The natural gas industry: equipment, materials, and corrosion

1 Introduction

Environmental quality, clean energy, and worldwide water scarcity have been established today as central disciplines in modern science, engineering, and technology. They are linked to the crucial problems of climate change and global warming (Raichev, Veleva, & Valdez, 2009; Roberge, 2009; Valdez et al., 2012).

Today, it is generally accepted that corrosion and pollution are interrelated harmful processes because many pervasive pollutants accelerate corrosion, and corrosion products such as rust, salts, and oxides also pollute water bodies. Both are pernicious processes that impair the quality of the environment, the efficiency of the industry, and the durability of the infrastructure assets. To complicate the situation, some contaminated water bodies also serve as sources of potable water (Marcos, Botana, Valdez, & Schorr, 2006; Schorr & Valdez, 2006, 2007; Schorr, Valdez, & Quintero, 2006).

Recent damaging cases of joint corrosion and pollution in which H₂S was a prominent factor have been reported (NACE, 2009; Rebak, 2001). This situation is aggravated when industrial, municipal, and agricultural pollutants are discharged into adjacent water bodies such as lakes, rivers, and estuaries (Schorr & Valdez, 2005).

In power-generating plants that burn fossil fuels such as coal, oil, and natural gas (NG), the last is generally preferred because of its transportation and production efficiency and favorable quantitative carbon/hydrogen ratio and it produces less combustion pollutants.

The April 2011 earthquake and tsunami in Fukushima, Japan, damaged electricity-generating nuclear plants, which led to problems of national security, industrial safety, and hazardous radiation and to a fundamental examination of the future of the nuclear industry by many countries (Park, 2011). Recently, workers at the wrecked Fukushima plant were exposed to radiation after contaminated water leaked from several pipes. The German government panicked into ordering the closure of several nuclear plants. Renewable energies such as solar and wind are intermittent, surging with the weather. Following these changes, the European aerial electricity grid, with its steel transmission towers and insulated aluminum and copper cables, is being expanded and modernized to supply the energy required by the increasing population. As a consequence of this critical situation, purified NG is now considered by European and American energy authorities as a “green” alternative, with lower corrosion and no radioactive or toxic pollutants (So, Valdez, & Schorr, 2013).

One of the latest developments in the struggle against corrosion is the creation of a central institution to serve the US Armed Forces in dealing with corrosion of military facilities, equipment, and weapons, which is one of the major consumers of energy, including NG (Dunmire, Thomson, & Yunovich, 2005; Greenwood, 2013; Hummel, 2014). Thanks to better NG technology and improved efficiency, it is becoming cleaner and more plentiful.

The economic and social relevance of the NG industry is evident in the activities of diverse international and national professional associations, R&D institutions, and industrial enterprises involved in all aspects of NG science, engineering, and technology (Table 1). These include authorities from the government, industry, and academia who are addressing the progress NG industry and its vital importance in national and global prosperity. Public and commercial journals publishing useful information on the NG industry are listed too.

2 Natural gas

NG is a source of energy for industrial, residential, commercial, and electric applications. It is also employed as a raw material for the production of polymers and plastics. The share of NG in the total energy consumption in the USA in 2013 was 23.7% (Lucas, 2015). The main sectors of the NG industry include drilling, production, storage, transportation, liquefaction, vaporization, transmission, and distribution, and all are affected to some extent by corrosion. NG is obtained from petroleum offshore wells using drilling and production marine platforms. It is transported to the marine coast through submarine pipelines. NG is obtained from onshore wells too. Usually, it is extracted with salty or briny water and corrosive gases, mainly H₂S and CO₂ (Mokhatab, William, & James, 2006; Smith, 1990; Wang, 2009). The principal component is CH₄, but it contains other light hydrocarbons as well (Table 2). H₂S present in NG oil wells generates sour gas and corrosion problems, denoted as sour corrosion (Quintero Nuñez, Valdez, & Schorr, 2010; Rebak, 2001; Roberge, 2009; Valdez & Schorr, 2011; Valdez, Schorr, So, & Eliezer, 2011; Wang & Atrens, 2004). It is a weak, reducing, water-soluble acid that can lead to the pitting of steels. An FeS film forms on steel surface, which is cathodic to the steel, enhancing further corrosion.

NG also contains CO₂, which converts into carbonic acid (H₂CO₃) when it is exposed to moisture, provoking corrosion and sometimes forming carbonate scales in well casings (Chilingar, Mourhach, & Al-Qahtani, 2008; Heidersbach, 2011; Philippine Corrosion Society, 2009; Waard, Lotz, & Milliams, 1991).

Wet acid gas, composed of a mixture of H₂S, CO₂, and water separated from offshore oil wells, is strongly corrosive to carbon steel (CS). This acidic gas is treated with amines, then compressed and injected into wells.

