Corrosion and electrochemical instruments are designed to measure corrosion and electrochemical conditions in plant machinery, field equipment, batteries, fuel cells, colloids, and other solutions or systems. They use a variety of technologies. Typically, nondestructive test (NDT) equipment is used to detect internal corrosion and measure corrosion thickness. Specialized instruments are used to measure the corrosion rate and to monitor media and system conditions. The corrosion rate, which is often measured in mils per year (mpy), is the amount of metal weight loss over a unit time due to corrosion. Many corrosion and electrochemical instruments include probes, provide numeric displays, and feature data logging capabilities. Some advanced devices include alarms that indicate when readings are outside a range of values.
Corrosion and electrochemical instruments use a variety of methods to detect and measure corrosion and electrochemical conditions. Acoustic emission tests use specific acoustic or vibrational responses to determine the structural adequacy of tanks and pressure vessels. Optical instruments use magneto-optical and holographic interferometry to detect flaws and residual stress. Eddy current tests expose flaws on rough surfaces, or surfaces wet with films or coatings. Other surface tests expose flaws such as inclusion, bubbles and boils, and pin point continuities. Hydrogen tests use probes to detect and measure hydrogen emissions, while ultrasonic techniques (UTs) compare the amplitude of a reflected echo from an interface with that of a reference interface of known size. Radiographic equipment uses penetrating X-rays or gamma rays to capture internal, structural images of cracks and pores. Zero resistance ammetry (ZRA) measures the current of a macrocell positioned between two sensors.
With electrochemical impedance spectroscopy (EIS), corrosion and electrochemical instruments apply small amplitude signals over a range of frequencies and record both the resistance and capacitance responses. Electric resistance (ER) tests measure changes in the electrical resistance of a metallic element immersed in a product media relative to a reference element sealed within the probe body. Inductive resistance probes are similar to ER probes, but measure changes in the inductive resistance of a coil that is located inside the element. Corrosion and electrochemical instruments that monitor electrochemical noise (EN) track current fluctuations in corroding metals. Galvanostats maintain electrodes at a constant current or a controlled set of scanned current values. Linear polarization resistance (LPR) uses a series of electrodes, a voltmeter, an ammeter and a current source.
There are many applications for corrosion and electrochemical instruments. Some are used in laboratories and test facilities. Others are used in storage facilities, steel manufacturing, and chemical processing. Some corrosion and electrochemical instruments are handheld and portable. Others mount on computer boards, sit atop benches, fit inside cabinets, or slide into racks. Corrosion and electrochemical instruments are an integral part of the monitoring systems used to continuously detect or measure flaws, thickness, or corrosion in a variety of production line and field equipment.
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