[ PIPING ISOMETRIC SYMBOLS · REFERENCE ]
How to read a piping isometric
A piping isometric shows one line, or part of one, in three dimensions on a flat sheet, with every dimension, weld and component needed to fabricate and install it. It is the drawing the fabricator, the welder, the inspector and the test team all work from.
- What it shows
- One pipeline from end to end, in isometric projection, not to scale
- Made from
- Usually generated from the 3D model, sheet by sheet, per line number
- Rules
- ISO 6412-2 for isometric projection of pipelines; the project legend for symbols
- Used for
- Spool fabrication, installation, weld tracking, NDT, test packs and line walks
Read it in this order
- 1. The title block: line number, size, service, piping class, design and test pressure, insulation and paint, revision. These apply to everything on the sheet.
- 2. The north arrow: it fixes the three isometric directions to the plant. See north arrow.
- 3. The route: follow the line from where it starts to where it ends, leg by leg, noting each change of direction and elevation.
- 4. The components: valves, fittings and flanges along the route, each with an item number in the bill of materials.
- 5. The joints: every weld and flange, with shop and field welds told apart.
- 6. The dimensions: written dimensions for every leg, and elevations at key points. The drawing is not to scale.
- 7. The extras: slopes, offsets, supports and the continuation to the next sheet.
The three directions
An isometric draws the three directions of the plant at 120 degrees to each other: north-south and east-west as lines at 30 degrees to the horizontal, and up-down as vertical lines. A leg that runs off these three directions is shown with a hatched triangle, so you can see which plane it lies in.
Welds and spools
The shop welds split the line into spools: pieces small enough to fabricate in the shop and ship to site. The field welds join the spools on site. Each weld gets a number, which the weld map, the NDT records and the welder records are all kept against.
That is why the isometric is the base of weld tracking on a project: which welds are done, which have passed NDT, and which are still open.
Isometrics in completions
Before a line is handed over it is pressure tested, usually in a test pack: the isometrics of the lines in the test, marked up with the test limits, blinds, vents and drains, together with the weld and NDT records. The line walk before the test is done with the isometric in hand, and anything found becomes a punch item.
See the hydrostatic test guide, the punch list template and the ITR guide for the records behind the test. Deskely Testpack builds the test packs from the line list and the drawings.
Frequently asked questions
What is a piping isometric drawing?
A drawing of one pipeline in isometric projection, showing its route in three dimensions with all dimensions, components, welds and the bill of materials needed to fabricate and install it.
Are piping isometrics drawn to scale?
No. They are not to scale. The written dimensions are what counts.
What is the difference between a shop weld and a field weld?
A shop weld is made in the fabrication shop as part of a spool. A field weld is made on site to join spools or connect to equipment.
What is a spool?
A section of the line fabricated in the shop between field welds or flanges, small enough to transport and install.
Which way is north on an isometric?
The north arrow on the sheet shows it, along one of the isometric axes.
- In production since 2014
- Thousands of daily users
- On MODEC FPSO projects since 2016
The symbols on this page were drawn by Deskely and are free to use. Standards are revised and every project issues its own legend sheets, which take precedence.