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dealloying
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Series: ASM Failure Analysis Case Histories
Volume: 3
Publisher: ASM International
Published: 01 December 2019
DOI: 10.31399/asm.fach.v03.c9001772
EISBN: 978-1-62708-241-9
.... After a thorough examination, it was concluded that the part had failed due to dealloying via desiliconification. pump impeller corrosion erosion cast silicon bronze porosity microstructural analysis chemical composition Silicon bronze alloy UNS C86700 Introduction A corroded pump...
Abstract
A cast silicon bronze (UNS C86700) impeller that had been severely corroded was submitted for failure analysis. The failed part was used to pump potable water, but service life and chlorine content of the water were unknown. The impeller displayed a Cu-rich red phase on its surfaces and showed a pattern very similar to dezincification. Further investigation to determine the cause of damage using light microscopy and SEM-EDS techniques revealed that the microstructure consisted of multiple phases and that a Si-rich phase was being preferentially attacked, leading to increased porosity. After a thorough examination, it was concluded that the part had failed due to dealloying via desiliconification.
Series: ASM Failure Analysis Case Histories
Volume: 3
Publisher: ASM International
Published: 01 December 2019
DOI: 10.31399/asm.fach.v03.c9001809
EISBN: 978-1-62708-241-9
... dealloying. The dealloying corrosion was exacerbated by erosion because the pump was slightly oversized. The investigation recommended better heat treating procedures and closer evaluation to ensure that new pumps are properly sized. pump impeller corrosion dealloying nickel-aluminum bronze pitting...
Abstract
A brackish water pump impeller was replaced after four years of service, while its predecessor lasted over 40 years. The subsequent failure investigation determined that the nickel-aluminum bronze impeller was not properly heat treated, which made the impeller susceptible to aluminum dealloying. The dealloying corrosion was exacerbated by erosion because the pump was slightly oversized. The investigation recommended better heat treating procedures and closer evaluation to ensure that new pumps are properly sized.
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
... 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. Control valves Cooling systems Cooling water Hydraulic valves...
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.
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in Failure of Silicon Bronze Impeller from Dealloying Via Desiliconification
> Handbook of Case Histories in Failure Analysis
Published: 01 December 2019
Fig. 5 Photomicrographs displaying the dealloying taking place at the various surfaces of the part. ( a ) at the tip of a corroded fin, ( b ) in the middle of the same fin, ( c ) a high magnification of the surface in the fin, and ( d ) at the external side of the base on the top half
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in Failure of Silicon Bronze Impeller from Dealloying Via Desiliconification
> Handbook of Case Histories in Failure Analysis
Published: 01 December 2019
Fig. 6 Photomicrograph illustrating the dealloying process observed. The Si-rich phase is preferentially attacked (dealloying) and the Cu constituents are depositing back onto the surfaces
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Published: 01 December 2019
Fig. 4 Selectively attacked region near the surface contained dealloying ( a ) 12.5× and ( b ) 50×, etchant: 45 mL nitric acid and 45 mL acetic acid. Figure 5 is a higher magnification image of the boxed area in image b
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Published: 01 December 2019
Fig. 5 Selectively attacked region near the surface contained dealloying ( a ) 100× and ( b ) 500×, etchant: 45 mL nitric acid and 45 mL acetic acid. Figure 6 is a electron micrograph of the boxed area in image b
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Published: 01 December 2019
Fig. 6 SEM image revealed selective grain attack and dealloying, etchant: 45 mL nitric acid and 45 mL acetic acid. The aluminum concentration was significantly lower than in the bulk material in the area of grain attack
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Published: 01 December 1993
Fig. 9 Cross section of valve with well-defined area of dealloying. Etched
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in Dezincification of a Chrome-Plated Cylinder Gas Valve
> Handbook of Case Histories in Failure Analysis
Published: 01 December 1993
Fig. 6 Micrograph of first valve, showing preferential dealloying of the β phase along an interface. Etched with NH 4 OH/H 2 O 2 . 315×
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in Dezincification of a Chrome-Plated Cylinder Gas Valve
> Handbook of Case Histories in Failure Analysis
Published: 01 December 1993
Fig. 11 EDS line scan for zinc. As the trace crosses the dealloying interface of the unaffected β grain, the line intensity increases, illustrating the selective removal of zinc from the β phase.
