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P&IDResources / P&ID symbols / By standardUpdated 29 Oct 2026

[ P&ID SYMBOLS · COMPARISON ]

ISA vs ISO P&ID symbols

The same plant can be drawn two ways. US legends use ISA 5.1 for instruments and PIP-style symbols for equipment. European and many international legends use ISO 10628-2 for equipment and IEC 62424 for instruments. Most symbols match, but the differences are in the ones you read most: valves, pumps and instruments.

US practice
ISA 5.1 instruments, PIP PIC001 equipment, valves and piping
ISO practice
ISO 10628-2 equipment, valves and piping, IEC 62424 instruments
Germany
DIN EN ISO 10628-2 and DIN EN 62424, the same as ISO practice

Valves

All valves
SymbolISA / US legendISO 10628-2Difference
Gate valveX8074ISO adds a short bar across the centre. A plain two-triangle body is the general valve, 2101.
Globe valveX8068SameDrawn the same way: a solid dot where the triangles meet.
Ball valveX8071The triangles stop at a circle in the middle instead of meeting at a point.
Check valveX8077A plain valve body with a small solid dot on the upper corner of the inlet side. Globe-type and swing check valves have their own numbers (X2113, X8078).
Butterfly valveX8075Form 1 is the valve body with a bar and a solid dot in the middle. Form 2 is a rectangle with a diagonal and a dot.
Needle valveX8076A small solid wedge points down onto the centre of the body.
Angle valve2102SameDrawn the same way: one triangle in the line, one turned 90 degrees.
Three-way valve2103SameDrawn the same way: a third triangle on the branch.

Control and actuated valves

All control and actuated valves
SymbolISA / US legendISO 10628-2Difference
Control valveX8087ISO shows modulation with a diagonal arrow through the body. It draws no actuator: how the valve is moved and controlled is shown with the instrumentation, usually to IEC 62424.

Safety devices

All safety devices
SymbolISA / US legendISO 10628-2Difference
Pressure safety valveX2125An angle globe valve (dot in the centre) with a spring on top and a heavy bar across the outlet side. The straight-through version is X2124.
Rupture discX8080A narrow holder in the line with the disc bulging towards the outlet.
Flame arrestor2036A box in the line with a grid inside. Explosion-proof, detonation-proof and fire-resistant versions add a side shape (C0087, C0088, C0091).

Pumps and compressors

All pumps and compressors
SymbolISA / US legendISO 10628-2Difference
Centrifugal pump2322The ISO pump is a circle with two lines meeting at the outlet. The centrifugal type adds a line through the middle. The general liquid pump, 2301, has no middle line.
Positive displacement pumpX8094ISO has no single positive displacement symbol. Each type has its own mark inside the pump circle: piston X8094, diaphragm X8095, gear 8091, screw 8092, progressive cavity 8093.
Gear pump8091Two small gear wheels inside the pump circle.
Screw pump8092A double zig-zag inside the pump circle.
Centrifugal compressorX8179The ISO compressor is a circle with two lines narrowing towards the outlet, without meeting. The centrifugal type adds a line through the middle. The general compressor is 2302.
Reciprocating compressorX8097The compressor circle with the piston mark inside.
Fan or blowerX8164The compressor outline with a three-blade rotor inside.
Turbine2571SameDrawn the same way: a shape widening towards the outlet.
Agitator2672A shaft with a simple blade. Paddle, anchor, propeller, turbine and other agitator types have their own numbers (C2019 to C2027). The drive is drawn separately, for example the electric motor C0082.

Vessels and tanks

All vessels and tanks
SymbolISA / US legendISO 10628-2Difference
Vertical vessel2062SameDrawn the same way. Supports have their own symbols: legs X8002, brackets X8003, skirt X8004.
Horizontal vessel2062SameDrawn the same way, turned horizontal.
ColumnX8101ISO draws trays as dashed lines across the column. Bubble cap, valve tray, packed and fixed bed columns have their own numbers.
Cone roof tankX2063SameDrawn the same way.
SphereX8010SameDrawn the same way. Without legs it is 2063.
Open tank2061SameDrawn the same way: open at the top.
Silo or hopper2064SameDrawn the same way.

Heat exchangers

All heat exchangers
SymbolISA / US legendISO 10628-2Difference
Shell and tube heat exchanger2511ISO draws the shell with the tube sheets and tubes inside. Floating head (2512) and U-tube (2513) types differ inside. The general heat exchanger, X8079, is a circle with a zig-zag line through it.
Plate heat exchanger2516A frame divided into plates, each with crossed lines.
Air coolerX2505A box with a fan above a finned tube. The finned tube on its own is X8018.
Fired heater2533An open-topped double outline. Burners (X8107) and combustion chambers (X8106) have their own symbols.
Cooling tower2521A tapered tower on a basin. Wet, dry, natural, forced and induced draught types are X8109 to X8115.
Kettle reboilerX8131A shell with a raised vapour space and a tube bundle, with the liquid level marked.

