We have discussed pressure and leak testing piping in our hazardous materials processes, specifically in our PSM/RMP-covered processes. The International Fuel Gas Code (IFGC) has some great specifics on how we test natural gas piping. Interestingly enough, the IFGC code defines “pressure test” as… (emphasis by me)
| An operation performed to verify the gas-tight integrity of gas piping following its installation or modification. |
SECTION 406 (IFGS) – INSPECTION, TESTING AND PURGING
406.1 General
Prior to acceptance and initial operation, ALL PIPING INSTALLATIONS SHALL BE VISUALLY INSPECTED AND PRESSURE TESTED to determine that the materials, design, fabrication, and installation practices comply with the requirements of this code.
406.1.1 Inspections.
Inspection shall consist of VISUAL examination during or after manufacture, fabrication, assembly or pressure tests.
406.1.2 Repairs and additions.
In the event repairs or additions are made after the pressure test, the affected piping shall be tested.
Minor repairs and additions are not required to be pressure tested provided that the work is inspected and connections are tested with a noncorrosive leak-detecting fluid or other approved leak-detecting methods.
406.1.3 New branches.
Where new branches are installed to new appliances, only the newly installed branches shall be required to be pressure tested.
Connections between the new piping and the existing piping shall be tested with a noncorrosive leak-detecting fluid or other approved leak detecting methods.
406.1.4 Section testing.
A piping system shall be permitted to be tested as a complete unit or in sections. A VALVE IN A LINE SHALL NOT BE USED AS A BULKHEAD between gas in one section of the piping system and test medium in an adjacent section, EXCEPT WHERE A DOUBLE BLOCK AND BLEED VALVE SYSTEM IS INSTALLED.
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 test pressure.
406.1.5 Regulators and valve assemblies.
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.
406.1.6 Pipe clearing.
PRIOR TO TESTING, the interior of the pipe shall be cleared of all foreign material.
406.2 Test medium.
The test medium shall be AIR, NITROGEN, CARBON DIOXIDE OR AN INERT GAS.
Oxygen shall not be used as a test medium.
406.3 Test preparation.
Pipe joints, including welds, shall be left exposed for examination during the test.
Exception: Covered or concealed pipe end joints that have been previously tested in accordance with this code.
406.3.1 Expansion joints.
Expansion joints shall be provided with temporary restraints, if required, for the additional thrust load under test.
406.3.2 Appliance and equipment isolation.
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.
406.3.3 Appliance and equipment disconnection.
Where the piping system is connected to appliances or equipment designed for operating pressures of LESS THAN THE TEST PRESSURE, such appliances or equipment shall be isolated from the piping system by disconnecting them and capping the outlet(s).
406.3.4 Valve isolation.
Where the piping system is connected to appliances or equipment designed for operating pressures EQUAL TO OR GREATER THAN the test pressure, such appliances or equipment shall be isolated from the piping system by closing the individual appliance or equipment shutoff valve(s).
406.3.5 Testing precautions.
Testing of piping systems shall be performed in a manner that protects the safety of employees and the public during the test.
406.4 Test pressure measurement.
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 caused by leakage during the pressure test period.
The source of pressure shall be isolated before the pressure tests are made.
Mechanical gauges used to measure test pressures shall have a range such that the highest end of the scale is not greater than five times the test pressure.
406.4.1 Test pressure.
The test pressure to be used shall be not less than 1-1/2 times the proposed maximum working pressure, but NOT LESS THAN 3 psig (20 kPa gauge), irrespective of design pressure.
Where the test pressure EXCEEDS 125 psig (862 kPa gauge), 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.
406.4.2 Test duration.
Test duration shall be not less than 1/2 hour for each 500 cubic feet (14 m3) of pipe volume or fraction thereof.
When testing a system having a volume LESS THAN 10 cubic feet (0.28 m3) or a system in a single family dwelling, the test duration shall be not less than 10 minutes. The duration of the test shall not be required to exceed 24 hours.
406.5 Detection of leaks and defects.
The 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.
406.5.1 Detection methods.
The leakage shall be located by means of
1) an approved gas detector,
2) a noncorrosive leak detection fluid or
3) other approved leak detection methods.
406.5.2 Corrections.
Where leakage or other defects are located, the affected portion of the piping system shall be repaired or replaced and retested.
406.6 Piping system and equipment leakage check.
Leakage checking of systems and equipment shall be in accordance with Sections 406.6.1 through 406.6.4.
