A glossary of boiler tube microstructures for some commonly used ASME B&PV Code Section II tube
materials has been compiled to show typical as-received microstructures and alterations created by
various exposure conditions. Materials include carbon steels (SA-178, SA-192, SA-210, SA-285, and
SA-515) and chromium-molybdenum steel alloys (SA-213, Grades T11 and T22). Exemplar samples
were prepared from new “stock” material as well as samples aged at set temperatures for various times
in the laboratory. This tool is useful in comparing actual boiler tube failures to quantify
temperature/time exposures. It is also valuable in verifying equivalent temperatures estimated from
oxide thickness measurements used to calculate remaining creep life. This paper will present
examples of this glossary and practical examples of the verification process for steam-touched tubes.
Key words: microstructure, carbon steel, chromium-molybdenum steel, remaining creep life, boiler
tube, thermal degradation, oxide thickness