Field Testing of Inhibitors

The most reliable test apparatus is field equipment itself. However, it is the most expensive because of the cost of the equipment and because testing in full-scale equipment is time consuming. 

No source of information should be ignored, though, in evaluating additives or process variables, and much valuable data can be obtained if careful day-to-day records are kept on equipment performance. A simple tabulation of failures versus time can show improvements resulting from inhibitor treatment. The records can be made even more sophisticated by identifying various parts of the equipment that fail and by deciding whether wear, stresses, or other factors have been involved. 

A method of record keeping that has been used in treated water systems is to plot the logarithm of cumulative leaks against time. A plot of this type wiU approximate a straight line, indicating that the number of leaks increases with time. As a treatment becomes effective, the slope of such a line will be reduced. 

Field testing usually is performed by means of coupons exposed to the test environment. The coupons can be installed on a holder in the full flow of a process line of interest. Another method is to use a test pipe nipple in the flow line to simulate more closely velocity conditions. 

When either of these techniques is used, however, inhibitor treatment of the complete stream is necessary for the relatively long times needed for coupon exposure. To minimize the test times, electrical resistance probes, polarization resistance electrodes, or iron counts can be used, when applicable, reducing test times to days instead of weeks. 

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