**3. Inhibitors for near-neutral solution**

The neutral medium includes circulating cooling water, boiler water, heating water, washing water, oil and gas field injection water and neutral salt water, etc., and the application of corrosion inhibitor is mainly in circulating cooling water system. During the operation of the cooling water in the circulating water system, the concentration of harmful ionic dissolved in the water increases with the continuous evaporation of water, which resulting in deterioration of the quality of the cycle water, and fouling and corrosion of the heat exchanger and the cooling tower. In the open circulating cooling water system, biological slime caused by the microbial growth can also accelerate the local corrosion of metal.

**159**

**Table 3.**

*Formulation of Corrosion Inhibitors*

and 5, respectively.

**3.1 Cooling water inhibitor**

*3.1.1 Chromate programs*

ratio of CrO4

ture, with the ratio of CrO4

water is typically 6.0–7.0.

*3.1.2 Stabilized phosphate programs*

program can often provide excellent corrosion inhibition.

*A typical "standard" formulation for a chromate product.*

**Chromate program formulation w/w %** Sodium dichromate, dihydrate 50 Chromic acid 1 H3PO4, commercial acid 8 ZnCl2 11 HEDP 14 Water 16 Total 100

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

The washing water and the neutral salt water systems, which are similar to the circulating water, will not be introduced in this section. The corrosion inhibitors for boiler water and water injection of oil and gas fields will be introduced in Sections 4

We can select water treatment agents according to the Ryznar index of cooling water or the possible problem. For example, zinc-phosphonate salts as water treatment agents can be chosen for serious erosion in circulating cooling water system, while polyacrylic acid, hydrolyzed polymaleic anhydride, or phosphonate can be used when a large number of scaling has occurred. As the limited compounds in the figure, it cannot be used as a standard method for choosing the right agents. However, it provides the vital reference for the design of the cooling water treatment system.

The complex corrosion inhibitors used in the neutral medium include chromate,

Formulations and chemical programs of some examples are discussed in this section.

The chromate programs are based primarily on the zinc and chromate mix-

respectively. In order to lower the health and environmental hazard by chromate, polyphosphate, phosphonate, or polyacrylate is often added as well. The level of zinc or other possible inhibitor is correspondingly raised for compensation. A typical "standard" formulation for a chromate product that may be used as shown in **Table 3**, for example, in a large coastal petrochemical facility, is described here. This program formulation will tend to be dosed continuously to achieve a 35–50 ppm product reserve in the recirculating cooling water. The pH of the cooling

In essence, stabilized phosphate programs involve the treatment of controlling ratios of oxygen and phosphate or phosphorus and phosphate and also the other inhibitors combining with a suitable "stabilizing" polymer. Various halogen-stabilized polymers are usually provided. Under prescribed operating conditions, this

varies from 10 to 25 ppm. If low or ultralow chrome program is employed, the

<sup>2</sup><sup>−</sup>: Zn2+ from 6:1 to 8:1, and the chromate reserve

<sup>2</sup><sup>−</sup>:Zn2+ is typically 1:1, and the chromate reserve is from 3 to 8 ppm,

phosphate, alkaline zinc/organic, molybdate, silicate, and organic programs.

### *Formulation of Corrosion Inhibitors DOI: http://dx.doi.org/10.5772/intechopen.88533*

The washing water and the neutral salt water systems, which are similar to the circulating water, will not be introduced in this section. The corrosion inhibitors for boiler water and water injection of oil and gas fields will be introduced in Sections 4 and 5, respectively.
