Corrosion control test methods

The decision to test is usually driven by unusual chemistry such as a new catalyst, reaction components, or reaction conditions. Immersion/mass loss method is primarily used in conjunction with microscopic examination. Process fluids from production or pilot runs are primarily used to best simulate potential corrosion. The test methods are custom designed based, in part, on cost and the ability to obtain sufficient quantities of test fluids, and handle the process conditions. Process conditions are tested outside the process control limits (e.g., temperatures, pH) to better accentuate the corrosion potential. These extremes have to be tempered by the stability of the products in the stream. For wall thicknesses greater than 0.250 in. (6.35 mm), a uniform loss of less than 10 mil/year (0.26 mm/year) is considered structurally acceptable. Signiflcandy lower levels of uniform loss are of concern for product or process contamination issues. Microscopic examination is used to determine potential localized corrosion concerns, such as pitting or stress cracking. Indications of pitting or stress corrosion in stamped areas of the coupon are of particular concern. U-bend tests are rarely used because of insufflcient test fluid quantities and availability. 

The sometimes contradictory results from different workers in relation to the elements mentioned above extends to other elements . Some of these differences probably arise from variations in test methods, differences in the amounts of alloying additions made, variations in the amounts of other elements in the steel and the differing structural conditions of the latter. Moreover, the tests were mostly conducted at the free corrosion potential, and that can introduce further variability between apparently similar experiments. In an attempt to overcome some of these difficulties, slow strain-rate tests were conducted on some 45 annealed steels at various controlled potentials in three very different cracking environments since, if macroscopic... 

Corrosion tests provide the basis for the practical control of corrosion and therefore deserve a more exhaustive discussion than limitations of space will permit. A detailed description of all the procedures and devices that have been employed in corrosion studies in many countries will not be attempted. Instead, attention will be directed principally to underlying principles and to comments on the significance and limitations of the results of the test methods that are considered. Further details may be obtained from the references and from the comprehensive works by Champion and Ailor ... 

Corrosion Monitoring in Industrial Plants Using Nondestructive Testing and Electrochemical Methods , Proc. Symposium Sponsored by ASTM Committee E-7 and G-1, Montreal, Canada, May 1984, ASTM Special Technical Publication 908 Internal Corrosion Control and Monitoring in the Oil, Gas and Chemical Industries Proc. 

In 1980 Bemhardsson et introduced an automated electrochemical method for CPT determination. The specimen is mounted as described in Section IV.2 (ii) using a stream of argon to avoid crevice corrosion and 0.02-5% sodium chloride as electrolyte. The CPT is determined by a potentiostatic test method using an instrument called the Santron CDT 400 for potential control, temperature control, and current measurements. 

Methods. To observe that corrosion testing in the laboratory frequently fails to predict what happens in real-world environments is to admit that the mechanisms controlling corrosion in such environments are not understood, even at this late date of study. Mechanism-based test methods for monitoring corrosion are needed that will provide reliable and rapid prediction of service life for corrosion-susceptible systems. It is expected that statistical analysis will play a... 

Corrosion detection plays an important role in any corrosion control program. Most of the methods employ nondestructive test methods and include hydrogen evaluation, radiography, dynamic pressure, corrosion probes, strain gauges and eddy current measurements. Of these, the methods employed in cooling tower practice are hydrogen evaluation and corrosion probes. 

Abstract Quality control of corrosion test results implies the validation of the corrosion test method and estimation of the uncertainty of corrosion rate measurement. The corrosion test in an artificial atmosphere of the salt spray mist needs evaluation of corrosivity of the test cabinet by reference specimens. Such calibration of corrosion environment raises very strict requirements for the method description and details of all procedures and used specimens. Reliable corrosion measurements by spray tests require validation of the experimental device together with the experimental procedure and determination of corrosivity uncertainty of the test cabinet environment. 

Some rubber compositions, for example those containing reactive chlorine, can promote the surface corrosion of metals in contact with them, and in certain applications this can be sufficient to impair component performance. To guard against the use of such materials, a test method is described in ISO 6505 (BS903. Part A37). The procedure is similar to that for contact stain, in that a. sandwich of rubber and test surface, in this case a specified metal, is stored under load in a temperature-controlled environment for a given period. The measurement is a visual one and includes an indication of the ease of separation of the test rubber and the metal at the conclusion of the test. 

B.S. Skerry, C.H. Simpson, Accelerated test method for assessing corrosion and weathering of paints for atmospheric corrosion control. Corrosion 49 (1993) 663—674. 

General corrosion control, prevention, and monitoring should be planned for from the onset. To detect and monitor corrosion, various methods must be used, while corrosion protection would be done by the addition of inhibition and use of protection coatings [5]. Visual examination, laser methods, the replication microscopy liquid penetration testing method, magnetic particles testing, the eddy current inspection method, acoustic emission technique, thermal methods of inspection, and nondestructive methods are the various methods to be adopted when monitoring pipeline corrosion [5]. 

Since kinetics and mechanism of corrosion is controlled by electrochemical principles, the technique based on electrochemical methods is used to determine the corrosion rate and understand the mechanism of corrosion process. The testing methods are based on principle of accelerating the corrosion process without changing the environment and the corrosion rates can be measured without removing the test specimens. 

Immersion tests provide no information about reaction mechanisms and often they require relatively long exposure times. Electrochemical tests do not have these drawbacks and they are therefore widely used in practice. In the following electrochemical polarization methods are presented that provide information on the rate of uniform corrosion under conditions where the rate is controlled by charge-transfer. Other electrochemical test methods will be presented in subsequent chapters. 

Section VII on Testing in Industries (S. Dean, Section Editor) provides an overview of corrosion testing unique to each industry and how these tests are used to address corrosion problems. Included are descriptions of environments encountered and materials used in specific industries. Test methods for corrosion control and evaluation are described along with appropriate stand2irds. Chapters in this section include automotive, commercial aircraft, military aircraft... 

Clearly defined goals and objectives are needed if corrosion tests are to produce results that affect materials selection, and methods of corrosion protection and corrosion control. Goals and objectives define test purpose and what is to be achieved. Economic considerations are always a factor in defining goals and objectives, along with other considerations (workforce, public safety, and environment). Figure 2 shows some of the quality criteria that affect plant economics in the CPI. The criteria have been grouped... 

The Mixed Flowing Gas Test, ASTM B 827, is used extensively in the electronics industry. As the name implies, the test method uses a combination of various gases at controlled temperatures and humidities to produce the desired conditions. The MFG test requires equipment of a more complex nature than other corrosive gas tests. A schematic of a typical chamber is shown in Fig. 3b, as depicted in ASTM B 827. 

Virtually all definitive test work is done in a pilot plant or plant. The final test is performance of actual operating equipment. A systematic, quantitative inspection program is the final measure of success of a corrosion control program. All other methods are evaluated in terms of how closely they approximate this method. Other methods used are listed and described briefly below. 

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