Page 5 - 2nd Quarter 2021 Newsletter
P. 5

INTRODUCTION TO P&IDs



        What is a P&ID? A P&ID is a diagram that depicts the interconnection of process equipment and

        instrumentation. The term “P&ID” is an acronym for “Piping and Instrumentation Diagram”. As a
        drawing, a P&ID includes all process equipment, interconnecting pipes, manual valves, control
        valves, and process-related instrumentation as necessary to fully represent and understand the
        system.


        A P&ID of a small system may fit on a single page, while a complex chemical process may be
        hundreds of pages.

        Why are P&IDs required? P&IDs are a fundamental requirement of the RMP and PSM
        regulations. Specifically, when developing and organizing process safety information, a facility

        must ensure that the information pertaining to the equipment in the process include P&IDs.
        Additionally, P&IDs are an essential tool to any operator who seeks to fully understand his system.
        These drawings are particularly important for ammonia refrigeration systems, and IIAR standards
        encourage P&IDs to be developed as part of the system documentation in the non-mandatory

        Appendix B of ANSI/IIAR 9-2020.

        Are P&IDs that important? P&IDs are the cornerstone of PSM process safety information (PSI).
        How is relief system design verified? How are inventory calculations performed? What compressor/
        condenser capacity is available? Oftentimes, this information is available through the P&IDs. If your

        system P&IDs are accurate, there is high likelihood that your PSI program will be in good shape.
        On the other hand, if your P&IDs are incorrect, your PSI is almost guaranteed to be riddled with
        inconsistencies.

        Where do P&IDs come from? P&IDs are typically developed by the engineering team when

        a system is initially designed. After installation, the diagrams can be audited and corrected if
        inaccuracies are observed. Once corrected, the P&IDs are considered ‘as built’ and fully reflect the
        system configuration. Unfortunately, many P&IDs have become outdated or lost altogether due to
        system modifications or changes in facility management. When changes to a system are vast or

        the drawings are misplaced, P&IDs can be developed from scratch, which is a labor intensive and
        costly endeavor.









        Article courtesy of: Resource Compliance
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