This paper describes the use of process hazards analysis (PHA) techniques and "API 579 Recommended Practice for Fitness-for-Service, Assessment of Existing Equipment for Brittle Fracture" to evaluate existing olefins plants. It also examines some of the identified transient process excursions that can result in operations below vessel minimum allowable temperature (MAT), creating the potential for brittle fracture, and the methods of the evaluation are described. The importance of identifying transient process conditions and making materials-of-construction selections based on these conditions is emphasized. Translation of the typical findings and lessons learned to other processes handling light-liquid hydrocarbon materials in carbon steel equipment is discussed, as well as the importance of operator training and response. (c) 2006 Elsevier B.V. All rights reserved.