7/26/2019 Non Destructive Testing of Rotors From the Bore

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TPW/BPROS/NDTRB/eng/STM/03.13/CH/7806 ALSTOM 2013. All rights reserved. Information contained in this document is indicative only. No representationor warranty is given or should be relied on that it i s complete or correct or will apply to any particular project. This will depend on the technical and commercialcircumstances. It is provided without liability and is subject to change without notice. Reproduction, use or disclosure to third parties, without express writtenauthority, is strictly prohibited.Alstom contributes to the protection of the environment. This leaet is printed on environmentally-friendly paper.

Proven, early aw detectionBACKGROUND

Early forging techniques used to form rotors have been largely superseded by modernmethods. Previously it was necessary to bore an axial hole through the centre of therotor to remove any inclusions that may have formed.

The rotor bore experiences high stress levels in operation. In 1974 a 275MW IP/LP unitsuffered a catastrophic failure due to a crack initiating near the rotor bore surface.This failure could have been prevented if the crack had been detected and suitablerepairs made.

ALSTOMSSOLUTIONAlstom recommends periodic rotor inspections to detect and/or monitor potentiallyharmful defects within the rotor. For these we provide non-destructive testing (NDT)of rotor forgings, including monobloc forgings, shrunk on disc rotor shafts andgenerator forgings. A complete service is provided, including bore plug removal,bore preparation (honing) and re-plugging.

The inspection is performed using an automated borescanner (Figure 1). The currentversion is equipped with a combination of Ultrasound (UT) and Eddy Current (EC)probes; the UT allowing for a thorough inspection of the rotor volume whilst the ECinspects the bore surface. The borescanner is also equipped with motorised legs,allowing it to adapt to the bore diameter even when in use; a particularly useful feature

for bottled bores.

Both the UT and EC sensors are mounted on the same probes and operate in parallel,giving a scanning rate at least four times faster than the equivalent coverage bymanual methods. Typically the probes scan axially forwards and backwards, whilst alsotracking circumferentially in a helical pattern (both clockwise and anticlockwise).

The borescanner uses a dedicated docking station which attaches magnetically to therotor. Once in place, the scanner is pushed to the far end of the rotor bore to begin thescan. An indexed motor then gives accurate scanning control as the scanner is pulledback towards the docking station. This arrangement allows for a smaller dockingstation than a front loading design.

Alstom offers compre-

hensive non-destructive

testing of rotors from the

bore during steam turbine

outages. This allows any

potential aws to be iden-

tied over the length of the

bore. Repairs can then bemade to ensure safe

operation of the rotor.

Non-destructive testingof rotors from the bore

STEAM TURBINESERVICESOLUTIONS

CUSTOMER BENEFITS

Proven technique numerous rotors tested withautomated borescanner

Experienced operators, backedby skilled engineering teams

Early detection of potentiallydamaging rotor defects

Increased reliabilityCollection of useful data fora Turbine Life Assessment

Figure 1: The borescanner at work

7/26/2019 Non Destructive Testing of Rotors From the Bore

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TPW/BPROS/NDTRB/eng/STM/11.12/CH/7806 ALSTOM 2013. All rights reserved. Information contained in this document is indicative only. No representationor warranty is given or should be relied on that it i s complete or correct or will apply to any particular project. This will depend on the technical and commercialcircumstances. It is provided without liability and is subject to change without notice. Reproduction, use or disclosure to third parties, without express writtenauthority, is strictly prohibited.Alstom contributes to the protection of the environment. This leaet is printed on environmentally-friendly paper.

STEAM TURBINESERVICESOLUTIONSNON-DESTRUCTIVE TESTINGOF ROTORS FROM THE BORE

The following is a summary of the borescanners detection capabilities:

Bore length < 15M

Bore 70-300mm

Number of diameters* 2 (for bottled bores)

Defect size detected 1mm (d50mm)

The data is immediately displayed and recorded for analysis. It can also be stored forfuture comparison, or form part of a Turbine Lifetime Assessment.

The timings for a typical bore inspection are as follows:

Set-up