Which method is used to accomplish cold-section repairs of an axial flow compressor?

• A. Blending
• B. Blade replacement
• C. Plasma surface repair coating
• D. Electron beam welding

Answer: (C)

Cold-section repairs aim to restore the surface and dimensions without applying significant heat that could distort the part or alter its metallurgy. Plasma surface repair coating fits this purpose because it builds up material on the damaged area with a controlled coating process, then the surface is machined back to the exact spec. This restores the original profile and clearance while adding a wear- and corrosion-resistant layer, all with minimal heat impact on the base metal. Blending only smooths small flaws and can’t restore lost thickness or the precise geometry required for high-speed compressor surfaces. Blade replacement trades downtime and cost for a fix that may be unnecessary for minor wear, and electron beam welding introduces substantial heat and potential distortion or microstructural changes, which is undesirable for cold-section components.