Experience Of Using Multiple-Technique Corrosion Monitoring In Real Time

摘要

For the last ten years, multiple-technique corrosion monitoring systems have been available, including those employing electrochemical noise (EN), linear polarization resistance (LPR), electrical resistance (ER), etc.. However, to date this has usually meant that large instrumentation cabinets have been employed with low portability and significant cabling costs with long runs of heavy duty shielded cables from the probes to the instrumentation. In addition, the data for EN is usually acquired second-by-second by the data acquisition computer and then analysed and displayed using proprietary software. The computer may be 100's of metres from the monitoring location but has to be housed in a clean, dry, warm room. Recent electronics developments have provided the microprocessor, 16-bit digital-to- analogue and 24-bit analogue-to-digital converters at the heart of the instrument. Miniaturization of electrochemical measurement circuitry has enabled the electrochemical noise, LPR, and harmonic analysis techniques to be incorporated in a small package, which can be located adjacent to the probe access fitting on plant. The module attaches to standard corrosion probes available from any manufacturer, and employs multiple electrochemical techniques to cover a wide spectrum of corrosion rates and mechanisms. The measurements taken by our multiple-technique corrosion monitoring modules include Electrochemical Noise (potential and current), Polarization Resistance, Solution Resistance, Harmonic Distortion, Galvanic Coupling and Hydrogen Permeation Currents. Digital communications cable daisy-chains the units together across distances of a kilometre of more. The cabling is simple twisted pair, and does not require the extensive shielding that was needed for long runs of analogue, small amplitude corrosion signals. Further, different communications protocols can be employed which opens the opportunity of connecting the multiple-technique corrosion monitoring module directly to plant DCS or SCADA network systems, without proprietary software. The key of gaining acceptance of advanced technology is often the ease with which the monitoring process integrates with existing plant activities. The paper will present a technical overview of the multiple-technique corrosion monitoring module design, covering its capabilities and use in the field. Data will be presented showing how the electrochemical noise monitoring technology has been 'demystified' to give direct readings of high relevance to operators for characterising localized corrosion. At the time of this conference, over 12 months field service experience has been gained with multiple-technique corrosion monitoring modules.