What a small-tube-boiler refit required

Did a small-tube-boiler refit replace the old boilers or only install smaller tubes?

It was a physical boiler replacement using a different structure, with opportunities to add features such as superheating.

A small-tube-boiler refit physically replaced the existing boilers rather than changing the tubes inside them. The new system used a different structural design. It could also incorporate features such as superheating. The refit demanded major machinery work and offered more than a minor alteration to the old plant.