03 Pipes That Break and Leak Natural Gas Flashcards
Most people can smell odorized NG at less than:
1ppm
Numbers for the LEL
10% or 5,000ppm
Key components of residential gas distribution:
- Curb Box (one quarter turn valve)
- Service Line (buried pipe connecting gas distribution main to customers riser, usually 3/4” to 1”)
- Riser
- Pressure regulator
Piping outside the house must be …
Galvanized
Pressure regulator converts street pressure to:
0.25psi for home use.
Half Foot dial
(on the meter) will be moving if gas is being used in the building.
Inside diameter of corrugated stainless steel tubing (CSST)
3/4”
Issue with CSST:
Must be grounded effectively to prevent damage from direct or nearby lightning strikes.
When responding to lightning strikes check:
for NG leaks (ask neighbors as well)
School or Commercial Gas Meter:
Gas flows: Service valve (50 - 70 psi) > Regulator (25-30 psi) > Metering Valve > Meter > Metering Valve > Second Regulator (< 5psi) > Out for distribution to building.
Which valve is most important to close if we are ordered to shut off the gas to the building?
Service Valve
Bypass Valve
Usually closed and locked. It is opened in order to service or replace the meter itself. (Close meter valve and open bypass valve)
Gas distribution systems operate at pressures ranging from 0.25 to 99 psi and consist of:
mains, services, valves and meters
constructed of: steel, cast iron, ductile iron, wrought iron, or plastic (depends on age and type of service)
Utility companies are responsible for …
Entire distribution system and usually the gas meter
Low pressure distribution systems are around:
0.5 psi
No pressure regulator needed
Medium pressures vary from __________.
25-33 psi
Pressure regulator needed
High pressure systems are in the ________.
99 psi range.
Use only steel pipe and select plastic pipe
A Valve
Mechanical device used to control the flow of gas
1. Manual operation
2. Remote operation
3. Automatic operation
Grades of Leaks: Grade 1
Existing or probable hazard. to persons or property requiring immediate repair or continuous action until the conditions are no longer hazardous.
Grades of Leaks: Grade 2
A leak that is recognized as being nonhazardous at the time of detection but justifies scheduled repair based on probable future hazard.
Grade of Leaks: Grade 3
A leak that is nonhazardous at the time of detection and can be reasonably expected to remain nonhazardous.
Gate Stations:
- Reduce pressure in the line from transmission level (200 - 1500 psi) to distribution levels (0.25 - 200psi)
- Odorant is added
- Measures the flow of the gas to determine the amount being received by the utility.
From the gate station, the NG moves into distribution lines or “mains” that range from 2” to 24” in diameter.
Gas Processing Plants
Remove contaminates to provide a consistent quality NG to consumers.
Wellhead and Gas Fields
Gas pushes through the earth under pressures up to 5,000 psi.
