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Title: Plasma Sprayed Ni-Al Coatings for Safe Ending Heat Exchanger Tubes

Abstract

Brookhaven National Laboratory (BNL) has developed thermally conductive composite liners for corrosion and scale protection in heat exchanger tubes exposed to geothermal brine. The liners cannot withstand roller expansion to connect the tubes to the tubesheet. It is not possible to line the ends of the tubes with the same material after roller expansion due to the nature of the current liner application process. It was requested that BNL evaluate plasma sprayed Ni-Al coatings for safe ending heat exchanger tubes exposed to geothermal brine. The tubes of interest had an internal diameter of 0.875 inches. It is not typical to thermal spray small diameter components or use such small standoff distances. In this project a nozzle extension was developed by Zatorski Coating Company to spray the tube ends as well as flat coupons for testing. Four different Ni-Al coatings were investigated. One of these was a ductilized Ni-AlB material developed at Oak Ridge National Laboratory. The coatings were examined by optical and scanning electron microscopy. In addition, the coatings were analyzed by X-ray diffraction and subjected to corrosion, tensile adhesion, microhardness and field tests in a volcanic pool in New Zealand.

Authors:
; ;
Publication Date:
Research Org.:
Brookhaven National Lab., Upton, NY (US)
Sponsoring Org.:
US Department of Energy (US)
OSTI Identifier:
6133
Report Number(s):
BNL-66149; B& R #: EB-40-01
R&D Project: AS-017-EECD; B&R #: EB-40-01; TRN: AH200115%%236
DOE Contract Number:
AC02-98CH10886
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: 1 Nov 1998
Country of Publication:
United States
Language:
English
Subject:
15 GEOTHERMAL ENERGY; 36 MATERIALS SCIENCE; SPRAYED COATINGS; FIELD TESTS; HEAT EXCHANGERS; PROTECTIVE COATINGS; NICKEL ALLOYS; ALUMINIUM ALLOYS; GEOTHERMAL FLUIDS; CORROSION PROTECTION; Geothermal Legacy

Citation Formats

Allen, M.L., Berndt, C.C., and Otterson, D. Plasma Sprayed Ni-Al Coatings for Safe Ending Heat Exchanger Tubes. United States: N. p., 1998. Web. doi:10.2172/6133.
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Allen, M.L., Berndt, C.C., & Otterson, D. Plasma Sprayed Ni-Al Coatings for Safe Ending Heat Exchanger Tubes. United States. doi:10.2172/6133.
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Allen, M.L., Berndt, C.C., and Otterson, D. Sun . "Plasma Sprayed Ni-Al Coatings for Safe Ending Heat Exchanger Tubes". United States. doi:10.2172/6133. https://www.osti.gov/servlets/purl/6133.
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@article{osti_6133,
title = {Plasma Sprayed Ni-Al Coatings for Safe Ending Heat Exchanger Tubes},
author = {Allen, M.L. and Berndt, C.C. and Otterson, D.},
abstractNote = {Brookhaven National Laboratory (BNL) has developed thermally conductive composite liners for corrosion and scale protection in heat exchanger tubes exposed to geothermal brine. The liners cannot withstand roller expansion to connect the tubes to the tubesheet. It is not possible to line the ends of the tubes with the same material after roller expansion due to the nature of the current liner application process. It was requested that BNL evaluate plasma sprayed Ni-Al coatings for safe ending heat exchanger tubes exposed to geothermal brine. The tubes of interest had an internal diameter of 0.875 inches. It is not typical to thermal spray small diameter components or use such small standoff distances. In this project a nozzle extension was developed by Zatorski Coating Company to spray the tube ends as well as flat coupons for testing. Four different Ni-Al coatings were investigated. One of these was a ductilized Ni-AlB material developed at Oak Ridge National Laboratory. The coatings were examined by optical and scanning electron microscopy. In addition, the coatings were analyzed by X-ray diffraction and subjected to corrosion, tensile adhesion, microhardness and field tests in a volcanic pool in New Zealand.},
doi = {10.2172/6133},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Nov 01 00:00:00 EST 1998},
month = {Sun Nov 01 00:00:00 EST 1998}
}
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Technical Report:
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DOI:  10.2172/6133
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  • ; ;
    Brookhaven National Laboratory (BNL) has developed thermally conductive composite liners for corrosion and scale protection in heat exchanger tubes exposed to geothermal brine. The liners cannot withstand roller expansion to connect the tubes to the tubesheet. It is not possible to line the ends of the tubes with the same material after roller expansion due to the nature of the current liner application process. It was requested that BNL evaluate plasma sprayed Ni-Al coatings for safe ending heat exchanger tubes exposed to geothermal brine. The tubes of interest had an internal diameter of 0.875 inches. It is not typical tomore » thermal spray small diameter components or use such small standoff distances. In this project a nozzle extension was developed by Zatorski Coating Company to spray the tube ends as well as flat coupons for testing. Four different Ni-Al coatings were investigated. One of these was a ductilized Ni-AIB material developed at Oak Ridge National Laboratory. The coatings were examined by optical and scanning electron microscopy. In addition, the coatings were analyzed by X-ray diffraction and subjected to corrosion, tensile adhesion, microhardness and field tests in a volcanic pool in New Zealand. It was determined that the Ni-Al coatings could be applied to a depth of two inches on the tube ends. When sprayed on flat coupons the coatings exhibited relatively high adhesion strength and microhardness. Polarization curves showed that the coating performance was variable. Measured corrosion potentials indicated that the Ni-Al coatings are active towards steel coated with thermally conductive polymers, thereby suggesting preferential corrosion. Corrosion also occurred on the coated coupons tested in the volcanic pool. This may have been exacerbated by the difficulty in applying a uniform coating to the coupon edges. The Ni-Al coatings applied to the tubes had significant porosity and did not provide adequate corrosion protection. This is associated with the short standoff distance and is not a reflection of the normal quality of plasma sprayed coatings. Even if coating porosity could be reduced, the coupling of an alloy coating to a polymer-based barrier coating in the same electrolyte is not recommended. Therefore, polymer coatings that can be field applied to the tube ends after roller expansion should be sought.« less

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