Evaluation and Prevention of Potential Cold Embrittlement Hazards in Petrochemical Facilities

A summary of contemporary practices and approaches for evaluating and preventing potential cold embrittlement hazards within ethylene production facilities will be presented.  The practices and approaches will be discussed in the context of API 579 Parts 3 and 9, ASME Section VIII Division 1, and ASME B31.1.  These three bodies of knowledge have been recognized by OSHA as RAGAGEP in the U.S. on fitness for service requirements that govern the design, fabrication, inspection, testing and certification of pressure vessels exceeding internal or external operating pressures of 15 psig and piping.

The primary materials that will be discussed include carbon and low alloy steels, 400-series stainless steels, duplex stainless steels and 300-series stainless steels.  The discussion will include considerations of grain size, steel chemistry, heat treatment, environmental conditions, process conditions, and their relative effects on material toughness and impact strength.  A brief summary of fracture mechanics will also be included, primarily to highlight the differences between ductile and brittle fractures and to draw a clear connection between the key factors that drive material toughness and how they can also influence the mode of fracture.

Potential cold embrittlement vulnerability varies according to a chemical plant’s vintage and design, and maintenance considerations can have an enormous impact on the suitability of these materials for cold temperature service.  This paper will walk readers through a practical means of assessing the suitability for service of existing equipment, properly specifying materials of construction for new designs, and apposite maintenance practices for preserving pertinent toughness qualities for existing equipment in cold temperature service.