: ASM International
Published: 01 December 2019
DOI: 10.31399/asm.fach.v03.c9001769
EISBN: 978-1-62708-241-9
... biomineralization in scale formation of heat exchanger tubes. As the identification of calcium precipitating bacteria (CPB) in heat exchangers of cooling water system appears lacking, this study would be useful for the selection of suitable biocides/inhibitors in the control of CPB on scale in cooling water system...
Abstract
This study examines the role of calcium-precipitating bacteria (CPB) in heat exchanger tube failures. Several types of bacteria, including Serratia sp. (FJ973548), Enterobacter sp. (FJ973549, FJ973550), and Enterococcus sp. (FJ973551), were found in scale collected from heat exchanger tubes taken out of service at a gas turbine power station. The corrosive effect of each type of bacteria on mild steel was investigated using electrochemical (polarization and impedance) techniques, and the biogenic calcium scale formations analyzed by XRD. It was shown that the bacteria contribute directly to the formation of calcium carbonate, a critical factor in the buildup of scale and pitting corrosion on heat exchanger tubes.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c9001682
EISBN: 978-1-62708-229-7
... Abstract The secondary cooling water system pressure boundary of Savannah River Site reactors includes expansion joints utilizing a thin-wall bellows. While successfully used for over thirty years, an occasional replacement has been required because of the development of small, circumferential...
Abstract
The secondary cooling water system pressure boundary of Savannah River Site reactors includes expansion joints utilizing a thin-wall bellows. While successfully used for over thirty years, an occasional replacement has been required because of the development of small, circumferential fatigue cracks in a bellows convolute. One such crack was recently shown to have initiated from a weld heat-affected zone liquation microcrack. The crack, initially open to the outer surface of the rolled and seam welded cylindrical bellows section, was closed when cold forming of the convolutes placed the outer surface in residual compression. However, the bellows was placed in tension when installed, and the tensile stresses reopened the microcrack. This five to eight grain diameter microcrack was extended by ductile fatigue processes. Initial extension was by relatively rapid propagation through the large-grained weld metal, followed by slower extension through the fine-grained base metal. A significant through-wall crack was not developed until the crack extended into the base metal on both sides of the weld. Leakage of cooling water was subsequently detected and the bellows removed and a replacement installed.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c0048747
EISBN: 978-1-62708-229-7
... Abstract A 455 mm diam x 8 mm thick wall carbon steel (ASTM A 53) discharge line for a circulating-water system at a cooling tower fractured in service; a manifold section cracked where a Y-shaped connection had been welded. Investigation (visual inspection and photographs) supported the...
Abstract
A 455 mm diam x 8 mm thick wall carbon steel (ASTM A 53) discharge line for a circulating-water system at a cooling tower fractured in service; a manifold section cracked where a Y-shaped connection had been welded. Investigation (visual inspection and photographs) supported the conclusion that the pipe failed by fatigue. Cracks originated at crevices and pits in the weld area that acted as stress raisers, producing high localized stresses because of the sharp-radius corner design. Abnormally high structural stresses and alternating stresses resulting from the pump vibrations contributed to the failure. Recommendations included changing the joint design to incorporate a large-radius corner and improving fitting of the components to permit full weld penetration. Backing strips were suggested to increase weld quality, and the pipe wall thickness was increased from 8 to 9.5 mm.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c9001700
EISBN: 978-1-62708-229-7
... Abstract A straight-tube cooler type heat exchanger had been in service for about ten years serving a coal pulverizer in Georgia. Non-potable cooling water from a local lake passed through the inner surfaces of the copper tubing and was cooling the hot oil that surrounded the outer diametral...
