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Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves (2024)

Chapter: 2 Background on Transmission Pipelines and Shutoff Valves

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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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2

Background on Transmission Pipelines and Shutoff Valves

This chapter provides background on the network of transmission pipelines in the United States. It begins by discussing the shared and distinct characteristics of the two main types of transmission pipelines, gas and hazardous liquid, including statistics on the use, scope, and age of their networks. Because the report’s focus is on pipelines in populated and environmentally sensitive areas, statistics are then provided on transmission pipeline mileage in high consequence areas (HCAs) and Class 3 and 4 locations.

Additional background is then provided on the valves used for controlling and shutting down pipeline flows during emergencies. The background includes information on the types of valves that are used for these purposes and their actuation methods, including automatic and remote-control shutoff valves (referred to collectively as rupture mitigation valves [RMVs]).

This discussion is accompanied by an overview of the methods used by pipeline operators to monitor and control the operations of their pipelines and valve actuations, focusing particularly on the role of supervisory control and data acquisition (SCADA) systems. The chapter concludes with estimates of the prevalence of RMVs on pipelines in HCAs.

U.S. PIPELINE SYSTEM SCOPE AND USE CHARACTERISTICS

Vast networks of pipelines move most of the natural gas and hazardous liquids shipped long distances across the United States. These networks are composed of three major categories of pipeline: gathering, transmission, and distribution. In general, gathering pipelines transport raw materials (e.g., crude oil, unprocessed natural gas) from the wellhead or production

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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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area to storage tanks and processing facilities. Depending on the commodity, larger-diameter transmission pipelines are then used to transport shipments from these upstream facilities to midstream and downstream storage depots, refineries, export terminals, distribution centers, and large end-point users such as electric utilities and chemical and manufacturing plants. In the case of petroleum products, transmission pipelines are also used to move product from refineries to downstream intermediaries and users. Distribution pipelines are used for gas systems and typically connect a natural gas distribution center to residential and commercial end-point users.

In keeping with the Statement of Task and legislative charge, this report focuses on the large-diameter (6 or more inches) onshore transmission pipelines that are used mainly for transporting gas and liquid commodities in high volume over long distances, as opposed to pipelines used for end-use distribution and field gathering (some of the latter can also have large diameters). Because they transport hazardous materials in large volumes under high pressure, transmission pipelines are subject to different safety regimes and regulations than pipelines in distribution and gathering systems, which have their own risks for consequential failures and imperatives for safety vigilance.

Both hazardous liquid and gas transmission pipelines are usually made from mild carbon steel and buried 2 or more feet underground. However, the two systems are configured and operate differently and are therefore distinguished and treated separately under federal safety regulations, as will be discussed more in Chapter 3. Gas transmission pipelines ae mainly used to transport natural gas in a gaseous state under high pressure (400 psi to 1,400 psi).1 The gas is typically transported from processing plants to storage depots, export facilities, and points of distribution known as “city gates,” where the product is delivered to homes, businesses, and industrial plants. Because of the ubiquity of natural gas demand, the 300,000-mile gas transmission pipeline network is dispersed across the country but with higher density in the gas-producing states along the Gulf Coast (see Figure 2-1, which also includes offshore mileage). Total U.S. mileage of the onshore hazardous liquid and gas transmission pipeline networks is shown in Table 2-1.

Hazardous liquid pipelines are used mainly to transport crude oil, refined petroleum products, and highly volatile liquids (HVLs).2 The latter includes ethane, propane, butane, pentane, liquid carbon dioxide, and anhydrous ammonia, which have high vapor pressures and are highly compressed in pipelines. The majority of the 220,000 miles of hazardous liquid pipeline crosses the interior of the United States to connect storage depots

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1 About 1,500 miles of gas pipelines are used to transport hydrogen.

2 About 5,000 miles of hazardous liquid pipeline are used to transport carbon dioxide.

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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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Image
FIGURE 2-1 Map of U.S. gas transmission pipelines, June 2023.
SOURCE: Pipeline and Hazardous Materials Safety Administration. National Pipeline Mapping System, https://www.npms.phmsa.dot.gov.
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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TABLE 2-1 Mileage and Diameters, U.S. Network of Onshore Hazardous Liquid and Gas Transmission Pipelines, 2021

Type of Transmission Pipeline Approximate Mileagea Diameter Range (inches)
Gas 300,000 4–48
Hazardous Liquid 220,000b 4–48
Crude oil 70,000 4–48
Petroleum products 74,000 4–40
HVL 76,000 4–30

a This value excludes transmission pipelines used to transport products other than crude oil, petroleum products, and HVLs.

b This report focuses on onshore pipelines having diameters of 6 inches or more.

SOURCE: Pipeline and Hazardous Materials Safety Administration, Gas Transmission and Hazardous Liquids Annual Report Data, https://www.phmsa.dot.gov/data-and-statistics/pipeline/gas-distribution-gas-gathering-gas-transmission-hazardous-liquids.

with one another and refineries (see Figure 2-2, which also shows offshore mileage).3 In the case of crude oil pipelines, their starting points are usually inlet stations in oil-producing regions and large storage centers, while their end points are usually other storage facilities, refineries, and export terminals. Some crude oil pipelines move product from import terminals to storage depots and refineries. Conversely, the transmission pipelines used to transport refined products such as gasoline, diesel, and jet fuel usually begin at refineries and terminate at storage farms, export terminals, and end-use distribution centers. HVL pipelines move their liquid shipments between processing facilities, refineries, and petrochemical plants.

