Reading a Saudi Aramco P&ID. SAES Instrument Tag Conventions.

Pick up a P&ID on a Saudi Aramco project and most of it reads like any other ISA 5.1 drawing: a bubble with a first letter for the measured variable, succeeding letters for the function, and a loop number. That is by design. Aramco's engineering standards supplement ISA 5.1 rather than replacing it, so the skill transfers. What catches people out is the handful of deliberate deviations, and one of them, the relief-valve tag, changes how you read every safety device on the sheet.

This is a field guide to those deviations: what to look for, what it means, and where a tag list built on plain-ISA assumptions will quietly go wrong.

SAES supplements ISA, it does not replace it

The tagging rules live in SAES-J-004, Instrumentation Symbols and Identification, and it takes ANSI/ISA-5.1 as its normative base. The instrumentation series (SAES-J) also covers the wider documentation set an Aramco project expects, from the instrument index through loop diagrams, cause-and-effect charts, and the ESD drawings, but J-004 is the one that governs how a tag is written.

The practical consequence: an engineer who reads ISA 5.1 fluently already reads most of an Aramco P&ID. You are not learning a new language, you are learning the exceptions. There are only a few, and they are consistent.

How an Aramco instrument tag is built

The base is the familiar ISA functional identifier plus a loop number:

[Plant / unit prefix] - [First letter][Succeeding letters] - [Loop number]

Worked through on an illustrative tag, 12-PZV-1001:

• 12 is the plant or unit prefix, present because this is a multi-train facility and the same tag would otherwise repeat on the sister train. On a single-train area this block is usually absent. The exact digit format is facility-specific, so treat the prefix as "a unit identifier" rather than a fixed width.
• PZV is the functional identifier. P is pressure, and ZV is the Aramco relief-valve convention (covered below).
• 1001 is the loop number, unique within the pressure-relief group on this unit.

The same tag string doubles as the equipment mark on the spec sheet, the requisition, and the schedules, so the number you read on the P&ID is the number you follow all the way through the document set.

Where Aramco differs from generic ISA

These are the commonly-cited, openly-discussed differences. They are house conventions layered on ISA 5.1, so read the tag with ISA rules first, then apply these:

Two more worth knowing: the indicate modifier I is sometimes dropped where a display is implied, so FIC may appear as FC; and tagging is mandatory, every instrument is identified, where plain ISA leaves that to the owner.

The safety layer: ZV, ZC, and J-601

The single most important distinction to get right is the emergency shutdown layer. Aramco implements its safety instrumented systems under SAES-J-601, which follows IEC 61511. On the drawing:

• ZV is a valve that belongs to the ESD system.
• ZC is the ESD logic solver that drives it.
• UC is non-ESD logic, sitting in the basic process control system.

The reason this matters beyond nomenclature: a ZV is a safety-instrumented final element with its own integrity target, and it must not be counted or wired as if it were an ordinary modulating control valve or a UC control point. When the tags flow into the I/O list, the ESD signals carry different handling from BPCS signals, so mixing them at the tag-reading stage propagates into the wrong signal-class split downstream.

Parallel loop numbering, and why it trips up a tag list

On many plain-ISA drawings the loop number runs in one sequence across the sheet. Aramco uses parallel numbering: each first-letter group keeps its own sequence. So on one unit you legitimately see:

• TIC-101 (temperature loop 101)
• FIC-101 (flow loop 101)
• LIC-101 (level loop 101)

all at once. None of these is a duplicate. The loop number is unique within the letter group, not across the plant. Anyone deduplicating a tag register on the loop number alone will wrongly collapse three distinct loops into one. The safe key is the full functional identifier plus the loop number, and, on a multi-train facility, the unit prefix as well.

Reading an Aramco P&ID: the quick checklist

• PZV / PZE, not PSV / PSE. Every relief device carries the Z. If you see PSV on an Aramco sheet, question it.
• ZV and ZC are the safety layer. Keep them separate from UC control logic and from modulating valves.
• MOV is a prefix, not an ISA combination. Read it as motor-operated valve directly.
• Parallel numbers repeat across letter groups. TIC-101 and FIC-101 are two loops, not a clash.
• The unit prefix appears only on multi-train sheets. Its absence is normal on a single train.

Everything else follows ISA 5.1. Learn the six exceptions above and an Aramco P&ID reads as cleanly as any other.

Further reading

• ISA 5.1 instrument tags, the base standard these conventions extend.
• What is ISA 5.1, the letter-code reference.
• AI, AO, DI, DO signal classes, where the ESD-versus-BPCS split lands on the I/O list.