Abstract
A straight-tube cooler type heat exchanger had been in service for about ten years serving a coal pulverizer in Georgia. Non-potable cooling water from a local lake passed through the inner surfaces of the copper tubing and was cooling the hot oil that surrounded the outer diametral surfaces. Several of the heat exchangers used in the same application at the plant had experienced a severe reduction in efficiency in the past few years. One heat exchanger reportedly experienced some form of leakage following discovery of oil contaminating the cooling water. This heat exchanger was the subject of a failure investigation to determine the cause and location of the leaks. Corrosion products primarily contained copper oxide, as would be expected from a copper tubing. The product also exhibited the presence of a significant amount of iron oxides. Metallographic cross sectioning of the tubes and microscopic analysis revealed several large and small well rounded corrosion pits present at the inner diametral surfaces. The cause of corrosion was attributed to corrosive waters that were not only corroding the copper, but were corroding steel pipes upstream from the tubing.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.chem.c9001174
EISBN: 978-1-62708-220-4
... collection manifolds with a system of pipes between them. Synthesis gas under high pressure and at about 300°C, consisting of approx. 10% NH 3 and unconverted gas of 25% N 2 and 75% H 2 content, was water-cooled externally to room temperature in this unit. Figure 1 shows the fracture location and Fig...
Abstract
A cooler of an ammonia synthesis plant was destroyed after three years of service due to the rupture of a distribution manifold. Synthesis gas under high pressure and at about 300 deg C, consisting of 10% NH3 and unconverted gas of 25% N2 and 75% H2 content, was water-cooled externally to room temperature in this unit. The fracture had the typical flat-gray fibrous structure of a material destroyed by hydrogen. Specimens for the metallographic investigation showed that the structure appeared to have been loosened by intergranular separations. DVM notched impact specimens from the affected area yielded low specific impact energy values. These are the significant characteristics of hydrogen attack. The attack penetrated to a depth of 13 to 16 mm. It was recommended that the manifolds be made of hydrogen-resistant steel instead of the unalloyed steel used.
Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001338
EISBN: 978-1-62708-215-0
... recycling system for the coolant is able to exclude oxygen, thus reducing corrosive attack.) Filling the tubes with water for pressure testing would, unfortunately, tend to flush out and dilute any soluble corrosion product. It thus seems impossible to determine the exact origin of corrosion at this stage...
Abstract
Copper tubes from the cooler assemblies of a large air-conditioning unit exhibited leakage upon installation of the unit. Sections from two leaking tubes and one nonleaking tube were subjected to pressure testing and microscopic examination. The cause of leaking was determined to be pitting corrosion. Extensive pitting was found on the insides of all sections examined, with deep and numerous pits in leaking areas. Circumstantial evidence indicated that antifreeze solution left in the tubes from the manufacturing operation was the most likely cause of the pitting.
Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001353
EISBN: 978-1-62708-215-0
... cooling system of a condenser. Visual examination of the flap showed crystalline fracture, indicating a brittle failure. Metallographic examination, chemical analyses, and tensile and impact testing indicated that the failure was caused by the notch sensitivity of the forging material, which resulted in...
Abstract
A reversible four-way carbon steel flap valve in a thermal power station failed after 7 years of service. The flap had been fabricated by welding two carbon steel plates to both sides of a carbon steel forging. The valve was used for reversing the flow direction of seawater in the cooling system of a condenser. Visual examination of the flap showed crystalline fracture, indicating a brittle failure. Metallographic examination, chemical analyses, and tensile and impact testing indicated that the failure was caused by the notch sensitivity of the forging material, which resulted in low toughness. It was recommended that fully killed carbon steel with a fine-grain microstructure be used. Redesign of the flap to remove the step in the forging that acted as a notch was also recommended.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c0091631
EISBN: 978-1-62708-229-7
... Abstract A steam-condensate line (type 316 stainless steel tubing) began leaking after five to six years in service. The line carried steam condensate at 120 deg C (250 deg F) with a two hour heat-up/cool-down cycle. No chemical treatment had been given to either the condensate or the boiler...