Transmission pipelines vary in design, fabrication, materials, configuration, and components depending on many factors including age, markets served, terrain crossed, and whether additional shipping services are provided, such as storage and transloading. Pipeline characteristics will be influenced by location, as pipelines span urban, suburban, and rural settings as well as a wide range of terrains and environments that expose them to different soil chemistries, moisture levels, temperature extremes, and risks of external damage from human activity (e.g., excavation) and natural hazards (e.g., floods, earthquakes, landslides). Their design and construction features will also reflect installation practices and technologies available when they were fabricated and installed, resulting in variations in pipe materials, external coatings, welding techniques, and valve types and placements. Figure 2-3 shows the age variation in the hazardous liquid and gas

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3 By virtue of geography, the Southern and Central Plains regions have long been convergence points for crude oil pipelines.

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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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FIGURE 2-2 Map of U.S. hazardous liquid pipelines, June 2023.
SOURCE: Pipeline and Hazardous Materials Safety Administration. National Pipeline Mapping System, https://www.npms.phmsa.dot.gov.
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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transmission pipeline systems. Note that more than 50% of gas transmission pipeline mileage was installed before 1970. While the hazardous liquid network contains more newly constructed pipelines, the share of mileage installed more than 50 years ago still approaches 50%.

Figure 2-3 also shows the diameters of hazardous liquid and gas transmission pipelines in the U.S. networks. Note that gas transmission pipelines tend to have larger diameters than hazardous liquid pipelines, due in part to the added volume required for moving low-density gaseous products. More than half of HVL pipelines have diameters of 10 inches or less. Most hazardous liquid pipelines, both HVL and non-HVL (i.e., crude oil, refined products), have diameters of 16 inches or less, whereas nearly half of gas transmission pipelines exceed 16 inches in diameter.

Rarely shutting down, natural gas transmission pipelines operate continuously to ensure service to end users.4 They are usually configured with compressor stations placed every 20 to 80 miles depending on factors such as topography, line configuration, and pipe size. Operators monitor volumes of gas being moved through the pipelines as well as volumes of gas being delivered, often directing the flow from various product sources to different delivery points.

Consumer and utility demand (e.g., for home heating and electricity generation) plays a large role in determining the volumes of gas moved during any given time of day and season. By comparison, most hazardous liquid pipelines operate by moving batches of different grades of crude oil (i.e., light and heavy grades) and batches of different petroleum products (gasoline, diesel fuel, and jet fuel) and HVLs. Pumps are spaced every 20 to 80 miles depending on many factors, including terrain profile. Pipeline operators prefer to start and stop their systems as infrequently as possible to maintain a continuous flow; however, a pipeline may start and stop at various time intervals to allow for in-line inspection and maintenance. Repetitive starts and stops are also avoided because they can create cyclic fatigue issues and the potential for crack propagation.

PIPELINES IN HIGH CONSEQUENCE AREAS

As Chapter 1 explains, during the 1990s the U.S. Department of Transportation (U.S. DOT) began to question the adequacy of a regulatory approach that depended heavily on a common minimum set of standards for all pipelines that did not account for the wide variability in pipeline designs, materials, fabrication methods, operations, age, products transported, and locations.

National Transportation Safety Board (NTSB) investigations of a number of catastrophic pipeline failures had revealed inadequacies in the minimum

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4 Intermediate compressors may be started or stopped to accommodate demand fluctuations.

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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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Image
FIGURE 2-3 U.S. onshore hazardous liquid and gas transmission pipeline systems, decade of installation and pipeline diameter, 2021.
SOURCE: Pipeline and Hazardous Materials Safety Administration, Gas Transmission and Hazardous Liquids Annual Report Data, https://www.phmsa.dot.gov/data-and-statistics/pipeline/gas-distribution-gas-gathering-gas-transmission-hazardous-liquids.
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×

standards, particularly for pipelines that traversed populated and environmentally sensitive areas that warranted additional protections.5 Many existing pipelines, for instance, had been installed decades earlier in what were once rural locations but that had since become more developed and heavily populated. Meanwhile, the public was demanding increased vigilance in protecting people and the environment from pipeline releases.

Congress responded to this interest by passing legislation (49 USC 60109(a)) during the 1990s requiring federal standards for identifying gas transmission pipelines located in populated areas and hazardous liquid pipelines that crossed navigable waters, population centers, and areas unusually sensitive to environmental damage. In the identified locations, now referred to as HCAs, the legislation called on U.S. DOT to establish supplemental requirements for operators to reduce risks, including requirements for enhanced inspection and standards for leak detection and notification, for when a pipeline operator must install an emergency flow restricting device (EFRD), and for procedures and systems (49 USC 60102(f)(2) and 49 USC 60102(j)).

These legislative requirements, along with NTSB recommendations, were factors in prompting U.S. DOT to promulgate the integrity management (IM) rules for hazardous liquid pipelines and gas transmission pipelines starting in 2000, as discussed in Chapter 1. The IM rules applied to pipelines in locations designated as HCAs and in locations where a release could affect an HCA (applicable to hazardous liquid pipelines because releases can spread long distances). It was understood that the amount of pipeline mileage in HCAs would change over any given time as pipelines were constructed and retired from service but also due to changes in the land uses where existing pipelines are located.

High Consequence Area Definitions

In the case of HCAs for hazardous liquid pipelines, their designations originated from an existing industry consensus standard developed by the American Society of Mechanical Engineers (ASME): B31.4, “Liquid Petroleum Transportation Piping Systems,” subsection 434.15.2, “Mainline Valves.” It established standards for installing mainline valves on both sides of major river crossings and at other locations along the length of a pipeline in accordance with the terrain traversed. U.S. DOT used the ASME standard to define HCAs for hazardous liquid pipelines as follows:

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5 Bellingham, Washington; Simpsonville, South Carolina; Reston, Virginia; and Edison, New Jersey.

