Abstract
Extreme service ball valves in the Gold mining industry, typically experience service damage by particulate abrasion, slurry erosion, lack of adhesion/cohesion, or shear. Repair of these expensive corrosion resistant alloy (CRA) balls typically require: GTAW welding of the substrate, grinding the ball surface, and applying a Ceramic thermal spray coating (TSC) by the Air Plasma Spray (APS) process. An alternative repair method is to machine the ball undersize, and put a thicker metal bond coat (MBC) under the Ceramic coating to re establish original dimensions. This study was performed to determine if the ASTM C633 adhesion strength of an APS Ceramic coating was dependent upon a thickness limit of a high velocity oxygen fuel (HVOF) applied NiCrMo (Hastelloy) MBC. 8 thicknesses of the MBC were applied to three CRA substrates: Titanium G12, Inconel 625, and 2507 Duplex SS. The MBC thicknesses were: 0.0015in, 0.005in, 0.015in, 0.030in, 0.045in, 0.060in, 0.075in, and 0.090in. The following 3 Ceramic coatings: Cr2O3, Cr2O3-Al2O3, and TiO2, were APS applied 0.015in on top of 8 thicknesses of MBC. The following tests were performed: adhesion strength (ASTM C633), metallography (ASTM E1920), and percent porosity (ASTM E2109 Method B).
