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21 2 Basic Configurations and Uses of LPG Distribution Systems This chapter provides an overview of liquefied petroleum gas (LPG) pipeline distribution systems, explaining their various uses and configurations, key components, and supply and operations. The information is presented at a generalized level for background and introductory purposes. More details about how different system operators and configurations are regulated and their specific safety-related requirements are given later in the report. SYSTEM USES AND CONFIGURATIONS LPG consists of propane, propylene, butane and its isomer, and mixtures of these hydrocarbon gases. Most of the LPG consumed in the United States is burned as household fuel, generally in areas lacking natural gas pipeline distribution networks or in places where the networks have gaps because of geographic features or insufficient consumer density to justify the pipeline investment. LPG is also used as feedstock for petrochemical plants and to power manufacturing. When used for these large industrial purposes, LPG is usually transported as a liquid in high-pressure, large- volume transmission pipelines, which are not examined in this study. The LPG pipeline facilities of interest in this study are small distribution sys- tems that serve households and mostly small businesses. Because propane is the predominant LPG used in these systems (by itself or in mixtures), âpropaneâ is often used interchangeably with âLPGâ in this report, ex- cept in instances when references to butane and other LPGs are necessary because of relevant differences in their particular transport, storage, and hazard characteristics.
22 SAFETY REGULATION FOR SMALL LPG DISTRIBUTION SYSTEMS LPG is a fuel used in 11.8 million homes and 510,000 businesses for space heating, water heating, clothes drying, and cooking.1 Altogether, about 5 percent of U.S. households use propane as their primary heating fuel.2 This figure does not include consumers and businesses who buy pro- pane in small volumes (e.g., 5- to 25-gal cylinders) for uses such as outdoor grills, recreational vehicles, portable generators, and forklifts. Compared with the nearly 75 million households and businesses that use natural gas,3 the number of households and businesses that rely on LPG as their primary source of fuel is small; however, LPG is an important fuel in rural areas and in many suburban locations lacking natural gas service.4 Unlike natural gas, which is transported in a compressed, gaseous state through a network of mains and service lines from a central plant to metered consumers, LPG is stored under high pressure as a liquid in con- tainers that are located on or close to the userâs premises. When used for primary fuel purposes such as whole-home heating, the containers usually consist of 500- to 2,000-gal steel tanks5 installed above or below ground and periodically refilled onsite by tank trucks, usually in âbobtailsâ that hold approximately 3,000 gal. Short service lines transport the LPG from the tank to the building and the userâs piping. A large majority of LPG distribution systems serve single-family homes and individual businesses. These single-user systems are not part of this study because nearly all of them are not regulated as pipeline facilities by the federal government or states (although these systems are usually subject to local building and fire codes governing their placement, design, 1 U.S. Energy Information Administration, âResidential Energy Consumption Survey (RECS),â accessed December 19, 2017, https://www.eia.gov/consumption/residential/data/2015/ index.php?view=characteristics; U.S. Energy Information Administration, âCommercial Build- ings Energy Consumption Survey (CBECS) Data,â accessed December 19, 2017, https://www. eia.gov/ consumption/commercial/data/2012; U.S. Energy Information Administration, âU.S. Number of Natural Gas Consumers,â accessed April 30, 2018, https://www.eia.gov/dnav/ng/ ng_cons_num_dcu_nus_a.htm. The estimate of residential households excludes households that use LPG only for outdoor grilling. 2 U.S. Energy Information Administration, âShort-Term Energy Outlook: May 2017,â May 9, 2017, https://www.eia.gov/outlooks/steo/report/winterfuels.cfm. 3 U.S. Energy Information Administration, âU.S. Number of Natural Gas Consumers,â accessed April 30, 2018, https://www.eia.gov/dnav/ng/ng_cons_num_dcu_nus_a.htm. 4 Consumers in urban areas also use LPG to a lesser extent for similar applications. In extremely cold weather, a common end use for LPG is âpeak shaving,â which supplements natural gas service by injecting LPG diluted with air into natural gas. For areas likely to transi- tion to natural gas service, diluted LPG, a propane and air mixture, has the same heating value as natural gas, making it suitable for users with natural gas appliances. 5 Tanks are limited in the amount of product that can be introduced to account for LPG contraction and expansion due to fluctuations in temperature and pressure. (National Fire Protection Association, NFPA 58, Liquefied Petroleum Gas Code (Quincy, MA, 2004). Tables 188.8.131.52(a)â(c) list the maximum permitted LPG volume.)
