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.
Three drawings included on a new account.
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.
Worked example, checking one connector pair.
A line leaves the right hand edge of sheet 12-2 with the annotation 2"-PG-1043-A1A TO P&ID 12-3, B4. Read it as four separate facts, each of which is checkable. The line number is 2 inch nominal bore, process gas service, sequence 1043, piping class A1A. The destination is drawing 12-3. The grid reference B4 says where on that sheet the mate should be found. So the check is: open 12-3, go to grid B4, and confirm an incoming arrow carrying the same line number and pointing back at 12-2. Three things go wrong here often enough to be worth looking for every time. The line number on the far sheet may differ in one field, most often the piping class, which means either a spec break is missing or one of the two is stale. The far sheet may carry no mate at all, which leaves an orphan and a pipe that stops existing at a drawing edge. Or the destination number may point at a drawing that has since been split or superseded, which shows up as soon as the connector is checked against the current document register rather than against memory.
Off-page connector types and what must match on the far sheet
Every connector is one half of a pair. The check that finds the errors is the reciprocity check: each connector should have exactly one mate, and the two annotations should agree.
| What continues | How it is usually drawn | What the annotation names | What must agree on the far sheet |
|---|---|---|---|
| A process line leaving the sheet | An arrow or flag on the end of the line, pointing off the drawing | The destination drawing number, often with a grid reference | The same line number, size, piping class and service |
| A process line arriving on the sheet | The mirrored arrow at the start of the line, pointing in | The source drawing number and grid reference | The far sheet carries the matching outgoing arrow for the same line |
| An instrument signal leaving the sheet | A small tag on the signal line, drawn in the line style of that signal | The loop or tag number and the destination drawing | The same loop number, and a signal line of the same type |
| A utility header continuing | An arrow carrying the header tag | The header line number and the destination drawing | The header number and service, and the branch arrangement |
| A connection to a vendor package drawing | An arrow at the package boundary | The vendor document number and the package tag | The vendor drawing shows the reciprocal connector at the same terminal point |
| A line continuing to a different area or unit | An arrow, often with the area or unit number called out | The area or unit and the destination drawing | The area boundary is drawn on both sheets in the same place |
What goes wrong at a sheet boundary, and what catches it
Every one of these is found by comparing the two halves of a pair, which is why a multi-sheet set is checked pairwise rather than sheet by sheet.
| Defect | What it looks like | What catches it |
|---|---|---|
| Orphan connector | An arrow that names a destination which carries no matching arrival | A reciprocity check across the whole set |
| Line number changes across the boundary | The same pipe carries two different numbers on the two sheets | Comparing the line number on both halves of each pair |
| Size or class changes without a spec break | The far sheet shows a different size or piping class with nothing drawn to explain it | Comparing size and class on both halves, then looking for a spec break symbol |
| Stale destination after a re-issue | The arrow points at a drawing number that was superseded or split | Checking every connector against the current document register |
| Signal type changes | A signal leaves as one line style and arrives as another | Comparing the line style on both halves of the pair |
| Duplicate arrival | Two sheets both claim the same incoming line | A reciprocity check; a pair should be one to one |
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.
Get the P&ID symbol cheat sheet.
The bubble, valve, line and connector symbols on one printable page, with what each one denotes. Plain PDF.