PIPELINES
DEFINITION
Pipelines consist of a series of pipes with pumps, valves, and control devices that convey fluids (e.g. water, oil, etc.), gases (e.g. natural gas) or solids suspended in liquid (e.g. sewage or some slurry mixtures used in industrial or mining processes). Modern communications lines such as fiber optics and electrical lines are also sometimes installed within pipelines. Pipelines may be constructed above or below ground depending on the conditions of the soil and the environment in which the pipeline travels.
SYNOPSIS
Pipelines are susceptible to extensive damage during earthquakes and in high seismic regions, often special connectors and fittings are used to allow the pipe to move elastically. Since pipelines often carry materials that are vital to sustain life and maintain property, they are usually referred to as lifelines. Pipeline networks may be placed above or below ground or run underwater. For the most part, pipeline networks are constructed below ground. All types of pipelines have been placed below ground including, energy pipelines like oil, natural gas, and gasoline, as well as water lines, sewer lines, storm sewers, telephone lines, television cables, and many types of electric lines.
Since natural resources like crude oil and natural gas are found in vastly different locations than where they are processed, it is necessary for pipeline networks to be placed underground in order to avoid safety and minimize their appearance.
Above-ground pipelines are subject to the same kinds of internal inertial loads as buildings and other structures, and their supports must be designed for these expected forces. Damage to buried pipeline systems can either be induced by permanent ground deformations or by transient seismic wave propagation. Permanent ground deformations can be categorized as surface faulting, landsliding, seismic compaction (settlement), or liquefaction. Along with transportation and utility systems, pipelines are lifeline components.
The United States has the largest network of energy pipelines, both oil and natural gas, of any nation in the world. The oil pipeline network alone in the U.S. is more than 10 times larger than that in Europe.
Components of Pipelines:
Pipe sections are made from a variety of materials including; reinforced concrete, steel, polyurethane, clay, etc. The type of material used for an individual pipeline network is specific to the type of material flowing through the pipe as well as the environment in which the pipeline travels. Other important components of pipelines are the connectors, such as couplings, tees, elbows, etc., shown in Figure 1. These connectors are used to join lengths of individual pipe sections as well as to divert the pipeline in one or many different directions. Welded steel pipe is generally more resistant than piping connected with other methods to damage from inertial forces (above-ground piping, such as in buildings or industrial facilities, or where transmission lines are above-ground) as well as more resistant to imposed soil deformations if buried. Incompatible motions between one section of pipe and another at a right-angle connection or where a tank is connected to a pipe, is often the most likely location of damage. Valves are another component of pipelines that play an integral part in the pipeline network (Figure 2). These valves, which are primarily used in fluid filled pipelines, are used to control the flow within and around the pipeline network. For pipelines traveling up an incline, pumps may be required to push the fluid up the incline. The pump component is especially useful on pipelines that travel through mountain regions, like the Alaskan Pipeline shown in Figure 3. The ability of pipelines to accommodate very large deformations, in this case from faulting, if properly designed is shown by the performance of the Alaskan Pipeline in the November 2003, Denali Earthquake.
The Trans-Alaskan Pipeline: A Brief Description of the Trans-Alaskan Pipeline
Although used less frequently than buried pipelines, above ground pipelines are just as effective in transporting products from one location to another. However, a clear disadvantage is that above ground pipelines may be visible to the public and are susceptible to damage from humans. A well known example of an above ground pipeline is the Trans-Alaska Pipeline. This pipeline, which travels through the environmentally sensitive Tundra, was build above ground in order to prevent the warm oil inside the pipe from melting the permafrost. This elevated pipeline also features a staggered shape, (Figure 4) which provides elasticity to the system during earthquake loads. It took $8 billion (U.S. dollars) and two years to build the Trans-Alaska Pipeline. It is said to be one of the most difficult engineering feats of all time. The pipeline is 5937 km long and has an outside diameter of 13.12 m. The pipeline carries crude oil from Prudhoe Bay on the Northern Slope of Alaska to the ice- free port of Valdez in southern Alaska. It crosses three mountain ranges, 34 major waterways, and 800 small streams. Figure 5 and Figure 6 detail the obstacles the pipeline had to overcome as well as the route which the pipeline travels. The oil travels at 40.1 kph and takes 6.2 days to travel the length of the pipeline.