BASIC CONFIGURATIONS AND USES 23 and installation). Of interest in this study are multi-user LPG systems that typically serve apartment buildings, small residential developments, resorts, hunting lodges, mobile home parks, strip malls, and the like. Some of these systems serve as few as two or three homes or businesses, while others serve dozens or even hundreds of customers in multiple buildings. Although most states have multi-user LPG systems, they are more com- mon in some states than others, in part because of regional differences in natural gas access (e.g., limited transmission pipelines to New England and no service on islands such as Puerto Rico and Hawaii) and the prevalence of certain types of businesses and land uses (e.g., states with large num- bers of remote resorts and lodges). According to the National Propane Gas Asso ciation (NPGA), more than 75 percent of multi-user systems have 50 or fewer users and about 95 percent of newly constructed systems serve fewer than 100 users.6 Figure 2-1 provides example configurations of multi- user LPG systems serving residential dwellings and businesses. KEY SYSTEM COMPONENTS The typical arrangement of a multi-user system is for individual end users to have an assigned meter that allows them to pay for the fuel as they use it, rather than in advance at the time of refilling a full tank. The cus tomers served by these systems will usually have steel tanks with capacities of at least 500 gal, but often 1,000 to 4,000 gal, and in rare instances up to 30,000 gal (see Figure 2-2). If more than one tank is used, they are usually located next to one another and connected by manifold piping, thereby providing a common supply source for pipelines leading to the customers. The tanks will be painted or have other coatings to reflect sunlight and prevent atmospheric corrosion, and a mastic (petroleum or coal tar) and cathodic protection may be applied to tanks that are buried underground or mounded. LPG tanks have certain common design features and fittings, many of them standardized as discussed later in this report. Most LPG tanks are designed with a maximum allowable working pressure of 250 pounds per square inch gage (psig; about 18 times atmospheric pressure). The ambi- ent temperature affects the internal vapor pressure of a tank, particularly when located above ground. Thus, in addition to leaving void space (filled to approximately 80 percent of capacity7), tanks are equipped with pres- 6 Michael Caldarera, Lyndon Rickards, and Rufus Youngblood, âNational Propane Gas Association: Study on Propane Gas Pipeline Facilitiesâ (June 8, 2017), http://onlinepubs.trb. org/onlinepubs/Propane/Caladeraetal6817.pdf. New LPG systems typically serve up to 30 customers. 7 See Footnote 5.
24 SAFETY REGULATION FOR SMALL LPG DISTRIBUTION SYSTEMS FIGURE 2-1 Multi-user LPG distribution system configurations for (a) residential and (b) commercial applications. sure relief devices to relieve excess pressure, usually when internal pressure exceeds 250 to 375 psig (see Figure 2-3). The tank will also contain other valves and fittings for gauging fill levels, refilling, and servicing (see Figure 2-4). On some tanks, the installation of wireless communication technology permits remote gauging of fill levels. These components are usually located on top of the tank and covered by a protective dome or lid. Buried tanks have risers that allow service technicians access to the valves and fittings. Product is withdrawn from the tank on demand by a service valve that connects to a supply line, ranging from Â¾ to 4 in. in diameter, but usually 2-1 b a
BASIC CONFIGURATIONS AND USES 25 FIGURE 2-2 LPG storage tanks: (a) 500 gal; (b) 1,000 gal; and (c) 30,000 gal. FIGURE 2-3 Pressure relief valve manifold. SOURCE: Gary McDonald, âNAS Study on Propane Gas Pipeline Facilitiesâ (June 8, 2017), 28, http://onlinepubs.trb.org/onlinepubs/Propane/McDonald6817.pdf. not more than 2 in., which is the maximum allowable size of plastic piping. As LPG enters the supply line, its vapor pressure is reduced by a series of pressure regulators. A regulator (called a âfirst stageâ regulator) is installed at the tank to control the service line (inlet) pressure, typically to a level of 10 psig or less, but not more than 30 psig in plastic pipes. Higher pres- sure could cause the product to re-liquefy (see Figure 2-5) and potentially 2-2 6 ft. 6 ft. 6 ft. a b c
26 SAFETY REGULATION FOR SMALL LPG DISTRIBUTION SYSTEMS FIGURE 2-4 Stationary LPG storage tank. rupture the pipe when the ambient temperature increases. A second regu- lator (the âsecond stageâ regulator) is located close to the building or at each userâs meter to further decrease the outlet pressure to a level that can be safely used by household appliances (~0.5 psig).8 A service line ends at the outlet of the customer meter or at the connection to a customerâs pip- ing, whichever is further downstream (, the line ends at the connection to customer piping if there is no meter).9 A second stage regulator may serve one customer or multiple customers through a meter header or manifold. The service lines are usually made of plastic, but sometimes made of steel, and can be as short as a few feet, such as when serving adjoining businesses (e.g., strip mall), adjacent homes, or an apartment building. However, the lines can extend for hundreds of yards in larger systems. Accord ing to PHMSA data, the length of a service line on a system having 100 or more customers is typically 54 ft.10 As the number of users and vari- ety of applications increase, so too will the storage capacity of the tanks 8 Most outlet pressures of second stage regulators are measured in inches water column, such as 11 in. water column, which is about 0.5 psig. 9 âDefinitions,â 49 CFR Â§ 192.3, 415, accessed April 24, 2017, https://www.ecfr.gov/cgi-bin/ text-idx?SID=eab46322fa6503dd280dde58f10fadda&mc=true&node=pt49.3.192&rgn=div5. 10 Pipeline and Hazardous Materials Safety Administration, âGas Distribution, Gas Gathering, Gas Transmission, Hazardous Liquids, Liquefied Natural Gas (LNG), and Underground Natural Gas Storage (UNGS) Annual Report Data,â accessed March 23, 2018, https://www.phmsa.dot. gov/data-and-statistics/pipeline/gas-distribution-gas-gathering-gas-transmission-hazardous-liquids. The length of service lines is based on median (53.5 ft) of data from the âAverage Service Lengthâ field in large LPG pipeline operatorsâ annual reports on system conditions. Internal Float Pressure Relief Valve Open Dome Cover Liquid Fill Service Valve% Gauge Liquid Withdrawal Liquid Withdrawal Tube to Bottom of Tank
