Internal inspections:

Check to see that nozzles are not worn, cracked or split. Examine inner wall sleeve edges to make sleeves are not breaking down under heat and thus failing to protect nozzle heads when they are retracted. See that nozzles are properly retracted for protection.

Examine thoroughly all tubes, cleaned these units by rubbing the hands over them to determine if there are any grooves or flat sports indicating erosion or cutting. Tube erosion or cutting with retractable units is invariably due to excessive blowing  pressure. This pressure should be controlled to avoid the damage.

Check the space between water wall tubes, where these lances entry is sometimes limited by boiler construction. Check to see that lances enter the center of the operation without striking the boiler tube which could be thus damages.

Lences  should be straight and true.