NG is treated to remove impurities and corrosive components, which are removed by applying membranes that prevent corrosion (Baker & Lokhandwala, 2008). It is burned in power stations to generate electric energy. Liquefied natural gas (LNG) is transported from continent to continent in cryogenic sea vessels (Figure 1) to marine ports and regasification plants (RPs). These giant steel and aluminum (for the sailors’ living quarters) ships are able to transport LNG from Indonesia to the Pacific Coast, from Algeria to the great cities of the Atlantic Ocean littoral and the Gulf of Mexico, and from NG countries on the Persian Gulf to the Mediterranean and the Baltic Sea coasts. Therefore, large quantities of NG are produced in countries where production far exceeds demand. It is converted to LNG by cooling and compressing after purification to remove water, solid particles, acidic gases, and heavy hydrocarbons.

Figure 1:

Cryogenic vessel carrier.

3 Shale gas

Shale gas (SG) is a type of NG that is entrenched in rock formations constituted mainly by layers of shale, a silicate mineral. It has been known in the USA since the early 20th century, but it has only been used as a central source of energy in the last decade. The US Department of Energy believes that the use of SG will dramatically reduce greenhouse emissions. Europe’s SG deposits almost match those across the Atlantic; many countries might enjoy a bonanza of cheap gas if production, corrosion, and environmental problems are overcome (Anonymous, 2013, 2015). The production of SG is increased by a mechano-chemical technique of hydraulic fracturing also called fracking, which is done by injecting large quantities of salty water, inorganic acids (HCl, H₂SO₄), and sand under pressure into the SG wells to break up the rock bed and increase the SG flow. This aggressive mixture of acid and saline water may corrode the gas wells’ steel equipment such as tubings, casings, pumps, and valves.

Some ecologists and environmentalists claim that fracking pollutes the air and drinking groundwater, but the evidence, presented by industry cycles, suggests that any such pollution is limited (Kargbo, Wilhelm, & Campbell, 2010). Due to the SG boom, many coastal RPs are being closed, because there is no need to import LNG. Meanwhile, companies seeking to exploit SG formations are first required to conduct environmental impact studies.

4 Natural gas industry infrastructure

The petroleum and NG industries are two key sectors of energy infrastructure, a powerful index of the vitality of a nation. NG is one of the most abundant sources of energy available today, and with continued innovation, it could provide cleaner energy for future generations. In many regions of the world, deals are in the work among countries, covering exploitation, production, and transportation of both oil and NG. Countries with no access to the sea are planning and installing long land steel pipelines for the exportation of NG, following the increasing global demand of energy.

The main sectors of the NG industry, arranged in chronological sequence of operation, are well drilling, production, cleaning, storage, transportation, liquefaction, vaporization, transformation, and distribution.

For the sake of brevity, this review deals with corrosion problems of the central assets of the oil and gas industry infrastructure, as follows:

• Drilling and exploitation of NG onshore wells;

• Marine petroleum platforms, their service vessels, and submarine pipelines;

• Pipelines for conveyance and distribution of NG;

• LNG RPs.

The corrosive characteristics of NG require the selection of corrosion-resistant alloys that will ensure long service life without corrosion. They include martensitic, austenitic, and duplex stainless steel (SS), precipitation-hardened steel, and acid-resistant Ni alloys. To maintain continuous and effective operation, a diversified assembly of equipment is employed in the NG infrastructure. These various equipment and their corrosion-resistant engineering materials are listed in Table 3.

4.2 Marine petroleum platforms

An offshore platform is a complex structure that is used to drill wells, extract and process oil and NG, and deliver them onshore. Fixed and floating platforms are built using two basic engineering materials: steel and reinforced concrete. They are constructed at European and Asian shipyards, towed out to sea, and installed at various depths in seas around the world, usually near the coast. The platforms are served by oil storage ships and other vessels and helicopters for transportation of personnel and supply of equipment. The platforms are provided with a flare stack made of corrosion-resistant Ni alloys to burn the excess, unused gas (Figure 2).

Figure 2:

Semi-submersible petroleum platform fitted with a gas flare tower.

The sea is a dynamic system in permanent motion, with complex surface currents and winds flowing over its surface, generating waves that affect marine installations and vessels. The central corrosive factors are salinity, dissolved oxygen, pH, velocity, and temperature (Heidersbach, Dexter, Griffin, & Montemarano, 1987). Corrosion is a major problem with offshore platforms because of the harsh environment; it appears at three levels: the atmosphere zone with salt-laden aerosols and sun radiation; the splash/tidal zone with violent waves and whitish oxygenated foam; the submerged and muddy zone, which sometimes contain corrosive pollutants.

