Testing, Purging, and Leak Detection Procedures

Introduction

This chapter covers one of the most critical aspects of the gasfitter trade: verifying the tightness of installations, purging piping systems, and detecting leaks. These procedures are not only regulatory requirements—they save lives. The Natural Gas and Propane Installation Code (CSA B149.1) strictly governs these operations. You must master the principles, pressure calculations, acceptable purge gases, and detection methods to pass the Red Seal exam.

Learning Objectives

By the end of this chapter, you will be able to:

Distinguish between the different types of tests (pressure, tightness, operational) and their applications

Calculate required test pressures based on the type of installation and gas used

Identify acceptable purge gases and safe purging procedures

Apply leak detection methods in compliance with CSA B149.1

Recognize common pitfalls and exam traps

Section 1: Fundamental Principles of Testing

1.1 Why Test?

A tightness test is proof of safety. It confirms that an installation has no leaks before it is put into service. Natural gas and propane are flammable and can form explosive mixtures in air between certain limits (lower and upper explosive limits). An undetected leak can lead to an explosion, carbon monoxide poisoning, or fire.

1.2 Types of Tests

Type of Test	Primary Purpose	When to Perform
Pressure test (pneumatic)	Verify tightness under pressure	Before commissioning, after any modification
Leak test (tightness)	Detect leaks on a system in service	During commissioning, during service work
Operational test	Verify proper operation of appliances and safety devices	After commissioning

1.3 Test Pressure vs. Service Pressure

Test pressure is always higher than service pressure. It is applied to create a pressure gradient that forces the detection of any leak. Test pressure must never exceed the maximum rated pressure of the installation components (pipes, fittings, valves, appliances).

Section 2: Pressure Testing According to CSA B149.1

2.1 General Rule (Article 4.8 of CSA B149.1)

The CSA B149.1 Code requires that every gas installation be subjected to a pressure test before being put into service. The specific requirements are set out in Article 4.8 of the Code. Here are the essential points:

Initial test: All new, modified, or repaired piping must be subjected to a pressure test.

Test medium: The test must be conducted using compressed air, an inert gas (nitrogen), or the gas the installation is designed to carry, as permitted by the Code.

Test duration: The pressure must be maintained for a sufficient period to allow inspection of all joints and connections. The Code does not set a universal minimum duration, but common practice is 10 to 15 minutes, or longer for large installations.

2.2 Minimum Test Pressures

The following table summarizes the minimum test pressures required by CSA B149.1 (Article 4.8.2):

Type of Installation	Minimum Test Pressure
Natural gas piping (service pressure ≤ 7 kPa)	14 kPa (2 psi)
Natural gas piping (service pressure > 7 kPa)	1.5 × maximum service pressure, with a minimum of 14 kPa
Propane piping (service pressure ≤ 7 kPa)	14 kPa (2 psi)
Propane piping (service pressure > 7 kPa)	1.5 × maximum service pressure, with a minimum of 14 kPa
Underground piping (all gases)	1.5 × maximum service pressure, with a minimum of 350 kPa (50 psi)

Important note: For underground piping, the minimum test pressure is significantly higher (350 kPa) due to soil stresses and the impossibility of visually detecting leaks after backfilling.

2.3 Calculating Test Pressure

For an installation with a maximum service pressure of 100 kPa, the test pressure would be:

Test pressure = 1.5 × 100 kPa = 150 kPa

Reminder: Test pressure must never exceed the rated pressure of the components. Always check the manufacturer's specifications.

2.4 Testing Procedure

33.Isolation: Close the main shut-off valve and isolate all appliances not designed to withstand the test pressure.

34.Connection: Connect the pressure source (compressor, nitrogen cylinder) to the piping via a regulator and a calibrated pressure gauge.

35.Pressurization: Gradually increase the pressure to the required test value.

36.Stabilization: Wait for the pressure to stabilize (temperature variations can affect the reading).

37.Inspection: Apply a leak detection solution (soapy water) to all joints, fittings, threads, and connection points. Observe for bubble formation.

