Deciphering 2 Engineering Drawings: P&ID and Piping Isometric

12/07/2025

Join Viet Han Engineering to discover the diverse world of industrial piping technical drawings: P&ID (Piping & Instrumentation Diagram), Piping Isometric (3D Implementation Drawing), and Spool (Prefabricated Pipe Sections). Together, we will explore the significance, framework, and utilization of each type, enhancing our ability to design, operate, and maintain piping systems with unparalleled effectiveness.

Table of Contents

1 P&ID Diagram Drawing

2 Isometric Piping Technical Drawing (ISO Drawing)

3 Pipe segments, sections, and connections (Spool)

P&ID Diagram Drawing

P&ID (Piping and Instrumentation Diagram) stands as a vital document in sectors like oil and gas, chemicals, electricity, water, and food. It reveals the intricate details of piping systems, equipment, valves, sensors, meters, and control systems. P&ID serves as a block diagram that illustrates the layout and connections between:

Piping
Technological apparatus (Tanks, pumps, compressors…)
Measurement and control instruments

This is not a blueprint for construction; rather, it serves as a design for control, operation, and maintenance systems.

Drawings — P&ID Diagram Symbols and Notations

A P&ID drawing generally encompasses:

Main equipment: including tanks, pumps, compressors, control valves, heat exchangers…
Pipe: reveals dimensions, pipe designation, material classification, thickness, connection technique…
Valve: type of valve (ball valve, gate valve, check valve…), position, purpose.
Measuring instruments: temperature, pressure, flow, and level sensors.
Device code and symbol: in accordance with established standards (ISA, ISO…).
Flow: the movement of fluid or gas within a system.
Control system: control cable, signal (mechanical, electrical, pneumatic), PLC/DCS connection.

Minh Hoạ Bản Vẽ P&id — P&ID Diagram Representation

Symbols in P&ID are regulated based on:

ISA S5.1 (United States standard)
ISO 14617 (global)

Purpose of utilizing P&ID:

Technology systems design assists engineers in planning control and safety systems.
Operation & Maintenance: Support technicians in identifying equipment and systems.
Safety evaluation: risk assessment (HAZOP, LOPA…).
System documentation: for training and technical administration.

Isometric Piping Technical Drawing (ISO Drawing)

An isometric projection drawing is utilized to represent 3D pipes on a 2D plane, commonly applied in:

Construction and installation of piping systems.
Manufacturing operations.
Verify the appropriate distance, direction, and materials.

Iso Bản Vẽ

Characteristic:

The X, Y, and Z axes are generally inclined at angles of 30° and 90°.
Does not accurately represent the true depth ratio but facilitates the visualization of the object’s geometry.

Isometric piping drawings must comprehensively display the following elements:

Details of fittings: Elbow, Tee, Reducer, Flange, Valve, …
Pipe number
Size
Object labeling
Welding mark
Spool number
Flow Orientation

Iso Bản Vẽ 2

Certain software applications facilitate the creation of isometric piping drawings:

AutoCAD Plant 3D
PDMS/E3D
SolidWorks

Pipe segments, sections, and connections (Spool)

A spool is a preconstructed segment of piping includes:

Pipe segments
Accessories (fittings such as elbows, tees, reducers, cap…)
Flange
Valve (if applicable)
The welds have been assembled into a complete unit.

Each spool functions as a “mini-pipe assembly” that can be prefabricated in the factory and subsequently transported to the construction site for assembly in accordance with isometric drawings. The rationale behind dividing the spool:

Reduce time spent on site construction.
Enhanced accuracy due to being manufactured under regulated conditions in the factory.
Materials are easy to manage, quality should be checked, and each cluster must be numbered.
Appropriate for shipping specifications (length, weight restrictions).

Spool division must adhere to several technical principles to guarantee feasibility in fabrication, transportation, installation, and operation. The following are the commonly utilized spool division guidelines for pipes:

Ø Ensure production capacity

Each spool must be engineered for machining, welding, and inspection in the workshop.
Steer clear of welding areas that are difficult to access.
Avoid cutting the spool near valves, equipment, or challenging-to-machine connections.

Ø Ensure portability

The dimensions and mass of the spool should adhere to transportable standards, typically ≤ 12m in length and a weight of ≤ 3-5 tons (depending on the vehicle).
Ensure that the height and width remain within the limits of the container size (if export is necessary).
Avoid designs that are cumbersome or prone to distortion.

Ø Confirm installation capability

The spool should be easily transportable to the designated job site.
The spool must be segmented to ease the processes of mounting, alignment, and welding at the site.
It is essential to consider the working environment of employees, particularly in confined spaces like drilling rigs, factories, and similar locations.

Ø Adhere to the construction sequence

The spool must be installed in the following order: Equipment → valve → main pipe → sub → support.
Refrain from splitting the spool, as this necessitates disassembling additional equipment or structures prior to installation.
Field weld points may be positioned in accessible locations.

Ø Reduce on-site welding

Factory welding should be prioritized due to its consistent delivery of superior quality.
Store welding supplies.
Minimize the number of field welds.
However, it is essential to take into account transportation and installation factors to identify the suitable split point.

Ø Spool numbering and administration

Each spool must possess a unique identifier (spool number).
Isometric drawings should distinctly indicate spool split points and welding locations.

Ø Additional notes

Different materials must not be welded together in a single spool.
Consider thermal expansion, pipe routing, and anchor points carefully.
When cutting the spool for stainless steel pipes, it is essential to reduce the number of welds to prevent any impact on physical and mechanical properties.

How is a spool represented in ISO technical drawing?

Each spool is assigned a unique number (e.g., Spool No. SP01, SP02…). The ISO drawing illustrates: