Repair technology
The sophisticated designs of the advanced
technology components used in the hot
sector of third generation gas turbines
have presented significant challenges to
the aftermarket repair sector. Many of the
standard repair processes could not be
applied to such complex designs. New
welding techniques, coating materials,
inspection procedures and tooling are
necessary to restore components to a safe
and serviceable condition.
The combustion section includes
components such as fuel nozzles, cowl
caps, combustion liners, transition pieces
and flow sleeves. These require specialist
dimensional and non-destructive
inspections to be completed before an
advanced weld repair method is used
to restore the component to its correct
dimensions. This can involve parent metal
bonding to restore wall thicknesses and
repair minor cracks.
For the rotating components within the
hot section, the advances made in laser
welding have allowed many blades, which
would have otherwise been scrapped, to
be saved and returned to service. Laser
welding allows rebuilding of fine details
with limited excess material. At the same
time, stronger and harder weld filler alloys
can be used for demanding applications.
Thermal barrier coatings (TBC) can
be applied to components to help
them withstand the high operating
temperatures of the gas turbine. They
can be applied to combustion liners,
transition pieces and also blades
and vanes. More advanced, extreme
temperature resistant TBCs have been
developed for application on first-stage
advanced technology turbine buckets.
The search for increased power output
using higher turbine inlet temperatures
over 1300 °C has led to the application
of single-crystal (SX) materials for
turbine blading. Without a suitable repair
procedure, SX blades must be replaced at
every major overhaul after approximately
24,000 operating hours. Based on the
investigations and the advanced repair
techniques developed by Sulzer, SX
blades can be refurbished to an "as-new"
condition. With the high-end repair
technology and the know-how of Sulzer,
users of SX blades can give a second life
to these components and thereby achieve
substantial savings.
The number of advanced gas turbines
installed is increasing rapidly due to rising
fuel costs and environmental regulations.
Higher operating temperatures and
mechanical stresses are creating the
need for the use of advanced technology
components and refurbishment processes.
In general, refurbishment activities consist
of the stripping and reapplication of the
coating, the rebuilding of the geometry
by welding, and the rejuvenation of the
material condition through appropriate
heat treatments. Advanced refurbishment
procedures also include changes in
materials, coatings, or designs, which
should reduce the risks of failure or the
reoccurrence of damage.
Sulzer offers many similar types of
advanced component refurbishment
solutions, thus demonstrating that a
combination of expertise in material
science, skilled workmanship, and
highly developed in-house processes
are prerequisites for the reliable and
cost-effective extension of the life of a
component. Repairs that improve the
machine create significant added value
and reduce the cost of ownership for the
owners and operators of gas turbines,
steam turbines, and compressors.
A well planned maintenance program will
deliver continued reliability, optimum
performance and improved efficiency
Issue 18 PECM
5