1 IntroductionrnIn the past, several oxide scale failure models were developed for different types of failure, and ap-proaches exist to combine these models with oxide failure diagrams . The most well known concept is described in EPRI report FP686 from 1978 which served as a basis for the assessment of strain tolerance of scales formed on heat exchanger tubes exposed to steam. This concept is solely based on oxide scale thickness as the parameter characterising susceptibil-ity to scale failure, (Fig.1). However, research over the last 3 decades showed that this simplified crite-rion can be misleading.