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in Failure of Silicon Bronze Impeller from Dealloying Via Desiliconification
> Handbook of Case Histories in Failure Analysis
Published: 01 December 2019
Fig. 7 EDS elemental dot map of one of the dealloyed regions that had been plated with copper
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Published: 01 December 1993
Fig. 7 Appearance of γ 2 phase in dealloyed area (arrows). 332×
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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.c0006898
EISBN: 978-1-62708-233-4
... after 42 days of exposure to NaNO3 + Ca(NO3)2 solution. None of the cupro-nickel specimens failed, but among those exposed to NH4NO3, 17% displayed crack initiation and 83% showed partial dealloying after 42 days. Based on the test results, the fuse material was changed from nickel silver to cupro...
Abstract
Several fuses made of nickel silver (57 to 61% Cu, 11 to 13% Ni, bal Zn) exposed to air containing ammonium and nitrate ions failed by SCC. Test solutions of 1 N ammonium nitrate (NH4NO3) and a 1:1 mixture of 1 N sodium nitrate (NaNO3) and 1 N calcium nitrate (Ca(NO3) 2) were prepared. In addition, stressed fuses made of nickel silver and of cupro-nickel (80Cu-20Ni) were exposed to a drop of corrosive solution in the stressed area. All nickel silver specimens failed after two days of exposure to NH4NO3 solution. However, 17% of them failed and 67% showed crack initiation but no failure after 42 days of exposure to NaNO3 + Ca(NO3)2 solution. None of the cupro-nickel specimens failed, but among those exposed to NH4NO3, 17% displayed crack initiation and 83% showed partial dealloying after 42 days. Based on the test results, the fuse material was changed from nickel silver to cupro-nickel, solving the SCC problem.
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Published: 01 January 2002
Fig. 7 Copper-nickel alloy heat-exchanger tubes that failed from denickelification due to attack by water and steam. (a) Etched section through a copper alloy C71000 tube showing dealloying (light areas) around the tube surfaces. Etched with NH 4 OH plus H 2 O. 3.7×. (b) Unetched section
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in Failure Analysis of Heat Exchangers
> Analysis and Prevention of Component and Equipment Failures
Published: 30 August 2021
Fig. 7 Copper-nickel alloy heat-exchanger tubes that failed from denickelification due to attack by water and steam. (a) Etched section through a copper alloy C71000 tube showing dealloying (light areas) around the tube surfaces. Etched with NH 4 OH plus H 2 O. Original magnification: 3.7×. (b
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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.c9001373
EISBN: 978-1-62708-215-0
... by intergranular attack and slight dezincification of the inner bore surface of the fitting. Dezincification and intergranular attack were attributed to excessive exposure to nonoxidizing acids in the pickling bath. Dezincification Inert gas service CDA 377 UNS C37700 Intergranular corrosion Dealloying...
Abstract
Two new chrome-plated CDA 377 brass valves intended for inert gas service failed on initial installation. After a pickling operation to clean the metal, the outer surfaces of the valves had been flashed with copper and then plated with nickel and chromium for aesthetic purposes. One of the valves failed by dezincification. The porous copper matrix could not sustain the clamping loads imposed by tightening the pressure relief fitting. The second valve failed by shear overload of the pressure relief fitting. Overload was facilitated by a reduction of cross-sectional area caused by intergranular attack and slight dezincification of the inner bore surface of the fitting. Dezincification and intergranular attack were attributed to excessive exposure to nonoxidizing acids in the pickling bath.
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Published: 01 December 1993
Fig. 10 EDS scans of various areas on elbow specimen. (a) Pipe material. (b) Dealloyed area. (c) Casting material
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Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c9001409
EISBN: 978-1-62708-229-7
... thickness. Condenser tubes Dezincification Steam turbines 80Cu-20Zn 70Cu-30Zn Dealloying/selective leaching Dezincification is a particular form of corrosive attack which may occur in a variety of environments and to which some brasses are susceptible. It is favoured by waters having a high...
Abstract
Dezincification is a particular form of corrosive attack which may occur in a variety of environments and to which some brasses are susceptible. It is favored by waters having a high oxygen, carbon dioxide, or chloride content, and is accelerated by elevated temperatures and low water velocities. In the present study, steam turbine condenser tubes had to be renewed after 25 years of service. The tubes were nominally of 70:30 brass. The appearance of a typically corroded one showed uniform dezincification attack on the bore, extending from one-half to two-thirds through the tube wall thickness.
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