In this article7 sections
ISA 5.1 is the identification standard behind almost every tag on a North American P&ID, and it had gone thirteen years without a revision when ISA published the 2022 edition. Two years later it published another. This note records what ISA itself says each revision changed, and what that means for an engineer reading drawings across editions into a tag list. It deliberately does not paraphrase the standard's clauses, because ISA publishes the document and the clauses are theirs to state.
Key takeaways
- ISA describes the 2022 revision as clarifications and corrections to the 2009 edition, and as the start of a regular maintenance cycle. It was not a redesign.
- The 2024 edition changed the title, moved two annexes into technical reports, reorganized the text, added new symbols and reference sections, and added a loop instrument diagram symbol table.
- Neither release note describes a change to the identification rules that produce a tag. Confirm against your own copy; do not take this article's word for the clauses.
- Drawings stay valid under the edition in their legend. Read the legend on every sheet.
The 2022 revision, in ISA's words
The ISA5 committee's own description, published in InTech in June 2022 by Jim Federlein, PE, is short: the 2022 revision "is intended to provide usage clarifications and to correct typographical and technical errors that have been uncovered over the years since the 2009 version," and it "will serve as a basis on which the ISA5 standards committee can begin a more regular maintenance/revision cycle for this widely used international standard." ISA also announced that a new working group would begin the next iteration.
That is the whole of the public account. A thirteen-year gap invites the assumption that the 2022 document must contain sweeping changes; the committee said the opposite. The corrections are enumerated inside the standard, and a house standard that references ISA 5.1-2009 should compare its own clauses against them rather than against a summary.
The 2024 edition, in ISA's words
ISA released ANSI/ISA-5.1-2024 on 10 October 2024, calling it the result of a two-year committee effort on what is ISA's oldest standard, seventy-five years in publication that year. The release note lists the changes:
| Change | What ISA says |
|---|---|
| Title | "Instrumentation Symbols and Identification" became "Instrumentation and Control Symbols and Identification", to make the inclusion of control symbols explicit |
| Annexes moved out | Two annexes became separate technical reports: ISA-TR5.1.02, Instrumentation and Control Identification System Guidelines, and ISA-TR5.1.03, Instrumentation and Control Graphic Symbols Guidelines |
| Readability | The committee "clarified and simplified the organization of the document, providing definition consistency and clarification and eliminating redundant text"; notes tied to a table now follow that table |
| New content | New symbols to "recognize new automation technology", new reference sections, and the loop instrument diagrams symbol table |
| Next | A technical report on instrumentation and control content in process flow diagrams and P&IDs is in development |
The release note does not name the individual new symbols, and it does not describe changes to the identification rules. Where a project needs to know exactly which symbols were added, the answer is in the 2024 document and in ISA-TR5.1.03, not in secondary coverage.
What this means for the tag list
The I/O list and instrument index are built from the tag, the symbol, the signal line and the loop sheet. Three practical consequences follow from the two revisions.
The identification rules are the stable part. ISA's notes describe corrections in 2022 and reorganization plus new symbols in 2024. They do not describe a change to how a first letter, a succeeding letter and a loop number combine into a tag. A drawing set that mixes 2009, 2022 and 2024 sheets will tag instruments the same way. Verify this against your own copy of each edition before relying on it, because this article reports what ISA published, not the clauses themselves.
The legend is the authority for symbols. A symbol added in 2024 will not appear in a legend drawn to the 2009 edition, and a sheet's legend, not the standard's year, says what its symbols mean. On a project that spans editions, the register should carry the drawing's revision and the edition its legend cites, so a reviewer knows which symbol table a sheet was drawn against.
The guidelines moved. Anyone who used the annexes of the 2009 or 2022 editions for identification or symbol guidance now finds them in ISA-TR5.1.02 and ISA-TR5.1.03. A house standard that cites an annex by letter should be updated to cite the technical report.
When to move a house standard
There is no compliance deadline in either revision; adoption is a house-standard decision. Three triggers make the decision easy:
- A greenfield project. New drawings follow the most current edition the owner accepts. If the owner's standard is still on 2009, follow it, and record the edition in the legend.
- A CAD template refresh. Symbol libraries in the major P&ID authoring tools are keyed to editions. When the library moves to 2024, propagate the legend across the drawing set in the same cycle rather than leaving new sheets on one edition and old on another without saying so.
- Inconsistent digital-device conventions across the set. If the existing drawings already disagree with each other, a revision is a natural lock point to standardize on, with the legend updated on every sheet.
The one thing that costs more than any adoption is a mixed-edition set whose legends do not say which edition each sheet follows.
Sources
- ISA, InTech, June 2022, "Widely Used ISA Symbols Standard, ISA-5.1, Updated", Jim Federlein, PE.
- ISA news release, 10 October 2024, "Widely Used Engineering Symbols and Drawings Standard ISA-5.1 Updated by ISA".
- ANSI/ISA-5.1-2022 and ANSI/ISA-5.1-2024, available from ISA and ANSI; ISA-TR5.1.02 and ISA-TR5.1.03, ISA.
Related
- ISA 5.1 letter codes. First letters, modifiers, and what settles the signal class.
- ISA letter index. First-letter reference pages.
- P&ID to I/O list. What the register carries from each sheet.