What it Takes to Pipe a Petroleum Terminal

In this first of his two-part series, designer of numerous large piping systems, David Willoughby discusses why and how terminal piping arrangements and routing systems can be both straightforward and complex.

Four-inch OPW A-frame petroleum bottom loading arms with API bottom loading couplers. Photo courtesy of OPW Engineered Systems.

When discussing the piping of a petroleum terminal, it is important to put the subject in context. Exactly what is a petroleum terminal? According to the Petroleum Equipment Institute’s manual Lexicon, written by Howard Upton and published in 1995, it is a “large facility for storing and handling petroleum products…[which] is usually located adjacent to a petroleum-product pipeline, a refinery, a railroad, or a waterfront ship-berthing area.

“A terminal receives bulk deliveries of gasoline and other products from a pipeline, tankers or barges, or directly from a nearby refinery….The products are stored in large tanks at the terminal. Equipment at the facility is usually capable of further processing the product: injection of additives, for example, or conversion of gasoline vapors received from transports after making deliveries using Stage I vapor recovery back to liquid form….

“A terminal should not be confused with a bulk plant. Although both are used for the temporary storage of petroleum products prior to delivery to gasoline stations, C-stores, and commercial accounts, bulk plants are much smaller (50,000-500,000 gallons) than terminals and are not normally equipped with any processing equipment.”

This terminal has been supplied with explosion-proof loading rack equipment for overfill protection. Photo courtesy of Civacon.

Planning and design
Given the definition above, it may be hard to believe but the design and installation of a piping system in a petroleum terminal is actually a straightforward process. This is true even though installation pipelines can connect petroleum terminals with a wide range of facilities, including those that handle marine-receiving and dispensing, aircraft fueling and ground vehicle fueling facilities.

At the same time, however, “straightforward” does not mean simple. The technology involved in the piping is extensive and requires the practical application of theory and workmanship from a number of technical disciplines. To put all the necessary technology and skills together, planning is vitally important. Many factors must be considered, including the mission of the terminal; the location of other structures; coordination with other work; the availability and qualifications of welders; and the availability of terminal equipment.

For the effective design of a piping system, we must consider the piping system as a whole. Decisions in one area will directly affect or limit options in other areas. For example, it may be necessary to locate a truck-loading stand near a road. This would directly impact our pipe routing, which, in turn, would impact the hydraulics and energy required for the network.

When designing a terminal piping system, the first task is to establish the piping arrangement, or pipe routing.

A terminal operator transfers product from a Standard Oil refinery into a holding tank at the Doraville terminal near Atlanta, GA. Photo courtesy of American Petroleum Institute.

Piping arrangement
We often say that the shortest distance between two points is the best route. This is usually true in the design of a terminal piping system, but, practically speaking, it is easier said than done. Seeking the shortest route is a good place to start, but there are many obstacles along the way.

In arranging the piping system, it is essential to avoid all other facilities in the terminal. This includes such structures as other piping systems, electrical systems, other utilities and other terminal equipment such as pumps, tanks and fill stands. In addition, consider the ease of access for construction equipment, materials and personnel.

Often we cannot use the shortest route, but we should always use the best route. Many items affect the pipe arrangement and route selection. Wherever possible, arrange piping in parallel groups to promote multiple use of supports for aboveground piping and to reduce the degree of trenching needed for underground piping.

The effects of thermal expansion on the pipe and fittings cannot be overlooked during the arrangement and routing of any piping system. A good pipe arrangement will provide the required flexibility with the minimum amount of pipe and fittings. Some important points to consider are:

  • Avoid having straight runs of rigid pipe between two pieces of equipment or between two anchors.
  • For pipe runs with an expected high thermal expansion, use an anchor near the center of the run to evenly distribute the expansion in two directions.
  • Provide looped piping systems whenever practical. Loops add to the flexibility and reliability of the system. Looping the piping arrangement is also beneficial in helping to reduce the magnitude of any hydraulic shock. (See Figure 1 below).
  • Whenever possible, install cross connections between the piping mains that serve the same product. Such connections add flexibility during operation and provide an auxiliary means of continuous operation in emergencies. Always provide a separate piping system for each grade of fuel handled. Do not provide cross connections between different grades of product.

Figure 1  Looped piping for flexibility and reliability

When determining piping arrangements, provide for proper draining of the product contained in the pipe. For short piping runs, pipe routing should provide for a line slope of at least two percent. For long runs, the line slope should be sufficient to establish positive drainage by gravity but without excessive burial depth.

Lay out your system so the elevation gradient is uniform between the high and low points. Make sure the piping does not have any traps. Such traps provide a place for water and sediment to accumulate.

Design your pipe with high-point and low-point drain connections in the proper locations. Install drains at low points to allow removal of any water from condensation and to provide the capability to remove fuel for line maintenance.

If a slope is not possible, design the system to accommodate cleaning and draining the pipe system with “pigs.” Pigs are devices that are forced through the pipe, usually with compressed air, to clean and empty the pipe. Design the piping system to support pigging by providing flange connections for pig launchers/receivers, long curvature fittings and full port valves. Install high point vents to remove trapped air from the piping system.

All in all
Designing and routing petroleum terminal piping systems usually involves complex projects, extended liabilities, tight cost controls and strict quality standards. It is essential that all aspects and phases of a project be effectively controlled and executed.

The available technology is extensive and growing every day, and the applicable codes and standards are numerous. To be successful requires the concerted efforts and teamwork of professionals in a number of engineering and construction disciplines. This is the reality of the challenge. In the next issue of PE&T, I will discuss crucial installation tips and techniques for aboveground and underground piping related to terminals.

Discuss