Steels continued corrosion testing

A dense and electronically insulating layer of LiA102 is not suitable for providing corrosion resistance to the cell current collectors because these components must remain electrically conductive. The typical materials used for this application are 316 stainless steel and chromium plated stainless steels. However, materials with better corrosion resistance are required for longterm operation of MCFCs. Research is continuing to understand the corrosion processes of chromium in molten carbonate salts under both fuel gas and oxidizing gas environments (23,25) and to identify improved alloys (29) for MCFCs. Stainless steels such as Type 310 and 446 have demonstrated better corrosion resistance than Type 316 in corrosion tests (29). 

A comprehensive table of corrosion rates in sea water has been compiled by LaQue . This appears to show no obvious dependence of corrosion rates on the geographical location of the testing site, and few of the rates depart widely from an average of 0-11 mm/y. It is suggested that a figure of 0-13 mm/y may be taken as a reasonable estimate of the expected rate of corrosion of steel or iron continuously immersed in sea water under natural conditions, in any part of the world. 

To ensure maximum continuity of the tin-iron compound layer between tin and steel. This layer is itself corrosion resistant and appears to act as a nearly inert screen limiting the area of steel exposed as tin is removed by corrosion. Its effectiveness is measured by the Alloy-Tin Couple (A.T.C.) test, in which the current flowing is measured between a sample of tinplate from which the unalloyed tin layer has been removed, and a relatively large tin electrode immersed in an anaerobic fruit juice. ... 

A polished steel spindle is immersed into 300 mL of fuel maintained at 100°F (37.8°C). The fuel is continually stirred during the entire test period. Upon immersion for 30 minutes, 30 mL of distilled water are added to the fuel. After remaining in the fuel for an additional 3lh hours, the spindle is removed and the surface is rated for percent corrosion. 

The cone calorimeter is also used to quantify the corrosivity of products of combustion as described in ASTM D 5485. The Cone Corrosimeter uses the same load cell, specimen holder, retainer frame, spark igniter, conical heater, and exhaust system as the cone calorimeter. A heated stainless steel sampling tube is connected to a funnel placed on top of the conical heater. A gas sample is continuously drawn from the tube at a rate of 4.5 L/min. The sampling tube is connected with silicone rubber tubing to the pump via an 11.2L exposure chamber, a filter, and a flow meter. A target is placed in the exposure chamber at the start of the test and exposed to the corrosive atmosphere of the gas sample for 60 min or until the specimen has lost 70% of its total mass loss, whichever occurs first. 

Second precondition. Dissolution of iron will take place only when the current circulates for sufficiently long periods and in high enough intensity to produce acidity that can destroy the conditions of passivity. For instance, Figure 9.6 show the results obtained with laboratory tests on specimens of cement paste subjected to the circulation of current densities of 1 and 10 A/m [5]. Corrosion initiated on steel embedded in cement paste without chloride ordy after more than 200 h of ap-pHcation of an anodic current density of 10 A/m. A current density of 1 A/m could not initiate corrosion even after 14 months (i. e. more than 10000 hours) of continuous application, although the charge that circulated (> 10000 A -h/m )... 

Interruptions in the stray current. Stray currents produced by rail traction systems are non-stationary, and thus the effect of interruptions of the current should be taken into consideration. In fact, gradients of ionic concentration in the pore solution near the steel surface, produced by the depletion of alkalinity due to the anodic reaction and increase in chloride concentration due to migration, can be mitigated during the interruption of current. Therefore, interruptions in the stray current may have a beneficial effect, as shown in Figure 9.6 where results of tests with continuous appHcation of the current are compared with tests with circulation of current at alternated hours (lon-loff). The periodical interruption of current had a beneficial effect, since it increased the charge required for initiation of corrosion. This effect was remarkable in cement pastes with chloride contents lower than 0.4 % by mass of cement... 

Water permeability test. Depending on the sea water level, the mortar used for corrosion protection can become wet or completely dry. Continuous fluctuations in moisture content increase the intrusion of damaging substances, which might attack the mortar as well as the steel tower. 

This study revealed no significant corrosion of material used during 40 years in sodium coolant, so it was possible to continue operation of the BR-10 reactor circuits (this study and laboratory tests of structural materials at 500°C have shown that the circuit components made of similar stainless steels can be used in sodium for 60 years without worsening of their... 

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