Tests for Corrosion Resistance

Traditionally, the corrosion resistance of refractories to molten A1 was checked by cup test [29, 30]. It is a widely used, simple, and cheap technique. Aluminium is poured or placed in pieces in a cup that was drilled in the brick or in a previously formed cup in the concrete. Usually, the dimension of the cup is 40 x 40 mm. The brick or prepared sample of concrete with aluminium is placed in a furnace for a certain period of time (the most common time is 72 h however, experiments may last from 12 h to weeks). The temperature may vary from 730 to 1,200 °C [14—16, 31, 32]. After cooling, the sample is cut to determine the interaction surface of the refractory with A1 as well as the state of the surface. It is possible to estimate the surface of the reacted refractory it is a static test The molten A1 is not stirred. This method can give an approximate estimation (Fig. 3.8). 

There are modifications to the corrosion test. In [32], rods of 25 x 25 x 51 mm are immersed in the aUoy with 5 % Mg, the temperature is 850 °C, the time of testing is 4 days, and magnesium is added to maintain the 5 % concentration. In order variant of testing [33] the amount of A1 in the crucible is bigger, the concentration of Mg is maintained at 6 %. 

Usually, testing castables for corrosion is done at temperatures of 800 °C and 1,200 °C, which refiects the service conditions of the castables in the furnace. 

In test [30], samples of 2.54 x 2.54 x 22.86 sm are immersed in molten A1 with 5% Mg and analyzed after 4 days of exposure at 1,150 °C, mainly on the triple border refractory-metal-air. A rod test at elevated temperatures gives more information than a cup test, but it is more time-consuming and more expensive. 

There are no strict criteria when choosing refractory materials for A1 melting and holding furnaces. The action of fluxes is not taken into account, but their influence on corrosion resistance in the metallurgy of A1 is not much. If the material is not corrosion-resistant, it is possible to estimate the depth of penetration The deeper the penetration, the less resistant the refractory. 

---

A common chemical laboratory test for corrosion resistance is a simple exposure test using metal coupons. The ASTM standard G48 —Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride Solution—describes a simple exposure test. The material coupons (e.g., 60 x 60 mm) are placed on a glass cradle and immersed in the solution in such a way that the coupons are evenly exposed. 

Part 1, p 874, Test A262-44T ("Tentative Recommended Practice for Boiling Nitric Acid Test for Corrosion-Resisting Steels ) Part 1, p 878, Test A279-44T (Total Immersion Corrosion Test for Stainless Steels) 18) Kirk Othmer 4 (1949)... 

In general Cu is added to lead in amounts of up to 0.08% Alloys with addition of Ba, Ca, Co, Au, Li, Mg, Ni, Pt, Na, Ti and Zn have been tested for corrosion resistance anodes made of Ni and Ti give good performance in sulfuric acid solutions Ni in lead improves the weldability of steel during lead coating... 

Corrosion resistance increases clearly when the degree of graphitization of the carbon support increases. ° Different carbon blacks have been tested for corrosion resistance and also... 

WS passivated as shown in Figs. 4.8a, b and Fig. 4.9 were tested for corrosion resistance in three types of electrolytes viz. neutral, alkahne and acidic medium. The details of results are given in Table 4.11 and polarisation diagrams are shown in Figs. 4.10, 4.11, 4.12, 4.13, 4.14, 4.15. 

Wrought or cast zinc is not usually given accelerated tests for corrosion resistance because slight variations in composition or form are of little... 

The world-accepted test for corrosion resistance is the SINTEF test (Fig. 2.73a). A lab reduction cell [151-154] comprises graphite crucible. On the bottom of the crucible there is a TiB2-coated cathode, the anode is in the upper part, and the tested SiC rods, dipped into the melts of aluminium and bath, are exposed to the bath, aluminium, and oxygen in the presence of vapors. The lab reduction cell is in the furnace. The corrosion resistance is determined by the volume change (Fig. 2.73b). The inventors [151] made a corrosion resistance scale, determined by the volume loss of the samples (Tables 2.16). 

FIGURE 5, Four different boit/nut materiai/piating combinations were tested for corrosion resistance. 

The Composition of Several Materials Tested for Corrosion Resistance... 