38.Duration: Maintain the pressure for the required duration and monitor the gauge. A pressure drop indicates a leak.

39.Depressurization: Release the pressure slowly and safely after a successful test.

2.5 Factors Affecting Pressure Gauge Readings

Temperature: A rise in temperature increases pressure; a drop reduces it. If the temperature changes during the test, the reading may vary without any leak being present.

System volume: A large piping volume requires more time for pressure to stabilize.

Gauge calibration: The pressure gauge must be calibrated and suitable for the pressure range being measured.

Section 3: Purging of Piping Systems

3.1 Definition and Purpose

Purging is the operation of removing air or another gas from piping before it is put into service, or removing gas before servicing. The purpose is to prevent the formation of a flammable air-gas mixture inside the piping.

3.2 Acceptable Purge Gases

According to CSA B149.1 (Article 4.9), the following gases may be used for purging:

Gas	Use	Remarks
Inert gas (nitrogen, helium)	Initial and final purging	Safe, does not form a flammable mixture
Natural gas	Purging a natural gas line	Must be done in a manner that avoids any flammable mixture
Propane	Purging a propane line	Must be done in a manner that avoids any flammable mixture
Compressed air	Purging a line before a pressure test	Must never be used to purge a line containing gas

Golden rule: Never use compressed air to purge a line containing natural gas or propane. The air-gas mixture can become explosive.

3.3 Initial Purging Procedure (Commissioning)

52.Verification: Ensure all appliances are turned off and the main shut-off valve is closed.

53.Connection: Connect the inert gas source (nitrogen) to the upstream end of the piping.

54.Venting: Open the furthest purge point (vents, purge taps) to allow air to escape.

55.Injection: Inject nitrogen until the air is completely displaced. The oxygen concentration must be below 1% (ideally 0%).

56.Measurement: Use an oxygen analyzer to confirm that the air has been removed.

57.Gas introduction: Close the nitrogen source, then slowly open the main shut-off valve to introduce natural gas or propane.

58.Final purge: Purge the residual nitrogen by allowing gas to flow through the furthest purge point until the gas concentration is sufficient (generally > 80% of the lower explosive limit, but ideally 100%).

59.Closure: Close the purge point and verify the tightness of the connections.

3.4 Purging a Line Out of Service (Servicing)

Before cutting into a line or disassembling an appliance, residual gas must be removed:

62.Isolation: Close the upstream shut-off valve.

63.Venting: Open the purge point closest to the work area to vent the gas.

64.Nitrogen purge: Inject nitrogen to displace the residual gas.

65.Verification: Use a gas detector to confirm that the gas concentration is below 1% of the LEL (lower explosive limit).

66.Safe work: You may now cut or disassemble safely.

3.5 Calculating the Volume of Gas to Purge

The volume of gas to purge depends on the volume of the piping. For a cylindrical pipe:

Volume (L) = π × (inside diameter in dm / 2)² × length (dm)

Example: A pipe with an inside diameter of 25 mm (0.25 dm) and a length of 10 m (100 dm):

Volume = π × (0.25 / 2)² × 100 = 3.1416 × 0.015625 × 100 = 4.91 L

You must therefore inject at least 4.91 L of nitrogen to purge this pipe, but in practice, you inject 3 to 5 times this volume to guarantee a complete purge.

Section 4: Leak Detection

4.1 Detection Methods

Method	Principle	Application
Detection solution (soapy water)	Bubble formation at the leak point	Detecting leaks on accessible joints and fittings
Electronic gas detector	Catalytic or infrared sensor	Detecting leaks on installations in service
Gas analyzer (oxygen / LEL)	Measures gas concentration in air	Verifying purging and detecting leaks in confined spaces
Flame test (never recommended)	Observing flame color change	Prohibited by the Code — risk of explosion

4.2 Detection Solution

Detection solution is a mixture of water and soap (or a commercial product). It is applied with a brush or spray to fittings, threads, welds, and valves. If a leak exists, bubbles will form.

