Piping and fitting symbols
Fittings and in-line items change the line itself: reducers change its size, flanges and blinds isolate it, expansion joints let it move, steam traps and sight glasses sit in it.
- Concentric reducerA concentric reducer joins two pipes of different sizes on the same centreline.
- Eccentric reducerAn eccentric reducer joins two pipe sizes with one side flat, so a pipe can stay level at the top or bottom.
- FlangeA flanged joint bolts two pipe ends together, so the line can be opened for maintenance, blinding or removing equipment.
- Blind flangeA blind flange closes off the end of a pipe or nozzle.
- Spectacle blindA spectacle blind is a plate with a solid disc and an open ring joined together.
- Pipe capA pipe cap is a welded or screwed fitting that closes the end of a pipe permanently.
- Expansion jointAn expansion joint absorbs movement in a pipe from thermal expansion, vibration or settlement, with a flexible bellows.
- Flexible hoseA flexible hose connects equipment that moves or is disconnected often, such as loading arms, temporary connections and utility stations.
- Steam trapA steam trap drains condensate from steam lines and equipment while holding the steam in.
- Sight glassA sight glass is a window in the line that lets operators see the flow, its colour or whether liquid is present.
- DrainA drain connection empties a line or vessel, often into an open funnel (tundish) leading to the drain system.
- VentA vent connection releases air or gas from the high point of a line or vessel, for filling, draining and testing.
- Off-page connectorAn off-page connector shows where a line continues on another P&ID sheet, with the drawing number and the destination.
Piping and fittings in ISO 10628-2
About ISO 10628-2- Concentric reducerReducer516
- FlangeFlanged connection511
- Blind flangeFlanged dummy cover517
- Spectacle blindInterchangeable disc (blind disc)2044
- Expansion jointCompensator533
- Flexible hoseHoseX411
- Steam trapSelf-operating release valve (steam trap)2181
- Sight glassViewing glass2034
- DrainFunnel2040
- VentVent (outlet to atmosphere for steam/gas)2039
These symbols are small but matter for isolation, maintenance and the test packs built from the P&ID: every blind, spectacle and flange break is a point the commissioning team needs to know.
The cards at the top use the forms of US legend sheets (PIP PIC001 practice). The grids below them show the same symbols as ISO 10628-2 or IEC 62424 draw them. See ISA vs ISO P&ID symbols for the differences.
Frequently asked questions
What are piping and fitting symbols on a P&ID?
Fittings and in-line items change the line itself: reducers change its size, flanges and blinds isolate it, expansion joints let it move, steam traps and sight glasses sit in it.
How many piping and fitting symbols are there?
This legend covers the 13 most common ones: concentric reducer, eccentric reducer, flange, blind flange, spectacle blind, pipe cap, expansion joint, flexible hose, steam trap, sight glass, drain, vent, off-page connector. Project legends may add company-specific variants.
Can I download these symbols?
Yes. Each symbol page has a free SVG and PNG, and the whole legend is available as a printable PDF chart on the P&ID symbols page.