Corrosion testing continued procedures

Corrosion testing in the pulp and paper industry is based both on standards developed for other industries and on methodologies developed by individual researchers in the pulp and paper industry. Relatively few corrosion test standards have been developed for the pulp and paper industry. Corrosion testing has been most often performed either to investigate the performance of alternative materials in existing processes or to assess the effects of process modifications on existing materials of construction. As new processes create new problems, new test procedures will continue to be devised. 

It is easy to buy safety equipment. All we need is money, and if we make enough fuss we get the equipment in the end. It is much more difficult to make sure the equipment is kept in full working order when the initial enthusiasm has faded. All procedures, including testing and maintenance procedures, are subject to a form of corrosion more rapid than that which affects the steelwork and can vanish without trace once managers lose interest. A continuous auditing effort is needed to make sure that procedures are maintained. 

If it is predicted that the test substance does not have the potential to be severely irritating or corrosive to the eye, continue to Section 11.4.2, Rabbit Screening Procedure. 

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. 

Another variation of the immersion test is the cyclic test procedure where a test specimen is immersed for a period of time in the test environment, then removed and dried (either air diy or use of heat lamps), then re-immersed to continue the cycle. Normally hundreds of these cycles are completed during the course of the test program. In ASTM G 60, test specimens are dipped in a test solution before being exposed to atmospheres varying in relative humidity. The intent of the test is to develop a layered corrosion product similar to that found on sheltered outdoor exposure test specimens. These tests can be either manually performed or conducted in apparatus equipped for automatic cycling. 

Testing procedures for cracked concrete are essentially the same as used for other laboratory specimens exposed to chloride solutions continuously or cyclically. Methods that can be used include polarization resistance, electrochemical impedance, and macrocell corrosion which were discussed above. Procedures for conducting these tests are described in Refs 27 and 28. 

The second procedure is the flow through test. Here, a properly conditioned fluid is continuously flowed over the metal specimen [22]. While this does not eliminate initial effects, a more realistic steady state can he obtained if the test duration is long enough. The changes in the corrosive fluids are chtiracterized hy the flow rate and the total corrosion per unit time (corrosion rate x surface area), and in some cases, the volume of the container holding the corrosion prohe. 

Third, a hybrid procedure is being used frequently where conditioned fluids are circulated over the test specimen from a reservoir [20]. If the reservoir is large enough, changes in fluid composition can he minimized. A particularly ingenious version of this hybrid test method has been developed in Norway [23], where the circulating fluids are continuously reconditioned by automatic pH maintenance and corrosion product removal. The distinction of these three approaches must always be kept in mind when discussing corrosion and inhibition tests. 

Procedures for monitoring corrosion of pipelines and related surface facilities using retrievable specimens are described in NACE Standard Practice for Preparation and Installation of Corrosion Coupons and Interpretation of Test Data in Oilfield Operations (RP0775). One of the main concerns in the use of such specimens is the problem of location, since corrosion is generally associated with a separate water phase. In some cases, special dropout pots are used to trap a water phase to provide a severe location for specimens. Electric resistance probes can be used in place of specimens. In locations where there is a continuous water phase and fouUng is not a problem, polarization type probes can be used [74,75]. 

The higher inherent corrosion resistance of aluminum alloys in saltwater, as compared to steel, has led to the use of a wet/dry saltwater immersion-type test being used at the Alcoa Laboratories instead of the ASTM B 117 procedure. In fact, the continuous immersion of aluminum bonded joints in 3.5% sodium chloride solution or even natural seawater may not deteriorate such joints as much as distilled or deionized water exposure. The amount of... 

The removal of large sintered particles resulted in a substantial reduction in corrosion rate for all materials in the tests shown in Table 5-12. This effect for thoria produced by high-temperature calcination was sufficient to justify including similar classification in the regular production procedure. Particles of large crystallite size (>0.25 micron) from which the sintered particles had been removed by classification were shown to produce comparatively low corrosion rates. Particles composed of large crystallites are not much degraded by continued circulation, and (mn.se-quently corrosion rates do not diminish much with time. 

Objectives. The objectives of the Homogeneous Reactor Test (HRE-2) are (1) to demonstrate that a homogeneous reactor of moderate size can be operated with the continuity required of a power plant, (2) to establLsh the reliability of engineering materials and components of a size which call be adapted to full-scale power plants, (3) to evaluate equipment modifications which will lead to simplifications and economy, (4) to test simplified maintenance procedures and in particular underwater maintenance, and (5) to develop and test methods for the continuous removal of fission and corrosion contaminants. 

Alternate Immersion in 3.5% NoCl. Exposure to 3.5% sodium chloride or to substitute ocean water (ASTM D 1141) by alternate immosion (ASTM G 44) (see Table 1) is a widely used procedure for testing smooth specimens of aluminum alloys. Aeration of the specimens, achieved by the alternate immersion, enhances the corrosion potential (Ref 26) and produces more rapid SCC of most aluminum alloys than continuous immersion. The ASTM G 44 standard practice consists of a 1 h cycle that includes a 10 min soak in the aqueous solution followed by a SO min period out of solution in air at 27 °C (80 °F) and 45% relative humidity, during which time the specimens are air dried, lliis 1 h cycle is repeated continuously for the total number of days recommended for the particular alloy being tested. IVpically, aluminum alloys are exposed from 10 to 90 days, depending on the resistance of the alloy to corrosion by salt water. This test ntethod is widely used for testing most types of aluminum alloys with all types of smooth specimens. 

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