Preparation of Piping Isometrics: A short presentation for the beginners
- Piping isometrics are three dimensional representation of the line.
- The main purpose of an isometric is to provide all information necessary for the fabrication and erection along with the bill of material required to do so.
- Isometric is also used to work out the exact MTO requirement.
- Generally isometrics are prepared / extracted by design group.
- A draft person (designer/engineer) who knows to read the piping GA. and conversant with a drafting tool can draft isometric.
Input required for piping Isometrics:
- Piping Plan
- Piping Specification
- Line List (Process)
- Latest PEFS (Process) (Issued signed copy)
- An isometric drawing covers a complete line as per the line list and PEFS. It shows all information necessary for the fabrication and erection.
- Isometrics are not drawn to scale but should be proportional for easy understanding.
- Dimension is given relative to centreline of piping.
Following information must be included in isometric drawings:
- Plant North: The direction should be selected so as to facilitate easy checking of Isometric with GA.
- Drawing number & revision.
- Reference number of PEFS (P&ID), GA drawings, line numbers, direction of flow and insulation tracing.
- Design pressure, design temperature, test pressure, testing medium, radiography requirement, Heat treatment requirement, painting requirement, internal coating requirement.
- Co-ordinates of equipment against equipment layout.
- Equipment number & appearance on isometric drawing.
- Line specification changes.
- Scope breaks.
- Change in direction and angles of line should be clearly shown.
- Representation is correctly made in line with the standard symbols.
- Location and identification of all instruments.
- Requirements of upstream/downstream straight lengths. Insulation requirements as per PEFS (P&ID).
- Details and section identification match.
- “Match line” provision and accuracy.
- Accuracy of BOM in Isometrics.
- Weld points & field welds.
- Insulation class., Insulation thickness & Flow direction are indicated.
- Give the details of flange on the equipment if the specification is different from the connecting piping.
- Size and type of every valve/direction of operation.
- Size and tag of control valve.
- Field weld- Location.
- High point vents and low point drains.
- Special support like support from flange or welded supports details to be shown.
- If line is stress critical, stress analysis results are incorporated.
- All the symbols are used as per Legend.
- Slope shown as per PEFS.
- Spectacle blind, spacer and blind open/close position as per PEFS.
- High point vents and low point drains have been provided for lines that will be hydro tested. (e.g. Inst. Air, Flare, Nitrogen lines may not be hydro tested, but pneumatically tested).
- Orifice tapping orientation is as per instrument standard for gas and liquid lines.
- Flow direction for items such as check valves, globe valves, strainers etc. is clearly marked.
- Isometric issued for Re-IFC to be marked with cloud and revision triangle.
- Insulation gasket demarcation to be shown.
- General notes.
- Bill of Material.
- Tie-in numbers.
Checking of Isometric Drawings
Checking shall be done only on a hard print as per the colour code procedure by an experienced engineer/designer. Normally checklists are followed to ensure quality of the isometrics.
The new print after correction is “back checked” for incorporation.