This paper describes the field investigation performed to characterize the corrosion behavior in a fully- inhibited water-containing hydrocarbon transport line. Modem multi-technique electrochemical monitoring instrumentation incorporating Electrochemical Noise and Linear Polarization techniques was employed. The data obtained were analyzed on-line and correlated with short-term upsets in process operation enabling a troubleshooting exercise to be undertaken, and ultimately validating the effectiveness of the existing chemical treatment program.
Historically, the major issue limiting the widespread application of Electrochemical Noise (EN) for corrosion monitoring was the complex data interpretation required. Raw EN data files required detailed analysis by corrosion experts to identify and categorize the rate and mechanism of corrosion attack tl-6). Since this analysis could only be performed retrospectively, this further hindered the use of EN-based corrosion monitoring for troubleshooting and proactive corrosion control applications. With advances in technology over the last several years, the commercial and industrial applications of EN as an on-line corrosion monitoring technique have been steadily increasing (7-17), and plant personnel are coming to terms with the usefulness of the technique. Overall, EN-based corrosion monitoring is gaining wider acceptance within the corrosion monitoring and plant operation communities. For the application described, modem multi-technique electrochemical monitoring instrumentation incorporating on-line EN and Linear Polarization Resistance (LPR) techniques, was employed to investigate and characterize the corrosion behavior in a hydrocarbon transport line. The instrumentation incorporated soil-ware capabilities to perform analysis of both the raw EN and LPR data, producing on- line displays of corrosion rate from each technique, and qualitative localization information from EN.
APPLICATION BACKGROUND
The location chosen for the installation was approximately at the mid-point on a pipeline between an offshore production facility and an onshore processing facility. This location was chosen primarily for ease of access since the pipeline was above ground and hence multi-technique electrochemical probes could be readily installed. A number of pre-existing 2" high-pressure access fittings were located mid- way between the three and six o'clock positions. Historically, a flush-mounted ER probe with associated data collector unit, and a flush-mounted weight loss coupon had been installed to monitor the long-term performance of the chemical inhibition program in place on the pipeline. The primary objectives of the application of multi-technique electrochemical probes were two-fold. The first objective was to demonstrate that on-line EN and LPR techniques could be employed for monitoring in the pipeline, and the second was to show that the speed of response and resolution of the multi-technique approach could provide a valuable insight into short-term effects of process operation on the corrosion behavior.
ELECTROCHEMICAL INSTRUMENTATION
Electrochemical Noise
Electrochemical Noise is the measurement of spontaneofis fluctuations in the current and potential generated by corrosion occurring at the metal-electrolyte interface of a three-electrode system. Ideally, the corrosion sensors comprise two identical working electrodes plus a reference electrode. The reference electrode can be a conventional solute electrode (such as Ag/AgCI) if sufficiently stable. For practical field monitoring applications a metal pseudo reference electrode of the same material as the working electrodes is typically used. Statisti
