Off-page connector.
An off-page connector is a P&ID symbol that hands a process line or instrument signal off to another drawing page. Drawn as a pentagon-shaped arrow with the destination annotated inside, e.g. TO P-12, it is the mechanism that makes a multi-page drawing set legible.
What Off-page connector means.
A process facility P&ID set can run from a few drawings on a small skid to several hundred sheets on a large refinery or offshore platform. Any pipe run or signal line that cannot fit on a single sheet must be continued on another sheet. The off-page connector marks that handoff. It terminates the line on the current page and provides the address of where it continues. For the drawing to be internally consistent, every TO annotation on one page must have a matching FROM annotation on the destination page. An unmatched pair is a drawing-integrity defect. On large drawing sets these defects accumulate silently when P&IDs are revised in isolation, because the engineer revising one page may not update the page the line comes from. Systematic checking of off-page connector pairs is part of HAZOP preparation, IFC issue review, and brownfield drawing reconciliation.
How off-page connectors are drawn
ISA 5.1 represents an off-page connector as a pentagon-shaped arrow oriented in the direction of flow or signal. The destination annotation lives inside or alongside the symbol. TO P-12 means the line continues on page 12. FROM P-04 means the line arrived from page 4. The pentagon shape distinguishes these connectors from continuation arrows used to wrap a long run within the same page. On signal lines, instrument air, electric signal, data bus the same symbol applies, with the signal line type, including the ISA 5.1 line convention for electric, pneumatic, or software, preserved across the page boundary.
Annotation conventions and dialect variations
The annotation format inside the connector varies by company standard. Common variants include. TO DWG-PID-0012, CONT'D ON P-12, or a simple drawing number with no label. Some house standards add the line number or the fluid service code alongside the drawing reference so a reviewer can confirm continuity without pulling the target sheet. ISO 14617 uses a similar pentagon convention with minor stylistic differences. KKS-tagged drawings and European projects following DIN 2481 or ISO 10628 use equivalent symbols, though the notation inside may follow different drawing-number formats.
Process lines vs instrument signal lines
Both process pipe runs and instrument signal paths use off-page connectors. A process off-page connector continues a pipe, including its line designation. Bore, material class, insulation to the next sheet. An instrument signal off-page connector continues the signal path between a field device on one page and its controller or indicator block on another, preserving the ISA 5.1 line style so it is clear whether the path is electric, pneumatic, or data. Reviewers checking SIS interlock logic across pages rely on the signal off-page connectors to trace the full trip path from initiating sensor to final element when the path spans multiple sheets.
What goes wrong on multi-page sets
On a 50-page set every off-page connector pair is a place the drawing can drift. A line annotated TO P-12 with no matching FROM on page 12 means either the originating page annotation is wrong, the destination page was renumbered, or a revision introduced a new line that replaced the old continuation without updating both ends. Cross-page interlocks, where an SIS trip signal from a pressure transmitter on one unit connects to a shutdown valve on another unit, depend on the matching pair to make the logic traceable. An unmatched pair is a drawing-integrity finding that blocks the IFC issue and must be resolved.
MOC implications
When a P&ID revision reroutes a line or changes a page boundary, every off-page connector pair that touches the revised section must be updated. Management-of-change procedures require that the affected drawing pages are co-issued so the set remains internally consistent at every revision level. In practice this means a single instrument relocation can require updates to two or three pages to maintain connector pair integrity. When extraction tools reconcile connector pairs across the full drawing set, unmatched connectors are surfaced as a list rather than discovered one by one during manual review.
Common questions
Are off-page connectors the same on every drawing standard.
Do off-page connectors carry process lines or instrument signals or both.
How do unmatched off-page connectors get caught during a drawing review.
Can an off-page connector reference a page that does not exist yet.
What is the difference between an off-page connector and a match line.
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