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.
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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.
Frequently asked.
Are off-page connectors the same on every drawing standard.
The pentagon arrow is the dominant North American convention per ISA 5.1. ISO 14617 uses a similar pattern with minor stylistic differences. House standards layer additional metadata such as drawing number, line type, and signal class inside the connector annotation. Drawings following KKS or DIN naming conventions use equivalent symbols but the destination annotation follows the numbering scheme of the project.
Do off-page connectors carry process lines or instrument signals or both.
Both. Process pipe runs that exceed a single page get off-page connectors with the line designation carried across. Instrument signal lines that connect a field transmitter on one page to a controller hexagon on another also use off-page connectors, with the ISA 5.1 signal line type preserved. The symbology is the same for both. The line type into the connector indicates whether it is process pipe or instrument signal.
How do unmatched off-page connectors get caught during a drawing review.
By cross-referencing every TO annotation on one page against the corresponding FROM annotation on the target page. On a 50-sheet set this check is done manually during HAZOP preparation or electronically by matching the full set of TO and FROM annotations so that a loop running off one page is confirmed to continue on the page referenced. An unmatched connector is a drawing-integrity finding that must be resolved before the set issues for construction or HAZOP.
Can an off-page connector reference a page that does not exist yet.
Yes, during early detailed engineering when the drawing set is still being assembled. Connectors to pages that have not been created are tracked as open items. Before the set issues for review or HAZOP, all referenced pages must exist and all connector pairs must resolve. Connector-to-missing-page is typically caught during the interdiscipline drawing review before the IFC issue.
What is the difference between an off-page connector and a match line.
An off-page connector represents a pipe or signal that leaves the current page and continues on another page. A match line is a vertical or horizontal boundary on a drawing that indicates the sheet continues adjacently, typically used on very large equipment layouts or plot plans. P&IDs use off-page connectors. Match lines are more common on plot plans, mechanical arrangements, and civil drawings. The two serve similar functions but are different symbols used in different drawing types.