[radiowave]

My dad worked on something similar, when during the 1980s the coal-fired station he worked at had to convert to two-shift operation, from the three-shift operation that it's 1950s design had intended. He described this process as, "bashing hell out the machines to make them do things they weren't designed to."

One interesting detail was that the more rapid startup and cooldown of turbines meant that blade spacing couldn't be as tight as before, reducing efficiency during operation. (The turbine casing has less thermal mass than the rotor, and hence contracts faster during cooldown. The spacing of the blades needs to account for this.)

[dehugger]

Would it not be more efficient to increase the mass of the casing so that the blades can remain as they were? or was that a non option for other reasons?

[defrost]

No matter the mass of the casing it will absorb and lose heat over some timescale and will expand and contract, changing dimensions.

The design is optimised so that the blade dimensions and the interior casing diameter closely match to a very high tolerance at the optimal operating tempreture.

The challenge is that the casing material and the blades are made of different materials and these materials will have different coefficients of expansion (although there is some room to 'dope' materials to change the CoE at the xpense of other material properties that can be more desirable).

The CoE means that the two expand at different rates as the tempreture changes - if they are "close" at optimal temp then they will drift away as the temp changes due to not expanding in lock step.

It's a tricky thing to get right.

( Also a challenge in multicoloured glass works as the differing colours must be batched to have similiar properties including matching CoE's so they don't pull away when anealing from hot glass work temps to room temp. )