Corrosion inhibitors performance characteristics

Importantly, stability and performance at acidic and alkaline pH extremes are a signature characteristic of these surfactants. Thus, for example, commercial amphoterics such as dihydroxyethyl alkyl glycinate are considered to be excellent thickeners for strongly alkaline oven as well as acid toilet bowl cleaners. Amine oxides enjoy similar properties. Resistance to both acids and bases make them suitable for use in products such as hypochlorite and phosphoric acid hard surface cleaners, hair dyes, corrosion inhibitors, and printing inks [4]. 

FIG. 4—Performance characteristic of an oilfield corrosion inhibiter in the HSACT at 1000 psi CO2 partial pressure, 200°F and 1500 rpm. The hypothetical Langmuir behavior is shown to Indicate the much stronger adsorption of the inhibitor. 

Transport of gasoline and other refined products in steel pipelines may result in corrosion products that can create a product contamination problem. Internal corrosion of the pipeline can also have an adverse effect on pipeline capacity. Corrosion results from condensation of a water film on the pipe wall plus dissolved air or SRB in the product. Corrosion control is commonly achieved by adding a corrosion inhibitor. Evaluation of inhibitor performance can be done using NACE Test Method for Antirust Properties of Cargoes in Petroleum Product Pipeline (TM0172). This test method is a modification of ASTM D 665, Test Method for Rust-Preventing Characteristics of Inhibited Mineral Oil in the Presence of Water. 

Rust problems during usage of certain refined products, such as steam turbine oils, are controlled by addition of corrosion inhibitors. Evaluation of the performance of these inhibitors is done using ASTM D 665 or ASTM D 3603, Test Method for Rust-Preventing Characteristics of Steam Turbine Oil in the Presence of Water (Horizontal Disk Method). 

The corrosion chemical inhibitor must meet certain requirements for each specific application such as stability against temperature, time, and exposure to the corrosive environment. It must function at low concentration and be easy to apply. Solubility characteristics must be designed for each application, and the inhibitor must be pumpable at the system temperature. It must be compatible with other chemicals in use and must meet performance specifications. It must inhibit corrosion. It must also be compatible with the system in which it is used and not cause system upsets. It cannot be too toxic and the flash point must be within specifications. Raw materials must be readily available and not too expensive, and manufacturing processes must be capable of control and reproducibility. Potential savings for each of those goals must be evaluated to determine if a program of corrosion inhibition will be economical. Because costs are sometimes difficult to estimate, the best method is to obtain data on maintenance, replacement, and so forth, from past history of the system to be protected or from a similar system. Literature on the economics of inhibition is a tremendous aid in estimating costs. 

Table 10.1 presents some inhibitors that have been used with success in typical corrosive environments to protect the metallic elements of industrial systems. Commercial inhibitors are available imder various trade names and labels that usually provide little or no information about their chemical composition. It is sometimes very difficult to distinguish between products from different sources because they may contain the same basic anticorrosion agent. Commercial formulations generally consist of one or more inhibitor compounds with other additives such as surfactants, film enhancers, de-emulsifiers, oxygen scavengers, and so forth. The inhibitor solvent package used can be critical in respect to the solubility/dispersibihty characteristics and hence the application and performance of the products. 

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