The present invention relates to an improved method suitable for long term creep strain measurement of the steam pipes and other high temperature components during operation in a power plant or other engineering facilities using digital image correlation (DIC). The inspection surface is prepared and at least two micro indents are created thereupon. An image of the surface is acquired and further images acquired at later times. The images are compared and using DIC techniques the creep deformation is determined. The inspection area is maintained in an inert gas environment (argon gas filled cavity 4) via a sealed protective case (in device 1) so as to prevent oxidations and other contaminations of said area due to high temperature exposure over an extended period of time. An embodiment of the protective case is also proposed that contains an optically transparent element (window 6) enabling image acquisition without loss of the inert gas.
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