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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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  • A commercially navigable waterway,
  • A high population area (an urbanized area that contains 50,000 or more people and has a population density of at least 1,000 people per square mile),
  • Another populated area (a place that contains a concentrated population or commercial activity), and
  • An unusually sensitive area (drinking water or ecological resource area).

U.S. DOT also used an ASME standard for designating HCAs for gas transmission pipelines. ASME’s class location concept, as discussed in Chapter 1, was incorporated into federal regulations during the early 1970s. ASME had established the concept to set different requirements for the design of gas transmission pipelines depending on the population densities of the areas through which the pipeline traversed (as part of ASME B31.8, “Gas Transmission and Distribution Piping Systems”). Four class locations were established, Class 1 to 4. Class 1 locations are very sparsely populated areas, such as farmland or rural areas, with no or few individuals potentially located adjacent to a pipeline right-of-way. On the other end of the spectrum, Class 4 locations are areas of high population density, such as urban or city areas, with many individuals potentially located adjacent to the pipeline right-of-way. In addition to requiring IM programs for gas transmission pipelines in Class 3 and 4 (i.e., populated) locations, the regulations required them for other identified sites defined as HCAs because they contain buildings that house people who have limited mobility and are in the vicinity of where people congregate. These designations stemmed from concern that releases from gas transmission pipelines can lead to explosions and fires that will harm people and property.

To illustrate how pipeline miles can be distributed across a metropolitan region and traverse HCAs and Class 3 and 4 locations, Figure 2-4 contains a map derived from the Pipeline and Hazardous Materials Safety Administration’s (PHMSA’s) National Pipeline Mapping System for Harris County, Texas. In the heart of the country’s oil and gas producing region, Harris County’s pipeline densities are likely to be higher than in many other regions of the country, but the map serves the purpose of illustrating how pipeline systems and HCAs can overlap.

Pipeline Mileage in High Consequence Areas

The amount of hazardous liquid and gas transmission pipeline mileage in HCAs and Class 3 and 4 locations in 2021 is summarized in Table 2-2. That year, about 19% of gas transmission pipeline mileage was located in an HCA or Class 3 and 4 locations. The hazardous liquid network is separated

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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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FIGURE 2-4 Hazardous liquid and gas transmission pipelines, Harris County, Texas, October 2023.
SOURCE: PHMSA. National Pipeline Mapping System. https://pvnpms.phmsa.dot.gov/PublicViewer.
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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into non-HVL (i.e., crude oil, refined products) and HVL mileage. About 40% of non-HVL mileage was located in an HCA in 2021, and about 40% of HVL mileage was located in an HCA. Table 2-2 shows mileage by type of HCA; however, because different types of hazardous liquid HCAs overlap, their totals are not additive.

Table 2-2 also shows how mileage in HCAs and Class 3 and 4 locations has changed over time by comparing 2010 to 2021 mileage. Gas transmission pipeline mileage in HCAs changed very little during this period, while non-HVL mileage in HCAs grew by nearly 7%. It is notable that the amount of HVL mileage in HCAs grew by 41%, as the total HVL pipeline network grew in mileage by 31%.

Operator Profiles

A review of pipeline operator reports of system mileage reveals that large shares of the mileage in HCAs and Class 3 and 4 locations are managed by a relatively small number of operators.

PHMSA’s annual report data for 2021 indicate that there were 563 operator identification numbers (OPIDs) for gas transmission pipelines and 516 OPIDs for hazardous liquid (HVL and non-HVL) pipelines located in HCAs and Class 3 and 4 locations. By consolidating instances where a single operator has multiple OPIDs, the total number of operators falls by more than half. After this consolidation is made, Table 2-3 shows that in 2021 just 12 operators managed more than 60% of gas transmission pipeline mileage in HCAs and Class 3 and 4 locations, while 18 operators managed more than 75% of the hazardous liquid pipeline mileage in HCAs. Table 2-4 shows pipeline mileage in HCAs and Class 3 and 4 locations by the largest gas transmission and hazardous liquid pipeline operators in terms of system mileage.

PIPELINE SHUTOFF VALVES

The placement of sectionalizing valves on pipelines serves operating purposes to manage the flow of product and safety purposes to mitigate the consequences of a rupture or leak by allowing for the flow to be shut off from a failed segment. These valves can also serve other purposes, such as closing a pipe segment for maintenance, construction, pressure relief, and changing products. The following sections describe common valve types and actuation methods used for shutting down pipeline flows to isolate pipeline segments.

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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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TABLE 2-2 Hazardous Liquid and Gas Transmission Pipeline Mileage in HCAs and Class 3 and 4 Locations, 2010 and 2021

2010 Mileage 2021 Mileage Percent Change
Gas Transmission
U.S. Network Total 299,481 298,748 –0.2
HCAs and Class 3 and 4a
HCA 20,022 21,108 +5.4
Class 3 33,884 33,688 –0.6
Class 4 1,365 871 –36
Hazardous Liquid (Non-HVL)
U.S. Network Total 123,948 153,364 +24
HCA Totalb 57,230 61,000 +6.6
High Population Areas 18,968 21,030 +10.9
Other Population Areas 27,624 31,597 +14.4
Drinking Water Resources 25,711 26,233 +2
Ecological Resources 21,641 23,228 +7.3
Commercially Navigable Waterways 8,116 7,173 –11.6
Hazardous Liquid (HVL)
U.S. Network Total 57,887 75,601 +31
HCA Totalb 20,786 29,356 +41
High Population Areas 5,514 8,398 +52.3
Other Population Areas 8,829 15,453 +75
Drinking Water Resources 6,641 7,800 +17.5
Ecological Resources 7,658 9,910 +29.4
Commercially Navigable Waterways 2,169 2,311 +6.5

a PHMSA does not calculate total HCA and Class 3 and 4 mileage for gas transmission pipelines, which cannot be determined by adding the reported mileage in each location due to overlaps among HCAs and Class 3 and 4 locations.

b Hazardous liquid mileage by type of HCA is not additive because HCA types can overlap geographically.

