the rotors to be repaired

I had opportunity to supervise overhaul of a couple of rotors.

The first one and the most complicated is the the repair of the LP rotor of 100 MW turbine.
It is double flow rotor and have 10 discs mounted on it.

During the NDT technicians found the cracks in the corner of keyway at 6 discs.
Let me present the pictures taken before discs dissasembly.

"Naked" rotor shaft with no discs, the bigest ones are visible.

Next pictures present the dissasembled disc

These cracks are the beginning of possible disaster, that is why we and customer took decision to repare the discs.
We proposed the followin steps :

- dissasembly of all discs,

- NDT examination,

- machining the internal diameter of discs to remove the craced area,

- prepare the bushes,

- mount the bushes into discs with light interference,

- drill radial holes through the bush and disc and install pins with light interference.

The customer accepted our solution, so we started to collect the material and parallel prepared the discs.

I ordered the bushes at foundry and prepared the drawnigs how to machine the discs.

After 4 weeks we got row bushes then they were machined and put into discs.

The next step was to drill radial holes inside the discs. It seems to be qiute easy and in fact it is easy but we have too big angle head for our milling machine them we had a lot of problems to obtain what was designed. At bigest discs, which has the least hole I asked designer not to drill holes as deep as it was drawn.

In the same time the pins were prepared, then we put them into drilled holes. I wrote, the pins to be installed with light interference but to make the assembly quick we used nitrogen to cool them down.

This part was finalized but it is not the end. Now is final machinig. The discs are installed onto rotor with interferance ~ 0.60 mm, so the diameter is very important and tolerances are very tide.

The very last step of machining is keyway milling. We did it partialy inhouse, and using external subcontactors.

I put a couple of pictures taken at differt assembly steps

This is the end of machining and the assembly phase was started.

Below we have the hanging rotor shaft a few secounds before 1st disc assembly

It took several hours to heat up the disc and get enough internal diameter. The interference is 0.6 mm. To mount discs on the rotor we decided to heat them untill the clerance is 0.5 mm.
We needed almost one week to put 10 discs on the rotor but it was not the end as the steam gland bushes and finally couplings had to be assembled as well.
We managed to it and after run out measurement it turned out that some surfaces should be machined when done the very last step - low speed balancing.
I will write a few words about turbine start up but wait some time.