**Abstract**

Corrosion inhibitors are widely used in the production process due to their significant effect. In this chapter, the formulation of typical corrosion inhibitors in acid solution, near-neutral solution, alkaline solution, and oil and gas systems will be discussed, respectively. Firstly, the importance of pickling corrosion inhibitors for thermal equipment in industrial production in different situations is discussed in the "Inhibitors for acid solution" section, and the types of pickling inhibitors are mainly applied in different kinds of acid media, such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, hydrofluoric acid, citric acid, and sulfamic acid. Secondly, in the "Inhibitors for near-neutral solution" section, the cooling water inhibitors principally include chromate, stabilized phosphate, alkaline zinc/organic, molybdate, all organic, soft and lean water, and environmental and closed-loop programs. The hot-water inhibitor is also mentioned here. Then in the "Inhibitors for alkaline solution" section, boiler water inhibitor, oxygen scavenger, and corrosion inhibitors for condensate line are talked over. Finally, in the "Inhibition for oil and gas systems" section, drilling fluid, fracturing acidizing, oil and gas well, and oil field which produced water treatment inhibitors are introduced here. The corrosion inhibition mechanism and development trend of inhibitors are also discussed.

**Keywords:** inhibitors for acid solution, inhibitors for near-neutral solution, inhibitors for alkaline solution, inhibition for oil and gas systems

## **1. Introduction**

Pickling is widely used in various production processes, such as for pickling and rust removal of metal pipes, plates, and wires, and products in the metallurgical and mechanical industries, scale cleaning of heat exchange equipment, heat transfer equipment, and cooling equipment in various industrial sectors, especially for pickling of thermal equipment such as boilers in the electric power sector. It is meaningful using pickling, for example, from a socioeconomic point of view, fuel consumption due to fouling can be reduced; from the perspective of environmental protection, fuel exhaust and atmospheric pollution are reduced; from a safety point of view, thermal equipment such as boilers and heat exchangers can be used well. As we know, various types of dirt are gradually formed in the process, and the poor thermal conductivity of the dirt causes the local temperature of the furnace tube to rise, which reduces the strength of the steel and often causes a pipe burst accident and affects the operation of the boiler. Therefore, pickling plays a very important role in the boiler operation of power plants. In addition, the use of industrial circulating cooling water technology to increase the

concentration of running water can save a lot of industrial water. In circulating cooling water, in order to avoid corrosion and scaling of equipment, it is often necessary to add water stabilizer. Also, in the process of crude oil and natural gas collection, the current drilling and oil recovery technology requires fracturing and acidification of limestone oil and gas fields with high concentration of hydrochloric acid solution. As the 15–28% hydrochloric acid solutions are often used in the oil wells, the corrosion problem of tubing and oil production equipment is serious in deep well acidification technology due to the high temperature in the well. Therefore, metal materials and products are subjected to various environments during production, storage, transportation, and use. Metal products are easy to vary from different degrees of corrosion. Corrosion problems in tubing and oil production equipment are serious, sometimes causing fracture accidents, resulting in construction failure.

Corrosion inhibitor is an anticorrosion chemical; it can be added to the corrosive environment to cause physical and chemical interaction with the metal surface, thereby significantly reducing the corrosion of the metal material. At the same time, the use of the corrosion inhibitor does not require special equipment, nor does it need to change the properties of the metal. Compared with other anticorrosion methods, corrosion inhibitors are easy to use, cost-effective, and widely used in industrial production and social life. Therefore, it is widely used in various industrial processes, such as pickling, cooling water systems, acidification of oil and gas wells, water injection in oil fields, storage and transportation of metal products, and so on. With the advancement of society and the enhancement of human environmental awareness, the development and application of corrosion inhibitors have received more and more attention. In recent years, countries around the world have paid great attention to the research and application of corrosion inhibitors, which can be used alone or in combination with other anticorrosion materials.

Herein, in view of the current requirements, the characteristic formulation of corrosion inhibitors in acid solution, near-neutral solution, alkaline solution, and oil and gas systems is discussed. The types of pickling inhibitors in different kinds of acid media, inhibitors for the cooling water, alkaline solution, and oil and gas systems are principally talked about in details, respectively.

#### **2. Inhibitors for acid solution**

In various corrosive media, acidic gases and liquids are of strong corrosive medium. The rate of metal corrosion in acidic medium is much faster than that in other media, especially in sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, hydrofluoric acid, citric acid, and sulfamic acid, which are commonly used in pickling and removing iron oxide, descaling and decontaminating of boiler equipment, and so on. In addition, high level of H2S and CO2 in oil and gas wells is also the corrosive acidic medium. Since acid has a corrosive effect on metal equipment, especially the corrosion effect of inorganic acid is more serious, and the released hydrogen will diffuse into the interior of the metal, causing hydrogen embrittlement of the equipment to be washed. In addition, as a large amount of acid gas will generate, it will deteriorate working conditions inevitably. Therefore, a suitable corrosion inhibitor should be added during pickling to inhibit the corrosion of the metal in the acidic medium, reduce the amount of acid used, improve the pickling effect, and prolong the service life of the thermal equipment. **Table 1** shows the commonly used corrosion inhibitors in corrosive acidic medium.

**155**

**Inhibitor** Advanced pyridine alkali

4-Methylpyridine residual

Nitroaniline 1-Phenyl-3-thioformamide

Reactant of amine and alkynol

Methenamine + CuCl2

Methenamine + SbCl2

Furfural Methenamine + KI

Methenamine + thiourea + Cu2+

1,3-Dibutyl-2-thiourea + OP

**Table 1.**

*Operating conditions and properties of some common corrosion inhibitors.*

**Acid concentration and temperature**

12% HCl + 5% HF, 40°C

10% HCl + 6% HF, 30°C

2–3 mol/L HNO3

20–35% HNO3

5–15% HCl, 93°C

2–25% HCl 10–15% HCl 0.2–6 mol/L HCl

20% H2SO4 10% H2SO4 10–20% H2SO4, 60–80°C

**Inhibitor dosage**

0.2% 0.2% 0.002 mol/L

0.0005% 0.01–0.25% 0.6 + 0.02% 0.8 + 0.001% 5–10/230 mL

0.6% (8:1) 0.14 + 0.097 + 0.003%

0.5 + 0.25%

**Inhibition efficiency**

<0.1 mm/a <0.1 mm/a High efficiency High efficiency

99.4%

99% 99% High efficiency

99% 99% High efficiency

*Formulation of Corrosion Inhibitors*

*DOI: http://dx.doi.org/10.5772/intechopen.88533*

**Metals** Carbon steel Carbon steel

Copper Aluminum Carbon steel Carbon steel

Carbon steel

Copper and alloy

Carbon steel

Carbon steel

Carbon steel

