Metal corrosion testing

Corrosion tests of metals under static conditions reveal nothing relating to erosion-corrosion susceptibilities. It is entirely possible that a metal tested under static conditions will fail in service when sufficient fluid velocity produces erosion-corrosion. Similarly, it has been observed that galvanic corrosion between coupled, dissimilar metals may be accelerated or even initiated under flow conditions when little or no galvanic corrosion is observed under static conditions (see Chap. 16, Galvanic Corrosion ). 

Water used in any testing procedure should be free of corrodents and of substances whose decomposition products may be corrosive. Metal surfaces should be dried after testing and kept dry prior to service. 

Lefrancois, P. A. and Hoyt, W. B., Chemical Thermodynamics of High Temperature Reactions in Metal Testing Corrosion , Corrosion, 19, 360t (1963)... 

Because cast iron components are normally very heavy in section, the relatively low rates of attack associated with atmospheric corrosion do not constitute a problem and little work has been carried out on the phenomenon. A summary of some of the data available is given in Table 3.42. The most extensive work in this field was initiated by the A.S.T.M. in 1958 and some of the results produced by these studies are quoted in Table 3.43. It will be noted that there is a marked fall in corrosion rate with time for all the metals tested. 

Wooden racks used in sea-water tests are likely to be subject to severe damage by marine borers. The wood used, therefore, must be treated with an effective preservative, for example creosote applied under pressure, if the test is to extend for several years. Organic copper compound preservatives may suffice for shorter tests, for example 2 or 3 years. Since the leaching of such preservatives may have some effects on corrosion, metal racks fitted with porcelain or plastics insulators have an advantage over wooden racks. 

The precautions generally applicable to the preparation, exposure, cleaning and assessment of metal test specimens in tests in other environments will also apply in the case of field tests in the soil, but there will be additional precautions because of the nature of this environment. Whereas in the case of aqueous, particularly sea-water, and atmospheric environments the physical and chemical characteristics will be reasonably constant over distances covering individual test sites, this will not necessarily be the case in soils, which will almost inevitably be of a less homogeneous nature. The principal factors responsible for the corrosive nature of soils are the presence of bacteria, the chemistry (pH and salt content), the redox potential, electrical resistance, stray currents and the formation of concentration cells. Several of these factors are interrelated. 

Recommended practice for conducting atmospheric stress corrosion tests on metals Test method for pH of soil for use in corrosion testing... 

Adsorption versus Polymerization. It is instructive to examine further the time dependence of the corrosion inhibition. In acid corrosion inhibition tests, steady state is customarily assumed to be reached within 10 to 20 min after initial exposure of the metal specimen. Since the inhibitors function by reducing the available active surface area, we expect an increase in and a corresponding decrease in P. The degree of corrosion protection the inhibitor provides is given by... 

Metals Handbook, Vols. 13A and 13B, Corrosion Fundamentals, Testing, and Protection, and Corrosion Materials, S.D. Cramer and B.S. Covino (eds.), ASM International, Metals Park, Ohio, U.S.A., 2003. 

Relative Corrosion Rates of Metals (Tests made within the complex level in a pilot-plant reactor)... 

High-Temperature Corrosion Bench Test at 135°C measuring increased corrosion by used oils of common metals in engines, e.g. copper and lead, from increased operating temperatures. 

Most known procedures of this group of methods are called oxidation and sulfuration tests. In the former case a metal test specimen wrapped in a VCI film material is placed in a desiccator (about 10 1 in capacity). The internal atmosphere reaches 100% RH using 20 cm of water. The desiccator is blocked up and is placed in a 50° C constant-temperature tank or in normal-temperature room to promote the growth of rust. In sulfuration test the desiccators about 2.5 1 capacity are used. After having adjusted the inside atmosphere to reach 93% RH using 10 cm of a saturated solution of Na2S04, a test metallic strip wrapped in inhibited film material is placed inside. The tests are continued until a corrosive phenomenon is observed. 

H.P. Hack, Evaluating Galvanic Corrosion, in Corrosion Fundamentak, Testing and Protection, ninth ed., in ASM Handbook, Vol. 13A, ASM, Metals Park OH, 1987, pp. 562—567. 

If 1,1,1-trichloroethane is not properly stabilized it forms hydrochloric acid in the presence of aluminum. HCl corrodes aluminum. The presence of free water invalidates the result of this test. An aluminum coupon is scratched beneafli flie surface of a solvent The coupon is observed for 10 min and 1 h and flie degree of corrosion is recorded in form of pass (no reaction) or fail (gas bubbles, color formation, or metal corrosion). The test is important to cleaning operations because aluminum should not be used for parts of machines (pumps, tanks, valves, spray equipment) in contact with corrosive solvent. 

The dissolution of material into an aqueous solution and so on, has a merit as well as a demerit to the enviroimient. Consider coated materials for an example. One of the objectives of a surface treatment such as plating is to improve corrosion resistance. In this case, it is preferable that the materials do not dissolve in water. This improvement of corrosion resistance enables the long-term use of materials, and will contribute to the reduction of resources and energy required for materials production. In Japan, JIS (Japanese Industrial Standards) H8502 (1999) regulates the methods of corrosion resistance tests for metallic coatings so as to evaluate the corrosion of a material. This standard includes the ISO 4540 (1980), ISO 4541 (1978) and others. 

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