Mandatory inspection points:

All threaded fittings

Welds

Compression fittings

Valves (body and packing gland)

Appliance connections

Seals and gaskets

4.3 Electronic Detector

The electronic gas detector is a valuable tool for installations in service. It must be calibrated regularly and used according to the manufacturer's instructions. It is particularly useful for:

Detecting minute leaks not visible with soapy solution

Checking hard-to-reach areas

Monitoring confined spaces (basements, crawl spaces)

4.4 Leak Detection Procedure on an Installation in Service

91.Preparation: Have a calibrated electronic detector and a detection solution ready.

92.Visual inspection: Examine the entire installation for signs of corrosion, deformation, or wear.

93.Electronic detection: Pass the detector along the entire piping system, especially at fittings and valves.

94.Confirmation: If the detector signals a leak, confirm with the detection solution.

95.Repair: Shut off the gas supply, purge the line, repair the leak, then perform a new pressure test.

96.Recommissioning: Purge again and verify proper operation.

4.5 Leaks in Confined Spaces

In a confined space (trench, basement, crawl space), leak detection is more complex. Gas can accumulate and create an explosion hazard. Use a portable detector with an alarm and ventilate the space before entering.

Section 5: Regulatory and Code Requirements

5.1 CSA B149.1 — Natural Gas and Propane Installation Code

Key articles to know:

Article 4.8: Pressure tests — general requirements, minimum pressures, test medium.

Article 4.9: Purging — acceptable purge gases, procedures.

Article 4.10: Leak detection — methods and requirements.

Article 5.2: Appliance connections — verification of connection tightness.

Article 6.1: Piping — materials, dimensions, supports.

5.2 Canadian Electrical Code, Part I

This Code applies to electrical installations in classified areas (where flammable gases may be present). When working near electrical equipment, ensure it complies with this Code to avoid ignition sources.

5.3 Other Relevant Codes

CSA B149.2: Propane Storage and Handling Code (for propane tanks).

CSA B149.3: Code for the Field Approval of Fuel-Related Components of Appliances and Equipment (for appliance installation requirements).

CSA B149.5: Installation Code for Natural Gas and Propane Vehicles and Fuel Containers.

Section 6: Practical Calculations for the Exam

6.1 Pressure Conversions

Unit	Equivalent
1 kPa	0.145 psi
1 psi	6.895 kPa
1 bar	100 kPa
1 atm	101.325 kPa

Example: Convert 14 kPa to psi: 14 × 0.145 = 2.03 psi.

6.2 Calculating Test Pressure

Typical problem: A natural gas installation has a maximum service pressure of 150 kPa. What is the minimum test pressure?

Solution: Test pressure = 1.5 × 150 = 225 kPa. Since 225 kPa > 14 kPa, the test pressure is 225 kPa.

Typical problem 2: A propane installation has a service pressure of 3.5 kPa. What is the minimum test pressure?

Solution: 1.5 × 3.5 = 5.25 kPa. Since this result is below 14 kPa, the minimum test pressure is 14 kPa.

6.3 Calculating Purge Volume

Typical problem: A pipe with an inside diameter of 50 mm (0.5 dm) and a length of 25 m (250 dm) must be purged. What volume of nitrogen should be planned?

Solution:

Volume = π × (0.5 / 2)² × 250 = 3.1416 × 0.0625 × 250 = 49.09 L

In practice, plan for 3 to 5 times this volume, approximately 150 to 250 L of nitrogen.

6.4 Leak Detection: Interpreting Readings

A gas detector displays a concentration of 15% of the LEL. The LEL of natural gas is 5% (volume in air). The actual concentration is:

Actual concentration = 15% × 5% = 0.75% (volume)

This concentration is below the LEL, but it indicates a leak that must be located and repaired.

Section 7: Safety During Testing and Purging

7.1 Associated Hazards

Hazard	Cause	Prevention
Explosion	Flammable air-gas mixture	Purge with nitrogen, verify concentration
Overpressure	Faulty regulator, improperly closed valve	Use a calibrated regulator, monitor the gauge
Asphyxiation	Inert gas (nitrogen) in a confined space	Ventilate, use an oxygen detector
Burns	Contact with a flame or hot surface	Wear gloves, maintain safe distances

7.2 Personal Protective Equipment (PPE)

Safety glasses

Work gloves

Safety footwear

Portable gas detector (in confined spaces)

Respiratory protection if necessary (rare)

7.3 Procedure in Case of a Detected Leak

141.Shut off the supply: Close the main shut-off valve.

