Standards and engineering codes rule design, construction and operation of chemical plant equipments to ensure reliability and safety. In this article, we exploit knowledge-based methodologies and technologies to guarantee safety rules compliance of pressure equipments. Specifically, we describe a knowledge-based tool defined on top of a knowledge-based computer-aided design system, which can serve inspection bodies. i.e. for certification purposes, and pressure equipment designers for the verification of the appropriate safety normative (i.e., the pressure equipment directive). The article focuses on the knowledge base of the tool. which has been formalized through the PEDE-I (Pressure Equipment Design and Inspection) ontology. The ontology has been enriched by logical axioms, which ensure the consistency of the knowledge base, and by reasoning rules, which enable to infer new relationships among the class instances stored in the ontology (C) 2008 American Institute of Chemical Engineers Process Saf Prog 27: 313-322, 2008