On‐site inspection of potential defects in wind turbine rotor blades with thermography

Abstract

Recurrent non‐destructive testing inspections are necessary to prevent damages in wind turbine rotor blades, but so far, there is no established method that detects defects in blades from greater distances – although this becomes increasingly important in the context of hardly accessible offshore wind parks. Thermography is a promising method for detecting subsurface defects, but various challenges arise when this method is applied on‐site to turbine blades in operation. Disturbing influences from the environment easily lead to a misinterpretation of thermograms (i.e. thermographic images), such as thermal signatures caused by reflections, dirt and other superficial inhomogeneities. This study explores several problems and effects that arise, when (rotating) blades are monitored with thermography. It will then be demonstrated that a meaningful defect inspection in this scenario is essentially restricted to a procedure following three steps: Firstly, calculating the so‐called difference thermograms of all blade pairs for eliminating disturbing reflections. Secondly, identifying potentially relevant signals, which are associated neither with structural features nor with dynamical effects, and the identification of these signals' allocations (through comparison of all difference thermograms with each other). And thirdly, comparing these signals with (processed) photos for excluding incorrect indications by surface effects. Unlike common thermographic analysis methods, which typically only include an aspect of this procedure, the composition presented in this contribution constitutes an advanced technique for minimizing disturbing influences in thermograms. The proposed thermographic technique enables the detection of potential subsurface defects within rotating rotor blades from greater distances – such as from the ground, air crafts or vessels. Copyright © 2015 John Wiley & Sons, Ltd.

Taxonomy of Gas Turbine Blade Defects

“…In principle, this work is expandable to other parts of gas turbine engines, such as annulus fillers, cases, discs, rotors, air seals, bearings, shafts, drums, liners, fuel nozzles and ducts. It is conceivable that the introduced defect list and ontology is further applicable to other industries where turbines with blades are deployed, such as marine craft propulsion [4], steam or hydropower generation [44,45] and even wind power systems [46,47]. The work was developed for the aviation maintenance industry, in particular for the visual inspection of gas turbine engine blades, but it may be possible to apply more widely.…”

Measurement of quality test of aerodynamic profiles in wind turbine blades using laser triangulation technique

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