Synthetic Natural Gas SNG System Testing and Commissioning Method Statement

Prior to acceptance and initial operation, all piping installations shall be inspected and pressure tested to determine that the materials, design, fabrication, and installation practices comply with the requirements of this code.

Inspection shall consist of visual examination, during or after manufacture, fabrication, assembly, or pressure tests as appropriate. Supplementary types of nondestructive inspection techniques, such as magnetic-particle, radio graphic, and ultrasonic, shall not be required unless specifically listed herein or in the engineering design.

In the event repairs or additions are made following the pressure test, the affected piping shall be tested.

A piping system shall be tested as a complete unit or in sections. Under no circumstances shall a valve in a line be used as a bulkhead between gas in one section of the piping system and test medium in an adjacent section, unless two valves are installed in series with a valved “tell tale” located between these valves. A valve shall not be subjected to the test pressure unless it can be determined that the valve, including the valve closing mechanism, is designed to safely withstand the pressure.

Regulator and valve assemblies fabricated independently of the piping system in which they are to be installed shall be permitted to be tested with inert gas or air at the time of fabrication.

Test Medium: The test medium shall be air or an inert gas (Nitrogen). OXYGEN SHALL NEVER BE   USED.

System Testing Preparation

1. Pipe joints, including welds, shall be left exposed for examination during the test.
2. Expansion joints shall be provided with temporary restraints, if required, for the additional thrust load under test.
3. Appliances and equipment that are not to be included in the test shall be either disconnected from the piping or isolated by blanks, blind flanges, or caps. Flanged joints at which blinds are inserted to blank off other equipment during the test shall not be required to be tested.
4. Where the piping system is connected to appliances, equipment, or equipment components designed for operating pressures of less than the test pressure, such appliances, equipment, or equipment components shall be isolated from the piping system by disconnecting them and capping the outlet(s).
5. Where the SNG piping system is connected to appliances, equipment, or equipment components designed for operating pressures equal to or greater than the test pressure, such appliances and equipment shall be isolated from the piping system by closing the individual equipment shutoff valve(s).
6. All testing of piping systems shall be done with due regard for the safety of employees and the public during the test. Bulkheads, anchorage, and bracing suitably designed to resist test pressures shall be installed if necessary. Prior to testing, the interior of the pipe shall be cleared of all foreign material.

Pressure Testing Requirements

Test pressure shall be measured with a manometer or with a pressure measuring device designed and calibrated to read, record, or indicate a pressure loss due to leakage during the pressure test period. The source of pressure shall be isolated before the pressure tests are made.

The test pressure to be used shall be no less than 11/2 times the proposed maximum working pressure, but not less than 3 psi (20 kPa), irrespective of design pressure. Where the test pressure exceeds 125 psi (862 kPa), the test pressure shall not exceed a value that produces a hoop stress in the piping greater than 50 percent of the specified minimum yield strength of the pipe.

Test duration shall be not less than 1/2 hour for each 500 ft3 (14 m3) of pipe volume or fraction thereof. When testing a system having a volume less than 10 ft3 (0.28 m3) or a system in a single-family dwelling, the test duration shall be permitted to be reduced to 10 minutes. For piping systems having a volume of more than 24,000 ft3 (680 m3), the duration of the test shall not be required to exceed 24 hours.

The range of the pressure gauge shall not be greater than 5 times the test pressure.

Detection of Leaks and Defects

The SNG/LPG piping system shall withstand the test pressure specified without showing any evidence of leakage or other defects. Any reduction of test pressures as indicated by pressure gauges shall be deemed to indicate the presence of a leak unless such reduction can be readily attributed to some other cause.

The leakage shall be located by means of an approved gas detector, a non-corrosive leak detection fluid, or other approved leak detection methods. Matches, candles, open flames, or other methods that provide a source of ignition shall not be used.

Where leakage or other defects are located, the affected portion of the piping system shall be repaired or replaced and retested.

Test Gases: Fuel gas shall be permitted to be used for leak checks in piping systems that have been tested in accordance with Pressure Testing and Inspection.

Before 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 manual valves at outlets on equipment are closed and all unused valves at outlets are closed and plugged or capped.

Purging: Wherever practicable, directly vent purged gases to a safe location outdoors, away from people and ignition sources. Never purge flammable gas inside the building. Use a suitable length and flexible hose to safety purge the gas outside the building. All ignition sources should be controlled or eliminated; ventilation should be adequate to maintain the gas concentration well below the lower explosive limit at all times. Always use combustible gas detectors to monitor the gas concentration during purging operations.

Tests 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. If leakage is indicated, the gas supply shall be shut off until the necessary repairs have been made.

Placing Equipment in Operation: Gas utilization equipment shall not be placed in operation until after the piping system has been tested for leakage and purged before placing in operation.