A general arrangement (GA) drawing is an engineering document that shows the overall layout of a structure, piece of equipment, or plant area, providing the principal dimensions, major components, orientation, and spatial relationships needed for design coordination, procurement, and construction. In piping and plant engineering, GA drawings serve as the bridge between the high-level plot plan and the detailed fabrication or construction drawings.
GA Drawing Types in Plant Engineering
GA Drawing Type Scope Primary Users Equipment GA Overall dimensions, nozzle locations, support details, and weight of a single piece of equipment (vessel, exchanger, column) Piping engineers (for nozzle connections), structural engineers (for foundations), procurement Structural GA Steel structure layout showing columns, beams, platforms, and access ladders Structural engineers, construction, piping layout Module/Skid GA Complete modular unit (e.g., metering skid, compressor package) showing all equipment, piping, and instruments within the module envelope Module fabricator, shipping, site installation Building GA Architectural layout of control rooms, substations, workshops Architects, electrical, HVAC engineers Pipe rack GA Pipe rack structure showing bay spacing, tier elevations, and width Piping engineers, structural engineers
Content of an Equipment GA Drawing
Element Description Overall dimensions Length, width, height (or diameter and tangent-to-tangent length for vessels) Nozzle schedule Nozzle tag, size, rating, flange type, orientation (angular position), elevation, projection Support details Saddle, skirt, or leg dimensions and bolt-hole pattern for foundation design Lifting points Trunnion or lug locations and capacities for erection planning Weight Empty, operating, and test (flooded) weights Material of construction Shell, head, and internals material (for reference) Design conditions Design pressure and temperature (for piping interface) Orientation reference North arrow or reference line for angular nozzle positions
How GA Drawings Are Used
Discipline Use of GA Drawing Piping Extract nozzle positions, sizes, ratings, and projections to connect piping; verify that piping isometrics match the GA nozzle arrangement Structural Design foundations and supporting steel based on equipment weight, dimensions, and support locations Civil Design plinths, piles, and grade beams from GA-derived loading data Electrical/Instrument Locate junction boxes, instrument nozzles, and cable routing based on equipment GA Construction Plan lifting, transportation, and erection sequence using weights, dimensions, and lifting point data Procurement Issue GA drawings with purchase orders so vendors understand interface requirements
GA Drawing vs. Other Drawings
Drawing Type Level of Detail Purpose Plot plan Low; shows equipment positions on the plant coordinate grid Overall plant layout and spacing GA drawing Medium; shows overall dimensions, nozzles, and key features Design coordination and interface definition Piping plan High; shows piping routing, supports, and valve positions in plan view Piping construction and installation Detail drawing Very high; shows fabrication details (welds, tolerances, surface finishes) Shop fabrication Piping isometric Very high; shows 3D pipe routing with full BOM Pipe spool fabrication and site erection
Starting piping layout before receiving approved (or at minimum “Approved for Design”) equipment GA drawings. Preliminary GAs often have nozzle positions, orientations, or projections that change during vendor design. Building piping models from unapproved GAs leads to costly rework when the final equipment dimensions differ from the preliminary data.
GA drawings are a critical interface document in plant engineering. They are reviewed during design coordination meetings and their data is verified against the as-built equipment during piping inspections and pre-commissioning checks.
Read the full guide to piping engineering
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