Small Punch Testing for Determining the Material Toughness of Low Alloy Steel Components in Service

The toughness of the low alloy ferritic steel material of structural components operating at elevated temperatures can degrade during service due to embrittling phenomena such as carbide coarsening and temper embrittlement. The extent of degradation and the current level of toughness are critical inputs to component structural integrity assessments and to operation and maintenance planning. Conventional test methods for measuring toughness require the removal of large material samples from the in-service component, which is generally impractical. However, the recent development of relatively nondestructive, miniature sample removal systems and the small punch test technique (which utilizes nonstandard, miniature specimens) now provides a convenient, practical means of evaluating the material of an in-service component for toughness and related mechanical properties. This paper describes the small punch test technique with selected examples of its application to various grades of low alloy ferritic steel.