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NACE Corrosion Control In The Refining Industry

The total annual cost of corrosion in the oil and gas production industry is estimated to be $1.372 billion, according to a NACE study. That figure can be broken down into $589 million on surface pipeline and facility costs; $463 million annually in downhole tubing expenses; and another $320 million in capital expenditures related to corrosion.

NACE Corrosion Control in the Refining Industry

The Refining Corrosion Technologist certification is targeted at individuals who are responsible for identifying, locating, and controlling corrosion in refinery environments. Those applying for this certification should possess an understanding of refinery process unit-specific corrosion mechanisms.

From the proximity of assets to saltwater, to the production and storage of hazardous chemicals, refineries pose unique challenges that require specialized training to combat corrosion. The coursework covers the effects of corrosion on the production environment and addresses methods to implement corrosion control throughout the full lifecycle, from material selection and design to maintenance.

They are a different thing. API inspector certificates provide general coverage of the inspection of vessels, pipework, pipelines and storage tanks including the corrosion mechanisms in API RP 571.NACE concentrates solely on corrosion control subjects.

The aim of this work is to describe and analyze corrosion problems and their solutions in oil, gas, and refining industry. Corrosion phenomena and factors influencing them are discussed. Corrosion control and monitoring methods are illustrated. Corrosion management plays vital role in the solving of corrosion problems. The results are summarized in new book of the author "Corrosion Problems and Solutions in Oil Refining and Petrochemical Industry " published by Springer in 2016.

Metallic equipment and constructions in oil, gas, and refinery plants contact crude oils, natural gas, petroleum products and fuels, solvents, water, atmosphere, and soil. All processes with participation of aggressive substances occur in metallic equipment at temperatures from -196 C to +1400 C and pressures from vacuum to 1000 bar. Oil, gas and refinery units represent a high hazard industry with media which are flammable, explosive, toxic to human health or harmful to the environment. The combination of numerous factors makes oil, gas and refinery equipment very vulnerable to a variety of corrosion phenomena that can lead to serious accidents.

On the one hand, oil, gas and refining industry has accumulated large experience. On the other hand, the development and production of new deep wells in harsh conditions, introduction of new technologies, materials, strict requirements to the quality of gas and fuels, and to the reduction of environmental pollution state new problems to safe functioning of equipment and constructions. In order to understand and to solve corrosion problems, corrosion and materials specialist should learn diverse physicochemical processes which are the basis of treatment of oil and gas and production of fuels and other chemicals. Humans in this industry are responsible in 65-85% of corrosion events. Using proper corrosion management it is possible do diminish them.

Like evolution of our planet, life and technology, oil, gas and refining industry has been developing with increasing complexity since its foundation in 1859. There are associated facilities, such as cooling water systems, power plants (with water treatment and steam providing), and units related to the protection of the environment and humans (the utilization of hydrocarbon wastes, purification of wastewater and emitted gases, and deodorization). Any gas plant and oil refinery is a very complicated alive "organism". Each gas plant and oil refinery has its own unique processing scheme which is determined by the process equipment available, crude oil and natural gas characteristics, operating costs, and product demand. There are no gas plants and refineries absolutely identical in their operations but most corrosion problems and solutions may be similar.

In order to understand corrosion problems and solutions in oil, gas and refining industry, we will describe physicochemical characteristics of crude oils, natural gas, fuels and their corrosiveness. Other media, such as water (cooling water, boiler feed water, extinguishing water, seawater), steam, different gases and chemicals also can participate in corrosion of equipment at oil, gas, and refining units.

Hydrogen sulphide (H2S). The presence of sulfur compounds (mainly H2S) defines the gas to set the sour. Sweet gas contains less than 4 ppmv H2S [1]. This value is the maximum approved one for the quality of natural gas during transportation in pipelines. H2S can cause general and pitting corrosion, and hydrogen attack (because of acid corrosion). The latter can appear as crack or blisters. H2S can be emitted through crack into environment and cause death of people and damage to the environment. Standards defining the conditions and requirements for using corrosion resistant alloys in the production and handling of natural gas that contains H2S were developed and widely used [2-4]. The following methods of prevention of sour corrosion are used: control pH by caustic injection; injection of H2S scavengers and corrosion inhibitors; organic and cement coatings; choose of alloys according to standard [2] for prevention SSC (Sulfide Stress Cracking).

