Loop Folder Index
Template (Excel)

A loop folder index, also called a loop folder register or loop sheet index, is the EPC register that lists every instrument loop on a project together with the supporting documents collated in that loop's physical or digital folder. For each loop it records the loop number per ISA 5.1, service description, loop type (indication, control, safety, sequence), P&ID reference, loop diagram reference per ISA 5.4, primary element tag, final element tag, controller tag, datasheet references, hook-up drawing, cable numbers, calibration record, loop check record, and SAT record. It is the single audit trail from engineering through commissioning for instrumentation.

Per ISA 5.4 (Instrument Loop Diagrams) and industry practice, each loop folder contains: the loop diagram (one sheet per loop showing all field instruments, junction boxes, marshalling, control system I/O, power, and signal flow), instrument datasheets per ISA 20 / IEC 61987 for every instrument in the loop, hook-up drawings per project standard, cable schedule extract for every cable in the loop, I/O list extract, calibration certificate per instrument, loop check record (field-to-DCS continuity verified), and SAT record (functional response verified against the control narrative). For SIS loops, the cause and effect matrix and SIL verification report are added. See the ISA 5.1 reference page.

Pathnovo, an engineering document intelligence platform, extracts every loop number annotation from the P&IDs, cross-references each instrument tag to the instrument index, I/O list, datasheet register, hook-up drawings, and cable schedule, then assembles one row per loop with all linked document references. The output is the loop folder index spreadsheet plus a folder structure (one folder per loop, populated with the linked PDFs). Typical project turnaround is 48 hours for the initial folder structure with 99.5% contractual accuracy. See the instrument index automation workflow.

The I/O list is the signal-level register, one row per signal exchanged with the control system, focused on signal type, range, cabinet, module slot, and channel. The loop folder index is the loop-level register, one row per functional control or safety loop, focused on the engineering and commissioning audit trail for that loop. A single loop typically contains 2 to 6 signals on the I/O list (one transmitter input, one valve output, optional position feedback, optional override switch). The two registers are joined on the loop number; together they drive instrumentation commissioning. See the I/O list template.

Safety Instrumented Function (SIF) loops carry additional documents per IEC 61511. The folder includes the cause and effect matrix row, SIL determination worksheet, SIL verification calculation (PFDavg vs SIL target), proof test procedure, and the SIS logic solver configuration extract. The loop folder index SIL Classification column flags SIL 1, SIL 2, or SIL 3 loops, and the audit ties each SIS loop to the SRS (Safety Requirements Specification) and the FSA (Functional Safety Assessment) report. Indian PSU sites under OISD also require the loop folder for SIS proof test history. See the SIL standard reference and the SIL determination template.

On brownfield revamps the existing loop folder index (paper or legacy DMS) is reconciled against the as-built P&IDs and field walk-downs. Loops that are unchanged retain their existing folder; loops that are modified (new control valve, new transmitter, changed control narrative) get a revision update on the loop diagram and new calibration and loop check records. Decommissioned loops are flagged with a Decommissioned status. Pathnovo extracts both legacy and revamp loop folders, flags any discrepancy, and produces the consolidated revamp loop folder index. Common on Indian refinery and fertiliser revamps under OISD-150.

Downstream consumers: pre-commissioning calibration scope (one calibration certificate per instrument in the loop), loop check execution sequence (cabinets and marshalling first, then loops), SAT execution per the control narrative (one SAT per loop), pre-commissioning punch list closure, mechanical completion certificate signoff, and the system turnover package per system. The loop folder index Status column tracks each loop from engineered through commissioned and is the single dashboard for instrumentation commissioning progress. See the pre-commissioning checklist and the system turnover package template.