Pipelines: Potential for a Major Incident
DEPARTMENTS
ON HAZARDOUS MATERIALS
Pipelines carry a wide variety of products either as a liquid or as a gas. The products include such things as ammonia, propane, gasoline, kerosine, fuel oil, crude oil and natural gas. Because of the large quantities of product moving at any given moment, the high pressures, the large-diameter pipe, and the time it takes to shut down the system, there is a great potential for a major incident at a pipeline leak.
Let’s talk about the liquid-carrying pipelines and their three types of systems. First, there is the gathering system that transports crude oil from the wellhead to a central distribution system. These pipes range from 4 to 12 inches in diameter.
The trunk line system carries the crude oil from the distribution system to either a storage area or the refinery. If the product is piped to a storage area first, it must then be brought to the refinery by rail, barge or truck.
The distribution system brings the product to the marketplace after refining. The key to remember is that a distribution pipeline can carry any of the refined products at any given moment. As a result, an accident involving the release of gasoline (if that’s what was in the pipe at the time) would be much more of a problem than if the product was fuel oil. The interface between products ranges from a few to several hundred barrels with some mixing occurring. Very rarely, a physical separator (such as a large rubber ball) is used between products.
Once the product has moved through the pipeline, it is tapped off near its final destination and placed into storage tanks. From these tanks, it is moved to the marketplace.
Gas pipelines operate in much the same way as the liquid lines. However, since gases by definition are compressible, the techniques for moving them differ from that for moving liquids.
Gas pipelines can be divided into two categories: transmission mains and distribution mains. Transmission mains move the product from the refinery to distribution facilities all over the United States. These mains can be up to 36 inches in diameter.
At a central distribution facility, the transmission pipeline is tapped and the product is sent to large compressors for distribution to consumers. It is at this point that the odorant is added to the gas to give it its characteristic smell. Therefore, a leak in a transmission line might not be detected by smell.
The distribution mains carry the product from the central distribution facility to the consumer. These mains range in size from 24 inches down to ¼ inch, which feeds an ornamental gas light in front of a home.
Moving liquids and gases over long distances is very similar to moving water. Because of friction losses due to flow and head pressures for going up and down hill, intermediate pumping stations are needed. These stations are usually not manned, but operated by remote control from the central pipeline control room. The stations have built-in safety devices, automatic fire protection systems and alarms for any pressure drops. Equipment can then be shut down from the control room.
One of the major potential problems for pipelines is corrosion. To help reduce the problem of metal breakdown and corrosion, the pipeline owner introduces a small direct current onto the pipe to match the surrounding soil and moisture conditions.
To ensure that the correct flow appears on the pipe, tap-off points are provided and, using meters, the voltage can be measured. Any adjustments can then be made.
Leak detection along a pipeline right-of-way occurs in several ways. These include:
- Flying over the right-of-way looking for dead vegetation, construction equipment, earth depressions and product on the water.
- Driving the right-of-way looking for the same items as well as determining if there is any odor.
- Pressure gage readouts to ensure that the pressure is being maintained.
- Product in the sewer system.
Pipelines take special precautions when crossing under roadways, waterways and railroad tracks. These precautions are necessary because the traffic over the pipeline has a tendency to flex it, increasing the potential for breakage.
In order to overcome this problem, when a pipeline goes under a roadbed where flexure will be a problem, it is encased in a separate, thinner pipe. This casing does not have to withstand high pressure so it can be fairly thin. The ends of the casing are sealed to ensure that moisture cannot enter and cause corrosion. In addition, a corrosion current is also placed on the inner pipeline to prevent any corrosion.
One of the problems presented, however, is that the space between the inner pipe and the outer pipe is now sealed. Should a leak occur, and with the electrical source right on the pipe, a massive explosion could occur. To prevent this potential, a vent pipe is placed between the void space and vents this area to the outside. Remember, this is not a relief valve for the pipeline but simply a direct opening from the void space to prevent pressure buildup.
These vents can be a simple pipe with a down curve on top to prevent water from entering; an airtight pipe with a loose cap which will pop off if there is a pressure leak; or a T connection that is open on both sides. Look for these where the pipeline goes under major roads or railroads.
Finally, pre-fire planning is the key to a fire department successfully handling an incident. An officer, never before having seen the problems, cannot arrive on the scene and make intelligent decisions.
With the basic information presented in this month’s column, fire officers should:
- Plot all of the pipelines, including major distribution mains in their area.
- Determine the 24-hour number for contacting all of the pipeline agencies in the area.
- Develop evacuation plans for all of the exposures adjacent to the pipelines.
- Develop alternate approach routes in case the normal way is blocked by the incident.
- Develop water supply alternatives.
You can handle an incident involving a pipeline if you understand what you are dealing with.
