The turbine shafts are the extremely loaded parts of the rotors. The high mechanical stresses accompanied with elevated ambient temperature may cause
appearance and growing of fatigue cracks followed by catastrophic failure. Thus the axis vicinity areas of rotor shafts have been inspected ultrasonically on
regular basis during the scheduled shutdowns. Usually the 100% inspection of the hollow shafts is performed with the use of probe system scanning over the
entire rotor length from the bored surface (ID side). For the solid shafts the inspection is performed from the OD surface; the same inspection is suitable for
the screening of the hollow shafts in the cross sections in between the rings carrying the turbine blades.
Depending on the rotor type the inspection with use of conventional probes lasts 6...7 work shifts. To reduce the inspection time to 1 work shift there was an
inspection procedure based on use of the PA modality developed by Sonotron NDT in cooperation with IEC several years ago. The inspection is implemented
with the use of ISONIC series PA instruments (ISONIC 3510, ISONIC 2010, ISONIC 2009 UPA-Scope) through running of the RODScan Inspection SW
application utilizing the True-to-Geometry (True-to-Shape) S-Scan coverage and imaging strategy. The complete cross sectional view is formed in one
revolution of the shaft through superimposing of all S-Scan images obtained within entire revolution. The raw data A-Scans (primary and superimposed
according to the settled focal laws) composing every recorded S-Scan image are stored completely and may be played back off-line providing all-standardscompliant
A-Scan based evaluation. The RODScan inspection SW option is used widely across the world.
In the recently issued new SW release for the ISONIC series portable PA instruments the RODScan inspection mode allows performing of the S-Scan
coverage and capturing of the S-Scans over entire shaft rotation following both EquPAS and FMC/TFM protocols simultaneously significantly increasing the
precision of the defects evaluation. This is especially important for the monitoring of the discontinuities in the shaft material until developed to the critical
shape / dimensions. The increased inspection speed and precision of the evaluation allow prolonging of the service life and save the expenses for the
turbines health monitoring.