SOURCE: Pipeline and Hazardous Materials Safety Administration, Gas Transmission and Hazardous Liquids Annual Report Data, https://www.phmsa.dot.gov/data-and-statistics/pipeline/gas-distribution-gas-gathering-gas-transmission-hazardous-liquids.

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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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TABLE 2-3 Mileage and Number of Operators of Hazardous Liquid and Gas Transmission Pipelines in HCAs and Class 3 and 4 Locations, 2021

Operators Mileage Within an HCA or Class 3 and 4 Location Number of Operatorsa Total Mileage of All Operators Average Miles per Operator Percent of All Mileage
Gas Transmissionb
Less Than 1 Mile 50 18 0.4 0.1
1–15 Miles 115 622 5.4 2.0
15–50 Miles 35 957 27.3 3.1
50–100 Miles 24 1,779 74.1 5.8
100–500 Miles 35 8,171 233.5 26.8
500–1,000 Miles 4 3,096 774.1 10.2
>1,000 Miles 8 15,859 1,982.4 52.0
TOTAL 271 30,502 112.6 100
Hazardous Liquid (HVL and Non-HVL)
Less Than 1 Mile 10 5 0.5 0.01
1–15 Miles 72 467 6.5 0.5
15–50 Miles 49 1,509 30.8 1.7
50–100 Miles 13 870 66.9 1.0
100–500 Miles 36 8,648 240.2 9.6
500–1,000 Miles 11 7,675 697.8 8.5
>1,000 Miles 18 71,182 3,954.6 78.8
TOTAL 209 90,356 432.3 100

a The email domains in each OPID reporting record were used to consolidate operators in cases where a single company operates multiple pipelines and uses multiple OPIDs.

b The gas pipeline data do not include mileage that falls under 49 CFR Part 192.710, which is any transmission pipeline segment with a maximum allowable operating pressure of ≥30% of the specified minimum yield strength that is located in a Class 3 and 4 location or a moderate consequence area, if the pipeline segment can be inspected with an instrumented inline tool and the location is not classified as an HCA. While this mileage does include some Class 3 and 4 data, one cannot determine the mileage of each class based on the information provided in the Annual Report.

SOURCE: Pipeline and Hazardous Materials Safety Administration, Gas Transmission and Hazardous Liquids Annual Report Data, https://www.phmsa.dot.gov/data-and-statistics/pipeline/gas-distribution-gas-gathering-gas-transmission-hazardous-liquids.

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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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TABLE 2-4 Hazardous Liquid and Gas Transmission Pipeline Operators with the Most Pipeline Mileage in HCAs and Class 3 and 4 Locations, 2021

Operator Name Operator’s Pipeline Miles in HCAs and Class 3 and 4 Locations Percentage of Total Pipeline Miles in HCAs and Class 3 and 4 Locations
Gas Transmission
Kinder Morgan 2,867 9.4
PG&E 2,335 7.6
Energy Transfer 2,112 6.9
TC Energy 1,973 6.5
Duke Energy 1,958 6.4
Williams 1,657 5.4
Enbridge 1,606 5.3
SoCalGas 1,351 4.4
TOTAL 15,859 51.9
Hazardous Liquid (HVL and Non-HVL)
Energy Transfer 8,926 9.9
Enterprise Products 8,393 9.3
Oneok 6,335 7.0
Kinder Morgan 5,511 6.1
Marathon Pipe Line 5,114 5.7
Colonial Pipeline 4,397 4.9
Phillips 66 4,284 4.7
Buckeye Partners 4,219 4.7
Enbridge 4,203 4.7
TOTAL 51,382 57

SOURCE: Pipeline and Hazardous Materials Safety Administration, Gas Transmission and Hazardous Liquids Annual Report Data, https://www.phmsa.dot.gov/data-and-statistics/pipeline/gas-distribution-gas-gathering-gas-transmission-hazardous-liquids.

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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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Common Types of Shutoff Valves

Valves are usually named based on the type of device that plugs or blocks the pipe to stop or regulate product flow. The two most common types of valves installed on gas and hazardous liquid transmission pipelines are gate and ball valves. A gate valve is designed with a solid rectangular or circular plate of steel (i.e., a gate-type disc) that is attached to a threaded stem that is turned to raise or lower the gate. When the gate is raised, product can flow freely past the valve; when the gate is lowered, the flow is stopped. Gate valves are typically designed to operate in either the fully open or fully closed position.

In a ball valve, the steel plate of the gate valve is replaced by a sphere (i.e., a ball-type disc) that is fabricated with a hole bored to the same diameter as the interior diameter of the pipeline. When the bore is aligned in the same direction as the pipe, the fluids can flow freely through the valve and into the pipeline. When the ball is rotated 90 degrees, the bore turns toward the body of the valve and the flow is stopped. Ball valves can also be designed for operation in a partially open position to throttle the flow, which can make them more versatile than gate valves.

Some valves are self-activating, such as a check valve. These flap-like valves are designed to prevent a reversal of flow direction. The check valve will remain open as long as there is free flow in the intended direction, as the fluid pressure lifts the flap upward toward the top of the valve body. If the flow stops, the pressure decreases, or the flow starts to reverse, the change in fluid direction and pressure will force the flap down into a closed position, stopping any back flow. The check valve, therefore, can be used to prevent downstream product that has passed a rupture site, but is no longer under pumping pressure, from reversing flow and escaping through the rupture site.

Valve Actuation Methods

Valves can be fitted with various systems for moving the disc that opens and closes the valve (e.g., turning the ball, lifting the gate), and as a means for initiating and controlling the movement. In a manual valve, both the opening and closing of the disc are handled by the person (or people) operating the handwheel or lever. Other means of moving the disc may include electric motors, pneumatic or hydraulic systems using a pressurized gas or fluid, and electromagnetic force via a solenoid. In many cases manual valves can be retrofitted with one of these other mechanized systems for opening and closing.

All means of actuation can be configured to be initiated by a person at the valve site, whether by physical action (e.g., turning a handwheel) or

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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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by toggling a switch that triggers a solenoid or turns on a motor, pump, or compressor. Non-manual valves can be activated remotely from a control room or automatically in response to a sensor reading (i.e., reaching a designated set point for pressure, flow rate, or temperature). The choice and practicality of different methods of activation depend on many factors, as will be discussed later.

Valve designs that combine mechanized valve actuation with monitoring and control systems afford pipeline systems with an ability to operate instrumented valves through automation and remotely from a control room. Application of these technologies on transmission pipelines is found in automatic and remote-control shutoff valves, collectively referred to as RMVs.

Operating without human intervention, an automatic shutoff valve is designed to monitor conditions and automatically close in response to a rapid change in pipeline pressure, flow rate, or temperature. Upon reaching a designated set point, generally operating pressure or flow rate, the actuator will automatically activate to close the valve. The actuator may be powered by electricity or gas in the case of natural gas pipelines. This functionality allows for fast isolation times for major leaks and ruptures.

Operating with human intervention, remote-control valves are designed and instrumented to be opened or closed in response to commands from a control room at a remote location.

Control room personnel monitor pipeline conditions with the assistance of SCADA systems (discussed in Box 2-1) for a range of parameters, including flow rate and pressure. An alarm may sound or another alert may be provided when condition thresholds are met. Control room personnel will review and evaluate the data to determine whether a problem exists. They may also receive direct notice of a problem from the public, emergency responders, or operator personnel at or near the site. If the control room determines there is an emergency condition based on available information, and possibly field confirmation, the decision may be made to close a valve or series of valves by executing commands to remote-control valves.

Automatic and remote-control shutoff valves provide common benefits, notably the mitigation of consequences from hazards by reducing the duration or volume of a release from a failed pipeline segment. The time differentials between isolating a pipe segment fitted with remote-control or manual shutoff valves will depend on a number of factors, including the amount of time before the controller determines that an abnormal and emergency condition exists, the time it takes for the controller either to initiate the remote valve closure or to alert local operating personnel to close a valve manually, and the location of the valve relative to available operating personnel. In the case of automatic shutoff valves, these timing issues are not factors.

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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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For gas transmission pipelines, both automatic and remote-control shutoff valves can shorten the time to closure, thus limiting the volume of natural gas—methane, a flammable and potent greenhouse gas—released at the incident site and into the atmosphere. Shortening the time to closure would reduce the spread or intensity of a fire if a natural gas rupture ignites. Rapid isolation of a rupture allows emergency response teams to begin rescue efforts sooner, which offers a chance to curb injuries, loss of life, and destruction of property and the environment.

For hazardous liquid pipelines, automatic or remote-control shutoff valves can likewise shorten the time to closure, reducing the volume spilled into the surrounding environment. Installing more valves onto a single pipeline also reduces the length of pipeline segments (i.e., the valve spacing),

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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×

allowing operators to isolate smaller sections and thus smaller volumes of a commodity. Consequently, smaller pipeline segments decrease the drain-down volume of a pipeline leak or rupture, especially where the leak or rupture is located at a low point within the pipeline, and product volume will flow from high ground to low ground and release from the leak or rupture site. In addition to segment length, the topography of the land where the pipeline is located is crucial in determining the drain-down volume at a specific location. For example, if a pipeline ruptures at the bottom of a hill, the liquid will flow down from the top of the hill and drain out of the rupture location below. The strategic placement of valves on a pipeline that considers the topography of the land, often through modeling of the pipeline system, can further reduce the volume of commodity released during an incident.

The use of both types of RMVs—automatic and remote-control—presents operators with potential challenges. Failures of both types of valves can be caused by random hardware and software failures. A particular challenge in designing and programming an automatic shutoff valve is keeping it from activating inadvertently by sensed conditions such as pressure fluctuations due to changes in operations or weather conditions as opposed to a change in pressure due to a rupture. While rapid actuation can be advantageous in an emergency, a potential consequence of rapid isolation includes hydraulic shock, also known as water hammer. Water hammer is a pressure surge or wave caused when a fluid, generally a liquid, is forced to stop or change direction abruptly such as when a valve suddenly closes. This phenomenon can be especially hazardous for high-pressure systems that carry hazardous liquids—which are not compressible—because it could cause mechanical stress or damage to components upstream on the pipeline such as at a bend or pump station. The risk of water hammer thus constitutes an important factor when determining whether to install an automatic shutoff valve on a hazardous liquid pipeline. While water hammer could lead to the damage of a pipeline system, countermeasures can also be put into place to mitigate the threat, such as surge tanks and chambers to suppress the pressure wave and thereby minimize the mechanical stress to the piping. In addition, the installation of pressure relief systems can provide a mechanism to release excess pressure if a safe location for ventilation and disposal is available.

The operation of a remote-control shutoff valve, unlike an automatic shutoff valve and like a manual valve, requires human decision making and intervention. Adding this human element to activation can prevent unnecessary, costly shutdowns but also slow the response process and introduce the possibility of human error, including failure to activate the valves when warranted. Poor decisions about when to activate remote-control valves

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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×

and their sequencing can cause damage and failures, including incidents of hydraulic shock. The potential exists for such human errors to arise from fatigue, although operators provide training and resources for control room personnel to prevent or mitigate such occurrences.