Abstract
A steam-condensate line (type 316 stainless steel tubing) began leaking after five to six years in service. The line carried steam condensate at 120 deg C (250 deg F) with a two hour heat-up/cool-down cycle. No chemical treatment had been given to either the condensate or the boiler water. To check for chlorides, the inside of the tubing was rinsed with distilled water, and the rinse water was collected in a clean beaker. A few drops of silver nitrate solution were added to the rinse water, which clouded slightly because of the formation of insoluble silver chloride. This and additional investigation (visual inspection, and 250x micrograph etched with aqua regia) supported the conclusion that the tubing failed by chloride SCC. Chlorides in the steam condensate also caused corrosion of the inner surface of the tubing. Stress was produced when the tubing was bent during installation. Recommendations included providing water treatment to remove chlorides from the system. Continuous flow should be maintained throughout the entire tubing system to prevent concentration of chlorides. No chloride-containing water should be permitted to remain in the system during shutdown periods, and bending of tubing during installation should be avoided to reduce residual stress.
Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001356
EISBN: 978-1-62708-215-0
... presence of moist hydrogen used to cool the ring. Factors which promoted the failure were higher than normal strength levels in the ring material, lower than normal ring operating temperatures, possible moisture in the lubrication oil system, periodic poor performance of the hydrogen dryers, and a ring...
Abstract
A shrunk-fit 18 Mn-5Cr steel retaining ring failed without warning during normal unit operation of a 380 MW electrical generator. The cause of the ring failure was determined to be intergranular stress-corrosion cracking (IGSCC) because of the high strength of the ring material and the presence of moist hydrogen used to cool the ring. Factors which promoted the failure were higher than normal strength levels in the ring material, lower than normal ring operating temperatures, possible moisture in the lubrication oil system, periodic poor performance of the hydrogen dryers, and a ring design which allowed water to become trapped in a relief groove. These factors caused pitting in the ring in an estimated 100 hours of operation. The ring had been inspected previously 18 months prior to the failure and no defects or pitting were found. Calculations showed that a 0.127-cm (0.050-in.) deep pit could grow to a critical size in 3000 to 4000 hours of operation. To prevent further failures, it was recommended that the ring be replaced with an 18 Mn-18Cr alloy with superior resistance to IGSCC. A program of periodic inspection and replacement of other retaining rings in the system was also recommended.
Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001305
EISBN: 978-1-62708-215-0
... Abstract An ASTM A 504 carbon steel railway car wheel that was used on a train in a metropolitan railway system failed during service, causing derailment. The wheel was completely fractured from rim to hub. Macrofractography of the fracture surface showed road grime, indicating that the crack...
Abstract
An ASTM A 504 carbon steel railway car wheel that was used on a train in a metropolitan railway system failed during service, causing derailment. The wheel was completely fractured from rim to hub. Macrofractography of the fracture surface showed road grime, indicating that the crack had existed for a considerable time prior to derailment and initiated in the flange. Failure propagated from the flange across the rim and down the plate to the bore of the hub. Two zones that exhibited definite signs of heating were observed. The fracture initiation site was typical of fatigue fracture. No defects were found that could have contributed to failure. The wheel conformed to the chemical, microstructural, and hardness requirements for class A wheels. Failure was attributed to repeated severe heating and cooling of the rim and flange due to brake locking or misapplication of the hand brake. It was recommended that the brake system on the car be examined and replaced if necessary.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.chem.c0091694
EISBN: 978-1-62708-220-4
... because of unrelated tube failures. Sanitary (chlorinated) well water was generally used in the system, although filtered process make-up water (river water) containing ammonia was occasionally used. Investigation (visual inspection, chemical analysis, mercurous nitrate testing, unetched 5X micrographs...
Abstract
Tube sheets (found to be copper alloy C46400, or naval brass, and 5 cm (2 in.) thick) of an air compressor aftercooler were found to be cracked and leaking approximately 12 to 14 months after they had been retubed. Most of the tube sheets had been retubed several times previously because of unrelated tube failures. Sanitary (chlorinated) well water was generally used in the system, although filtered process make-up water (river water) containing ammonia was occasionally used. Investigation (visual inspection, chemical analysis, mercurous nitrate testing, unetched 5X micrographs, and 250X micrographs etched in 10% ammonium persulfate solution) supported the conclusion that the tube sheets failed by SCC as a result of the combined action of internal stresses and a corrosive environment. The internal stresses had been induced by retubing operations, and the environment had become corrosive when ammonia was introduced into the system by the occasional use of process make-up water. Recommendations included making a standard procedure to stress relieve tube sheets before each retubing operation. The stress relieving should be done by heating at 275 deg C (525 deg F) for 30 min and slowly cooling for 3 h to room temperature.
Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001343
EISBN: 978-1-62708-215-0
... Abstract A section of type 304 stainless steel pipe from a stand by system used for emergency injection of cooling water to a nuclear reactor failed during precommissioning. Leaking occurred in only one spot. Liquid penetrant testing revealed a narrow circumferential crack. Metallographic...
Abstract
A section of type 304 stainless steel pipe from a stand by system used for emergency injection of cooling water to a nuclear reactor failed during precommissioning. Leaking occurred in only one spot. Liquid penetrant testing revealed a narrow circumferential crack. Metallographic examination of the cracked area indicated stress-corrosion cracking, which had originated at rusted areas that had formed on longitudinal scratch marks on the outer surface of the pipe. The material was free from sensitization, and there was no significant amount of cold work. It was recommended that the stainless steel be kept rust free.
Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001329
EISBN: 978-1-62708-215-0
... Abstract Various aluminum bronze valves and fittings on the essential cooling water system at a nuclear plant were found to be leaking. The leakage was limited to small-bore socket-welded components. Four specimens were examined: three castings (an ASME SB-148 CA 952 elbow from a small-bore...
Abstract
Various aluminum bronze valves and fittings on the essential cooling water system at a nuclear plant were found to be leaking. The leakage was limited to small-bore socket-welded components. Four specimens were examined: three castings (an ASME SB-148 CA 952 elbow from a small-bore fitting and two ASME SB-148 CA 954 valve bodies) and an entire valve assembly. The leaks were found to be in the socket-weld crevice area and had resulted from dealloying. It was recommended that the weld joint geometry be modified.
Series: ASM Handbook
Volume: 11
Publisher: ASM International
Published: 15 January 2021
DOI: 10.31399/asm.hb.v11.a0006788
EISBN: 978-1-62708-295-2
... low flow where surface deposits can collect ( Fig. 10 ). Microbiologically influenced corrosion has been found in refineries, cooling-water systems, sprinkler systems, potable water-distribution networks, oilfield water-handling systems, oil pipelines, pulp and paper mills, and so on but not in steam...
Abstract
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.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c0091807
EISBN: 978-1-62708-229-7
... in the operating system and on test coupons exposed to the operating environment. Nitrate-reducing bacteria from the lakewater used in cooling were found to produce high levels of ammonia (5.8 mg/L) when established in biofilms. Ammonia levels at the metal surface were 300 times higher than...
Abstract
Failures occurred in admiralty brass condenser tubes in a nuclear plant cooled by freshwater. About 2500 tubes had to be replaced over a span of six years. Investigation (visual inspection, chemical analysis, water chemistry (for both intake and outfall), and corrosion products in the operating system and on test coupons exposed to the operating environment) supported the conclusion that the failure was caused by microbe-initiated SCC. No recommendations were made.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c9001651
EISBN: 978-1-62708-229-7
... Abstract Some of the admiralty brass tubes were failing in a heat exchanger. The heat exchanger cooled air by passing river water through the inside of the tubes. The wall thickness of all tubes ranged between 1.19 to 1.27 mm (0.047 to 0.050 in.). General intergranular corrosion occurred at the...
Abstract
Some of the admiralty brass tubes were failing in a heat exchanger. The heat exchanger cooled air by passing river water through the inside of the tubes. The wall thickness of all tubes ranged between 1.19 to 1.27 mm (0.047 to 0.050 in.). General intergranular corrosion occurred at the inside surfaces of the tubes. Transgranular stress-corrosion cracking, probably the result of sulphates under basic conditions, and dezincification occurred also as the result of galvanic corrosion under the deposits in the tubes. Recommendations were to use a closed-loop water system to eliminate sulphates, ammonia, etc., and to run trials on one unit with tubes of other alloys such as 80-20 Cu-Ni or 70-30 Cu-Ni to evaluate their performance prior to any large scale retubing operations.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c9001146
EISBN: 978-1-62708-229-7
... a brittle fracture which resulted from cooling the vent header material to a temperature below the Nil Ductility Transition Temperature (NDTT) by the uncontrolled release of liquid nitrogen. The nitrogen discharge system is needed to evolve an inert environment in the torus. This system was designed...
