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The presence of stray current is detected through the use of structure-to-soa`1 <br /> potential measurements. The structure-to-sail potent ols. are taken and recorded <br /> avec a period of time, using a 516C Polyccrder, microcomputer data logger <br /> manufactured by Omnidata International, Ihc. Fluctuations ions in potential indicate <br /> the presence and magnitude of exposure to stray current. <br /> IV. PH <br /> pH is the negative logarithm of the hydrogen ion concentration. For ferrous <br /> materials of construction, pH in the range of 4 to 10 has little effect on the <br /> rate of corrosion under oxidizing conditions at ambient temperatures. Acid scats <br /> are mare conducive tr) ferrous corrosion because at pH values above 10, the <br /> steel readily polarizes which tends to passivate the c rrosion cells. At pH <br /> values below 4, the rate of corrosion accelerates rapidly. <br /> The method used to measure pH is ASTM Standard Test Method D2976-71 with <br /> an accuracy of +0.01, Sail samples are dissolved in distEed water and placed in <br /> a centrifuge to remove the suspended solids. The supernatant is then tested <br /> with a glass-calomel pH electrode in conjunction with an Orion Research Model <br /> 601 A meter. Liquid samples are tested directly without dilution. <br /> V. Chloride Ion <br /> Chloride ions are depolar=u—ig agents and cause corrosion pitting of many <br /> common materials of construction. ASTM Standard Test Method D512-81 is used <br /> to measure the chloride ion concentration with an accuracy of +0.5 ppm. This <br /> method utilizes an ion selective electrode and an Orion digital ionalyzer. The <br /> chlrxide inn concentration for sail, samples is measured from the supernatant <br /> extracted for the pH testing. Liquid samples are tested directly. <br /> 3 <br />