Air Instrumentation Network Sizing: Best Design Practices

Proper instrument air network design is critical to ensuring the accuracy, reliability, and safety of automated industrial systems. These networks play a critical role in providing clean, dry, and properly pressed air to operate pneumatic instruments and control systems. However, poor design can lead to operational failures, high costs, and significant risks. In this note, we address applicable regulations, common risks, best practices, key aspects, and common errors in sizing instrument air networks.

Key Regulations

The design and construction of instrumentation air networks must comply with international and local regulations governing air quality, pipe design and technical requirements. The main standards include:

1. International Regulations

ISA S7.0.01-1996 (R2013): Quality specifications for instrument air.
ISO 8573: Classification of compressed air purity in terms of particulate matter, water and oil.
ISO 1217: Standards for performance testing of air compressors.
ASME B31.3: Code for process piping and pneumatic systems.
API 554: Guidelines for process control systems, including pneumatic networks.

2. Local Regulations

NCh 2192: Safety in pneumatic and hydraulic systems.
SEC Standards (Chile): Regulations for industrial control systems.
Technical Regulations for Compressed Air Installations (RETAC, Colombia): Design and safety parameters in pneumatic networks.

These regulations ensure that instrument air networks meet the quality, reliability and safety requirements in industrial environments.

Risks Associated with Poor Design

Inadequate design of instrument air networks can generate risks that affect both equipment and production processes. The main risks include:

1. Air Pollution

Presence of particles, moisture or oil that can damage sensitive instruments, causing operational failures and high maintenance costs.

2. Pressure Losses

Undersizing pipes or designing with excessive elbows, valves and restrictions can generate pressure drops that compromise the operation of pneumatic instruments.

3. Leaks in the System

Leaks due to inadequate connections or low-quality materials that generate loss of efficiency, higher energy consumption and high operating costs.

4. Lack of Redundancy

Networks without redundancy in compressors or accumulators that put the continuity of the air supply at risk in the event of failures.

5. Compressor Overload

Incorrect selection of compressors or inadequate network design that forces equipment to operate outside its recommended ranges, reducing its useful life.

Best Practices in Instrumentation Air Network Design

To ensure optimal network performance, it is essential to follow these best practices:

1. Air Quality

Comply with ISA S7.0.01 , which specifies air with a maximum particle content of 40 microns, free of moisture and oil.
Incorporate air dryers (e.g., refrigerant or desiccant type) and coalescing filters to remove contaminants.

2. Pipe Sizing

Calculate the diameter of the pipes considering the maximum flow, the total length of the system and the allowed pressure drops.
Use materials such as stainless steel, copper or high-strength polymers that minimize pressure losses and the accumulation of contaminants.

3. System Design

Design the system so that the working pressure is between 90 and 120 psi, considering the specific requirements of the instruments.
Minimize unnecessary elbows and joints to reduce friction losses.
Incorporate accumulators or reserve tanks to absorb pressure fluctuations.

4. Monitoring and Control

Implement pressure, flow and air quality sensors at key points to ensure continuous and safe operation.
Design redundancy into compressors to maintain air supply during maintenance or in the event of failure.

5. Energy Management

Select highly energy-efficient compressors and design systems that minimize losses, optimizing energy consumption.

Relevant Aspects in Design

System Security
Incorporate relief valves to prevent overpressure in the system.
Design accessible routes for inspection and maintenance.
Instrument Compatibility
Ensure that the quality of the supplied air meets the requirements of pneumatic instruments.
Flexibility for Expansions
Design a scalable network that allows the incorporation of new instruments or equipment in the future without affecting system performance.
Compressor Location
Locate compressors in well-ventilated areas, free of dust and moisture to maximize their efficiency and service life.
Leak Management
Implement leak detection and repair programs to maintain system efficiency.

Common Design Mistakes

Despite the importance of good design, some common errors can compromise the efficiency of instrument air networks:

1. Under-sizing of Pipes

Selecting inappropriate diameters causes significant pressure drops.

2. Lack of Air Treatment

Failure to install proper dryers or filters, resulting in contamination and equipment damage.

3. Use of Incorrect Materials

Selecting low-quality pipes that corrode easily, causing contamination and leaks.

4. Design without Redundancy

Failure to provide alternative systems to ensure a continuous supply of air in the event of failures.

5. Improper Component Placement

Placing compressors or accumulators in hard-to-reach places, complicating maintenance and inspections.

Conclusion

Proper sizing and designing of instrument air networks is key to ensuring the safe and efficient operation of industrial systems. Applying appropriate regulations, assessing risks, implementing best practices and avoiding common errors is essential to achieving a reliable and long-lasting system.

At Acciomate Engineering & Projects , we have a team of experts in instrumentation air network design, capable of designing customized and efficient solutions to meet the needs of each client.