CONTENT IN DEPTH
Buried Pipelines: Chapter 23 of the Earthquake Engineering Handbook, edited by Wai-Fah Chen and Charles Scawthorn, discusses pipeline performance in past earthquakes, as well as the various types of failure modes.
http://www.engnetbase.com (search keyword “Pipelines”)
Construction of Marine and Offshore Structures, Second Edition: This site provides an online copy of the book written by Ben C. Gerwick which outlines the procedures for constructing marine and offshore structures.
http://www.engnetbase.com/ejournals/books/book_summary/toc.asp?id=502
Pipe Line & Gas Industry: This is an online publication that presents information on general aspects of the oil and gas pipeline industry.
http://www.pipe-line.com/
Pipeline and Gas Journal.com: This site provides journal articles on a variety of pipeline related issues.
http://www.undergroundinfo.com/PGJ/pgj_home.html
The American Lifelines Alliance (ALA): This site provides information about the public-private partnership project, which has a specific seismic mission, funded by the Federal Emergency Management Agency (FEMA) and managed by the National Institute of Building Sciences (NIBS). The Alliance has the goal of reducing risks to lifelines from hazards.
http://www.americanlifelinesalliance.org/
The Association of Bay Area Governments (ABAG): This site provides information on a variety of earthquake-related hazards (http://quake.abag.ca.gov/). Also included in this site, is a link that discusses the damaging effects of utility pipeline leaks. (http://www.abag.ca.gov/bayarea/eqmaps/liquefac/pipes.html).
Endbridge Pipelines Inc.: This site is the homepage for Endbridge Pipelines Inc. which operates the world's longest and most sophisticated crude oil and petroleum products pipeline system.
http://www.enbridge.com/pipelines/
The Alyeska Pipeline Service Company: This site is the homepage of the company responsible for the operation of the Trans-Alaska Pipeline.
http://www.alyeska-pipe.com/
Pacific Gas and Electric (PG&E) Gas Transmission: Northwest: This site outlines the steps that PG&E employees take to ensure the integrity of their pipelines and the safe transmission of liquid natural gas.
http://www.pge-nw.com/company_info/?content=/safety/our_role.html&nav=nav.html?navObj=elThree
Southern California Gas Company: This site provides information on how to turn off your natural gas lines in the event of an earthquake.
http://www.socalgas.com/general/safety/whattodo.shtml
Pacific Earthquake Engineering Research Center (PEER): Providing data, models, and methods needed to improve the earthquake reliability and safety of lifelines systems, including electric and gas transmission lines.
http://peer.berkeley.edu/
Pipeline Design
The design of a pipeline network is a process which must take a variety of factors into consideration. Engineers must consider the types of loads that are going to be imposed on the pipeline, the environment that the pipeline will travel in, and the type of material that the pipeline is going to convey. Whether a pipeline is onshore or offshore, there are an assortment of different loads that could potentially damage the pipeline, including bending moments, internal or external pressures, surrounding soil, and dynamic loading. The capacity of a pipeline to resist bending, as well as axial tension or compression, is particularly important in areas where there is a potential for differential settlement or during the construction process when lengths of pipe are placed on uneven surfaces. While seismic considerations are important, there are other criteria, such as initial construction cost and durability over the years with the associated maintenance cost,
When designing liquid pipeline networks such as fire fighting water network systems, large cooling water systems, and long distance liquid pipelines, fatigue loading must be taken into consideration. Fatigue loading can either be caused by a variation in internal fluid pressure and/or temperature or by a phenomenon know as water hammer, were by a severe dynamic shock force and vibration on the piping structure is introduced due to the sudden closer of a system valve. Dynamic loading of buried pipelines, including earthquake loads, moving vehicle loads, railroad crossings, pile driving, blast loading and impact loads due to falling objects, is another important design consideration that engineers must take into account. Dynamic loading is a case that involves a variety of different loading combinations, including flexural loads and fatigue loads. For example a pipeline that travels beneath a major truck route. The pipeline must be strong enough to withstand the repeated flexural loads that are imposed every time a truck passes over as well as the fatigue loads that are present ever time the pipe deforms. Designing a pipeline for earthquake imposed loads is difficult since there is such a variety of ways in which the system might deform relative to the ground. However, through the use of technologically advanced connections and state of the art materials, engineers are finding ways to design pipelines to withstand a gamut of imposed loads.
