Many parts subject to wear can be repaired or have their life prolonged coating them when new. Aqumarine Subsea have success stories delivering to Hydropower for years.
2004: Guide blades coated by Aquamarine.
2018: Inspection show no sign of wear in coated area.
Subject to wear and corrosion shafts are heavily replaced at a high cost. Extending lifecycle on shafts is cost effective and environmental.