Your Subsea News reports that subsea pipelines have become more economical due to recent innovations and new technology. A current project mentioned in Offshore Magazine is Australia's Ichthys in the Timor Sea.Now 50% complete, it combines three different offshore facilities with a 552 mile (889 km) pipeline. The FSPO facility includes floating production, storage and offloading, tankers, plus the pipeline to move the gas to Darwin, on Western Australia's coast. When finished, it will be the fifth-longest subsea pipeline in the world.
Damage of a subsea pipeline can be costly both environmentally and for the company involved. In 2000, a Shell Pipeline Company crude oil line was ruptured by a ship anchor. 94,000 gallons of crude were spilled off the Louisana coast creating an oil slick 2 miles by 7 miles wide. In 2006, the Prudhoe Bay oil spill was caused by corrosive build-up inside the pipe. An estimated 5,000 barrels spread over the Arctic tundra and in the bay. Also in 2006, a pipeline exploded two miles from shore near New Orleans after a tugboat pushing two barges hit it. This year, a contractor vessel hit the Houston-to-Houma (Ho-Ho) crude oil pipeline, spilling 364 barrels of crude.
There are basically two different types of subsea pipelines: A flowline is used to connect subsea wellheads, manifolds and a drilling platform within an individual drilling project. An export pipeline is one employed in the transport of oil, gas or water to shore.
Subsea pipelines vary in diameter from 3 inches for gas lines to 72 inches for high capacity lines. The pipes are usually protected against corrosion by coatings, concrete or fiberglass wrappings, and, in order to compensate for a pipeline’s negative buoyancy when carrying low density materials, a final concrete coating for weight. Pipes are often laid down in an open trench if there is a large amount of anchoring or trawling activity expected; alternatively, a pipeline may be covered with soil or rocks, although when covering the pipeline, repairs become more costly and complicated.
Placing the pipeline involves careful planning to choose the most efficient and safest route. Considerations are myriad and include the condition and makeup of the seabed, currents and waves in the area, potential movement of the seabed, whether there are any ice-related issues, where to place joints or turns, the amount of commercial fishing and trawlers in the area, vessel anchoring in harbor areas, and military activities. The Ichthys pipeline mentioned above traverses a variety of seabed types – sand, clay, silt, rock – and includes a large dogleg to avoid a 98 foot escarpment.
In addition to these concerns, simple manufacturing defects, corrosion and even hurricanes can cause failures.
Hurricanes (some with winds up to 130 mph have been recorded) can create unusual currents and waves, and even undersea mudslides. In 2010, for example, USA Today reported that Hurricanes Katrina and Rita caused 124 pipeline spills, with 17,700 barrels of petroleum products released into the Gulf of Mexico. At that time there were more than 31,000 miles of pipelines on the Gulf seafloor -- a number that surely has grown in the past four years.
The actual movement of liquid through the pipeline can initiate pipeline failure. Pump pressure causes longitudinal movement which, over many years, can result in thinning of the pipe walls.
Pipeline operators have inspection and maintenance programs in place to combat pipeline failure due to corrosion and materials defects, but damage to pipelines by passing or anchoring commercial vessels is a real threat to pipeline safety.
Some pipeline damage can be avoided by the use of AIS technology to monitor ship movements. As reported on The Digital Ship site, a current AIS pilot project between the Coastal and Marine Operators (CAMO), the US Coast Guard, and PortVision is underway regarding submerged pipelines. PortVision provides AIS-based Offshore Asset Protection to automatically notify pipeline operators and AIS-equipped vessels when it appears that a vessel is encroaching within a safety zone of pipelines or other fixed offshore assets.
In September, PortVision received an FCC license which allows it to transmit AIS safety messages directly to the wheelhouse of any vessels that appears to be stopping or encroaching on a fixed asset such as an offshore pipelines. These automatic notifications will proactively alert vessels and help to avoid the damage to infrastructure and loss of lives that pipeline disasters have caused. Read more about PortVision's efforts here.