P is for - PIPELINE MARKERS - Since pipelines are usually buried underground, line markers and warning signs like the ones shown below are used to indicate their approximate location along the pipeline route. The markers and warning signs are in high-visibility colors (yellow or orange) and are located at frequent intervals along the pipeline right-of-way. The markers can be found where a pipeline intersects a street, highway, railway, or waterway, and at other prominent points along the route. The markers display the material transported in the line, the name of the pipeline operator, and a telephone number where the operator can be reached in the event of an emergency. Pumping stations, tank farms, and cleared rights-of-way also help signal that a pipeline is located nearby.
The first marker and the third marker and fourth marker ,are used anywhere a line crosses a road or a railway, they are usually on both sides,
The second one is a aerial marker , in this part of country they are usually yellow, with a number on them , and they are placed at about 4 mile intervals, so airplanes can see the area, in case theres a leak in line. they use the number to know what area the ground crew needs to look in.
The fifth one is a casing vent, when there gets to much pressure in the line, this is designed to bleed the pressure off.
Pipeline right-of-ways are well marked to help prevent damage from digging, the most common cause of pipeline accidents. Anyone planning to dig, especially in an area that appears to be a pipeline right-of-way or where the presence of a pipeline is suspected, should contact the 8-1-1 one-call center at least 72 hours in advance of beginning the excavation.
These calls are extremely important as they can help avoid pipeline ruptures resulting from digging which is the largest single cause of pipeline accidents. Based on the excavation location information provided in the call to the one-call center, the pipeline owner (and the owners of other nearby underground utilities) will be notified. The pipeline operator will locate and mark the specific location of the pipeline relative to the location of the planned excavation.