While actuation of remote-control valves through SCADA systems is a common and effective approach for mitigation of rupture consequences, the use of these systems can also introduce new hazards that must be considered and controlled. While pipeline failures can be caused by a malicious attack performed locally at a pipeline equipment site (e.g., by crossing wires at a local control panel at a valve station), SCADA infrastructure can be subjected to a remote cyberattack. As a result, both physical and cyber security are necessary to limit opportunities for threat actors.

Whether the result of the actuation of automatic, remotely controlled, or manual valves, errant shutdowns of pipelines systems can have harmful effects on the integrity of the pipeline and on customers due to disruptions in the delivery of fuel and other commodities. The issues and concerns identified in this chapter are discussed with regard to the current state of technology and practice. Advances in control systems that reduce the uncertainties that slow the confirmation of ruptures, and thus slow the deployment of valves, can be expected in the future. Similarly, technological advances are likely to reduce the probability of errant and uncoordinated activations of automatic shutoff valves. While this report does not examine such possibilities, or the state of research and technology, they will undoubtedly be factors in the development of standards and methods for RMVs in the future.

PREVALENCE OF RUPTURE MITIGATION VALVES IN HIGH CONSEQUENCE AREAS

While PHMSA’s annual statistical reports provide operator-reported data on the mileage and certain other characteristics of the pipelines in HCAs and Class 3 and 4 locations, operators are not required to report on the installation of shutoff valves on the pipeline segments located within or that could affect an HCA.6 However, a PHMSA database that can offer some insight into valve use and type is the Pipeline Incident Flagged Files.7 Between 2010 and 2022, 427 incidents were reported for gas transmission and hazardous liquid pipelines in HCAs and Class 3 and 4 locations in which valves were closed and their types identified in the incident record

___________________

6 See https://www.phmsa.dot.gov/data-and-statistics/pipeline/pipeline-mileage-and-facilities.

7 PHMSA. Pipeline Incident Flagged Files. https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/data_statistics/pipeline/PHMSA_Pipeline_Safety_Flagged_Incidents.zip.

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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×

(see Figure 2-5).8 According to a review of these records, manual valves were used exclusively to shut down the pipeline in 48% of incidents. By comparison, remote-control valves were used to shut down the pipeline in one-third of the incidents, and automatic shutoff valves were used in another 5%. In addition, there were seven incidents in which a combination of automatic and remote-control shutoff was used, bringing the total for RMVs to 39%. In 12% of the incidents, manual valves were used in combination with RMVs.

Extrapolating from these data, almost 55% of valves on all transmission pipelines located in HCAs are manually operated (48% plus half of 12%), and the remaining 45% are RMVs (39% plus half of 12%). These percentages, however, differ for gas and hazardous liquid pipelines. The prevalence of incidents in which shutdowns were performed exclusively using manual valves was much higher for incidents involving gas transmission pipelines (84%) than for incidents involving non-HVL hazardous liquid and HVL pipelines (40% and 54%, respectively).

It is also notable that in approximately 87% of the 427 pipeline incidents, a SCADA system was in place and functioning at the time (see Figure 2-6). This finding is notable because it suggests that most hazardous liquid and gas transmission pipeline miles are under the kind of centralized supervision and control that would be required for the operation of remote-control valves.

While these incident records offer some insight into the prevalence of RMVs, the study committee wanted to obtain additional sources of information on the use and spacing of these devices in HCAs and Class 3 and 4 locations. The committee therefore asked the main industry associations for natural gas and hazardous liquid pipeline operators—the American Gas Association, Interstate Natural Gas Association of America, and American Petroleum Institute—to forward questionnaires to their members (see Appendix C) asking for information on their pipeline mileage and valves in HCAs and Class 3 and 4 locations. Specifically, operators were asked to report anonymously their pipeline mileage by diameter, decade of installation, and commodity transported. Furthermore, they were asked to report on the number of shutoff valves on the pipelines; the average spacing between valves; and whether the valves are operated manually, automatically, or remotely. In the case of hazardous liquid pipelines, the operators were also asked to report by type of HCA—that is, high population area, other population area, commercially navigable waterway, drinking water, and

___________________

8 As in Chapter 4, the incidents examined do not include those involving pipeline system components whose valves, manual or otherwise, are not normally intended for emergency shutdowns, such as valves at compressor stations and drain lines. Furthermore, the incident reports examined included only those involving pipelines having diameters of 6 inches or more.

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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×
Image
FIGURE 2-5 Types of valves used to shut down hazardous liquid and gas transmission pipelines in reported incidents in HCAs and Class 3 and 4 locations, 2010 to 2022.
NOTES: The reports are for both insignificant and significant incidents, pipelines with diameters of at least 6 inches, and when valve types were reported. “Mixed” refers to when the upstream and downstream valves used to isolate the incident were of different types.
SOURCE: PHMSA. Pipeline Incident Flagged Files: file title “gtggungs2010toPresent,” https://www.phmsa.dot.gov/data-and-statistics/pipeline/pipeline-incident-flagged-files.

ecologically sensitive area. In addition, operators were asked to report on their total onshore pipeline system mileage by main commodity type (to include mileage outside HCAs and Class 3 and 4 locations) but without providing the same level of detail about pipeline characteristics (age, diameter).

A total of 21 gas transmission and 7 hazardous liquid pipeline operators completed the questionnaire, including 4 of the latter who reported data for pipelines carrying HVLs. For the 21 gas transmission pipeline operators, their individual system-wide total mileage ranged from 20 miles to more than 51,000 miles. For the seven hazardous liquid pipeline operators, their system-wide total mileage ranged from 120 miles to more than 13,500 miles. The gas transmission pipeline operators reported mileage ranging from 0.5 miles to more than 3,700 miles in HCAs or Class 3 and 4 locations. The hazardous liquid pipeline operators reported mileage ranging from 5 miles to more than 3,800 miles of pipeline in HCAs.

