Piping General Arrangement (GA) Drawings

Typically, Piping General Arrangements (GA) are drafted on A-size sheets. When the area to be covered is smaller, the same A-size sheet is used. The piping team often creates a 'Key Plan,' which is a scaled-down plot plan (e.g., 1:500, 1:750, or 1:1000) that can fit onto an A-size sheet. This plan divides the site into smaller sections, which are identified by key letters or numbers. These sections are referenced in the piping drawing, and the specific area under focus is shaded or hatched for clarity.

The title block’s dimensions and details are outlined according to the Indian Standard IS11665. The sheet is divided into equal sections along both the length and the width. The longitudinal sections are labeled alphabetically, while the width sections are labeled numerically. These coordinates are used to pinpoint specific areas on the drawing. The north direction is usually indicated at the top of the sheet, either to the right or left, and remains consistent across all drawings for a project. Similarly, the drawing scale is kept constant.

Steps for Creating a Piping GA

1. Title Block: Start by obtaining the drawing numbers and filling in the title block, which includes the drawing number and title in the bottom right corner.
2. North Arrow: Position the north arrow at the top left or right corner to indicate the plant’s north.
3. Reserved Areas: Avoid planning any drawings in the area above the title block, as this space is reserved for general notes, references to other drawings, revision information, and the bill of materials if applicable.
4. Priority: In the Piping GA, process equipment and piping are prioritized. The piping drawing begins once equipment locations are finalized.
5. Equipment Layout: The layout of equipment is replicated to scale on the Piping GA. For manual drafting, this is done on the reverse side, while for CAD drawings, a separate layer is used. Indoor areas also depict major beams and secondary beams.
6. Background Details: Important background elements that affect piping routes—like floor drains, HVAC systems, electrical cables, and instrument trays—are lightly sketched or displayed on a separate layer.
7. Utility Stations: Utility stations are also marked to assist in convenient utility header routing.

Developing a Piping General Arrangement Drawing

1. Process Requirements: The piping drawing should be structured to meet all necessary process requirements.
2. Variations from P&ID: Piping drawings may not always strictly follow the logical sequence of Piping & Instrumentation Diagrams (P&IDs). In some cases, piping may need to be routed differently, requiring adjustments in line numbers.
3. Performance and Economics: The routing of piping should consider both performance and economic factors.
4. Single vs. Double Line Representation:
   • Piping smaller than 150 NB is represented by a single line.
   • Larger piping (200 NB and above) is depicted with double lines.
   • Single-line depictions show the pipeline’s centerline as a solid line.
   • Double-line drawings show the actual size to scale, with the centerline marked by a dashed line.
5. Line Numbers: Line numbers should be clearly shown on the GA, matching their representation in the P&IDs.
6. Specification Changes: Any change in piping specifications, as per the P&ID, should be shown downstream of a valve, flange, or equipment.
7. Valves:
• Valves should be drawn to scale and labeled with their identification numbers as per the P&ID.
• Hand wheels and valve handles should be displayed to scale, including stem positions and operating mechanisms (e.g., levers or chains).

Additional Guidelines

1. Instruments: Instrument connections should be clearly marked, referencing their P&ID numbers.
2. Multi-Floor Plants: For multi-floor plants, each floor’s layout should be shown in the GA, illustrating how the piping and equipment layout transitions between floors.

Additional Notes:

• Each piping line should be identified by its line number and should indicate insulation and tracing requirements.
• Hidden lines or details should be shown using broken lines or in additional views, as needed.
• For complex sections, larger-scale views or isometric sketches can be used for clarification.
• Detailed sections or plans should be labeled accordingly, such as "Detail A" or “Section 1-1,” to clearly identify specific parts of the drawing.