Why Isometric Drawings are required?: Generally in the development of a project, a conceptual 2D drawing is first created. In this all pipelines are drawn at zero z co-ordinate. This is then converted into a 3D scale model, to check interference of pipe lines. 2D General Arrangement (GA) drawings are used for fabrication on site. A GA drawing is generally on A0 or A1 size paper and contains a lot of lines, and may not be easy to understand pipe routine. A0 or A1 size drawing is to big to handle. A pipe fabricator can understand GA drawing better only with the help of 3D scale model. But 3D scale model can not be put on a paper, and 3D scale model does not indicate dimensions. To aid pipe fabricator on site, isometric drawings are prepared. An isometric drawing is generally on a A3 size paper. A pipe fabricator can read the drawing and understand pipe routine easily. Also pipe fabricator can pick up material required for fabrication of pipe line from stores, with the help of Bill of Material given in isometric drawing.
Unlike orthographic drawings, piping isometric drawings allow the pipe line 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 sectional elevation views. The symbols that represent fittings, Valves and flanges are modified to adapt to the isometric grid.
Isometrics are drawn on b-size paper (11 x 17) in imperial units and on A3 size paper (297 mm x 210 mm) in metric units. Drawing number and revision number is indicated in box on top left corner. Drawing number and revision number is also shown in title box. The table at bottom indicates the numbers of relevant P&ID drawing and General Arrangement (GA) drawing. The bill of material appears in top right corner. A table is also provided for indicating revisions made. The rectangular area on left is reserved for Isometric drawing.
The line number is shown in space in right column. General notes appear below line number.
Every company has its own template, showing company's name, address, logo etc.,
Arrow showing north direction is shown in top left corner. A north arrow shows North direction with respect to North direction in GA drawing. The direction orientation depends on North Direction of Plan drawing. This helps in reading the Plan and Isometric drawings together.
Preparing a sketch to draft isometric drawing: View the model in the direction of north of model and start sketching pipe lines.
The line may start from nozzle of an equipment, such as a vessel or a pump. Indicate nozzle number and equipment tag near nozzle. In some cases, pipe line may originate from some other line. Indicate line number of that pipe line, its center line elevation, and isometric drawing number of that pipe line.
Branches of the pipe run or continuations are placed on other drawings, typically shown as short portion of dashed line on main pipe run. Dashed lines show pipe continuation. Reference drawing information is given for continuation.
One run of pipe is drawn in one isometric drawing. If one pipe run can not be accommodated in one drawing, pipe run is continued in next drawing. Two identical pipe lines (Two similar suction lines of two pumps) are generally drawn in one isometric drawing.
Isometrics are rarely drawn to scale. A longer pipe, (on left), may be shown shorter, if pipe line does not have any fittings in it. However, a small length pipe may be shown with longer length, to show all the fittings in that portion of line. However, pipe lengths should be shown accurately. In this case, Isometric is limited by space, so sometimes proportion may be sacrificed but it is important that the written dimensions are accurate. If the pipe is vertical, the lettering should be written vertically and at 30° obliquing angle. Text in dimension in vertical lines, should always be parallel with dimension line.
Direction & Location: Location and direction helps to orient the isometric drawing properly. Structural reference points that provide location of column along the grid can be shown on isometric. Dimensions must always be given to points of reference, such as structures, center line of existing equipment etc. Co-ordinates should also be shown on the isometric drawing.
When orienting fittings or valves, it is important to draw the fittings or valves, so that they are inclined to the last direction change or branch in the pipe. Fittings or valves are drawn the same shape as they appear on the plan & elevation drawings but they are drawn at an isometric angle.
Looking at the orientation of model, go on sketching the line from one end to other. To get the length of each cut pipe, get distance between two ends of 3D pipe. To get the length of pipe from center line of fitting to center line of anathor fitting get distance between insertion points of two fittings.