Floating marine platforms stand in 500-m shallow waters, but water elsewhere reaches depths of 2300 m and beyond. There are 4000 fixed platforms off the US coast and 300 in the Bay of Campeche. Eighty percent of Mexico’s petroleum and 30% of its NG are extracted in this area. The nearby maritime oil terminals have facilities to control and threat oil spills during loading operations into huge tankers bound toward USA and Europe.

Sea macroorganisms and microorganisms settle down and adhere on installation surfaces and ships’ hull, enhancing corrosion (Acuña, Schorr, & Hernandez, 2004; Dürr & Jeremy, 2009). Special paints, charged with biocides, may prevent or avoid these pernicious phenomena. Leakage of petroleum, which contains CO₂ and H₂S, from wells and submarine steel pipelines, results in corrosion damage and environmental pollution.

4.4 LNG regasification plants

In 2012, around 100 RPs were operated worldwide, including plants in Mexico, Latin America, the USA, Europe, and Asia. There are a number of technologies for exporting NG energy from oil and gas fields to market, including pipelines, LNG, compressed NG, gas to wire, i.e. electricity (Sidney & Dawe, 2003). Various installations, structures, and equipment are utilized in RPs to convert LNG back to its gas form. They comprise two central units: the port terminal for the cryogenic ships’ mooring and the open-rack vaporization for conversion, which is heated by seawater, since the LNG temperature is −160°C (Figure 3). After regasification, the NG is transferred to an onshore pipeline distribution system for the ultimate consumers (Quintero et al., 2014; Valdez, Schorr, Quintero, García, & Rosas, 2010).

Figure 3:

LNG rack vaporizers.

The RP equipment is fabricated from a wide spectrum of engineering materials, metallic and nonmetallic, that display reasonable endurance to fluids (liquid, vapor, and gases) handled and processed in the RP installations and facilities. The main LNG equipment and their engineering materials are listed in Table 3. Onshore installations and equipment include the chemical facilities used in the RP operation and service for the production of chlorine, alkali, ammonia, nitrogen gas, potable water, electricity, etc. Figure 4 presents a block diagram of an RP.

Figure 4:

RP schematic flow diagram.

Because of the locations of the RPs on ocean and sea coasts and due to the complex equipment being operated, several types of corrosion are distinguished:

• Marine corrosion, particularly in splash zones where violent waves break down and generate whitish, oxygenated foam, which increases local corrosion.

• Coastal atmospheric corrosion with salt-laden mist that condenses on the equipment surface during cold nights. Relevant environmental parameters are air temperature, relative humidity (sometimes <70%), salinity deposition rates, rainfall, wind effect, and air pollution, such as SO_x and NO_x from fossil fuel combustion, which causes acidic rain and subsequent corrosion.

• Industrial corrosion of land equipment and machinery by humidity, dust deposition, galvanic couples, and surface paint deterioration.

Corrosion has a major impact on the economics of LNG facilities, safety, and environmental preservation.

5 Corrosion and protection control

The concepts of inspection to determine the conditions of a system, monitoring to assess the need for corrosion control in laboratory or field/plant testing, and evaluating the equipment and materials are essential to ensure the efficient operation of the NG facilities. A special technique was developed and applied for the detection of localized and general corrosion of NG transmission of pipelines using electrochemical noise sensors (Bullard et al., 2002). An additional technology employs sensors compatible with a robotic vehicle for in-line inspection that can maneuver within the pipe (Bickerstaff, Vaughn, Stoker, Hassard, & Garrett, 2002).

Practical methods that minimize or eliminate corrosion include the selection of suitable, corrosion-resistant engineering materials and application of paints and coatings to CS equipment, CP mainly for steel pipelines, and corrosion inhibitors for NG. Frequently, corrosion, scaling, and fouling phenomena appear simultaneously in vast and diverse installations and equipment of the NG industry. NG contains some associated water, which becomes acidic due to the presence of dissolved gases, mainly H₂S and CO₂. Scaling and fouling often derive from the salty water generated together with oil and gas in the production wells. Dissolved CO₂, forming carbonic acid, may react with Ca²⁺ salts, depositing CaCO₃ scale in CS surfaces.

5.3 Cathodic protection

The combination of coating as the primary method of corrosion control, with CP as a supplementary method, is the most economical way to control corrosion, in particular, for submerged steel structures and pipelines. CP is applied by two techniques: sacrificial anodes (Figures 5 and 6), made of Al, Mg, and Zn, and by an impressed direct current, at an electrochemical potential sufficiently negative to convert the steel structure in a cathodic surface. CP efficiency depends on the electrical conductivity of the environment and the continuous protection function of the sacrificial anodes (Garcia et al., 2015).

