Corrosion tests design

When there is no information on the behavior of a metal or alloy or a fabrication under specific environmental conditions (a newly formulated alloy and/or a new environment), it is essential to carry out corrosion testing. Designer Designer, user... 

The cells that contain the specimen and environment for stress-corrosion tests frequently need to be more than a vessel made in some substance, usually glass, that is inert to the environment and which produces no electrical response upon the test specimen. Where cracking is initiated at surfaces through which heat transfer occurs it may be necessary to design a cell in... 

Corrosion testing data. The pitfalls in corrosion testing and the test methods are described in Chapter 19, but several points need underlining from experience in the design of chemical plants ... 

Performance Tests. The underlying goal of corrosion testing is generally the prediction of service performance, whether directly for a device or system, or indirectly in the design or formulation of a... 

Corrosion rates are expressed in terms of inches per year of surface wastage and are used to provide a corrosion allowance in the design thickness of equipment such as vessels and pipes. Operators will often use data based on historical experience from plant operations to aid them in determining appropriate corrosion allowances. Alternatively, corrosion charts are widely available that give corrosion rates for many combinations of materials of construction and process fluids, and normally a range of values will be provided for various process temperatures. In some instances, particularly where there is a mixture of chemicals present, appropriate data may not exist and corrosion tests may be necessary in order to determine the suitability of equipment. Operators should be able to demonstrate the use of corrosion allowances in equipment specification and design. The sources of data used should be traceable. 

Laboratory corrosion tests are conducted in order to obtain information on the interaction of a metal with a particular environment. The tests are generally designed to simulate some field situation. Studies in the laboratory are either aimed at obtaining data in a more convenient way and in a shorter time than on-site determinations or are to provide information, either mechanistic or simulated use, before field application. Final testing should therefore correlate closely to the results obtained from field studies [31]. In devising tests, detailed consideration of their applicability is necessary. Short-term laboratory tests are always a compromise and this should be borne in mind when interpreting results. The number and diversity of test results are such that it is only possible to give a brief description of the more common tests. 

Krystow, P. E., Evaluating Materials of Construction in Pilot Plant Corrosion Tests, in Scaleup of Chemical Processes. Conversion from Laboratory Scale Tests to Successful Commercial Design Bissio, A. Kabel, R. L Eds. Wiley New York, 1985 pp. 620-654. 

ASTM Chemical Environment Test Standards. Since intergranular corrosion is one of the most serious problems in the satisfactory application of stainless steels, several procedures are available for the measurement of the susceptibility of these steels to this type of corrosion. The procedures have been formalized as standardized tests, designated as ASTM A 262 (Ref 102), and are widely accepted as a basis for certifying that a specific stainless steel meets specifications. A limitation of these tests is that they specify specific environments rather than the environment of the actual application. In many applications, however, reasonable correlations have been established between acceptable response to the tests and successful service performance. 

The Battelle-NBS study (1) used an economic input/output analysis to estimate the cost of corrosion in the United States. In the model, the US economy was divided into 130 industrial sectors. For each sector, estimates were made on the costs of corrosion prevention, as well as the cost of repair and replacement because of corrosion. The following direct costs were included in the study replacement of equipment or buildings loss of product maintenance and repair excess capacity redundant equipment corrosion control such as inhibitors organic and metallic coatings engineering research and development testing design insurance parts and equipment inventory. 

Electrochemical methods have been used in corrosion testing ever since the electrochemical nature of corrosion processes was discovered. In the present age electrochemical measurements involve the use of sophisticated black boxes which are invariably blamed for any pitfalls which occur. Hence the European Federation of Corrosion Working Party on Physicochemical Methods of Corrosion Testing felt it desirable to remind research workers, students and instrument designers of the more fundamental aspects of the measurements. 

---