Glossary of Boiler Tube Microstructures and Its Use to Verify Oxide Thickness Temperature Estimations

M&M Engineering has compiled a glossary of boiler tube microstructures for ASME B&PV code Section II tube materials.  The glossary shows typical as-received microstructures and alterations created by various exposure conditions.  Materials include carbon steels (SA-178, SA-192, SA-210, SA-285, 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.  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.

Keywords: microstructure, carbon steel, chromium-molybdenum steel, remaining creep life, boiler tube, thermal degradation