Both of these are used in engineering design, particularly in the process and mechanical industries. Here’s a summary of their primary differences: 

P&ID (Piping and Instrumentation Diagram) 

• P&ID is a schematic representation of the process flow in a plant or industrial system. 
• It shows the relationship between the equipment, piping, and instrumentation within the system. 
• P&IDs are typically 2D drawings that use standardized symbols and notations to depict the components and their connections. 
• These diagrams serve as a basis for the design, construction, and operation of the plant, as well as for maintenance and safety purposes. 
• P&IDs do not show the physical layout of the components or their dimensions; instead, they focus on the functional relationships between them. 
• P&IDs are created during the early stages of a project, and they evolve as the design progresses. They provide a clear understanding of the process flow, control schemes, and safety systems in a plant. 
• Engineers from various disciplines, such as process, mechanical, electrical, and instrumentation, use P&IDs to coordinate their work and ensure proper integration of the different systems. 
• P&IDs serve as a basis for creating other detailed engineering documents, such as equipment datasheets, instrument lists, and control system configuration documents.
• Regulatory authorities and safety engineers also rely on P&IDs for evaluating the safety and operability aspects of the plant design. 
• P&IDs are critical for plant operations and maintenance personnel, as they help in understanding the process, locating equipment, and troubleshooting issues. 

Isometric Drawings 

• Isometric drawings are a type of 3D representation used to show the physical layout of a system or component. 
• They are used primarily for piping, mechanical, and structural designs. 
• These drawings display the 3D layout of the system by projecting its elements onto a 2D plane while maintaining the relative proportions and angles. 
• Isometric drawings provide a more accurate representation of the system’s geometry, which can be helpful for fabrication, construction, and maintenance purposes. 
• Unlike P&IDs, isometric drawings focus on the spatial arrangement and dimensions of the components and their interconnections. 
• Isometric drawings are usually created during the detailed design phase of a project, after the P&IDs and other high-level design documents have been finalized. 
• These drawings are particularly useful for pipe fabrication and installation, as they provide a clear understanding of the routing, support locations, and material requirements for the piping system. 
• Isometric drawings include information such as pipe size, material specifications, insulation, and painting requirements, as well as the locations of valves, flanges, and other components. 
• They are also essential for accurate cost estimation and procurement, as they help in determining the quantities of materials and labor required for the construction of a system. 
• Isometric drawings can be used by construction personnel to visualize the spatial arrangement of the components, making it easier to plan and execute the installation work. 

P&IDs and isometric drawings are complementary tools used in the engineering design and construction of industrial plants and systems. P&IDs focus on the functional relationships and process flow, while isometric drawings provide a detailed representation of the physical layout and dimensions of the components. Both types of drawings are essential for successful project execution, as they facilitate communication and coordination among various stakeholders, such as designers, fabricators, construction personnel, and plant operators.