What is the difference between a transmission pipeline and a distribution pipeline?
Transmission pipelines are generally larger and operate at a higher pressure than distribution pipelines. Transmission pipelines transport the natural gas from the compressor stations and storage facilities to regulators which reduce the pressure before reaching the distribution system. The distribution system feeds the smaller lines that deliver gas to individual businesses or residences. What is the typical operating pressure of a Transmission line?
On PG&E'sGas Transmission Pipeline System Map
, PG&E included any transmission pipeline operating at or above 60 psig (pounds per square inch gauge). This means that additional miles of pipeline are included on PG&E's online map that might not be included on other maps that use a different parameter or definition of a transmission pipeline. Should I be concerned if the transmission pipeline in my community is more that 50 years old?
A properly maintained pipe can operate safely for 100 years or more. Although pipeline age is a relevant factor in reviewing the status of pipeline, it is not in itself a cause of concern. What is Maximum Allowable Operating Pressure (MAOP)?
Federal law requires that we establish a Maximum Allowable Operating Pressure, or MAOP, for all pipeline systems. MAOP includes a wide margin of safety and is set at a fraction of the pipe's calculated strength, which is the minimum pressure at which the pipe is expected to begin deforming. For example, the MAOP for pipelines in areas with more than 45 homes within 220 yards per linear mile on either side of the pipeline is set at no more than half the pipe's calculated strength. How is Maximum Allowable Operating Pressure (MAOP) determined?
MAOP is determined by one of three ways. First, MAOP can be determined by calculating the Specified Minimum Yield Strength, or SMYS, of the pipe. SMYS is the minimum pressure at which the pipe is expected to begin deforming. MAOP is then set at a fraction of the SMYS, thus allowing for a wide safety of margin. For example, MAOP is 50 percent or less for a pipeline in a more populated area. Second, MAOP can be set based upon pressure tests, where MAOP is set safely below the pressures used in the pressure test. Third, for pipe installed years ago, the MAOP can be based upon the pressure at which the pipeline has operated safely for years. Who sets Maximum Allowable Operating Pressure (MAOP) levels?
Federal law requires that pipeline operators establish MAOP for each section of pipeline or each distinct segment of a gas pipeline system. How is pipeline pressure controlled?
PG&E controls pressure on its pipeline system through a series of safety measures, including pressure regulator stations and overpressure protection devices. These systems operate to keep pressure within specified limits. They are surveyed and maintained regularly. More information about how our natural gas system operates can be found here
. Do you have emergency equipment that allows automatic shutdown of pipes?
PG&E has hundreds of automatic over pressure protection control valves that protect pipelines and are activated if the pressure gets too high. PG&E also has some lines with rupture control valves for specific needs and the 24 hour control center has the ability to shut down some pipeline systems via remote control. What is the difference between manual valves, automatic shut-off valves and remote controlled valves?
Manual valves can only be operated by a trained, federally-qualified individual at the valve location. Automatic shut-off valves are fully automated shut-off valves that will operate without human intervention when specific operating conditions on the pipeline arise. Remote-controlled valves can be remotely operated from a control center. How is a valve turned off? What is the process?
The process is different for each type of valve: remote controlled, automatic, manual.
- Remote controlled valves: these are valves operated by remote control from our 24-hour manned Gas Control Center
- Automatic shut-off valves: these are valves with control programs triggered to operate via a specified change in pipeline conditions and do not require remote control or personnel on site
- Manual valves: these are valves hand-operated by wheel and gear assembly or by wrench with an indicator to show whether it is open or closed