Abstract
A metallurgical failure analysis was performed on pieces of the cracked vent header pipe from the Edwin I. Hatch Unit 2 Nuclear power plant. The analysis consisted of optical microscopy, chemical analysis, mechanical Charpy impact testing, and fractography. It was found that the material of the vent header met the mechanical and chemical properties of ASTM A516 Grade 70 carbon-manganese steel material and microstructures were consistent with this material. Fracture faces of the cracked pipe were predominantly brittle in appearance with no evidence of fatigue contribution. The NDTT (Nil ductility Transition Temperature) for this material was approximately -51 deg C (-60 deg F). The fact that the material's NDTT was significantly out of the normal operating range of the pipe suggested an impingement of low temperature nitrogen (caused by a faulty torus inerting system) induced a thermal shock in the pipe which, when cooled below its NDTT, cracked in a brittle manner.
Series: ASM Failure Analysis Case Histories
Volume: 1
Publisher: ASM International
Published: 01 December 1992
DOI: 10.31399/asm.fach.v01.c9001045
EISBN: 978-1-62708-214-3
... dezincification-resistant alloy was recommended. Cooling systems Dezincification Hydroelectric power generation Lubrication systems Yellow brass, 65% Cu UNS C27000 Dealloying/selective leaching Several brass alloy 270 heat exchanger tubes began to leak after approximately 5.5 years...
Abstract
A failure analysis was conducted on brass alloy 270 heat exchanger tubes that were pulled from a unit used to cool oil for the speed regulators and thrust bearings of a hydroelectric power plant. The tubes began to leak after approximately 5.5 years of service. Macrophotography and scanning electron microscopy were used to examine samples from the tubes. An energy-dispersive electron microprobe analysis was carried out to evaluate the zinc distribution. Results showed that the failure was due to dezincification. Replacement of the tubes with new tubes fabricated from a dezincification-resistant alloy was recommended.
Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001313
EISBN: 978-1-62708-215-0
... used. Admiralty metal Ammonia, environment Cooling systems Heat exchanger tubes, corrosion Hydroelectric power generation C44300 UNS C44300 Pitting corrosion Stress-corrosion cracking A brass finned tube in a generator air cooler unit failed. The as-received...
Abstract
An arsenical admiralty brass (UNS C44300) finned tube in a generator air cooler unit at a hydroelectric power station failed. The unit had been in operation for approximately 49,000 h. Stereomicroscopic examination revealed two small transverse cracks that were within a few millimeters of the tube end, with one being a through-wall crack. Metallographic examination of sections containing the cracks showed branching secondary cracks and a transgranular cracking mode. The cracks appeared to initiate in pits. EDS analysis of a friable deposit found on the inside diameter of the tube and XRD analysis of crystalline compounds in the deposit indicated the possible presence of ammonia. Failure was attributed to stress-corrosion cracking resulting from ammonia in the cooling water. It was recommended that an alternate tube material, such as a 70Cu-30Ni alloy or a titanium alloy, be used.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c9001709
EISBN: 978-1-62708-229-7
... (367 deg C) and 2935 psi (20.5 MPa), failed near the IK boxes as a result of thermal fatigue. Thermal fatigue damage was accelerated by repetitive exposure to water droplets from the soot blower and the associated rapid cooling. Boilers Electric power generation Tubes ASME SA210-A1 Thermal...
Abstract
Several waterwall tubes in a power station boiler failed after ten years of service. The boiler is a suspension type equipped with 30 IK boxes where retractable soot blowers are inserted to clean the inside of the boiler using high-pressure steam. The tubes, which operate at 693 deg F (367 deg C) and 2935 psi (20.5 MPa), failed near the IK boxes as a result of thermal fatigue. Thermal fatigue damage was accelerated by repetitive exposure to water droplets from the soot blower and the associated rapid cooling.