Figure 5:

Legs of a petroleum marine platform fitted with aluminum alloy sacrificial anodes.

Figure 6:

Ship propeller and rudder with aluminum alloy sacrificial anodes.

6 Discussion

NG is an abundant resource across the USA. New extraction methods have led to a dramatic change in its supply. Years ago, virtually all NG production came from traditional gas or wells reached by vertical drills. In 2009, according to the Energy Information Administration, about 20% of American NG came from shale formations. Compressed NG can be used for motor vehicles, after some adaptation.

The SG boom is increasing American NG exports, but it is closing coastal RPs that imported LNG from countries far away. NG and oil companies work to secure critical infrastructure against cyber threats and terrorist attacks (Melman, 2014).

On the one hand, decreasing oil prices harm Mexico’s economy. On the other hand, Mexico is undergoing an intensive reform process of the energy sector, including its oil, NG, and electricity industries. Mexico’s abundant resources such as deep-sea oil in the Gulf of Mexico (Hernandez, Schorr, Carpio, & Martinez, 1995; Raichev et al., 2009; Veleva, Castro, Hernandez-Duque, & Schorr, 1998) and SG will be exploited, and additional refineries and pipelines are being planned and built with the active participation of heavy foreign investments. The reform was recently approved by the Mexican Parliament (Anonymous, 2013; Mexican Energy Reform, 2013) and is setting Petróleos Mexicanos (PEMEX), the national oil company, on the way to becoming a world oil enterprise, producing 3 million bpd (477 million L/day) (Duran, 2014; Garcia et al., 2015).

The oil and NG industries in Mexico, including LNG RPs and the profitable petrochemical industry, are managed by PEMEX. These industries deal with exploration, production, transportation, and distribution of crude oil and its many derivatives.

To maintain a continuous and efficient operation, a massive assembly of structures and equipment is used, including marine petroleum platforms, service vessels, and submarine pipelines; semi-submersible vessels for drilling offshore petroleum wells; land pipelines for conveying and distributing; fuel storage tanks; sea wind turbines; oil transportation tankers, cargo ships, and harbor structures; heat exchangers; oil well casings; etc. All these diversified facilities and installations require the applications of protection with sacrificial anodes, which are produced by local Mexican companies (Garcia et al., 2015).

Recent discoveries of new sources of NG along the coast of the Mediterranean Sea have altered the energy balance of the region. The use of NG started in Israel in 2004, mainly by the Israel Electric Corporation and supported by the Natural Gas Authority (2015) (Table 1) in the Ministry of Energy and Water Resources. NG is extracted from wells operated by marine platforms and passes a system of steel pipes, until it reaches reception stations on the country shore. The gas flows through a nation transmission system to supply the country and other neighbors. The development of NG fields by Israel, Syria, and Lebanon are paving the way toward a new reality in the region – of a probable useful coordination about NG exploration security (Melman, 2014). Israel proposes to build a “Euro” pipeline, in cooperation with Cyprus, Greece, and Italy, to supply NG to Europe.

The Technion-Israel Institute of Technology has established a postgraduate MSc degree program in energy source engineering and technology. The Israel Chemical Society organizes symposia and courses on the application of NG in chemical, electricity, water, and transportation industries, including corrosion control.

Europe’s SG deposits almost match those across the Atlantic in America. Determining which countries might enjoy cheap NG is not yet certain. Many things are in flux, including extraction technologies and production rates. Meanwhile, the European Union (EU) is being supplied by a long pipeline system from Russia, passing through Ukraine. The EU NG network has become more integrated, with the installation of interconnector pipes. Countries in central Europe can receive NG from the west via Germany, from Russia through alternative pipelines such as the Nord Stream, or from North African countries through submarine pipelines installed on the Mediterranean seabed. European national corrosion institutes and experts oversee and manage the corrosion problems of this huge system of pipes, pump stations, and valves to regulate NG flow and supply (Figure 7).

Figure 7:

European network of NG pipeline.

7 Conclusions

• NG is the preferred fossil fuel for the operation of electricity-generating plants because of its low cost, ease of transport, and low pollution.

• The world’s abundant SG beds in many countries in Europe and in America are becoming the most important factor in the global energy revolution.

• The production well is the main component of the oil and gas system. Their steel drilling strings, well casing, and tubing are attacked by downhole corrosive factors.

• The NG infrastructure requires the implementation of corrosion control methods through the stages of design, construction, installation, and operation.

• Corrosion prevention and mitigation is achieved by the application of modern corrosion control technology including the correct selection of engineering materials, covering the surface of steel equipment by chemical conversion coating and industrial paints, employing CP with sacrificial anodes for marine platforms and impressed current for pipelines, and choosing suitable corrosion inhibitors.