To check the representativeness of the 28 respondents, the mileage reported was compared to mileage reported to PHMSA by all operators in fulfillment of annual reporting requirements. As shown in Table 2-5, the respondents accounted for 25% and 22% of total (national) gas transmission and hazardous liquid pipeline mileage, respectively. The responding gas pipeline operators accounted for a comparable share (more than 25%) of all gas transmission pipeline mileage in HCAs and Class 3 and 4 locations. The responding hazardous liquid pipeline operators accounted for a comparable

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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×
Image
FIGURE 2-6 Share of reported hazardous liquid and gas transmission pipeline incidents in HCAs and Class 3 and 4 locations where SCADA systems were installed, 2010 to 2022.
SOURCE: PHMSA. Pipeline Incident Flagged Files: file title “gtggungs2010toPresent,” https://www.phmsa.dot.gov/data-and-statistics/pipeline/pipeline-incident-flagged-files.

share (more than 20%) of all hazardous liquid pipeline mileage in HCAs. Comparing PHMSA statistics9 and the questionnaire-generated data about HCA pipeline mileage by diameter and year of installation, similar consistencies emerged to suggest that the respondents provide a reasonably good indication of the prevalence of shutoff valves of different types on hazardous liquid and gas transmission pipelines and their average spacing.10,11

As will be discussed more in Chapter 3, PHMSA regulations set maximum spacing intervals for shutoff valves on gas transmission pipelines in

___________________

9 See https://www.phmsa.dot.gov/data-and-statistics/pipeline/pipeline-mileage-and-facilities.

10 For gas transmission pipelines, PHMSA’s 2022 Annual Report reports 6–12-inch pipelines corresponding to 29% of the total pipeline system, 14–22-inch pipelines at 20%, 24–36-inch pipelines at 39%, and greater than 38-inch pipelines at 4%. The survey responses reported 26%, 26%, 42%, and 1.5%, respectively. The Annual Report also corresponds to 31% of pipelines installed pre-1960s, 22% in the 1960s, 10% in the 1970s, 8% in the 1980s, 10% in the 1990s, 9% in the 2000s, 8% in the 2010s, and 2% in the 2020s. The survey responses reported 27%, 24%, 10%, 11%, 9%, 9%, 8%, and 1%, respectively.

11 For hazardous liquid pipelines, PHMSA’s 2021 Annual Report reports 6–12-inch pipelines corresponding to 60% of the total pipeline system, 14–22-inch pipelines at 24%, 24–36-inch pipelines at 13%, and greater than 38-inch pipelines at 1%. The survey responses reported 54%, 31%, 10%, and 3%, respectively. The Annual Report also corresponds to 24% of pipelines installed pre-1960s, 15% in the 1960s, 13% in the 1970s, 8% in the 1980s, 8% in the 1990s, 7% in the 2000s, 20% in the 2010s, and 3% in the 2020s. The survey responses reported 28%, 17%, 13%, 10%, 9%, 7%, 11%, and 4%, respectively.

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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×

TABLE 2-5 Mileage Operated by Hazardous Liquid and Gas Transmission Pipeline Operators Responding to Study Survey, Spring 2023

Mileage Reported by Survey Respondents
Pipeline Type System Class 3 Class 4 HCA
Gas Transmission (21 operators) 74,999 8,873 258 5,574
Share of All Miles in National Systema 25% 26% 35% 26%
System High Population Other Population Drinking Water Ecological Resource Navigable Waterway
Hazardous Liquid (7 operators) 48,433 5,967 10,407 9,165 8,841 2,194
Share of All Miles in National Systemb 22% 20% 24% 28% 28% 26%

a The percentages calculated use 2022 data for gas transmission pipelines from PHMSA’s annual report. For gas transmission pipelines, PHMSA reported 298,325 miles of onshore pipeline, including 33,543 miles in Class 3 locations, 744 miles in Class 4 locations, and 21,369 miles in HCAs.

b The percentages calculated use 2021 data for hazardous liquid pipelines from PHMSA’s annual report. For hazardous liquid pipelines (HVL and non-HVL), PHMSA reported 224,695 miles of onshore pipeline, including 29,427 miles in high population HCAs, 47,050 miles in other population HCAs, 34,033 miles in drinking water HCAs, 33,137 miles in ecological resource HCAs, and 9,484 miles in commercially navigable waterway HCAs.

SOURCE: Transportation Research Board (TRB) survey of pipeline operators, Spring 2023.

Class 3 and 4 locations.12 The maximum spacing for a gas transmission pipeline is 5 miles for a Class 4 location and 8 miles for a Class 3 location. Valves on pipelines in Class 1 and 2 locations must be spaced no more than 20 miles apart. There are no maximum valve spacing requirements for existing hazardous liquid pipelines specific to HCAs; however, the April 2022 rule requiring RMVs on newly constructed and entirely replaced pipelines13 establishes a maximum valve spacing of 7.5 miles for HVL pipelines and 15 miles for all other hazardous liquid pipelines in HCAs.

Although not all respondents to the questionnaire reported their average valve spacings, 20 did. As shown in Figure 2-7, all 15 responding gas pipeline operators reported an average valve spacing within the 5- and 8-mile maximums established in regulation. Five of the seven responding hazardous liquid pipeline operators would have high compliance if they

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12 49 CFR Part 192.179.

13 49 CFR Part 195; Amendment to Require Valve Installation and Minimum Rupture Detection Standards.

