Thursday 4 March 2010

Non destructive testing of blades before installation

Again questions arise if there is a way to test blades before installation or even after mounting with ultrasonics and/or infrared technology in order to quantify quality level or invisible or masked failures.

NDT techniques like the mentioned (US and IR) today (and I think for a long time in future) are not made to be used as a method for inspection of blades before installation in farms under construction. Both techniques have to be selected and adapted for the case of inspection one intends to do. IR has good features if you search for defects close to the surface. US have better potential if you want to look into the deep layers of structure. But non of these techniques can be used from root section to tip without dramatic change of parameters and system devices and measuring methods like frequencies, coupling heads, calibration and software setup. In other words: if you already know what kind of local fixed defect you are searching for and you already have tested and evaluated all these parameters for this case of testing, you have a slightly chance to be successful to find what you search for.

NDT like US and IR is not an all-purpose inspection feature and are to be chosen for very special assessment of blade defects. A day to day holistic blade quality inspection (inside and outside) like we do in many cases before installation is based on knowledge of the specific production process of the series production, the experience of noticed problems with this type of blade and the intuition of an old fox in the field of polymer chemistry, structural principles of blade design, aerodynamics, mass-dynamics of lightweight structures and last but not least independent standing of experts reference.

If you believe NDT blade testing is ready and in place for an universal monitoring of blade quality you may have been trapped by pseudo-scientific stories about fantastic new imaging techniques which is fiction for sure.