Coordination System..
Unlike orthographics, piping isometrics allow the pipe to be drawn in a manner by which the length, width and depth are shown in a single view. Isometrics are usually drawn from information found on a plan and elevation views. The symbols that represent fittings, Valves and flanges are modified to adapt to the isometric grid. Usually, piping isometrics are drawn on preprinted paper, with lines of equilateral triangles form of 60°.
The Iso, as isometric are commonly referred, is oriented on the grid relative to the north arrow found on plan drawings. Because iso's are not drawn to scale, dimensions are required to specify exact lengths of piping runs.
Pipe lengths are determined through calculations using coordinates and elevations. Vertical lengths of pipe are calculated using elevations, while horizontal lengths are caculated using north-south and east-west coordinates.
Piping isometrics are generally produced from orthographic drawings and are important pieces of information to engineers. In very complex or large piping systems, piping isometrics are essential to the design and manufacturing phases of a project.
Piping isometrics are often used by designers prior to a stress analysis and are also used by draftsmen to produce shop fabrication spool drawings. Isometrics are the most important drawings for installation contractors during the field portion of the project.
How to read a Piping Isometric?
A pipe into a isometric view, is always drawn by a single line. This single line is the centerline of the pipe, and from that line, the dimensions measured. So, not from the outside of a pipe or fitting.
The image below shows a orthographic view of a butt welded pipe with three sizes (A, B, C).
- The A size is measured from the front to the center line of the elbow / pipe.
- The B size is measured from centerline to centerline.
- The C size is like the A size, measured from the front to the center line of the elbow / pipe.
Isometric view
The isometric view shows the same pipe as in the orthographic view
As you can see, this drawing is very simple and quick to implement. The red lines show the pipe, the black dots are the butt welds and A, B and C are the dimensions of front to center line and center line to center line.
The simplicity with which a pipe isometric can be drawn is one reason to made iso's.
A second reason to made isometrics; if a pipe should be drawn in several planes (north to south, then down and then to the west, etc.), orthographic views really not an option. In a orthographic view it is not a problem if the pipe runs in one plane, but when a pipe in two or three planes to be drawn, a orthographic view can be unclear.
Another reason why isos are preferred, is the number of drawings that for orthographic views should be made.
For example.. for a complex pipeline system, 15 isometrics must be drawn. I've never tried, but I think for orthographic views maybe 50 drawings are needed to show the same as the Iso's.
Isometric, Plan and Elevation Presentations of a Piping System
The image below show the presentation used in drafting. The isometric view clearly show the piping arrangement, but the plan view fails to show the bypass loop and valve, and the supplementary elevation view is needed.
Below are some examples of isometric drawings. The auxiliary lines in the shape of a cube, ensure better visualization of the pipeline routing.
Hatches on isometric drawings being applied, to indicate that a pipe runs at a certain angle and in which direction the pipe runs.
Sometimes, small changes in the hatch, the routing of a pipe is no longer the east, but for example suddenly to the north.
The two drawings above show, that changing from only the hatch, a pipeline receives a different direction. Hatches are particularly important in isometric views.