If you conduct trials on parts and materials to prove reliability or durability, these can be considered to be verification tests. For example, you may test metals for corrosion resistance or hinges for reliability in the laboratory and then conduct validation tests under actual operating conditions when these items are installed in the final product. 

Apparatus and procedures for testing the corrosion resistance of alloys in brines at temperatures up to 120-150°C are described by Hart . 

Specification for electroplated coatings of 65/35 tin/nickel alloy Method for the evaluation of results of accelerated corrosion tests on metallic coatings Methods of test for paints Cross-cut test Pull-off test for adhesion Resistance to artificial weathering (enclosed carbon arc) and Addendum No. 1 Resistance to continuous salt spray Notes for guidance on the conduct of natural weathering test... 

D 2933 1974 (1986) Test method for corrosion resistance of coated steel specimens (cyclic method)... 

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. ... 

It has been established that salts can deposit or form on metals during gas-metal reactions. Molten layers could then develop at high operating temperatures. Consequently, the laboratory testing of corrosion resistance in molten salts could yield valuable results for evaluating resistance to some high-temperature gaseous environments. 

Changes in corrosion resistance of the electrolytic tin coatings were determined by the iron-solution-value test and the alloy-tin-couple test (6). Corrosion resistance data for the 43 kg (95 lb), Type MR-TU, No. 25 tinplate are presented in Table VIII. These data show that there is no significant difference in the corrosion resistance of the unirradiated... 

Various membrane materials are to be compared for corrosion resistance in hydrochloric acid. Membrane samples are ultrasonically cleaned with Freon for 5 minutes and dried at 200°C for 2 hours followed by similar steps of ultrasonic cleaning with demineralized water and drying. The conditioned membrane samples are then immersed in 35% HG solution, making sure that no air bubbles are trapped in pores. The acid exposure at the test temperature (e.g. 25°C) continues for a given period (e.g. one week). The tested samples are ultrasonically washed with demineralized water for 5 minutes and dried at 200°C for 2 hours. The weights of the cleaned membrane samples before and after the acid exposure are compared to assess the relative corrosion resistance of various membrane materials. 

In a chemical plant nine aluminum alloys were tested for their resistance to corrosion. Four locations were chosen inside the chemical plant for this experiment and at each such place one plate of all nine alloys was placed. Exposure to chemical corrosion lasted one year. After the experiment four researchers examined the plates randomly and gave a mark from 1 to 10 to each plate depending on the observed resistance to corrosion. The experiment was aimed at asserting which of the offered aluminum alloys had the best resistance to corrosion at one or at all locations of the chemical plant. It was also interesting to see how much the researchers agreed or disagreed in their estimates of resistance to corrosion. Thus, the experiment had included three factors nine aluminum alloys, four locations and four researchers. Experimental results are shown in the following table ... 

Materials selection for corrosion resistance is as reliable as the information upon which it is based. Corrosion information derives from two sources— experience or test results. 

For corrosion resistance of a series of Sn RE TiO,, g (RE = Y, Yb, Gd, Sm, Nd, Pr, La) and Sri xTii yMyO3+5 (M = Nb, Ta) perovskites, the sintered specimens and sample powders were evaluated in the 50 wt % H2SO4 aqueous solution at 353K. Figure 4 shows the three-neck glass cell used for the corrosion test. After the corrosion test, dissolved A-site and B-site elements in the H2SO4 solution were measured using Inductively Coupled Plasma Mass Spectrometry (ICP-MS, Shimazu, ICPM-8500). 

Because many polymers are resistant to attack by corrosives, tests for chemical resistance of polymers are particularly important. ASTM-D-543-67 (1977) measures weight and dimensional changes of test samples immersed for 7 days in many different test solutions. These tests may be coupled with tensile tests. Other ASTM tests include those under accelerated service conditions [ASTM-D756-76 (1971)], water absorption [ASTM-D570-63 (1972)], and environmental stress cracking of ethylene plastics [(ASTM-D1693-70)]. 

D2803—09 Standard Guide for Testing Filiform Corrosion Resistance of Organic Coatings on Metal... 

Vendor shall give composition of the glass lining and guarantee for corrosion resistance to the reaction mass at operating conditions. A test coupon of the glass-lined piece may be obtained from the vendor and tested independently in purchaser s own laboratory. 

---