API RP 551:2016

This document provides recommendations about the selection and design of process measurement systems. Further, it supplies information on their implementation and commissioning. It covers the instrumentation life cycle including selection, design, installation, commissioning and operation. It is pertinent to those involved with instrument application including design firms, owner/operators, equipment package suppliers/integrators, construction and service personnel, as well as instrument manufacturers. Instrument systems are often a compromise between the installed performance and maintainability. A system has to balance these requirements while ensuring that basic principles are upheld. This document assists in the understanding of these principals and making proper decisions. This recommended practice is intended to be a source of good engineering practice. Its recommendations are practical and safe, which yield consistent and effective results.