PVF Reference Library · Wall Charts

Isometric Drawing Symbols Chart

Common symbols for joints, fittings and valves on piping isometric drawings, and how to read an isometric to build a material list.

Ref PV-0056ISO 6412

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

A piping isometric (iso) is a single-line drawing that shows a pipe run in three dimensions on a flat sheet. Each line is the pipe centerline. Symbols on the line show joints, fittings and valves. ISO 6412 sets out simplified representation of pipelines, including isometric projection. Many companies use their own symbol sets based on it. The legend on the drawing always governs.

How to read it

Find the north arrow and the axes. Lines drawn at 30° show horizontal runs; vertical lines show rises and drops.
Read the line number, size, spec and service in the title block or on the line.
Follow the line from one end to the other, noting each symbol.
Read the dimensions between fittings and centerlines.
Read the bill of materials on the sheet and check it against the symbols.

Common symbols

Item	Typical symbol	Notes
Pipe	Single solid line	Line is the centerline
Butt weld	Dot on the line	Shop or field weld noted separately
Field weld	Dot with a flag or "FW" note	Check the drawing legend
Flanged joint	Two short parallel lines across the pipe	Flange pair with gasket
Threaded or socket joint	Short single line across the pipe	Legend shows which
Elbow	Change of direction at a corner	Long or short radius in the BOM
Tee	Branch line meeting the run	Reducing tee noted by size
Reducer	Small trapezoid or cone on the line	Concentric or eccentric noted
Cap	Short heavy end mark	End of line
Gate valve	Two triangles point to point (bow tie)	Valve type often in the BOM
Globe valve	Bow tie with a dot or filled center	Check the legend
Check valve	Bow tie with one side filled, or an arrow	Shows flow direction
Ball valve	Bow tie with a circle in the center	Check the legend
Valve stem	Short line off the valve symbol	Shows stem orientation
Slope	Arrow with slope note	Direction of fall

Key points

Isometrics are not drawn to scale. Use the dimensions, not a ruler.
One iso usually shows one line number. Continuations to other sheets are noted at the break.
Pipe supports, insulation, tracing and test points often have their own symbols. Check the legend.
The bill of materials lists size, schedule, rating and material. Symbols only show type and location.

Common mistakes

Scaling dimensions from the drawing.
Missing a field weld note and short-shipping weld fittings.
Assuming every company uses the same valve symbols.
Reading a vertical line as horizontal.

Governing standards: ISO 6412 (simplified representation of pipelines); the project drawing legend and piping specification.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

More in Wall Charts

← All PVF sheets