Filters and strainers

All filters and strainers
SymbolISA / US legendISO 10628-2Difference
FilterX8116A box with a dashed line for the filter element. Gas filters (X8122) and cartridge, bag and bed filters have their own numbers.
Y-strainerX8090ISO has one strainer symbol for all body shapes: a narrow box with a dashed diagonal. The cone type is X8150.
Basket strainerX8090ISO has no separate basket strainer. The general strainer is used, with the type written next to it.
CycloneX2618A separator outline with a spiral inside.

Instruments

All instruments
SymbolISA / US legendIEC 62424Difference
Field-mounted instrumentAn oval with no line: the function is operated or displayed locally, in the field.
Panel-mounted instrumentA line through the oval: operated and displayed in the central control room.
DCS shared displayIEC 62424 has no separate shared-display shape. A function on the control system is an oval with the control room line.
Pressure gaugeLetters P (pressure) and I (indication), with no line because it is read locally.
Pressure transmitterIEC 62424 describes the function, not the device, so there is no T for transmitter. A pressure shown in the control room is PI with the control room line.
Level transmitterL (level) and I (indication) with the control room line. A safety-relevant low-low trip would add Z with L, for example LIZ LL.
Flow transmitterF (flow) and I (indication) with the control room line. Q added after F means totalised flow.
Temperature transmitterT (temperature) and I (indication) with the control room line. TIC would add control.
Level gaugeL and I with no line: read at the vessel.
Orifice plateC0096A circle with a centre dot on a short stem across the line. Measurement itself is shown with the instrumentation.

Line types

All line types
SymbolISA / US legendISO 10628-2Difference
Process line405SameA solid line, as in every standard.
Heat traced lineC0106A second line along the pipe with a dash and dots in it. Insulated lines (X322) are hatched.
Jacketed lineX409An outline drawn around the pipe for the length of the jacket.

Piping and fittings

All piping and fittings
SymbolISA / US legendISO 10628-2Difference
Concentric reducer516ISO draws one reducer symbol, a narrowing triangle, and does not separate concentric from eccentric.
Flange511SameDrawn the same way: two short bars across the line.
Blind flange517The line ends at a flange pair. A single flange is X8152.
Spectacle blind2044Two discs on a stem across the line. The disc next to the line is the one in use: solid for blind (2044), open for flow (2045).
Expansion joint533A lens shape in the line.
Flexible hoseX411SameDrawn the same way: a wavy line.
Steam trap2181A circle in the line, half filled across the diagonal.
Sight glass2034A box in the line with a circle inside. With lighting it is X8089.
Drain2040The drain point is shown with the funnel symbol below the line.
Vent2039A line up from the pipe under a small cover.

Which one is on your drawing?

Look at the legend sheets at the front of the P&ID set: they name the standards the project follows. If there are none, three symbols give it away. A gate valve with a bar in the middle, pumps drawn as a circle with a chevron and instruments in ovals mean ISO and IEC. A plain gate valve, pumps with a tangential outlet and round instrument bubbles mean ISA and US practice.

Many international projects mix the two, with ISO equipment symbols and ISA instruments. The legend sheet decides.

Frequently asked questions

What is the difference between ISA and ISO P&ID symbols?

ISA 5.1 covers instruments and control, and is usually paired with PIP-style equipment symbols on US projects. ISO 10628-2 covers equipment, valves and piping, and is paired with IEC 62424 for instruments. The main visible differences are the gate, check and control valves, pumps, compressors and the instrument bubbles.

Can a P&ID use both ISA and ISO?

Yes, and many do: ISO symbols for equipment and valves with ISA 5.1 instrument bubbles is a common mix on international projects. The legend sheets define which is used.

Which is more common, ISA or ISO?

ISA 5.1 is the most widely used instrumentation standard, especially in the Americas and on oil and gas projects. ISO 10628-2 and IEC 62424 are the norm in Germany and much of Europe.

The symbols on this page were drawn by Deskely to the forms of the standard and are free to use. Standards are revised and every project issues its own legend sheets, which take precedence.

Whichever standard your P&IDs follow.Deskely Extract reads ISA and ISO P&IDs alike, finds each tag with its type, system and subsystem, and hands your engineers a register to check instead of a spreadsheet to type.
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Other standardsStandardISA 5.1 symbolsStandardISO 10628 P&ID symbolsStandardPIP P&ID symbols (PIC001)StandardDIN P&ID symbols (R&I-Fließschema)StandardIEC 62424 P&ID symbolsLegendAll P&ID symbols

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