National Physical Laboratory

Measuring heat shield tiles

NPL's freeform service measures turbine engine heat shield tiles for thermal coating analysis.

3D scan comparison of tiles with standard and trial coating
3D scan comparison of tiles with standard and trial coating


As part of a case study for the Supergen project, the performance of a thermal barrier coating system in laboratory furnace tests was compared with the performance of the same coating system on real components in an industrial gas turbine.

The in-service tests were performed courtesy of RWE npower who allowed heat shield tiles coated with the trial coating system to be placed inside a gas turbine engine.

The coating system failed more rapidly in the gas turbine environment (within six months) than in the laboratory test furnaces, and one of the aims of the work was to find out why.

The ex-service tiles appeared warped, and the first step of the investigation was to determine if there was any correlation between coating spallation and component shape change.

The Challenge

The shapes of six tiles were measured: two of the tiles were coated with the standard coating and four of the tiles were coated with the trial coating system.


A Faro Quantum™ articulated arm equipped with a laser scanner was used to digitally scan a complete 3D image of each tile.

To produce a full 3D image each tile was scanned in three positions and Polyworks™ software used to align the datasets into a single image.

The datasets for the two good tiles were used to produce polygonal models of the tiles, which could be then taken as a reference. Finally, the datasets for each tile were then compared to the reference.

In order to do this, dataset from the tile and the reference needed to be aligned into the same coordinate frame. The part was aligned using the features where it is secured in the engine so that any deformations could be measured as relative to the tiles location in the engine.


The inspection results showed clearly how each tile had deformed from its original form. It was then possible, in conjunction with microstructural characterisation, to determine which occurred first - tile deformation or coating spallation.


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Last Updated: 31 Jul 2017
Created: 22 Dec 2010


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