A removed blade is a useful reference for damage and configuration, but it is not automatically an accurate dimensional master. You will be able to trace the part, select the correct replacement, compare controlled dimensions, and verify seating, clearances, orientation and balance before release.
Key takeaways
- Record stage, position, part revision and removal reason before selecting a replacement.
- Measure replacement blades from the approved datum scheme, not worn contact surfaces.
- Use removed hardware as evidence of service condition, never as the dimensional master.
- Release the part only when fit, configuration and inspection records agree.
Record the removed part before choosing its replacement
Before selecting a replacement, record the removed hardware in its installed condition. Capture the engine or turbine model, stage, blade or vane position, circumferential location, airfoil orientation, part number and revision, serial or batch number, material, coating condition, and removal reason.
Preserve its position in a marked tray and mark blade numbering; memory is not configuration control.
Photograph each defect before cleaning or blending:
- Tip rubs and shroud impact with a scale and clear circumferential reference.
- Platform distress, root fretting, oxidation, and previous blends from perpendicular angles.
- Cooling-hole damage, blocked or enlarged holes, and their clocking relative to the platform or leading edge.
For gas turbine blade and vane manufacturers, replacement blade fit after removal begins with configuration control, not visual resemblance.
| Configuration item | Verify before fit | Why a mismatch matters |
|---|---|---|
| Part number and revision | Work order and controlled drawing | Same engine family does not prove interchangeability |
| Platform, cooling design, coating system | Approved configuration and coating record | Changes alter clearance, cooling flow, or durability |
| Root geometry and repair standard | Drawing, overhaul manual, or approved repair scheme | A different root or blend limit can prevent safe seating |
Before dimensional inspection starts, reconcile the work order, life limits, repair history, serial or batch traceability, material and heat-treatment records, and coating status. Use the removed part as evidence of service damage, not as the master dimension: fretting, plastic deformation, tip rubs, shroud impact, and blends can change its geometry.
A turbine vane fit inspection likewise begins with controlled identity and records.
Measure the replacement from the approved datum scheme
A replacement fits only when every locating and aerodynamic feature meets the approved datum scheme, not when its overall length or chord looks correct. Check dovetail or root flank geometry, serrations, tangs, fillets, insertion depth, axial restraint, platform width and height, bolt or pin-hole position, and datum-to-feature dimensions.
Then record airfoil span and chord at specified span stations, twist, camber, leading- and trailing-edge coordinates, and tip or shroud dimensions. Measure cooling-hole diameter and location against the drawing.
The root and platform usually establish the airfoil datum because they locate the blade in the disk and casing. A best-fit alignment of two scanned airfoils can hide incorrect stagger, sweep or twist.
| Tool | Assigned checks | Control |
|---|---|---|
| Micrometers and bore gauges | Accessible thicknesses, diameters and internal holes | Measure at the drawing’s defined locations |
| Height gauges and optical comparators | Datum-to-platform dimensions, profiles and hole locations | Use the approved orientation |
| CMM, profilometer and fixture | Coordinate-based root and airfoil geometry; surface condition; repeatable seating | Preserve the drawing coordinate system |
Record part temperature, fixture orientation, calibration status and coordinate transformation. State coating thickness and whether each limit is bare-metal or as-coated; a coating can close a tip clearance or alter platform fit. Use the approved fixture, not hand pressure, to seat the part before measurement.
- Hold the part if root contact occurs only at an edge, insertion is incomplete, or the report lacks calibration or datum information.
Use the removed blade as evidence, not as the master
A removed blade is evidence of operating condition, not a dimensional master. Fretting, plastic deformation, tip rub, oxidation, shroud impact and earlier blending can alter its root, platform and airfoil geometry. Measure both parts against the approved engine-component drawing, overhaul manual, repair scheme or controlled inspection program.
| Part condition | Acceptance basis | Required decision |
|---|---|---|
| Identical replacement | Same approved part number and revision | Compare every datum and feature with the drawing |
| Oversize or undersize repair part | Altered dimension permitted by approved repair data | Confirm the repair limit, not similarity to the removed blade |
| Reverse-engineered component | Documented design-authority or customer approval | Reject visual matching without controlled approval |
For replacement aero engine blade fit, confirm the correct stage, blade numbering, camber direction, cooling-hole pattern, platform marking, root insertion direction, cooling-passage orientation and lockwire or retainer position. Left- and right-hand parts require separate confirmation; a reversed camber or hole pattern can look correct until installation.
