4.2.22 Performing Gas Distribution System Leak Checks Requirements for vapor distribution system leak checks are found in Chapter 7 of NFPA 54, National Fuel Gas Code, 2002 edition. Suggested methods for conducting leak checks are found in Annex D to the code. • In this module you will learn to identify: • NFPA 54 regulations & guidelines for gas distribution system leak checks • Procedures for testing for leakage using a manometer • Procedures for testing for leakage using pressure or block gauges • Procedures for testing for leakage using the gas meter • Other considerations regarding leakage in a gas distribution system
NFPA 54 2002 NFPA 54 Requirements & Guidelines for Leak Checks 7.2.1 Test Gases. Leak checks using fuel gas shall be permitted in piping systems that have been pressure tested in accordance with Section 7.1. 7.2.2Before Turning Gas On.Before gas is introduced into a system of new gas piping, the entire system shall be inspected to determine that there are no open fittings or ends and that all valves at unused outlets are closed and plugged or capped. 7.2.3 Test for Leakage.Immediately after the gas is turned on into a new system or into a system that has been initially restored after an interruption of service, the piping system shall be tested for leakage. Where leakage is indicated, the gas supply shall be shut off until the necessary repairs have been made. 7.2.4 Placing Equipment in Operation. Gas utilization equipment shall not be placed in operation until after the piping system has been tested in accordance with 7.2.3 and purged in accordance with 7.3.2. A leak check performed on an LP-Gas system should include all regulators, including appliance regulators, and 100% pilot safety control valves in the system.
Figure 1. Leak Checking Using a Manometer Procedures for Testing for Leakage Using a Manometer • Piping systems serving appliances which receive gas at pressures of ½ psig or less may be leak checked by inserting a water manometer or equivalent device downstream of the final system regulator. • This leakage check is performed with propane vapor at 9 inches water column + or - ½ inch for a period of 3 minutes.
Procedures for Testing for Leakage Using a Manometer Figure 2. U-Tube Manometer Mounded on Water Heater Leak Check Pressure Reading is 8.8 inches w.c. If the pressure decreases, one or more leaks exist in the system. The source(s) of leakage must be located using a combustible gas indicator, suitable leak detection solution, isolated testing and inspection of piping segments, or a combination of these methods. After the source(s) of leakage are located and repaired, the leak check must be restarted and continued until no change in pressure is observed.
Procedures for Testing for Leakage Using a Pressure Gauge Block Figure 3. Leak Checking Using Pressure or Block Gauges
Procedures for Testing for Leakage Using a Pressure Gauge Block Figure 4. Zero to 300 Psig Block Gauge
Procedures for Testing for Leakage Using a Pressure Gauge Block If the pressure increases, propane may be leaking into the system from a container service valve. If the pressure decreases, one or more leaks exist in the system. The source(s) of leakage must be located using a combustible gas indicator, suitable leak detection solution, isolated testing and inspection of piping segments, or a combination of these methods. After the source(s) of leakage are located and repaired, the leak check must be restarted and continued until no change in pressure is observed.
NFPA 54 2002 Procedures for Testing for Leakage Using the Gas Meter Annex D to NFPA 54 outlines the following suggested method of testing for leakage using the gas meter (when present in the distribution system). • Immediately prior to the test, determine if the meter is in good operating condition and has not been bypassed. Inspect the vapor distribution system and ensure valves and appliance controls are set as described in the procedures for leak checks using a manometer or gauge test block. • Check for leakage by carefully watching the test dial on the meter to determine whether gas is passing through the meter. • To assist in observing any movement of the test hand, wet a small piece of paper and paste its edge directly over the centerline of the hand as soon as the gas is turned on. This observation should be made with the test hand on the upstroke.
Procedures for Testing for Leakage Using the Gas Meter • The following table (Figure 1) can be used for determining the length of observation time. For SI units, 1 ft3 = 0.028 m3 Figure 5. Test Observation Times for Various Meter Dials • If there has been no movement of the test hand for the required length of time, it is assumed that no leakage is present. Record the starting and ending time of the leak check, and the meter register reading on appropriate company forms.
Procedures for Testing for Leakage Using the Gas Meter Figure 6. Observing and Recording Meter Reading & Leak Check Start and Ending Times
Other Considerations Regarding Leakage in a Gas Distribution System • Once a leak in a propane distribution system is known, the leak may be located by using an approved gas detector, a non-corrosive leak detection fluid, or other approved detection method. • Matches, candles, open flames, or other methods that provide a source of ignition shall not be used. • Artificial illumination used in connection with a search for gas leakage should be restricted to battery-operated flashlights (preferably of the safety type) or approved safety lamps. • When searching for leaks, electric switches should not be operated. If electric lights are already turned on, they should not be turned off.
Time to See If You Got the Key Points of This Module… • Complete the Review on pages 9 & 10. • See if you are ready for the Certification Exam by checking off the performance criteria on pages 11 & 12.