National Physical Laboratory

Thermal imaging reveals the invisible

Summary

Turbine blade defects
Turbine blade defects

NPL saved a UK business a potential US$700,000 risk by using a thermal imaging method called pulsed thermography. NPL's expertise revealed an invisible problem with the coating of a power station gas turbine vane, which would have caused it to crack, and led to expensive downtime.

Background

Wood Group Gas Turbine Services, a company that provides industrial gas turbine repair and overhaul services, asked NPL to investigate a number of gas turbine vanes which had been coated by another vendor. The results of NPL's testing led to massive cost savings for Wood Group.

Turbine blades are coated in batches, prior to being put into service. Two blades out of a coating batch of six had been fitted in an operational power station but had developed defects to the extent that the power station would potentially have to shut down, which would have been extremely costly for the power company.

Solution

Wood Group wanted to be sure that the remaining four vanes of the batch were not faulty too, so they asked NPL to check the vanes to see if this would reveal any problems. NPL decided that the best way to proceed was to carry out pulsed thermography on the blades.

Pulsed thermography is a form of thermal imaging where a very short intense flash of light is directed at the sample, in this case - the turbine vanes - and infrared cameras record how the heat passes through different areas of the sample. This kind of imaging technique can reveal structural problems that are invisible to the naked eye.

By using this technique, NPL was able to confirm that there was indeed a problem with the coating on the remaining four vanes and that they would most probably fail in a similar way to the two already in operational use. Wood Group were delighted with NPL's initial investigation and through their own subsequent testing, confirmed that there was a problem with the adhesion of the blades' coating in exactly the spots identified by NPL's thermal imagery.

Impact

The impact of this work was significant in two respects - firstly, Wood Group were able to save at least US$700,000 in warranty costs (i.e. the insurance they provide the customer if their products or services lead to power station downtime), and secondly they were able to avoid putting the faulty blades into service at a power station which could have damaged Wood Group's relationship with that customer.

For more information, please contact John Nunn

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Last Updated: 17 Apr 2012
Created: 12 Nov 2010

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