Turbine Engine Overhaul (Jeppesen Powerplant 4-B)

4-18 through 4-40, only the overhaul portions and terms related to overhaul.

Who can overhaul a turbine engine?

* The Manufacturer
* An approved overhaul facility (Repair station)

What are the general steps in an engine overhaul?

1. Disassembly
2. Cleaning
3. Inspection
4. Remove & Replace
5. Reassembly
6. Testing

INSPECTION TERMS

__**Blending**__

A method of filing compressor or turbine blades and vanes to remove damage and reestablishing the appropriate contour for an aerodynamic shape.

INSPECTION TERMS

__**Blistering**__

Raised areas that indicate a separation of a surface layer from a base metal. Blistering is often evident as peeling (or flaking) of a metal plating.

INSPECTION TERMS

__**Bow**__

A stress-induced bend or curve in a blade's contour.

INSPECTION TERMS

__**Bulge**__

An outward bending or swelling caused by excessive pressure or weakening due to excessive heat.

INSPECTION TERMS

__**Compression**__

A squeezing force produced by two opposing forces acting on a part.

INSPECTION TERMS

__**Creep**__

A condition of permanent elongation in rotating airfoils resulting from thermal stress and centrifugal loading. Creep is also referred to as growth.

INSPECTION TERMS

__**Dynamic Balancing**__

A procedure used to balance the main rotating assembly of a turbine engine along both its rotational plane and the rotor axis.

INSPECTION TERMS

__**Electrolytic Action**__

Breakdown of surfaces caused by electrical activity between dissimilar metals. Electrolytic action is also known as galvanic corrosion.

INSPECTION TERMS

__**Flowing**__

The spreading out of a plated or painted surface caused by poor adhesion to the base or excessive loading on the part's surface

INSPECTION TERMS

__**Galling**__

The fretting ( or chafing) of a mating surface by sliding contact with another surface or body.

INSPECTION TERMS

__**Glazing**__

The development of a hard, glossy surface on bearing surfaces in the presence of oil, heat, and pressure.

INSPECTION TERMS

__**Growth**__

A term synonymous with creep.

INSPECTION TERMS

__**Guttering**__

Deep concentrated erosion that results from an enlargement of cracks or repeated exposure to a concentrated flame.

INSPECTION TERMS

__**Profile**__

The contour or aerodynamic shape of a blade or surface.

INSPECTION TERMS

__**Shear**__

A tearing force produced by two opposing, parallel forces acting on a part.

INSPECTION TERMS

Static Balancing

A procedure that balances the main rotating assembly of a turbine engine to reduce vibration

INSPECTION TERMS

Tension

A force that tends to pull an object apart.

INSPECTION TERMS

Untwist

A straightening and loss of blade curvature that results from gas loads, thermal stress, and centrifugal loading.

What is a blisk?

A turbine wheel that incorporates the blades and disk in one piece

What is the purpose of blending a compressor or turbine blade?

* Reduce concentrated stresses at sharp points in the blade
* reduce the possibility of the crack or defect spreading

Common defects found in the combustion section of a turbine engine

* Cracks
* Burner-can shift
* Hot spots or scorched areas
* Warpage
* Erosion
* Excess weld material over welded repair seams

Hottest part of a turbine engine?

The first set of turbine nozzle vanes

This makes them susceptible to the most cracking and stress

You should replace a cracked component whenever cracks appear to be ________

Converging

What is Primary Creep?

Creep related to an engines first run

What is Secondary Creep?

Creep that happens slowly over many hours of operation

What is Tertiary Creep?

Creep related to hot starts, overtemp events, and extended high power operation

\
**This is the one that is dangerous and warrants Turbine Over Temperature (TOT) inspections.**

As a general rule, where on a turbine or compressor blade is NO damage allowed?

Near the blades base or, if shrouded, where the blade meets the shroud

What are the typical options when repairing a combustion liner?

* Weld (or reweld) cracks
* Replace liner

Why is balancing critical for rotating assemblies on a turbine engine?

High rotational speeds can cause severe vibration if parts are unbalanced

When replacing turbine or compressor blades, what is the general procedure?

If the blades are marked with their weight, you can install just one, given the weights of the other blades are approximately the same. you may have to install more than one new blade if the engine blades have been worn over time. This is done to ensure proper balancing.

\
On wheels that have an even number of blades, 2 blades can be installed 180 degrees apart

On wheels that have an odd number of blades, 3 blades can be installed 120 degrees apart