What are the most common signs of refrigerant piping damage or corrosion?

During visual inspection, look for signs of damage or corrosion such as rust, pitting, or flaking on the pipe surface, as well as dents, kinks, or scratches. Check for loose or damaged fittings, and inspect the pipe supports and hangers for signs of wear or damage. Additionally, check for oil or refrigerant leaks, which can indicate internal corrosion or damage.