I love such questions. Do you think that it can be explaind in a couple of sentences?
Let me try :
The turbine casing has to be in proper technical conditions after overhaul.
The necessary machining has to be carried out in a way to get right dimensions.
The welding works have to be performed using proper technolgy to assure long operation of turbine after, avoiding tripp incidents beacuse of poor welding.
People are working hard to obtain such experience and you want to be given with ready to use solutions for free with no efforts?