Meaning
Surface modification technique involving the deposition of a cobalt alloy to enhance component durability. Stellite hardfacing is commonly applied to valve seats, discs, seals and stems via welding or thermal spray processes. It allows the underlying part to be made of a cheaper steel while the contact surfaces withstand extreme mechanical loads.
Erosion Protection
High velocity steam and abrasive slurries quickly degrade standard stainless steel alloys through metal loss. Because stellite hardfacing maintains its hardness even at red heat, it prevents the wire drawing effect caused by high pressure drops across a partially open valve. This durability extends the time between major overhauls in power plants and refineries.
Procurement Cost
Specifying this treatment increases the initial price of the valve due to the cost of the cobalt alloy and the specialized labor required for deposition. Buyers weigh the higher capital expenditure against the reduction in downtime and the lower frequency of replacement parts. A stellite hardfacing requirement is a standard feature in severe service specifications for high pressure steam lines.
Quality Verification
Inspection of the welded layer involves non destructive testing to check for cracks or porosity. The thickness of the stellite hardfacing must meet the design minimum to ensure the component remains protected through multiple grinding and lapping cycles. Hardness testing confirms that the application process achieved the necessary metallurgical properties.
