Nickel aluminum bronze (NAB) alloys are used in naval and maritime applications for their excellent corrosion resistance under the influence of seawater. One application involves the use of a NAB butterfly valve within a NAB fluid line to control fluid flow of seawater. Due to the chaotic environment, the corrosion rate of the NAB tubing downstream from the valve increases significantly. The disc angle at which the valve alters fluid flow causes an increase in the fluid velocity and an increase in the turbulence produced on the downstream side of the valve. These fluid conditions contribute to the increase in the corrosion rate of the NAB piping downstream from the valve. This thesis aims to characterize how the change in the disc angle of the butterfly valve causes a change in the erosion-corrosion rate of NAB downstream from the valve. A butterfly valve is simulated using orifice plates of varying diameters to mimic flow conditions at different disc angles. An orifice plate is a simple device with a hole in its center that is designed to restrict fluid flow across a fluid line. Under the same hydrodynamic conditions, the orifice produces nearly the exact same flow coefficients as the valve. At a volumetric flowrate of 0.00757 m^3/s a total of eight locations found along the liquid/metal interface produced pitting sites. The average passivation layer thickness is also measured. / Master of Science / Nickel aluminum bronze alloys are used within the naval and maritime industries for many different types of applications. The main use of this material as studied within this project entailed the use of this alloy within a piping structure downstream from a type of butterfly valve. When seawater flows through this piping structure, the valve distortions within the fluid are believed to cause degradation of the piping material. This project aimed to look at how the change in the disc angle of the butterfly valve caused disruptions in the fluid and thereby changes in how nickel aluminum bronze degrades over time. It was found that as the disc angle inside of the butterfly valve decreased towards being completely closed, the greater the amount of degradation was produced upon the alloys surface. Micrographs within this paper aimed to characterize the amount of degradation upon the alloy surface and also report the overall thickness of oxide deposited onto the metal surface during testing.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/83818 |
| Date | 29 June 2018 |
| Creators | Taylor, Ryan Chandler |
| Contributors | Materials Science and Engineering, Hendricks, Robert Wayne, Reynolds, William T. Jr., Corcoran, Sean G. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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