Hot Corrosion of Nickel-Base Exhaust Valves in a Natural Gas Engine 910055
Many heavy duty valve applications require high strength materials to survive severe loading and dynamic conditions. In some applications, the engine environment may dramatically reduce the useful life of the valve to a fraction of the required life-span.
Inconel 751 exhaust valves failed at low hours of operation in a natural gas engine. The valve separated at the stem blend causing extensive damage in the cylinder. The valve failure was caused by liquid phase hot corrosion. Sulfate deposits left by burned engine oil provided the sulfur source to start the corrosion reaction. The combination of the sulfate deposits and rich fuel-air ratio created the proper conditions for valve failure.
The recommended course of action entailed changing the valve base material to an iron-based austenitic stainless steel alloy (23-8N). The 23-8N alloy is resistant to hot corrosion attack.