406.6.1 Test gases.
Leak checks using fuel gas shall be permitted in piping systems that have been pressure tested in accordance with Section 406.
406.6.2 BEFORE TURNING GAS ON.
During the process of turning gas on 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.
406.6.3 Leak check.
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 checked for leakage.
Where leakage is indicated, the gas supply shall be shut off until the necessary repairs have been made.
406.6.4 Placing appliances and equipment in operation.
Appliances and equipment shall not be placed in operation until after the piping system has been checked for leakage in accordance with Section 406.6.3, the piping system has been purged in accordance with Section 406.7 and the connections to the appliances have been checked for leakage.
406.7 Purging.
The purging of piping shall be in accordance with Sections 406.7.1 through 406.7.3.
406.7.1 Piping systems required to be purged outdoors.
The purging of piping systems shall be in accordance with the provisions of Sections 406.7.1.1 through 406.7.1.4 where the piping system meets either of the following:
1. The design operating gas pressure is greater than 2 psig (13.79 kPa).
2. The piping being purged contains one or more sections of pipe or tubing meeting the size and length criteria of Table 406.7.1.1.
406.7.1.1 Removal from service.
Where existing gas piping is opened, the section that is opened shall be isolated from the gas supply and the line pressure vented in accordance with Section 406.7.1.3. Where gas piping meeting the criteria of Table 406.7.1.1 is removed from service, the residual fuel gas in the piping shall be displaced with an inert gas.
406.7.1.2 Placing in operation.
Where gas piping containing air and meeting the criteria of Table 406.7.1.1 is placed in operation, the air in the piping shall first be displaced with an inert gas. The inert gas shall then be displaced with fuel gas in accordance with Section 406.7.1.3.
406.7.1.3 Outdoor discharge of purged gases.
The open end of a piping system being pressure vented or purged shall discharge directly to an outdoor location. Purging operations shall comply with all of the following requirements:
1. The point of discharge shall be controlled with a shutoff valve.
2. The point of discharge shall be located not less than 10 feet (3048 mm) from sources of ignition, not less than 10 feet (3048 mm) from building openings and not less than 25 feet (7620 mm) from mechanical air intake openings.
3. During discharge, the open point of discharge shall be continuously attended and monitored with a combustible gas indicator that complies with Section 406.7.1.4.
4. Purging operations introducing fuel gas shall be stopped when 90 percent fuel gas by volume is detected within the pipe.
5. Persons not involved in the purging operations shall be evacuated from all areas within 10 feet (3048 mm) of the point of discharge.
406.7.1.4 Combustible gas indicator.
Combustible gas indicators shall be listed and SHALL BE CALIBRATED in accordance with the manufacturer’s instructions.
Combustible gas indicators shall NUMERICALLY DISPLAY a volume scale from zero percent to 100 percent in 1-percent or smaller increments.
406.7.2 Piping systems allowed to be purged indoors or outdoors.
The purging of piping systems shall be in accordance with the provisions of Section 406.7.2.1 where the piping system meets both of the following:
1. The design operating gas pressure is 2 psig (13.79kPa) or less.
2. The piping being purged is constructed entirely from pipe or tubing not meeting the size and length criteria of Table 406.7.1.1.
406.7.2.1 Purging procedure.
The piping system shall be purged in accordance with one or more of the following:
1. The piping shall be purged with fuel gas and shall discharge to the outdoors.
2. The piping shall be purged with fuel gas and shall discharge to the indoors or outdoors through an appliance burner not located in a combustion chamber. Such burner shall be provided with a continuous source of ignition.
3. The piping shall be purged with fuel gas and shall discharge to the indoors or outdoors through a burner that has a continuous source of ignition and that is designed for such purpose.
4. The piping shall be purged with fuel gas that is discharged to the indoors or outdoors, and the point of discharge shall be monitored with a listed combustible gas detector in accordance with Section 406.7.2.2. Purging shall be stopped when fuel gas is detected.
5. The piping shall be purged by the gas supplier in accordance with written procedures.
406.7.2.2 Combustible gas detector.
Combustible gas detectors shall be listed and shall be calibrated or tested in accordance with the manufacturer’s instructions. Combustible gas detectors shall be capable of indicating the presence of fuel gas.
406.7.3 Purging appliances and equipment.
After the piping system has been placed in operation, appliances and equipment shall be purged before being placed into operation.