Corrosion inhibitors measurement

J. Cossar and J. Carlile. A new method for oilfield corrosion inhibitor measurement. In Proceedings Volume. Annu NACE Corrosion Conf (Corrosion 93) (New Orleans, LA, 3/7-3/12), 1993. 

Lubricants. Petroleum lubricants continue to be the mainstay for automotive, industrial, and process lubricants. Synthetic oils are used extensively in industry and for jet engines they, of course, are made from hydrocarbons. Since the viscosity index (a measure of the viscosity behavior of a lubricant with change in temperature) of lube oil fractions from different cmdes may vary from +140 to as low as —300, additional refining steps are needed. To improve the viscosity index (VI), lube oil fractions are subjected to solvent extraction, solvent dewaxing, solvent deasphalting, and hydrogenation. Furthermore, automotive lube oils typically contain about 12—14% additives. These additives maybe oxidation inhibitors to prevent formation of gum and varnish, corrosion inhibitors, or detergent dispersants, and viscosity index improvers. The United States consumption of lubricants is shown in Table 7. 

Petroleum greases and oils can be excellent corrosion inhibitors on a variety of alloys. The hydrophobic layer produced by oil or grease can prevent water from contacting surfaces and can, therefore, almost eliminate corrosion. Unfortunately, the addition of oil and grease cannot be recommended as a corrosion-reduction measure in cooling water systems for three basic reasons. 

In all space heating boiler systems there is a tendency to keep water treatment programs as simple as possible. Ideally, chemical inhibitors should be added in proportion to MU demands, metered water consumption, oxygen content, or other preemptive measurement. More typically, the standard process is to periodically (weekly to monthly) analyze the BW for a few basic control parameters, including measuring the multimetal corrosion inhibitor reserve, and then to merely top-up the inhibitor when the reserve is below the minimum specification. Chemical treatment often is added directly to the BW by hand-pump via a hose cock (bib cock) connection. 

The common method of treating rod-pumped wells is to periodically batch inhibitor into them. The treatment period for a given well is selected using empirical rules based on well production volumes. A successful and economic corrosion inhibition program must carefully control the inhibitor concentration in the well fluids. Environmental aspects and efficacious inhibitor usage necessitate the measurement of very low corrosion inhibitor concentrations. Inhibitor concentrations as low as one part per million are significant, thus... 

Use of carefully selected surfactants in well treatment fluids is a way to accomplish this. Rock wettability can be altered by adsorption of polar materials such as surfactants and corrosion inhibitors, or by the deposition of polar crude oil components (173). Pressure appears to have little influence on rock wettability (174). The two techniques used to study wettability, contact and and relative permeability measurements, show qualitative agreement (175-177). Deposition of polar asphaltenes can be particularly significant in carbon dioxide enhanced oil recovery. 

Classical IS measurements indicate that corrosion inhibitors reduce surface heterogeneity and function primarily by adsorption. Furthermore, the sorbed monolayer is either (I) permeable and insulating or (II) impermeable and conductive. Analysis of the time-constant, T, for the corrosion process, suggests that mechanism (I) is operative. 

X-Ray photoelectron spectroscopy (XPS) was used to examine the surface of steel that had been exposed to 1.0 M hydrochloric acid in the presence of 3,5-diphenyF4//-l,2,4-triazole 27 as corrosion inhibitor. These measurements demonstrated that the inhibitor 27 was chemisorbed on to the metal surface the protection afforded by 27 was still... 

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 ... 

The methods of measuring corrosion rates in the course of testing corrosion inhibitors are conventional weight loss, electrochemical techniques such as linear polarization resistance, potentiodynamic polarization, AC impedance, and electrochemical potential or current noise. 

Conventional weight loss measurements in testing inhibitors are time-consuming since measurable weight loss is required to obtain meaningful data on corrosion rates. In general the performance of corrosion inhibitors is expressed in terms of percentage inhibition. 

What do you expect in a potentiodynamic polarization measurement if you have corrosion inhibitor in a CMP slurry, and what are the reasons for expecting such behavior ... 

As a valuable step toward rationalizing the approval procedure for aviation fuel additives, guidelines are available (ASTM D-1655, ASTM D-4054).Tests are available for measuring or specifying additives such as color dyes (ASTM D-156, ASTM D-2392, ASTM D-5386, IP 17), corrosion inhibitors (often measured by the corrosivity of the fuel— ASTM D-130, ASTM D-5968, IP 154), lubricity (ASTM D-5001), fuel system icing inhibitors (ASTM D-910, ASTM D-4171, ASTM D-5006, IP 277), and static dissipator additives (ASTM D-2624, ASTM D-4865, IP 274). 

If materials selection depends on corrosion control by process-related measures (such as chemical treatment), these should be indicated on the MSD. Indicate the intended injection points and the type of chemical to be injected. Examples include corrosion inhibitors, scale inhibitors, biocides, pH control chemicals, wash water, etc. Also indicate the location of proposed corrosion monitoring and sampling sites. If anodic or cathodic protection is to be part of the corrosion control design, the MSD or its Notes section should indicate the piping and/or equipment to be protected. 

To establish if these conditions could be met, the literature of aluminium corrosion inhibitors was searched, suitable inhibitors were chosen for evaluation, and a programme of measurements and testing Initiated. 

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. 

Prevention and Reduction of Liquid-Side Fouling. Among the most frequently used techniques for reduction of liquid-side fouling is the online utilization of chemical inhibitors/ additives. The list of additives includes (1) dispersants to maintain particles in suspension, (2) various compounds to prevent polymerization and chemical reactions, (3) corrosion inhibitors or passivators to minimize corrosion, (4) chlorine and other biocide/germicides to prevent biofouling, and (5) softeners, acids, and poliphosphates to prevent crystallization. Finally, an efficient mechanical removal of particles can be performed by filtration. An extensive review of fouling control measures is provided in Ret 150. 

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