Compressed Air, Medical Gas, and Process Piping

Compressed Air, Medical Gases, and Process Piping

Chapter Introduction

This chapter covers three specialized piping systems that the journeyman plumber must master: compressed air systems, medical gas networks, and process piping. Although distinct, these systems share common principles: pressure control, fluid purity, specific materials, and strict regulatory requirements. For the Red Seal exam, you must know the applicable standards, installation methods, required testing, and sizing calculations.

Section 1: Compressed Air

1.1 Fundamental Principles

Compressed air is atmospheric air whose volume has been reduced by mechanical compression. In a piping system, three main components are distinguished:

Pressure is measured in kilopascals (kPa) or pounds per square inch (psi). In Canada, kPa is commonly used in technical calculations, but industrial gauges often display both units. Remember: 1 psi ≈ 6.895 kPa.

1.2 Types of Compressors

For the exam, remember that the piston compressor is the most common for small and medium installations, while the rotary screw dominates industry due to its reliability in continuous service.

1.3 System Components

The compressed air circuit includes:

1.4 Piping Sizing

Sizing a compressed air system is based on three factors:

The simplified formula for estimating the inside diameter (d) in millimetres:

d = √(4 × Q × 10⁶) / (π × V)

Where:

Rule of thumb: air velocity in main lines must not exceed 10 m/s. Beyond this, pressure losses become excessive and noise increases.

1.5 Piping Materials

For compressed air, acceptable materials are:

Prohibited: PVC and CPVC for compressed air. These plastics can fracture explosively under pressure.

1.6 Slope and Drainage

Compressed air lines must be installed with a minimum slope of 1% (1 cm per metre) in the direction of air flow. Condensate traps must be installed:

The main line must be connected to the tank from the top to prevent condensate from backing up into the line.

1.7 Testing and Commissioning

Before commissioning, the compressed air system must undergo:

Section 2: Medical Gases

2.1 Definition and Regulatory Framework

Medical gases are gases used in healthcare facilities for patient treatment. They include:

The primary regulatory framework is the CSA Z7396.1 standard — "Medical gas and vacuum systems" — which covers the design, installation, testing, and maintenance of these systems.

2.2 Gas Identification and Colour Coding

Each medical gas has a standardized colour and a specific connection to prevent any confusion:

Essential rule: the connections are non-interchangeable between gases. Each gas uses a different thread profile or diameter to prevent any incorrect connection.

2.3 Piping Materials for Medical Gases

The requirements of CSA Z7396.1 are strict regarding materials:

Copper must be joined by capillary brazing with a high-silver-content alloy (minimum 15% silver). Soft soldering (tin-lead) is strictly prohibited as it cannot withstand temperatures and vibrations.

2.4 Brazing Procedure

The brazing procedure for medical gases requires:

Important trap: flux must be applied in a thin, uniform layer. Excess flux can contaminate the inside of the tube and clog downstream filters.

2.5 Testing Medical Gas Systems

CSA Z7396.1 requires a rigorous testing sequence:

Critical point: tests must be performed by a certified organization and results recorded in an official report. Without this report, the installation cannot be commissioned.

2.6 Hazard Zones and Safety Distances

Medical gas cylinders and storage units must maintain minimum distances from ignition sources:

Section 3: Process Piping

3.1 Definition

Process piping refers to systems that transport industrial fluids in plants, processing facilities, and heating/cooling systems. These fluids can be:

3.2 Applicable Standards

Process piping is governed by the Canadian Electrical Code, Part I for electrical aspects, but primarily by the following standards:

For the Red Seal exam, focus on the general principles of CSA B51 and the requirements of ASME B31.3.

3.3 Fluid Classification per ASME B31.3

ASME B31.3 classifies fluids into categories based on their hazard level:

Each category imposes different requirements for materials, welding, testing, and inspection.

3.4 Materials for Process Piping

The choice of material depends on the fluid being transported, temperature, and pressure:

Compatibility rule: the material must be compatible with the fluid at all operating temperatures. A chemical compatibility chart must be consulted before any selection.

3.5 Fittings and Joints

Assembly methods for process piping:

3.6 Supports and Thermal Expansion

Process piping undergoes significant temperature variations. Thermal expansion must be accommodated by:

The linear expansion formula:

ΔL = α × L × ΔT

Where:

Example: a 30-metre steel pipe undergoes a temperature change of 80 °C.

ΔL = 0.0000117 × 30,000 × 80 = 28.08 mm

The pipe will elongate by 28 mm. An expansion joint or loop must be provided to absorb this expansion.

3.7 Process Piping Testing

Mandatory tests before commissioning:

Caution: pneumatic testing is dangerous. The energy stored in a compressed gas is far greater than that of a liquid. Special precautions are required (safety zones, gradual depressurization).

Section 4: Useful Calculations and Conversions

4.1 Pressure Conversions

4.2 Pressure Drop Calculation

The pressure drop in a compressed air line can be estimated using the Darcy-Weisbach formula:

ΔP = f × (L/D) × (ρ × V² / 2)

Where:

For the exam, remember that pressure drop increases with the square of the velocity. Doubling the velocity quadruples the pressure drop.

4.3 Tank Volume

The volume of a cylindrical tank:

V = π × r² × h

Where:

Traps to Avoid

Summary

Key Points to Remember

Exam Strategy

Final Review

Before the exam, ask yourself these questions:

If you can answer these questions correctly, you are ready for this section of the Red Seal exam.