Corrosion inhibitors practical applications

The scientific and technical corrosion literature has descriptions and lists of numerous chemical compounds that exhibit inhibiting properties. Of these only a very few are ever actually used in practical systems. This is partly due to the fact that in practice the desirable properties of an inhibitor usually extend beyond those simply relating to metal protection. Thus cost, toxicity, availability, etc. are of considerable importance as well as other more technical aspects (see Principles). Also, as in many other fields of scientific development, there is often a considerable time lag between laboratory development and practical application. In the field of inhibition the most notable example of this gap between discovery and application is the case of sodium nitrite. Originally reported in 1899 to have inhibitive properties, it remained effectively unnoticed until the 1940s it is now one of the most widely employed inhibitors. 

At pHs5.6, both UDI and PVI-1 cast films produce passivation, UDI reducing the anodic currents by an order of magnitude more than PVI-1. Linear polarization measurements on Cu in UDI solution (pHs5.6) indicate that UDI may have practical application as a corrosion inhibitor for copper. 

This phenomenon degrades the Coulombic efficiency of the anode, then it has to be minimized for practical applications where high capacity is required. This could be overcome by particular aluminum alloys more resistant to corrosion, but the competing requirement of fast anodic dissolution makes very difficult the research of the suitable material [36, 37]. Another possibility to improve the anode performance is to modify the electrolyte composition by adding corrosion inhibitors [38]. The difficulties met up today in this field leave the possibility to use the aluminum-air batteries only as mechanically rechargeable systems, with practical performance (300-500 Wh/kg) very far from the theoretical values (Table 1.8 Fig. 5.14). 

Titanium in Practical Applications. International conferance, Trondheim, 19-20 June 1990. The Norwegian Association of Corrosion Engineers, 1990. Uhlig HH. Corrosion and Corrosion Control. John Wiley Sons, 1971. Nathan CC, editor. Corrosion linhibitors. Houston, Texas NACE, 1973. RozenfeldlL. Corrosion inhibitors. McGraw-Hill, 1981. 

The methods evaluated for KHI analyses are colorimetric, iodine complexation, and size exclusion chromatography (SEC). The colorimetric method is subject to intense interference by Cl, limiting its application for KHI determination in the presence of Cl blends. The iodine complexation method is chosen as a practical wet chemical method for KHI analysis.lt is modified to minimize the interferences due to brine concentration, corrosion inhibitor, condensate, and sulfide. However, the selectivity of the iodine complexation method is still not at the desired level. As an improvement to selectivity and accuracy, the SEC method is evaluated. The SEC method offers better selectivity and characterization of KHI. The characterization of molecular weight distribution is critical in the evaluation of treatment and removal efficiency of KHI in produced water streams. 

The relationship between a corrosion product layer and inhibitors has also been discussed, among others, by Lorenz [66], and Lorenz and Mansfeld [67]. These authors point out that in many practical systems, for instance aerated water and carbon steel, an interaction occurs between, in this case, iron oxide and the inhibitor to the point where the inhibitor is not only adsorbed on the oxide surface, but actually incorporated into the three-dimensional oxide layer. Clearly, three-dimensional or interphase inhibition caimot be achieved in short tests or by filming procedures. Furthermore, measuring techniques have to take into consideration the altered chemical and electrochemical conditions across such bulk interphase layers. It is unfortunate that this aspect of corrosion and corrosion inhibition has not received more attention, and it is suggested that this lack of attention has seriously held back all aspects of corrosion inhibitor applications and monitoring of effectiveness. 

MBT in comparison to the corresponding N-hydroxymethyl derivative (3.4.12.) which is a formaldehyde releasing substance. As a fungicide MBT is especially toxic to superficial moulds and cellulose-decomposing fungi. The antibacterial activity of MBT is marked by a lack of efficacy for Pseudomonads. In practical application, mainly as slimicides, MBT sodium salt solutions therefore contain additionally other dithiocarbamates (e.g. 11.10.1., 11.11.1.). Moreover MBT/sodium MBT is characterized by dual utility, as it serves also as a popular corrosion inhibitor for non-ferrous metals. 

Recently migrating corrosion inhibitors have been proposed as surface applied liquids (Mader, 1994). It is claimed that the inhibitor will migrate both in the gas and in the liquid phase to the reinforcement. The results reported are conflicting a recent laboratory study on precorroded (both chloride induced and carbonated) mortar samples showed practically no effect in reducing the corrosion rate even after several immersion cycles in the inhibitor solution (Elsener et al., 1999b). Despite some field tests (Laamanen et al., 1996) and an increasing number of applications, very few documented and conclusive results exist on the inhibitor efficiency. A first field test with different surface applied inhibitors on a well characterized and instrumented side wall of a tunnel started in Switzerland in 1998. 

Abstract The incorporation of rare earth compounds as corrosion inhibitors in polymeric paint systems is presented. Specifically, uses of cerium salts in an electrolytically deposited coating commonly used in the automotive industry and praseodymium oxide in spray applied epoxy-polyamide primers for aerospace applications are discussed. Special emphasis is placed on the importance of phase of the rare earth material in relation to polymeric matrix as the effectiveness of the corrosion inhibition is strongly link to the starting materials, the formulated paint system and the ambient environment in which the coating operates in practice. 

The principles and practice of corrosion inhibition have been described in terms of the factors affecting inhibitor performance and selection (principles) and the more important practical situations in which inhibitors are used (practice). For the latter a brief account is given of the nature of the system, the reasons for inhibitor application and the types of inhibitor in use. 

In practice, inhibitors are often defined according to their field of application. In aqueous environments, inhibitors for acid environments are typically used to minimize metal corrosion during pickling of steel, an operation that removes oxide scales by dissolution in an acid. In the petroleum industry, large quantities of inhibitors for acid environments are used to avoid corrosion of drilling equipment. Inhibitors for neutral environments are used above all for the protection of cooling-water circuits. Inhibitors not only reduce the rate of uniform corrosion, but they also serve to protect metals from localized corrosion and stress corrosion cracking [18]. 

Pros and cons of the application of the polarisation methods in studies related to microbial corrosion are addressed in Chapter 6. In the next chapter, the implementation of theoretical electrochemistry will be discussed to show how and why some techniques such as inhibitor addition or coating application work in practice. 

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