Mark elbows on the drawing. Show location of valves, with type of flange. The location of the valve is shown by dimension of the center of valve. Show direction of flow, with pipe NB. If a horizontal pipe line has a slope, indicate slope on that pipe line.
Use branching table to select end connection of Elbows. Normally, Elbows with NB less than 50 are socket weld or secrewed and Elbows with NB greater than 40 have butt weld ends. Elbows can be drawn in a couple of ways.
Add any branch to the drawing, like, Tee, Reducing Tee, Weldolet, Socolet, elbolet etc.
If the line is reduced in its path, add a reducer. Reducer can be concentric, eccentric with flat top or eccentric with flat bottom. Concentric reducer is generally used in a vertical line or line where flow pattern should not get disturbed, as in case of line of Control Valve. Eccentric reducer with flat top is generally used in suction line of a pump. Eccentric reducer with flat bottom is generally used in horizontal lines. Eccentric reducer maintains the bottom level of pipe line after reduction in size. Swage is used to connect a pipe with butt weld end to a pipe with a socket weld end.
If there is any Coupling, Union, Hose or trap in a pipe line, draw it on line.
Spec change is generally implemented at isolating valve or at flange of different pressure rating. The spec of valve depends on Fluid in this and next pipe line or pressure ratings of this and next pipe line. Demarcation is shown between new and existing pipe spec and reference line number, drawing number and center line elevation is indicated for new drawing. Usually a note indicates the name or specification of the branch line.
Offsets: To indicate an offset, hatches on isometric drawings are applied, to indicate that a pipe runs at a certain angle and in which direction the pipe runs. Offset is shown with a fitting (typically a 45° elbow).
Horizontal Offset: If a line turns at 30° to 45° in horizontal plane, you draw a pipe with a 45° elbow. But pipe line would look like a vertical line. To avoid confusion, the offset is drawn 22½° horizontal offset to give the illusion of the angle.
Vertical Offset: If a line turns at 30° to 45° in vertical plane, you draw a pipe with a 45° elbow. In this case, too, to avoid confusion, the offset is drawn 22½° vertical offset to give the illusion of the angle.
Dimensioning: Dimensions should preferably appear above if the pipe line is horizontal and on left hand side, if the pipe line is vertical. Best way to dimension a pipe line is between its center line at the intersection points. Try to keep all dimensions outside the piping view when possible. Dimensions should always be shown between points in the same plane. One of the extension lines of the dimension should be a center line of the run of pipe.
To create an isometric drawing, first create a true three-dimensional piping model. Although you can use explicit modeling as a conventional drafting system, it is recommended that you use it as an intelligent 3D modeling aid.
Most CAD packages are prepared in such a manner that these can be easily customized. 4 Programs of OpenPipe are such customized programs. The Iso program is totally based on LISP programs and there are only 4 small symbols or blocks to be inserted as in other programs, due to which there is a lot of saving of Disk space as well as the drawing also has very small size. Since the program is written in LISP, you can even modify PROGRAM for PIPING ISOMETRIC DRAWINGS further as per your choice. The different piping entities are arranged on layers 1 to 6 (which is compatible with Microstation). Special Dialogue Boxes are created to make the program more user friendly. The drawing can be converted to Microstation DGN format.
To try the program, send a request for trial package. The package is a zip file, iso_demo.zip. There is no setup.exe file as in other packages. Download and unzip iso_demo.zip and copy files in a folder. While running AutoCAD program, click on tools ->Options (or Preferences) -> Files -> + of Support File Search Path -> Add -> Browse -> Select the folder. The iso_demo.zip file contains iso*.lsp, iso.dcl and iso.slb, iso.dwg (Border drawing).
ASME, Triclover and Victaulic package Bought so far by 11 parties
Professional Charges for CAD Ad-on Software for
Piping Isometrics for ASME Fittings US$ 50
Piping Isometrics for ASME + Tri-Clover + Victaulic Fittings US$ 70
Sourse programs for all the above are also available for sale. Price will be double the indicated price.
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