Technique selection, corrosion

The purpose of this section is to show, by example, how the concerns of technique selection, potential problems, data acquisition and analysis have been applied for several different corrosion problems and techniques. Examples of fundamental research work and industrial problem solving have been included to show the range of applicability of the techniques. In most cases, more than one technique was used to solve the problem. Frequently, a surface analysis technique was used in combination with one or more other types of analysis method. These examples are not comprehensive it is hoped that sufficient references have been supplied to enable the reader to find other work of relevant interest. 

Whatever repair or rehabilitation option we choose, most investigations start after concrete has already been damaged by corrosion. Some concrete removal and repair is therefore required on most jobs regardless of the rehabilitation technique selected. 

Technique selection needs to be considered alongside the effluent content. Corrosive effluents are particularly difficult to deal with. Mixed metal effluents also cause considerable problems, especially when toxic metals are at low concentrations. Although some techniques are being developed (like selective ion-exchange) to treat such wastes but they are years away from widespread commercial application. 

Tras CHAPTER HIGHLIGHTS the coiTOsion resistance of nickel and its alloys and identifies relevant ASTM standards associated with their evaluation. The test technique selected ultimately will depend upon the specific alloy involved, the type of corrosion in question, or the end application, or a combination thereof. The following discussions will deal primarily with aqueous corrosion and the nickel-base (greater than about 30 % nickel) alloys designed for aqueous corrosion resistance. High-temperature gaseous corrosion will be addressed in other sections. 

The particular corrosion monitoring techniques selected depend upon their applicability to the system and the information being sought. Some techniques provide information that is effectively instantaneous. Other techniques provide... 

The first requirement can be met with real-time corrosion monitoring systems, provided that the monitoring techniques selected are sufficiently sensitive to respond rapidly to changes in the process conditions. Corrosion monitoring techniques (such as coupons) that yield only retrospective, cumulative corrosion damage data are not suitable for this purpose. 

Requirements for cans for beer and soft drinks differ from those for food cans in that (a) only low tin and iron contents can be tolerated in the product and (t>) the anticipated shelf-lives are much shorter. Specialised lacquering techniques including striping the seams are used to give complete cover to the metal. For soft drinks it is sometimes possible to select colouring matters and acids least likely to give rise to corrosion troubles, and rapid methods of testing formulations have been devised . Steel quality is also controlled by special tests. 

A matter of considerable importance in the selection of an application method is its efficiency. Spray techniques are usually inefficient, since many droplets drift past the target and are lost. Even electrostatic spraying can waste as much as 35% of the paint. There is some loss of paint in most methods, but roller coating, curtain coating and electrodeposition are very efficient. Electrodeposition is also a very useful technique where corrosion resistance is important, since it applies a uniform coating over nearly all surfaces of even the most complex-shaped article. 

The determination of polarisation curves of metals by means of constant potential devices has contributed greatly to the knowledge of corrosion processes and passivity. In addition to the use of the potentiostat in studying a variety of mechanisms involved in corrosion and passivity, it has been applied to alloy development, since it is an important tool in the accelerated testing of corrosion resistance. Dissolution under controlled potentials can also be a precise method for metallographic etching or in studies of the selective corrosion of various phases. The technique can be used for establishing optimum conditions of anodic and cathodic protection. Two of the more recent papers have touched on limitations in its application and differences between potentiostatic tests and exposure to chemical solutions. ... 

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. 

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