Instruments for controlled-flow laboratory tests
Controlled-flow laboratory tests are performed to study flow assisted corrosion (FAC) and erosion-corrosion phenomena, to select inhibitors and to study the effect of mass-transfer phenomena on material’s electrochemical properties. Cormet manufactures several controlled-flow laboratory tools for high-temperature high-pressure environments.
Useful information about controlled-flow laboratory instruments is given in ASTM G170 – 06 “Standard Guide for Evaluating and Qualifying Oilfield and Refinery Corrosion Inhibitors in the Laboratory” and ASTM G184 – 06 “ Standard Practice for Evaluating and Qualifying Oil field and Refinery Corrosion Inhibitors Using a Rotating Cage”.
Rotating electrodes are the most widely used controlled-flow lab instruments. A Rotating Disc Electrode (RDE) is a simple tool where the working electrode current depends on the square root of the angular velocity. A Rotating Ring Disc Electrode (RRDE) is used for the quantitative and qualitative identification of species dissolving on the disc shaped working electrode. A Rotating Cylinder Electrode (RCE) provides a uniform shear stress on the cylindrical surface. A Rotating Cage (RC) is a specimen holder for rotating coupons – the weight-loss data is basically used for inhibitor selection.
An Impingement Jet has a pump that pumps water through a relatively small diameter nozzle perpendicular to a specimen. At a certain distance of the jet centre point, the shear stress can be defined. The Impingement Jet creates higher shear stresses than a regular RCE.
A high speed loop is a versatile instrument to study the effects of flow on corrosion and electrochemical behaviour of materials. It can be used to test not only standard specimen geometries but different kinds of real-life geometries such as elbows, bends, valve bodies, etc. A high-speed loop can also be used to simulate heat exchanger operation. These instruments are often complicated, large and expensive.