Pipeline Construction
Unlike the planning phase for a building structure on one site, the planning phase of a pipeline project is the most crucial and usually begins years in advance. Some initial steps in the planning process include determining market need, route selection, pipeline design, land acquisition and permitting. Each of these steps, and many others, play an intricate role in allowing the construction phase of the project to proceed without any delays.
In general, the design and construction of a pipeline occurs in three stages; pre-construction, construction, and post-construction. The pre-construction phase involves engineering and design, land acquisition, and environmental impact studies. In the United States, all federal and state requirements must be met by the pipeline planning team as well as obtaining any permits that pertain to the construction of the pipeline. Planning teams must also respond to any and all concerns that are brought forth by the local community. In order to secure easement rights to place the pipeline along the selected route, land or right-of-way agents, hired by the pipeline operator, are assigned to work with potential landowners to meet their needs.
On average, the actual construction phase of a project occurs in the shortest amount of time. But the construction phase can only begin after all of the pre-construction actions have been accomplished. Before the pipeline can be buried or erected, the right-of-way must be cleared and prepared for construction. Once the right-of-way is ready, the pipeline is assembled and is either lowered into a pre-dug trench, bored under waterways or roads, or placed above ground on system of columns and hangers. Figures 1 and Figure 2 are examples of buried pipelines still in the placement stage of the construction process.
The post-construction phase of a pipeline project primarily addresses the restoring of the land affected by trenching and placement of the pipeline. Before the pipeline goes on line, the pipe and components are tested in the field with water pressure, weld x-rays and an assortment of other inspection tests. Each stage of the post-construction process is overseen by qualified inspectors to ensure compliance with the engineering plan, codes, permit conditions, landowner and easement agreements, and regulatory requirements. For more information and photographs of the pipeline construction process, please visit Welded Construction Company, L.P at, http://www.weldedconstruction.com/process.html.
Pipeline Operation and Maintenance:
Whether they are carrying oil, water, or electrical power, most pipelines are required to operate all-day, everyday. With the help of powerful pumps, oil additives and the laws of physics, pipelines can transport product efficiently and effectively, with little or no down time.
With today’s advancements in technology, pipeline operators can watch the rate, pressure and movement of product at points along the system. This technology also enables operators to detect any breaks in the pipeline, allowing for quick containment of spilled product and minimization of environmental impact. While every pipeline company strives to achieve incident-free operation, accidents do happen. Figure 3 shows the aftermath of a ruptured natural gas pipeline in Venezuela. Pipeline operators are trained to shut down pipeline systems quickly and safely when accidents do occur.
One of the most crucial tasks in pipeline operation is maintenance. Just like the pipeline, pipeline maintenance crews work all-day, everyday. Their job is to ensure the integrity of pipeline infrastructure. These maintenance crews ensure that welding operations, valve inspections, pipeline repairs, corrosion prevention system checks and electronic equipment maintenance are performed safely and according to procedures that have been established by code or by the company.
Under-sea Gas Transmission Pipeline near Osaka, Japan:
In general, underwater pipelines are used to transport oil and gas products from offshore drilling structures to mainland refineries. However, in countries where the ability to run a new pipeline is limited due to for example, existing infrastructure, if the continent or region is near water, underwater pipelines may be placed offshore in order to alleviate constructability issues. One example of this type of offshore pipeline is the gas transmission pipeline connecting the Senboku Liquid Natural Gas (LNG) terminal to the Hokko pressure regulating station near Osaka, Japan. Figure 4 shows the route of this new pipeline. This pipeline is 96.5 km in length, 769 millimeters (mm) in diameter and is buried 39.9 m below the seabed of the Osaka Bay area. The pipeline is encased in a shield tunnel, with an inner diameter of 2.4 m, which was designed to protect the pipeline from the elements and external forces. If this pipeline had been run above ground, heavy traffic in the Osaka Bay area would have made construction very difficult.
To achieve the engineering feat of placing this pipeline under the seabed and through reclaimed land, shielded tunnel and horizontal directional drilling methods were implemented for the installation, see Figure 5. Since the pipeline would be transitioning between reclaimed lands (built of fill material) and the bays seabed, engineers had to design this structure to resist the effects of subsidence and seismic forces. In order to protect the pipeline from the differential settlement of the reclaimed fill, flexible segments were used at the interface between the reclaimed land and the seabed. To protect against seismic activity, the joints of each tunnel segment were outfitted with elastic washers that provided flexibility for the system.