Inhibitors film measurements

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. 

Nevertheless, EIS has its place in mechanistic studies. For instance, organic inhibitor films constitute imperfect dielectric barriers. The capacitance of the intetphase is no doubt affected by the inhibitor film. Therefore, if the system were to lend itself to the measurement of the incremented capacitance due to the presence of the inhibitor film, such change... 

Inhibitor Testing—There are no standardized laboratory tests for evaluating oilfield inhibitors. A number of tests have been described in the literature, but none has been adopted by NACE. The ideal test would determine the inhibitor effectiveness for the specific well fluids, would evaluate any secondary effects (e.g., emulsion problems), and would measure persistence of the inhibitor film. 

The copper ion displacement test is another method that measures directly the barrier effect of an inhibitor film. In this technique, steel coupons are immersed in the inhibited solution to develop a protective film formed under the conditions of the environment. Then on a go/no-go basis, the coupon is removed and immersed in an acidified copper sulfate solution. 

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. 

The protective film formed by corrosion inhibitors can act as a lubricating film to help in reducing fluid friction within a pipeline. This property can be measured and is termed the C Factor. This friction factor is expressed as follows ... 

Figure 22.2 Scanning vibrating electrode (SVET) measurements of the ionic currents above the surface of the inhibitor-free SiOx ZrOx hybrid film (a) to (c) and of the SiOx ZrOx hybrid film with inhibitor-loaded Si02 nanocontainers (d) to (f). (a, d) at the beginning (b, e) after 42 hours of corrosion (c, f) after 60 hours. Scale units p,A cm 2, spatial resolution 150 pm. Solution 0.1 M NaCl.

In extreme cases, such as boiling HC1 in contact with stainless steel, inhibitors can still be found that work very well indeed. Ellipsometric measurements show that they can form polymer layers five and six molecular layers thick—a kind of in situ formation of a paint film, built up by successive adsorption, layer upon layer. 

In experiments aimed at measuring pit and crevice growth kinetics, chromate is not a potent anodic inhibitor (27). The growth of film pits in A1 films is not slowed unless high chromate chloride ratios exist. The addition of 0.05... 

Tran-Minh et al. (1986) fixed BuChE in a film of 10 nn thickness around the active tip of a pH glass electrode and measured the pH decrease during substrate hydrolysis. The electrode was inserted into a flow-through cell. When a steady pH value in 5 mmolA butyrylthiocholine solution was reached, a competitive inhibitor, e.g. carbamate, was injected. The inhibition of the hydrolytic reaction resulted in an in-... 

Simple but pedagogically useful theories of electrode kinetics are presented in Chapter 3. This permits discussion of models for anodic and cathodic reactions at the metal/environment interface and for diffusion of species to and from the interface. Mathematical models of these theories lead to so-called kinetic parameters whose values govern the rate of the interface reaction. The range of values that these parameters can have and some of the variables that can influence the values are emphasized since these will relate to understanding the influence of such factors as surface conditions (roughness, corrosion product films, etc.), corrosion inhibitors and accelerators, and fluid velocity on corrosion rates. This chapter also introduces electrochemical measurements to determine values of the kinetic parameters. 

The concepts in Chapters 2 and 3 are used in Chapter 4 to discuss the corrosion of so-called active metals. Chapter 5 continues with application to active/passive type alloys. Initial emphasis in Chapter 4 is placed on how the coupling of cathodic and anodic reactions establishes a mixed electrode or surface of corrosion cells. Emphasis is placed on how the corrosion rate is established by the kinetic parameters associated with both the anodic and cathodic reactions and by the physical variables such as anode/cathode area ratios, surface films, and fluid velocity. Polarization curves are used extensively to show how these variables determine the corrosion current density and corrosion potential and, conversely, to show how electrochemical measurements can provide information on the nature of a given corroding system. Polarization curves are also used to illustrate how corrosion rates are influenced by inhibitors, galvanic coupling, and external currents. 

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