142.Ventilate: Open doors and windows to clear the gas.

143.Evacuate: Move people out of the area.

144.Alert: Call the gas supplier's emergency line or the fire department.

145.Do not ignite: Do not operate any electrical switches, do not smoke, do not create any sparks.

Pitfalls to Avoid

147.Confusing service pressure and test pressure: Test pressure is always higher (1.5 × service pressure, with a minimum of 14 kPa).

148.Forgetting the 14 kPa minimum: For low-pressure installations (3.5 kPa), the test pressure is 14 kPa, not 5.25 kPa.

149.Using compressed air to purge a gas line: This is prohibited and extremely dangerous.

150.Neglecting the initial purge: A new line contains air; it must be purged with nitrogen before introducing gas.

151.Ignoring temperature variations: A pressure drop may be due to a temperature decrease, not a leak.

152.Not verifying gauge calibration: An uncalibrated gauge gives false readings.

153.Testing only visible joints: All connections must be tested, including those that will later be covered (walls, ceilings).

154.Venting outdoors without protection: Purged gas must be directed to a safe location, away from ignition sources.

155.Confusing LEL and UEL: The LEL (lower explosive limit) is the minimum gas concentration in air for ignition to occur. For natural gas, it is approximately 5%; for propane, approximately 2.1%.

156.Not documenting tests: Test results must be recorded and provided to the owner or inspector.

Summary

Pressure test: Mandatory before commissioning any installation. Minimum pressure of 14 kPa for low-pressure installations, 1.5 × service pressure for higher-pressure installations, and 350 kPa for underground piping.

Test medium: Compressed air, nitrogen, or the service gas, as applicable. Never use air to purge a line containing gas.

Purging: Removal of air or residual gas. Nitrogen is the safest purge gas. Oxygen concentration must be < 1% after initial purge.

Leak detection: Detection solution (soapy water) for accessible joints, electronic detector for installations in service. Confirm any detection with a second method.

Safety: Shut off the supply, ventilate, evacuate in case of a leak. Never create sparks.

Codes: CSA B149.1 (Articles 4.8, 4.9, 4.10), CSA B149.2, CSA B149.3, Canadian Electrical Code, Part I.

Review Questions

165.What is the minimum test pressure for a natural gas installation at 3.5 kPa?

166.Which gas must never be used to purge a natural gas line?

167.What is the maximum acceptable oxygen concentration after an initial nitrogen purge?

168.An underground line must be subjected to a minimum test pressure of how many kPa?

169.Which leak detection method is most appropriate for an accessible threaded joint?

170.If the temperature drops by 10 °C during a pressure test, what might you observe?

171.What is the volume of a pipe with an inside diameter of 25 mm and a length of 15 m?

172.Why is the test pressure for underground piping higher than for exposed piping?

173.What is the LEL of natural gas? And of propane?

174.What should you do if you detect a gas leak in a building?

Answers to Review Questions

176.14 kPa (absolute minimum).

177.Compressed air.

178.Less than 1% (ideally 0%).

179.350 kPa (50 psi).

180.Detection solution (soapy water).

181.A pressure drop due to gas contraction, without there necessarily being a leak.

182.Volume = π × (0.25 / 2)² × 150 = 7.36 L.

183.Because leaks are difficult to detect after backfilling and soil stresses are higher.

184.Natural gas: approximately 5%; propane: approximately 2.1%.

185.Shut off the supply, ventilate, evacuate, alert the authorities, do not create sparks.

This chapter prepares you for exam questions on testing, purging, and leak detection. Review Articles 4.8 to 4.10 of CSA B149.1 and practice pressure and volume calculations. Good luck with your preparation!

Testing, Purging, and Leak Detection Procedures