It is not complicated to carry out this job but there are some steps critical which done improperly can cause disaster. Frankly speaking, reparing steam turbines, there is allways a must to think what would be the results of some "shorcuts".
That is why, the experience is very important. Especially, a blading work is one of the most sensitive. Take into account that the turbine rotor works in exceptional conditions: high temperature (~ 550 C deg), high pressure and forces created by elements weight, a rotor rotation (a couple of thousand rpm's), etc ... .
Anyway, the first stage consist of 52 blade sets, each set contains two blades welded together. Two sets are the locking sets. The locking sets are fixed to the disc using 4 pins. The core of reblading activity is to remove the pins. Usually, the pins are removed by boring them and here we have the most dangerous part of whole procedure. The pins boring have to be done in this way that the holes diameter in disc will be the same after boring - the holes clean up is acceptable but the diameter must not be bigger than certain value. A material thickness on the rotor disc in pins mounting area determines the pin holes diameters.
It can happen that after a few repairs of this rotor stage the pin holes are an ovals or were not bored perpendicular to the rotor disc.
Than it is technical correct to bore new holes but they will be bigger but as mentioned above holes can be increased only to some level as the stresses are important.
This conditions were met during a project supervised by me.
We had ovality on pin holes and some ot them were not perpendicular to the rotor disc.
I defined what would be the diameters of new holes and asked my colleague to perform stress calculation if disc material left is enough to carry forces.
He used FEA method to do it. I am not familiar with this but it is common for design dept. around the world.
Fortunatelly, it turned out that new holes diameters are ok and we act in this way.
Below, there are a couples of pictures presenting MES calculation.
