Experiences in Repair of Hot Section Gas Turbine Components

The repair and recovery of both the stationary and the rotating parts of the hot section of a gas turbine are becoming more and more generally accepted practice.

Due to the necessity for repairs on heavily loaded rotating blades and buckets made out difficult to weld nickelbase superalloys, such as In738, U720 and In939, the need arose for fundamental investigations on repair and recovery procedures with a high turbine operation reliability. The investigation began at Elbar about 5 years ago under different contracts from the Ministry of Economic Affairs, within a European collaboration in the fields of :

• a)
  welding of superalloys
• b)
  powder metallurgy including hipping of superalloys
• c)
  diffusion bonding of superalloys
• d)
  repair brazing of superalloys
• e)
  development of new diffusion coatings for superalloys, such as 1 step NiCrAlYs, sulfidation resistant coatings such as "Silicon-Titanium" and new thermal barrier coatings for superalloys.

As result of this research, new repair techniques have been developed which improve the reliability of repairs extensively.

It has been proved that repaired blades are often better than new blades because of the use of superior materials, better coatings and modified heat treatments.