Refurbishment

Alongside the simple replacement of components subjected to operating stresses, the refurbishment of worn-out components is practical because complex capital assets generally contain very valuable component parts. Their replacement with new parts uses valuable resources and results in high costs. Successful refurbishment of component parts restores the functionality of turbine and compressor units. A multitude of interlinked production processes are required in order to achieve this. The special processes used by OT Schwerin are technically highly sophisticated and are set out below:

 

 

Plant for chemically removing (stripping) of used MCrAlY coatings

Component cleaning

  • Grit blasting with corundum & glass beads
  • Kolene cleaning in a salt bath
  • Versene cleaning, using ultrasonic methods if necessary
  • Cleaning with citric acid
  • Pickling with phosphoric acid

 

Coating removal

  • Chemical removal of coatings (hydrochloric acid)
  • Mechanical removal of coatings (grinding/milling)
  • Paint removal by grit blasting (corundum)
  • Local removal using electrochemical machining (ECM)

 

Heat treatment of GT high-temperature components in vacuum furnace, optional vacuum hardening

Heat treatment

  • Vacuum heat treatment
    (in accordance with the aviation standard AMS 2750E)
  • Atmospheric heat treatment
  • Stationary and mobile heat treatment

 

Non-destrucitve testing

  • Visual inspection (VT)
  • Surface crack inspection – fluorescent dyes (PT)
  • Magnetic crack inspection (MT)
  • Eddy current inspection (ET)
  • Ultrasonic inspection (UT)

Equipment for non-destructive testing (NDT)
Shown here: surface crack inspection using fluorescent dye penetration

 

Laboratory technology

  • Metallographic laboratory
  • Chemical laboratory

 

Measurement technology

  • 3D metrology
  • Ultrasonic wall thickness measurement
  • Eddy current coating thickness measurement
  • Surface roughness measurement
  • Airflow measurement (DFMM)

Airflow measurement test bench to determine the mass flow of turbine blades with critical flow nozzles

Water jet cutting

  • Cutting of gas turbine components
  • Preparation for coupon repair welding
  • Cutting for metallographic tests

 

Repair welding

  • Manual tungsten inert gas welding (m-WIG)
  • Mechanised metal active gas welding (MAG)
  • Manual or semi-automated laser welding with welding fillers (LWW) or without welding fillers
  • Adaptive laser welding with welding powder (LPW)
  • Adaptive laser welding with welding powder (LPW) of the same type and inductive preheating

 

Restoration of contours

  • Drawing-based manual grinding and milling to restore
    the original contour
  • Drawing-based machining (CNC milling, grinding, turning)
  • Electrical discharge machining (wire and sinker EDM)

Ultra-thin repair welding of hot components using manual laser wire welding Delicate repair of hot gas path components by manual laser wire welding

 

Laser curing

  • Leading edges of steam turbine blades (DTS)

 

High-temperature brazing (HTL)

  • Narrow-gap brazing during the course of repairs
    (HT brazing)

 

Straightening

  • Cold and hot levelling of deformations

Effective repair welding of hot gas components using adaptive laser powder welding, optional laser hardening

 

Shot peening (DS)

  • Built up of compressive stresses to increase crack resistance