Piping GA Drawing: A Comprehensive Guide Series - Part 4: Drawing Content & Dimensioning Guidelines

II JAY SHRI KRISHNA II

Hello friends, hope you found our previous Piping GA Drawing series parts helpful! In Part 4, "Piping GA Drawing: A Comprehensive Guide Series - Part 4: Drawing Content & Dimensioning Guidelines," we'll dive into the essential details and dimensioning rules for creating professional piping plans. Accurate drawings are crucial for successful piping projects, and this guide will help you master plant orientation, equipment layout, piping specifications, valve and fitting details, and, of course, precise dimensioning.

Piping Plan Drawing Content & Dimensioning Guidelines

Piping GA Drawings: Content & Dimensions

A well-executed Piping Plan Drawing serves as the roadmap for the entire piping project. It's the primary communication tool between engineers, designers, fabricators, and installers. Therefore, clarity, accuracy, and completeness are paramount. This guide will delve into the key elements and dimensioning guidelines necessary for producing professional-grade piping plans that minimize errors, reduce rework, and ultimately contribute to a successful project outcome.

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Key Elements of Piping Plan Drawings

1. Plant North Direction & Key Plan:

Clearly indicate the Plant 'NORTH' direction on the drawing. If the key plan’s north direction differs, both must be specified.

2. Equipment Layout & Representation:

Display all equipment as per the plot plan, ensuring accurate representation.

Indicate all piping nozzles, instrument nozzles, manholes, and other nozzles. Mark the locations of platforms, stairways, and ladders.

3. Piping General Arrangement (GA) Drawing:

Lines up to NS 6” should be shown as single lines; NS 8” and larger must be drawn in double lines and to scale.

Clearly indicate all on-line fittings, valves, and instrument connections.

Ensure all flanged joints are marked accurately.

Mark piping class changes after flange joints, where applicable.

Assign tag numbers to piping items, instrument items, and process equipment in accordance with P&ID diagrams.

Clearly specify special fittings not covered in piping specifications (e.g., 60° elbows).

Each line should be designated using its complete identification as per the line list.

Clearly indicate the flow direction for each line.

Use appropriate symbols to differentiate valve types (e.g., gate, globe, non-return, butterfly).

Indicate valve handwheel/stem orientation and specify the requirement for extended spindles, headstocks, or chain-operated valves where necessary.

Mark the locations of drain funnels, utility stations, and safety showers.

Indicate centerline elevation or Top of Steel (TOS) elevation for each line.

Ensure all lines are fully dimensioned for accuracy.

Indicate pipe support points with a cross-mark. Primary support coding is not required, but secondary or special supports must be properly coded and marked.

Clearly depict battery limits and match lines on the drawing.

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Dimensioning Guidelines for Piping Plan Drawings

1. General Dimensioning Rules:

Avoid duplicate dimensions and unnecessary repetition of notes.

Keep dimensions within the drawing limits (i.e., match lines, battery limits).

Dimension lines should be continuous, not staggered or offset.

Group dimensions outside detailed areas to avoid clutter.

Prevent dimension or extension lines from crossing drawing elements.

Avoid placing dimensions between coordinate references.

2. Placement of Dimensions:

Place horizontal dimensions on plan drawings.

Show vertical dimensions in sections or elevations.

Dimension piping from centerline to centerline, centerline to face of flange, or face of flange to face of flange.

Avoid dimensioning to welds.

Include gasket thickness in dimensions where required, and specify gasket locations relative to flange extension lines.

Provide spacing dimensions for lines in a pipe rack.

Do not place a continuous string of dimensions across a pipe rack if column coordinates are provided.

Clearly indicate TOS or Bottom of Pipe (BOP) elevation for lines in the pipe rack.

Minimize dimensioning to essential elements only, ensuring accurate piping isometric and spool fabrication.

Show all angular offsets, specifying the degree of offset and directional plane (horizontal/vertical).

Mark finished grade or floor level.

Indicate the top of grating or platform plates.

Provide BOP elevation for pipelines installed on shoes.

Include centerline elevations of relief valves.

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Dimensioning Do's and Don'ts (Common Errors to Avoid):

Do not dimension from underground pipelines to aboveground lines.

Do not dimension between lines running at different elevations in a pipe rack.

Do not dimension to the center of a valve, except for small bore screwed/socket-weld valves.

Do not dimension piping relative to electrical trays, conduits, or instrument trays.

Do not dimension internal equipment piping in relation to external piping.

Do not dimension piping relative to building outlines or structural elements.

Do not specify the length of standard piping components such as elbows, tees, and reducers.

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Callouts for Section & Elevation Drawings

1. Pipe Support Elevations:

Indicate the Top of Steel (TOS) elevations for all pipe supports.

2. Equipment & Piping Elevations:

Specify the centerline elevations of exchangers and horizontal vessels.

Mark Top of Concrete (TOC) or grout elevations for all equipment foundations.

Provide centerline elevations for horizontal nozzles on equipment, including piping and instrumentation nozzle connections.

Indicate the face of flange elevations for nozzles attached to vertical vessels, exchangers, pumps, turbines, and compressors.

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Final Thoughts and Conclusion:

By following these best practices, piping plan drawings become precise, informative, and easy to interpret, facilitating effective communication among all project stakeholders. These guidelines, focused on clarity, accuracy, and efficiency, contribute to successful piping design and installation. While comprehensive, these guidelines may need to be supplemented by relevant industry standards and engineering documentation for project-specific requirements.

Consult these resources for further customization or additional details to ensure the piping plan meets all applicable specifications. Mastering piping plan drawings is crucial, and these guidelines provide a strong foundation for creating technically sound and usable drawings.