Corrosion testing continued

Deflagration Arrester Testing For end-of-line and tank vent flame arresters, approval agencies may require manufacturers to provide users with data for flow capacity at operating pressures, proof of success during an endurance burn or continuous flame test, evidence of flashback test results (for end-of-hne arresters) or explosion test results (for in-line or tank vent arrester applications), hydrauhc pressure test results, and results of a corrosion test. 

The most widely used accelerated tests are based on salt spray, and are covered by several Government Specifications. BS 1391 1952 (recently withdrawn) gives details of a hand-atomiser salt-spray test which employs synthetic sea-water and also of a sulphur-dioxide corrosion test. A continuous salt-spray test is described in ASTM B 117-61 and BS AU 148 Part 2(1969). Phosphate coatings are occasionally tested by continuous salt spray without a sealing oil film and are expected to withstand one or two hours spray without showing signs of rust the value of such a test in cases where sealing is normally undertaken is extremely doubtful. 

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... 

The CMT method was primarily developed to replace traditional corrosion tests with a faster, quantitative test. Since the course of corrosion with time is continuously shown on the screen, it is easy to see if and when a stable situation has been established, resulting in a constant rate of corrosion. The rate of corrosion at that stage can often serve as a safe measure of the lifetime of the object. An assessment of quality on the basis of such a measurement can be made in a much shorter time than by a chamber test. In the latter, a good quality product should typically have a time to failure of more than 100 h, whereas a CMT test of a similar product mostly shows a stable, constant rate of corrosion (on the order of 5-10 fiAJcrn ) after less than 2 h. 

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). 

The use of surface tools need not be limited only to thin layers or small dimension corrosion. Creative application of surface methods to larger scale corrosion products, more characteristic of industrial problems, has provided useful information not previously available. More sophisticated uses of surface methods that are being developed and tested continually will provide even more information for corrosion research. 

Corrosion will always remain a significant challenge to the process industries. Process technologies will continue to develop into areas where there is no relevant experience of materials performance. There are inevitable risks in the use of corrosion testing to predict materials performance. With the exception of... 

Coupon and autoclave corrosion tests to screen equipment materials for the advanced SI process are being carried out and their experimental data is being continuously logged. The database of merchantable catalysts for a HI decomposition is being constructed through experimental activities. 

In one of the tests, the corrosion potential of the sample in 9 g/1 sodium chloride is noted. The pH, initial, and final potential are noted. The current at -1-0.8 V versus SCE is noted. If localized corrosion is not simulated in the first 20 s, the polarizing currents will be small and decrease with time. If localized corrosion is not stimulated in 15 min, the test is terminated, and the sample is resistant to localized corrosion. Localized corrosion is indicated by increasing polarizing current with time (>500 pA/cm ). The potential is then returned to corrosion potential to determine if the sample will repassivate or the localized corrosion will continue to occur. Evidence of pitting and crevice corrosion should be noted in ASTM F 746 (30). 

Atmospheric corrosion tests were continued for years with number of panels, and to have traceability, each uncoated panel was marked by hole with respect to reference plate made as per standard [3] as shown in Fig 2.5. The reference plate made of Aluminium has identical size of test panels and a hole is made in left hand corner marked as R, which stands for reference mark. Just below this hole, nine holes are made vertically engraving numbers 1-9 and similarly, in the right hand side, again nine holes are made vertically giving numbers 10-90 from top to bottom. At the top of the panel, five holes are made horizontally to represent hundreds. 

Anderson and Reinhard (1939) observed definite differences in the corrosion rates of sheet zinc exposed during different periods of the day. Specimens were exposed for 8 hours per day and were stored in dry, unheated rooms for the other 16 hours. The test was planned so that a different group of specimens was exposed during each 8-hour period 08 15 to 16 15, 16 15 to (X) 15, and 00 15 to 08 15. The test continued for 6 years, and thus each set was exposed to the atmosphere of Palmerton, Pennsylvania, for a cumulative... 

---