Page 46
Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×
Image
FIGURE 2-7 Average shutoff valve spacing for pipelines reported by gas (left) and hazardous liquid (right) pipeline operators responding to the study survey, Spring 2023. NOTE: The box and whisker charts show the mean (x), median (horizontal line within the box), upper and lower quartiles (top and bottom of the box), minimum and maximum values excluding outliers (whisker), and outliers (o).
SOURCE: TRB survey of pipeline operators, Spring 2023.

were subject to the valve spacing maximums that apply to newly constructed pipelines. This concordance is not surprising in light of the ASME B31.8 block valve spacing requirement that has been in place since the 1950s and was incorporated into the federal gas transmission standards in the 1970s.

The data from the questionnaires and the PHMSA incident reports suggest that manually operated sectionalizing valves are already installed along the lengths of gas transmission and hazardous liquid pipelines at intervals in general accordance with the April 2022 rule for newly constructed and entirely replaced segments of pipelines.

In addition to reporting average valve spacings, operators reported the total number of valves on pipelines in each HCA and Class 3 and 4 location, as shown in Table 2-6. Based on the responses, manually operated valves are predominant, accounting for more than three-quarters of valves installed on gas transmission pipelines, more than half of valves on hazardous liquid pipelines, and about two-thirds of valves on HVL pipelines. The RMVs on gas transmission pipelines are primarily automatic and remote-control shutoff valves. By contrast, the RMVs on hazardous liquid and HVL pipeline systems are almost entirely remote-control valves and other types (i.e., check valves) of EFRDs. The near absence of automatic shutoff valves on hazardous liquid pipelines may be explained by concern that activation of an automatic shutoff valve without other system adjustments could cause mechanical damage to the pipeline by hydraulic shock (i.e., water hammer).

Page 47
Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×

TABLE 2-6 Number and Types of Valves Installed on Hazardous Liquid and Gas Transmission Pipelines in HCAs and Class 3 and 4 Locations, as Reported by Operators Responding to the Study Survey, Spring 2023

Valve Type
Type of Pipeline Manual Automatic Remote Other EFRD
Gas Transmission
Number of Valves 4,205 545 702 86
Percent of Valves 76 10 13 <2
Hazardous Liquid (Non-HVL)
Number of Valves 3,491 1 1,713 1,081
Percent of Valves 56 ~0 27 17
HVL
Number of Valves 579 0 341 20
Percent of Valves 62 0 36 2

SOURCE: TRB survey of pipeline operators, Spring 2023.

Thus, when comparing the data on valve types from incident reports and the questionnaire responses, there is a fair amount of consistency. To recap, the incident data suggest that about 55% of valves on all transmission pipelines located in HCAs are manually operated and the remaining 45% are RMVs. The survey data suggest that the ratio of manual valves to RMVs is somewhat higher, on the order of 65% to 35%. The incident reports also suggest that manual valves are most common on gas transmission pipelines, accounting for about 85%, while the questionnaire data suggest that manual valves account for about 75%. The prevalence of manual valves is lower for hazardous liquid (including HVL) pipelines according to both the incident (~55%) and questionnaire data (~60%).

Chapters 3 and 5 of this report go into greater depth on operator-reported cost ranges for installing RMVs; how operators make determinations about when and where to install these devices; and current regulatory requirements, direction, and guidance on their use.

SUMMARY POINTS

Most Pipeline Miles in High Consequence Areas Are Part of Large Systems

As reported by operators, at year-end 2021 about 40% of hazardous liquid pipeline mileage was located in HCAs, while 19% of gas transmission

Page 48
Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×

pipeline mileage was located in HCAs and Class 3 and 4 locations. Large shares of the HCA mileage were managed by a relatively small number of operators with large systems. In the case of gas transmission pipelines, 12 operators managed more than 60% of the mileage in HCAs and Class 3 and 4 locations. In the case of hazardous liquid pipelines, 18 operators managed more than 75% of the HCA mileage.

Rupture Mitigation Valves Are Being Used on Existing Transmission Pipelines in High Consequence Areas

A combination of operator survey results and data from incident reports suggests that the most prevalent valves on hazardous liquid and gas transmission pipelines in HCAs are manual valves; however, RMVs are common, accounting for about 35% to 40% of valves. Although RMVs are more common in hazardous liquid pipelines than gas transmission pipelines, operators of both types of pipelines have significant operational experience using RMVs. The data suggest that for both types of pipelines, valves are currently spaced at intervals that either comply or are in general accordance with the spacing requirements for RMVs for newly constructed and entirely replaced segments of pipelines. Furthermore, the data suggest that SCADA systems are almost universal on existing hazardous liquid and gas transmission pipelines, meaning that much of the connectivity and telemetry required for RMVs may already be in place. Existing valve spacings and the prevalence of SCADA systems suggest that it may be possible to add RMVs to many existing pipelines through manual valve retrofits and replacements rather than investments in new valve locations and centralized control mechanisms.

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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
×
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Suggested Citation:"2 Background on Transmission Pipelines and Shutoff Valves." National Academies of Sciences, Engineering, and Medicine. 2024. Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves. Washington, DC: The National Academies Press. doi: 10.17226/27521.
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Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves Get This Book
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Since 2022, automatic or remote-control shutoff valves have been required on new hazardous liquid and gas transmission pipelines located in or near populated and environmentally sensitive areas. They are intended to enable faster shutdowns of ruptured pipe segments. However, the requirement for “rupture mitigation valves” does not apply to pipelines installed prior to 2022. This report examines the regulatory requirements that apply and recommends options for making sounder decisions about when to install these valves.

TRB Special Report 349: Ensuring Timely Pipeline Shutdowns in Emergencies: When to Install Rupture Mitigation Valves from the Transportation Research Board of the National Academy of Sciences, Engineering, and Medicine is the product of an expert committee convened to assess regulatory standards and criteria for deciding when the valves should be installed on pipelines. This review, which was mandated by Congress, issues a series of recommendations designed with pipeline safety in mind.

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