This sweet corrosion is widespread in natural gas pipelines. Passive black film FeCO3 is formed under particular conditions on the surface of carbon steel and low-alloy steels (to 9% Cr) and can protect from corrosion. Protective iron carbonate layer often breaks down because of high velocity stream and stresses. In this case, carbonic acid results in localized corrosion under the name "mesa" corrosion because the shape of the damage of the steel surface is similar to the shape of the mountains "Mesa", California, USA [5]. The following methods of prevention of sweet corrosion are used: injection of corrosion inhibitors (they are not effective at high temperatures); use of martensitic stainless steels (>12% Cr); and control pH by caustic injection.

Selection of corrosion control measures are based on the influence of chemical composition of natural gas (corrosive impurities) and process conditions (temperature, pressure, and flow rate regime) on corrosion. Three major factors affect corrosion: metal type, environmental features and conditions, and the border metal-environment [14]. Thus, we take care of three factors above to prevent corrosion in natural gas systems. We classify all the methods into three groups: the metal treatment (selection of material), the treatment of the environment (neutralization, removing of water, CO2, H2S, O2 and salts) and boundary metal-environment (injection of inhibitors, use of coatings, and cathodic protection). We can add technological methods, which means maintaining the process conditions (temperature, pressure, flow rate). We will start from engineering design.

b)The use of knowledge of principles, processes and possible corrosion phenomena in natural gas systems. It is necessary to take into account the geometry of the equipment, to make less crevices, to control flow rate, to prevent air infiltration, to avoid "dead legs" (gathering areas and stagnation of water).

c)Selection of suitable materials of construction, methods of protection, control and corrosion monitoring for designed period of service. Choosing suitable coatings, corrosion inhibitors, biocides, ant-scaling agents, cathodic protection and removing corrosive impurities (H2S, H2O, O2) belong to this group.

The philosophy of cathodic protection use is that organic coatings' application on metallic structures is the main (leading) method of corrosion control, and cathodic protection is a complement to protect the defects that are always exist or appear in organic coatings during application and service. Electrochemical mechanism of corrosion of metals in solutions of electrolytes allows the use of electric current and electric potential to protect metal surface from corrosion. Therefore, cathodic protection works only in solutions of electrolytes and does not work in media of high electrical resistivity which cannot conduct electrical current: in natural gas, air, oil, and fuels. Two ways exist for cathodic polarization in practice: connection the main metal to be protected (for example, iron) to less noble metal (aluminum, zinc, magnesium, or their alloys), or connection to the negative pole of outer power supply (rectifier or battery). The first method is based on sacrificial anodes use, because they are sacrificed being dissolved as anode, and turn the metallic construction to cathode which does not corrode. Sometimes this method of cathodic protection is called a passive one (there is no relationship to passivity!), because we connect equipment to be protected to sacrificial anode, and "forget" about corrosion for some period. The second method of cathodic protection is based on the connection to the negative pole of the rectifier and use of impressed electric current. This method is called sometimes an active method of cathodic protection. Cathodic protection is one of wide spread methods of corrosion control of underground and submerged metallic structures and equipment. Cathodic protection works only on external surfaces that contact with the electrolyte and it does not mean the media flowing or stored inside: gas, oil, fuel, or water. Many standards exist to implement cathodic protection, testing methods and monitoring efficacy [43-50]. High temperatures, destroyed coatings, shielding, microbial attack, areas of pipes and tanks that are not in contact with the electrolyte and dry soil are the conditions when cathodic protection is not effective or is working only a part of time. Cathodic protection does not work for thermal insulating structures [47]. It is important to remember that cathodic protection is working when the following components exist: an anode, a cathode, an electrolyte, and a complete electrical circuit. The absence of one of these components prevents the activity of the cathodic protection. Sometimes people forget about it and try to use cathodic protection for hot pipes when hot water evaporates and there is no electrolyte for the passage of an electric current. American engineer Robert Kuhn was the first who used cathodic protection on pipelines for transporting natural gas in the U.S. in 1928 and more widely in the 1930s [5, 51-54]. There are several methods to test the efficacy of cathodic protection [5, 32, 42, 43]. 041b061a72


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