Laboratory Method for Corrosion Inhibitor Evaluation^⋆

A screening method has been developed which permits rapid, convenient testing of inhibitors. Unlike weight-loss methods, this new method is well adapted to follow non-linear corrosion-time curves, such as those commonly found when adsorption-type inhibitors are used. The method makes use of quart bottles containing the corrosive agents; the bottles are rotated end over end at about three rpm. This rotation brings about alternate immersion of test probes where the corrosive system consists of two or more phases. The test probes are used to follow the course of corrosion without requiring the bottles to be opened. A probe consists of a corroding specimen (metal ribbon) to which is attached a protected specimen serving as a temperature-compensating element. These specimens form two arms of a resistance-measuring bridge. Electrical leads, brought through the rubber stopper to the outside of the bottle, permit the probe to be connected when desired to a bridge circuit which internally converts any change in resistance to loss of metal thickness. The corrosion loss in millionths of an inch is read directly from a meter and can be followed conveniently during the course of the test. An application of the method in testing gasoline rust inhibitors is discussed. 5.8.1