Check root seating, platform gaps, shroud position, cooling-hole alignment and casing interference with a borescope when removal is impractical. Record the datum scheme used for both measurements, because aligning scanned airfoils by best fit can hide root-driven errors in twist or stagger.
A new blade that matches the worn part but fails the controlled datum limits is not an acceptable replacement.
Separate blade seating checks from vane fit inspection
A rotating blade is located by its root, not by visual airfoil alignment. Check full root or dovetail seating, flank contact with blue-check transfer compound when the approved procedure calls for it, tang and retainer engagement, platform alignment, shroud contact, axial and radial clearances, tip-rub evidence, and freedom from rocking or bottoming.
| Blade | Rotating fit checks | Balance and clearance basis |
|---|---|---|
| Blade | Root, flank, tang, retainer, platform, shroud, tip, axial and radial clearances | Confirm mass, center-of-gravity or moment data, then apply the rotor manufacturer’s balance or moment-matching procedure |
| Vane | Inner and outer platforms, hooks or rails, carrier, seal lands, location, gaps and cooling passages | Verify clocking, throat alignment and platform overlap; visual seating alone is insufficient |
For a stationary vane, a turbine vane fit inspection must cover inner and outer platform dimensions, hooks or rails, carrier engagement, seal lands, axial and circumferential location, inter-vane platform gaps, and cooling-air passage alignment. Check nozzle-guide-vane clocking and throat alignment because an apparently seated vane can change throat area or flow angle.
Rotate or cycle the assembly only under the approved procedure. Verify that no platform, shroud, seal or airfoil feature contacts the casing, and record any rub evidence. Geometric interchangeability does not remove the balance requirement for a rotating blade; missing moment data is a hold condition.
Release the part only when fit, configuration and records agree
Release the replacement only after the dimensional report, configuration records and authorized sign-off tell the same story. A good fit cannot compensate for an unidentified part, missing material evidence or an approval gap.
1. Reconcile the report with the controlled drawing revision or approved repair scheme. Confirm part number, turbine stage, left- or right-hand orientation, coating status, material and heat-treatment records, serial or batch traceability, and applicable repair history or life limits.
2. Confirm the measured root, platform, airfoil, shroud and clearance values use the specified datum scheme and limits. Record the CMM or optical inspection reference, fixture, coordinate transformation and whether limits apply to bare metal or the as-coated condition.
3. Match the balance, moment or center-of-gravity data to the rotor manufacturer’s procedure. Geometric interchangeability does not remove the balance requirement.
4. Obtain sign-off from the named engineering, quality or design authority before installation or release. The signature must identify the person’s approval authority, not merely the person who performed the measurement.
Place the part on hold for root contact limited to an edge, incomplete insertion, platform mismatch, out-of-limit shroud or tip clearance, incorrect cooling-hole clocking, casing interference, missing balance data, unexplained left- or right-hand mismatch, or unproven replacement approval.
If controlled manufacture or reverse engineering is required, BVPL Turbine Parts becomes useful only when you provide the inspection datum scheme, CMM or optical output, material and coating records, configuration revision, and applicable drawing or approved repair requirements.
The decision is not whether the part resembles the removed one; every locating feature, aerodynamic feature, clearance and record must meet the controlled acceptance basis.
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Frequently asked questions
What should you record before choosing a replacement turbine blade?
Record the engine or turbine model, stage, blade or vane position, circumferential location, airfoil orientation, part number and revision, serial or batch number, material, coating condition and removal reason.
How should you perform replacement blade dimensional checks?
Measure the replacement from the approved datum scheme and compare its controlled dimensions with the applicable drawing, inspection plan or repair standard.
Can the removed blade be used as the master for replacement fit?
No. Use the removed blade as evidence of service condition, wear, distortion or damage, but use approved engineering data as the dimensional master.
What is the difference between blade seating checks and vane fit inspection?
Blade seating checks focus on root engagement, platform contact, retention and airfoil orientation. Vane fit inspection focuses on segment location, end clearances, seals, platform alignment and circumferential fit.
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