ISA51

ISA51, commonly referred to as ISA-5.1, is a standard published by the International Society of Automation (ISA) that specifies instrumentation symbols and identification conventions used on process diagrams. The standard provides a comprehensive set of standardized graphical symbols for process equipment, instruments, actuators, controllers, and ancillary devices, as well as rules for device tagging and identification in instrumentation diagrams and P&IDs (piping and instrumentation diagrams). Its primary purpose is to promote consistency and clarity across engineering drawings, facilitating communication among engineers, operators, and maintainers.

ISA-5.1 covers symbol shapes for devices such as transmitters, sensors, valves, pumps, motors, and controllers, and defines line types and connection conventions for process lines, instrument lines, and electrical lines. It also describes symbol combinations to represent instrument loops, controllers and interlocks, and provides guidelines for instrument tag numbering schemes, including function codes, location, and service.

The standard is used across industries including chemical, oil and gas, refining, pharmaceuticals, and water treatment, and is often referenced in project specifications and vendor drawings. It exists in multiple editions, reflecting updates to symbol sets and tagging practices, with revisions coordinated with related standards in the ISA 5.x family and other international norms.

Critically, ISA-5.1 is frequently used in conjunction with other ISA standards such as ISA-5.3 (P&ID conventions) and ISA-20 (functional safety) to ensure comprehensive and interoperable diagrams.

See also: ISA (International Society of Automation), P&ID, instrumentation symbols.