Corrosion Control by Inhibitor

When the above-mentioned corrosion control systems are impractical and/or uneconomical the corrosion control by inhibitor should be implemented. 

The chosen corrosion control system should control corrosion effectively and economically with regard to available Engineering Standards. 

Selection of inhibitor should be based on knowledge of the production characteristics of the system, field performance tests, and laboratory confirmation of performance. 

A partial list of field factors that should be considered in inhibitor selection are fisted witfi brief notes below. 

1 Transmission Lines Gas Factors affecting inhibitor selection  

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Results of the study of corrosion control by inhibitors in producing oil wells in carbon dioxide flooded fields showed imidazolines are successful in protection in CO2 brines. The inhibitor was found to be incorporated in the carbonate corrosion product layer but was still more effective if the surface film contained sulfide. Also, better results were obtained with inhibitors, such as nitrogen-phosphorus compoimds or compounds with sulfur in the organic molecules. 

Inhibition of storage tanks and tankers handbng crude oil and/or petroleum products should be based on consideration of corrosion control by inhibitor. 

Primary alkanolamine solutions require a relatively high heat of regeneration. Also excessive temperatures or localized overheating in reboilers cause the MEA to decompose and form corrosive compounds. An inhibitor system, such as the Amine Guard system developed by Union Carbide, is an effective method of corrosion control (52). Inhibitors permit the use of higher (25—35%) concentration MEA solutions, thus allowing lower circulation rates and subsequendy lower regeneration duty. 

If materials selection depends on corrosion control by process-related measures (such as chemical treatment), these should be indicated on the MSD. Indicate the intended injection points and the type of chemical to be injected. Examples include corrosion inhibitors, scale inhibitors, biocides, pH control chemicals, wash water, etc. Also indicate the location of proposed corrosion monitoring and sampling sites. If anodic or cathodic protection is to be part of the corrosion control design, the MSD or its Notes section should indicate the piping and/or equipment to be protected. 

Corrosion control by pigments relies on well-known principles of corrosion inhibition. Iron and steel exposed to air are quickly covered by an oxide film aqueous electrolytes tend to break down this film, and further oxidation of the metal surface ensues. The role of anodic corrosion inhibitors is to supplement or to aid in the repair of the surface oxide film. Basic pigments may form soaps, for example, with linseed oil autoxidation of these soaps may yield soluble inhibitors in the film. Some other pigments of limited solubility act directly as inhibitors. Active metal pigments supply electrons to the iron substrate and thus lower its potential and prevent metal dissolution. 

Protection of cooling system metals involves complex interrelated problems of scale and deposit prevention, control of microbiological growths and other fouling sources, in addition to corrosion mitigation by inhibitors. Corrosion control programs may be expected to vary considerably between systems, since each installation presents different environmental factors and operating problems which affect response. 

Corrosion control by use of inhibitors is extremely useful in many environments, however, there are certain exceptions, such as ... 

Corrosion Control by Protective Coatings and Inhibitors, Corrosion Understanding the Basics, J.R. Davis, Ed., ASM International, 2000, p 363 06... 

It also deals with the control of corrosive environments by inhibitors, general requirements for the petroleum and chemical industries, and utility systems such as cooling water, boiler water systems etc. 

Rajendran, S. Apparao, B. V. Palaniswamy, N. Symposium on Corrosion Control by Coatings, Cathodic Protection and Inhibitors in Seawater, Dubrovnik, Crotia, 23rd Event of the European Federation of Corrosion, 1998. 

Alkenylsuccinic anhydrides made from several linear alpha olefins are used in paper sizing, detergents, and other uses. Sulfosuccinic acid esters serve as surface active agents. Alkyd resins (qv) are used as surface coatings. Chlorendric anhydride [115-27-5] is used as a flame resistant component (see Flame retardants). Tetrahydrophthalic acid [88-98-2] and hexahydrophthalic anhydride [85-42-7] have specialty resin appHcations. Gas barrier films made by grafting maleic anhydride to polypropylene [25085-53-4] film are used in food packaging (qv). Poly(maleic anhydride) [24937-72-2] is used as a scale preventer and corrosion inhibitor (see Corrosion and corrosion control). Maleic anhydride forms copolymers with ethylene glycol methyl vinyl ethers which are partially esterified for biomedical and pharmaceutical uses (189) (see Pharmaceuticals). 

