CHAPTER 26

OIL AND GAS PIPELINE

ENGINEERING

Thomas Miesner

Pipeline Knowledge & Development

Katy, Texas

David Vanderpool

Vanderpool Pipeline Engineers Inc.

Littleton, Colorado

26.1 Introduction

Using hollow tubes to direct the movement of fluids has been around for many years. Some say the first use dates back to ancient Chinese salt works. Legend has it that hollowed-out bamboos logs were sealed together with mud and used to transport natural gas, produced along with salty brine, short distances, where it fueled fires to evaporate water from the brine, leaving salt. Others cite the bath works of ancient Rome. Regardless of when pipelines were first employed, they came into extensive use during the 20th century.

Pipelines are critical to modern society. Millions of miles crisscross cities, towns, states, countries, and even continents and carry essential products for modern lifestyles: water, wastewater, liquid fuels, gaseous fuels, and chemical feedstocks. Regardless of nationality, location, or fluids moved, all these pipelines obey the same laws of physics.

But the practices and precautions involved when transporting natural gas, crude oil, refined products, natural gas liquids, chemical feed stocks, CO2, and other hazardous and flammable fluids are quite different from those involved with moving clean water, liquid wastes, slurries, and many other fluids. This chapter leaves behind other pipelines to focus on oil and gas transmission (long-distance) pipelines and specifically onshore rather than offshore pipelines. Before moving on to the details of engineering, however, a brief introduction to oil and gas pipelines is in order.

26.2 Oil and gas pipeline functions and classifications

Oil and gas pipelines are categorized according to the fluids they transport, the pressures involved, where they are located (onshore or offshore), and their function. Oil pipelines primarily move crude oil and refined products (gasoline, diesel, jet, and other fuels and chemical feedstocks). Gas pipelines move natural gas, composed of methane (CH4) with smaller concentrations of ethane (C2H6), propane (C3H8), and perhaps other light hydrocarbons.

Functionally, lines consist of the following:

- Gathering. Generally low pressure (<500 psi), used to aggregate oil or gas production from wells and producing facilities and deliver it to crude oil gathering stations and terminals, gas plants, or sometimes directly into transmission lines

- Transmission (also called trunk lines or main line). Generally high pressure (up to 2,500 psi), receives fluids from gathering lines, storage facilities, crude oil and refined-products terminals, other transmission lines, refineries, and gas plants and delivers them to storage facilities, crude oil or refined-products terminals, other transmission lines, or natural gas city gates

- Distribution. Generally low pressure (<500 psi), receives fluids from transmission lines, storage facilities, refined-products terminals, and city gates and delivers them to final destinations, including individual homes and businesses

Crude oil and gas gathering lines, natural gas transmission, crude oil and refined main or trunk lines, and natural gas distribution lines are each shown in Figure 26.1.

Some gathering lines operate in two-phase flow, moving both liquids and gases. All refinedproducts main or trunk lines are designed to operate primarily in the liquid phase. Although both the Trans Alaska pipeline and the Baku—Tbilisi—Ceyhan pipeline have a portion designed for 2-phase flow. Different types of crude oil sometimes are moved in batches on the same pipeline, as are grades of refined products. For example, 87, 89, and 92 octane gasoline are moved on a pipeline in batches, and moved end to end on the same pipeline along with diesel and jet fuel (Figure 26.2). Physics—turbulent flow—keeps the batches from mixing with those at their beginning and end.

FIGURE 26.1. Oil and gas value chain. (Source: Introduction to the Oil and Gas Pipeline Business for Executives. Courtesy of Pipeline Knowledge & Development.)

FIGURE 26.2 Typical refined-products and crude oil pipeline batching sequences. (Source: Miesner and Leffler, Oil and Gas Pipelines in Nontechnical Language, Pennwell Corp., 2006.)

Natural gas transmission and distribution lines, on the other hand, move natural gas as a relatively homogeneous commodity. Batching for oil lines and compressibility for gas lines introduce some significant difference in how the two types of pipelines are designed and operated.