P&ID Editor — Process & Instrumentation Diagrams with ISA 5.1 Symbols

ANSI/ISA-5.1-2009 (Instrumentation Symbols and Identification) defines the graphical symbols and alphanumeric tag notation used on P&IDs throughout the process industries. The standard divides symbols into four categories: primary elements and sensors (flow, level, pressure, temperature, analytical, multi-variable), final control elements (control valves, on/off valves, regulators), general instruments and controllers (indicators, transmitters, controllers, recorders), and process equipment (vessels, heat exchangers, pumps, compressors, columns, tanks).

Every symbol in the editor is drawn to ISA 5.1 geometry. Equipment symbols (circle for centrifugal pump, triangle-in-circle for compressor, rectangle for heat exchanger shell) are immediately recognisable to any process engineer trained under the standard. The instrument bubble — a circle carrying the instrument tag — is the cornerstone of ISA 5.1: the tag code encodes the measured variable (first letter) and the function class (subsequent letters), e.g. FIC for Flow Indicating Controller or PT for Pressure Transmitter.

ISA 5.1 specifies distinct line styles for each class of interconnection on a P&ID, so a reviewer can instantly trace whether a path carries process fluid, measurement signal, control signal, electrical power, or pneumatic supply without reading every label. The MechanixCalc editor reproduces these conventions: process lines are solid and the heaviest weight (matching the dominant visual hierarchy of ISA 5.1 Figure 1); instrument signal lines are dashed fine-weight; electrical lines use a dot-dash pattern; pneumatic supply lines use a fine dotted pattern.

Connections between nodes are drawn as smooth orthogonal or curved paths that snap to the named port positions on each symbol (suction, discharge, top nozzle, instrument connection, etc.), so the topology of the P&ID is encoded in the graph structure — not just its appearance. This means the BOM engine can count every placed symbol and the CSV export can list each connection type, giving downstream document-control and HAZOP teams a machine-readable inventory.

Process plants are documented on multiple indexed P&ID sheets: one for each process section or unit operation (feed preparation, reactor, separation, utilities). The editor supports any number of named sheets within a single project file. A symbol placed on Sheet 1 (e.g. a pressure transmitter PT-201) can reference the corresponding control loop shown on Sheet 2, with annotation nodes carrying the cross-reference tag — consistent with the ISA 5.1 convention for off-sheet continuations.

The bill of materials is auto-generated from the placed node inventory: for every equipment category the BOM lists the symbol type, count, and any user-assigned tag. The CSV export serialises the same data in RFC 4180 format (fields quoted and escaped), suitable for import into CMMS, document-management, or HAZOP-study spreadsheets. The engineering-title-block PDF embeds the sheet number, revision level, project name, and date — the minimum traceable header required by most management-of-change procedures.