Whereas sulfamic acid is a relatively strong acid, corrosion rates are low in comparison to other acids (Table 3). The low corrosion rate can be further reduced by addition of corrosion inhibitors (see Corrosion and corrosion control). 

Water plays a primary role in corrosion of the metal walls of tanks and pipes (17), and increases the tendency for high speed pumps to produce wear particles and to exhibit shortened life. Formation of corrosion products can be controlled by addition of corrosion inhibitors, a mandatory additive in military fuels. However, corrosion inhibitors may also degrade other fuel properties and adversely affect ground filtration equipment. Thus they are not generally acceptable in commercial fuels where rigorous attention is given to clean and dry fuels upon aircraft fueling. 

Carbon dioxide corrosion can be controlled by the use of caustic soda and lime and the addition of various inhibitors. Film-forming amine inhibitors are used to reduce the corrosion rates. The control measures will be discussed later. 

Scale formation Controlled scale deposition by the Langelier approach or by the proper use of polyphosphates or silicates is a useful method of corrosion control, but uncontrolled scale deposition is a disadvantage as it will screen the metal surfaces from contact with the inhibitor, lead to loss of inhibitor by its incorporation into the scale and also reduce heat transfer in cooling systems. Apart from scale formation arising from constituents naturally present in waters, scaling can also occur by reaction of inhibitors with these constituents. Notable examples are the deposition of excess amounts of phosphates and silicates by reaction with calcium ions. The problem can be largely overcome by suitable pH control and also by the additional use of scale-controlling chemicals. 

Hence whilst in the past corrosion control has involved, in the main, the use of metal alloys, protective coatings, inhibitors, etc. corrosion problems may now often be circumvented by the use of self-supporting organic polymers in the form of either rubbers or plastics. It must however be immediately stressed that such materials are not invariably inert to chemicals and they display their own particular response to such materials. A consideration of such behaviour will be a prior object of this section. 

The polarization characteristic of a corroding metal can be controlled by various additives to the solution, called corrosion inhibitors, which adsorb on the metal and lower the rates of the cathodic and/or anodic reaction. Inhibitors are used primarily for acidic electrolyte solutions, sometimes also for neutral solutions. Various organic compounds with -OH, -SH, -NHj, -COOH, and so on, as the functional groups are used as inhibitors. The effects of an organic inhibitor, tetradecylpiperidinium... 

Z. Jiashen and Z. Jingmao. Control of corrosion by inhibitors in drilling muds containing high concentration of H2S. Corrosion, 49(2) 170-174, February 1993. 

K. C. Koshel, J. S. Bhatia, S. Kumar, and A. K. Samant. Corrosion problem in kalol injection water pipeline system and its control by using corrosion inhibitors. Ongc Bull, 25(2) 115-133, December 1988. 

Corrosion is effectively controlled by using chemical inhibitor systems which are added to the glycol to make a complete coolant concentrate formulation commonly referred to as permanent engine coolant. 

Since HtS dissolved in water is very corrosive to carbon 4 steel, a comprehensive corrosion-control program is being conducted. In the field, each well is treated once per month by displacing inhibitor down to the perfora-. tions with stock tank oil. Corrosion coupons in the flow-lines are inspected every 6 months Little corrosion has been detected in the field. In the plants, corrosion in-hibitor is added daily to the gas-sweetening solvent, the salt water system, and the stabilizer overhead. Inhibitor is -Jj also added to bulk chemicals as received. Numerous corrosion coupons and probes are installed in each facility and are pulled for inspection every 1 to 3 months Corrosion rates have been low (less than I mil/year) asY result of the inhibitor injection program. 

Oxygen, carbon dioxide and various chemicals used to reduce scaling can cause corrosion. Corrosion control is provided largely by the use of inhibitors such as chromates, polyphosphates, silicates and alkalies. 

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