Corrosion weight-loss tests

FIG. 2—Typical Huey test apparatus with water-cooied condenser for conducting sample general corrosion (weight-loss) tests up to the solution boiiing point. Samples are typically suspended In the solution by Teflon string or glass rods. 

Determination Test, Weight loss test, Eschke test, Salt spray test and Sulphur dioxide test at 50°C. Mechanism of inhibition of corrosion and surface study of mild steel was also studied by Metallurgical Resesarch Microscopy and Scanning electron Microscopy. 

By performing weight loss tests, technical personnel can estimate the corrosiveness of an environment over a period of time. If the corrosion rate is determined to be high, preventive measures can be taken to prolong the remaining life of the equipment. The preventive measures can include the addition of a corrosion inhibitor, a change in the process, an application of anticorrosion coatings, or the addition of a CP system. 

A conductive polymer film of polypyrrole doped with polymolybdate anions was electrodeposited onto steel and found to provide corrosion protection in neutral and acidic 3.5% NaCl solution [152]. The anodic codeposition of polypyrrole and Ti02 onto mild steel in an oxalic acid medium has been described [153,154]. The PPy and Ti02 composite showed a considerable improvement in anticorrosion properties with respect to PPy films in salt spray and weight-loss tests. It was suggested that these composite films could be applied as a primary coating replacement for the phosphatized layers on mild steel [154]. 

F ure 1038 Effect of electrolyte on cavitation corrosion. Weight loss of a carbon steel after 15 minutes as a function of temperature during cavitation tests using a vibrating device (a) in distilled water (b) in water buffered to pH 8 and (c) in a 3% NaCl solution [25],... 

Specimens with step and dual structures do not drop grains in boiling acid tests, and therefore have acceptable or passing corrosion rates in weight-loss tests. Materials represented by such specimens can therefore be accepted for plant use on the basis of the 1.5 min oxalic acid etch test. Only those materials that have a ditch structure must be submitted for testing in the hot acid tests to determine whether or not their corrosion rates fall below or above the acceptance rate for the given alloy. 

Information on "acceptable and nonacceptable corrosion test results has been given for the two EPR tests in the section above on these tests. Acceptable etch structures (step, and in some cases, dual) are also identified for the oxalic acid etch test. The absence of fissures in bends after certain copper sulfate tests is considered an indication of acceptable results. However, in the case of weight-loss tests (nitric acid, ferric sulfate, and certain copper sulfate tests) the standard ASTM test methods merely show how corrosion rates are calculated without identification of rates which are evidence of the onset of susceptibihty to intergranular attack. 

Weight loss is the easiest and least expensive method since that method requires only test specimens, the solution, a container, and the appropriate environmental parameters. Weight loss tests can be conducted in low and low conductivity solutions, even in the atmosphere. An analytical balance is required for both before and after weight measurements. Multiple specimens must be used when evaluating the change in corrosion rate over time. Sp>eci-mens cannot be reused for corrosion rate versus time measurements after first exposed and cleaned because high initial corrosion rates will occur each time the specimen is used. This will lead to artificially high corrosion rate data. 

ASTM G 31 Standard Practice for Laboratory Immersion Corrosion Testing of Metals Describes procedures for conducting laboratoiy weight loss tests Provides information on reporting and factors to be aware of. 

Corrosion in brownstock and post-oxygen washers has been investigated by Bennett and Magar [795] using electrochemical procedures. Their results showed that corrosion is affected by pH, chloride concentration, temperature, and aeration. These tests were complemented with instantaneous corrosion rate measurements by linear polarization resistance methods and by weight loss tests. 

Corrosion in mechanical pulping processes was investigated by Crowe [202] via weight loss tests and potentiody-namic polarization tests. Vapor phase condensate corrosion was more severe than liquid phase corrosion. 

Figs. 14(a)-(b), whose data were listed in Table 2, show Tn and Ipass vs. A1 content x plots, respectively. One can easily see that both bri and Ipass increase with x. This implies that the passive corrosion property of AbCoCrFeNi decreases with A1 content x. Fig. 14(c) shows Wioss vs. X plot. Like bri and Ipass, Wioss also increases with x. Notice that, unlike potentiodynamic polarization, immersion weight-loss test is a natural electrochemical reaction, i.e., without applying any voltage on the test sample. On the other hand, bn and... 

Aqueous corrosion is electrochemical in nature. It is therefore possible to measure corrosion rate by employing electrochemical techniques. Two methods based on electrochemical polarization are available The Tafel extrapolation and linear polarization. Electrochemical methods permit rapid and precise corrosion-rate measurement and may be used to measure corrosion rate in systems that cannot be visually inspected or subject to weight-loss tests. Measurement of the corrosion current while the corrosion potential is varied is possible with the apparatus shown in Figure 1.4. 

Whatever treatment is used to clean specimens after a corrosion test, its effect in removing metal should be determined, and the weight loss should be corrected accordingly. A blank specimen should be weighed before and after exposure to the cleaning procedure to estabhsh this weight loss. 

Nickel and nickel alloys do not form thick layers of corrosion products when freely exposed to outdoor atmospheres in circumstances where the surface is periodically washed by rain, but such deposits may form on sheltered surfaces. Quantitative data on the rate of loss of metal and of pitting of nickel and nickel alloys exposed to outdoor atmospheres are avail-able . Figure 4.38 shows results obtained at three sites in the USA over a 7 year period and Fig. 4.39 gives results from a 10 year test at Birmingham. In both series of tests, Ni-Cr-Fe alloys gave lower weight losses than nickel itself or Ni-Cu alloys and the American results bring out the... 

In tests carried out by the National Bureau of Standards in the USA specimens of copper alloys, lead, zinc and zinc alloys were buried at a number of different sites for periods varying from 11 to 14 years. The soils tested covered a pH range from 2-6 to 9-4 and resistivities ranged from 62 to 17 800 fi cm. The weight losses and maximum depths of pitting were recorded, and the results indicated that the most severe corrosion occurred in soils of poor aeration having high acid and soluble-salt contents. 

The redox potential of the solution is that of the Fe /Fe equilibrium and lies within the range 0-80-0-85 V (v. S.H.E.). The high weight loss of susceptible alloys is due to undermining and grain dislodgement at the sensitised zones, which occurs at about twice the rate of that in the Huey test. Another difference is that whereas in the Huey test corrosion products... 

D 2688 1983 Test method for corrosivity of water in the absence of heat transfer (weight loss methods)... 

ENA was recently used for remote on-line corrosion monitoring of carbon steel electrodes in a test loop of a surge water tank at a gas storage field. An experimental design and system for remote ENA and collection of electrochemical impedance spectroscopy (EIS) data (Fig. 13) have been presented elsewhere. In the gas storage field, noise measurements were compared with electrode weight loss measurements. Noise resistance (R ) was defined as... 

A plot of mass loss versus time can provide information about changes in the conditions under which the test has been run. One example of such a plot comes from the ASTM Standard G96, Standard Guide. As mentioned previously, weight loss measurements are appropriate for measurement of localized pitting corrosion, including that caused by MIC. 

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