BASIC CONFIGURATIONS AND USES 27 FIGURE 2-5 LPG tank regulator system. NOTE: WC = water column. in the systems as well as the likelihood that the tanks will be buried along with their service lines. Installation of LPG pipelines is typically accomplished using one of three methods: trenching, horizontal directional drilling, or pneumatic piercing. Trenching relies on the use of a backhoe or similar equipment to dig a trench into which the pipe is placed. Horizontal drilling and pneu- matic piercing are forms of trenchless excavation technology, which has the advantage of minimizing ground disturbance and disruption to traffic and infrastructure. Standards governing pipeline installation state that when ser- vice lines are buried, their burial depth must be at least 12 in. below grade in private property and at least 18 in. below grade in streets and roads. Although seldom a component in LPG systems with fewer than 100 customers, tanks may be equipped with a vaporizer in colder climates and for high-consumption applications. These devices heat the LPG liquid until it vaporizes without increasing pressure inside the system. The accelerated production of vapor ensures that customers have an adequate supply of fuel during low-ambient temperature when vaporization is suppressed or to supply industrial users. SYSTEM SUPPLY AND OPERATIONS In many cases, the LPG supplier is the owner of the tank and service lines leading to the meter. Under these proprietary arrangements, the customer leases the tank and is contractually obligated to purchase propane ex- clusively from the supplier. In return, the LPG supplier is responsible for inspecting and maintaining the system and is the operator of record from a regulatory standpoint. When the customer owns the tank, an LPG supplier may still be hired to inspect and maintain the system, usually coupled with the customerâs purchase of fuel. LPG distribution system configurations can have much in common with master meter systems used for natural gas dis- 2-5 Usually 10 psig First Stage Regulator Second Stage Regulator 11â WC
28 SAFETY REGULATION FOR SMALL LPG DISTRIBUTION SYSTEMS tribution, whereby the operator of the system purchases gas from a supplier through a single large meter and resells the gas to the ultimate consumer for uses such as heating and cooking.11 That customer either purchases the gas directly through a house meter or by other means, such as a rental payment that includes all utilities. In a less common scenario, the operator may be neither the supplier nor the customer, such as at mobile home parks where office staff manage the distribution system operations through the use of contractors and bill the mobile home residents for use of fuel.12 There are an estimated 3,000 propane suppliers in the United States, many consisting of small, often family-owned, businesses.13 The three largest suppliers are AmeriGas, Ferrellgas, and Suburban Propane, which operate nationally. These three firms supply about one-third of all LPG consumers. Table 2-1 provides a snapshot of the three firmsâ customer base, sales volume, and number of states served. SUMMARY This chapter described the configurations, components, and use character- istics of the multi-user pipeline systems that distribute LPG to homes and businesses. In these systemsâwhich can have as few as two users or as many as several hundredâLPG is stored under high pressure as a liquid on 11 Although rare, there are LPG master meter systems. 12 Neil Pascual, âThe National Association of Pipeline Safety Representativesâ (Meeting 1, Washington, DC, June 8, 2017), 13, http://onlinepubs.trb.org/onlinepubs/Propane/Pascual6817. pdf. 13 This figure was provided by NPGA, whose membership consists of 2,300 propane sup- pliers and is believed to account for about three-quarters of suppliers nationally. TABLE 2-1 Characteristics of Three Major LPG Firms, 2016 Firm Customers (million) Propane, Gallons Sold (million) States with Operations AmeriGas 1.9 1,100 50 Ferrellgas 1.0 779 50 Suburban Propane 1.1 415 41 NOTE: The fuel reported as sold does not differentiate by type of LPG; the table reflects the terminology used by the firms. SOURCES: Annual financial reports of AmeriGas and Suburban Propane, 2016; Ferrellgas, https://www.ferrellgas.com/our-company and https://www.ferrellgas.com/media/1167/co-23458. pdf, accessed May 9, 2017.
BASIC CONFIGURATIONS AND USES 29 or close to the userâs premises. The systems usually consist of one or more storage tanks, a first stage regulator, service lines, a second stage regulator, and a customer meter. The tanks, fittings, and service lines may be located above or below ground, usually the latter as system size increases. Service line lengths tend to be measured in feet or yards, as opposed to the miles of service line found in natural gas systems. LPG service in a multi-user system is usually metered so that custom- ers pay for the fuel as they use it rather than having to pay in advance for refilling a full tank. The typical commercial arrangement is for the LPG supplier to be the owner of the tank and service lines, and thus responsible for operations and maintenance. Many small- and medium-sized firms serve in this capacity as operators, along with three large national LPG suppliers.