Strip and Recoat a Blade, or Buy a New One

Recoating makes sense when the damage is mostly in the coating. New-make makes sense when the wall, a crack or the shape cannot be defended. HIP sits between the two if the problem is internal voids. Below are those three jobs as separate decisions, with a plant-style case for each.

This is the job when the ceramic or MCrAlY has gone, the wall is still inside the repair minimum, cooling holes can be cleared, and airflow still matches the band. The shop strips by the specified method — chemical or controlled grit — maps remaining wall, coats, heat-treats, and airflow-tests if the blade is cooled. Case: a 9E first-stage bucket with TBC spall on the leading edge, metal still thick, holes open. Euroturbine writes strip and recoat, not new-make. Spraying ceramic onto a thin wall is not this result; that is hiding result 3.

This is the job when NDT or metallography shows internal voids, remaining wall is still enough, and the alloy is a HIP candidate — typically equiax or DS nickel such as IN738, GTD111, MM247. HIP is hot isostatic pressing: a furnace under pressure that closes porosity. After HIP the blade is still coated and inspected. Case: a V94.2 first-stage vane with sound wall and a porosity map inside the HIP envelope. Euroturbine writes HIP plus recoat. HIP is not a cheaper new blade. If the wall is already gone, HIP does not grow metal.

This is the job when remaining wall is below the minimum, a crack has entered the metal, the airfoil shape cannot be restored, or the coating process that row needs cannot be put back on that serial. Case: first-stage cooled blade with wall loss at the trailing edge and a blocked cooling hole that cannot be cleared to the airflow band. Euroturbine writes new-make for that OEM number. Mixing recoated and new blades in one rotating row is only allowed with a written note on mass and coating family.

Writing “پوشش شد” is not a certificate. The shop names the process: APS (air plasma spray) for most ceramic TBC, LVPS or similar for some bond coats, CVD or pack cementation for certain diffusion coats, then the thickness band in millimetres or micrometres, and the heat treatment after coating. A recoated blade without those lines is as weak as a blade with no heat number. Euroturbine prints those lines on the same paper as the serial.

Coating process names · When HIP sits in the middle · Repair and recoat