Guidelines for evaluating in-service creep damage (NT TR 302)

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  • Report #: NT TR 302
  • Approved: September 1995
  • Author(s): Pertti Auerkari, Jorma Salonen, Kjeld Borggreen
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To indicate safe life or re-evaluation periods for high-temperature components, assessment based on measured creep cavitation damage is used worldwide. To interpret the observed damage unambiguously requires evaluation of the extent of damage on a unique, clearly defined and accepted scale. The presently available European damage scales in the guidelines NORDTEST NT TR 170 and VGB-TW 507 provide reference micrographs for a range of creep damage in the most common high-temperature steels. However, these guidelines differ in their stated and implicit definitions of a given class (extent) of damage, although both guidelines are nominally based on the same original Neubauer scale of creep damage.


This work provides a comparison of the guidelines NORDTEST NT TR 170 and VGB-TW 507 guidelines, as well as an attempt to unify the European creep damage scales. The proposed unified definitions of damage are based on the quantified damage scales of NORDTEST NT TR 170 with limited revisions and simplifications. The new definitions for damage classification also aim to correct inconsistencies in the present guidelines, with minimum modifications to the actual example micrographs. The main use of the definitions is foreseen in constructing or extending compilations of reference micrographs on in-service damage, and in calibrating image analysis of such damage.