INTRODUCTION
A study was conducted in a broad range of multiphase (oil/gas/water) environments to assess the ability to assess corrosion/pitting in petroleum production environments using an automated (field) electrochemical monitoring system. Corrosion measurements were made in both liquid and vapor phase environments under various conditions of velocity, oil/water mixtures, oil type, H2S/CO2, and additions of various impurities found in oil systems. The results demonstrate the widely varying corrosivity (both general and localized attack; in both liquid & vapor phases) of these systems, while also showing the extensive abilities of real-time electrochemical monitoring to assess varying conditions commonly found in gathering lines, pipelines and facilities.
Advances in technology (e.g. microchip encoding and miniaturized, distributed hardware with direct to DCS capabilities) have made it possible to apply automated electrochemical monitoring in commercial and industrial applications. In turn, automated, online corrosion monitoring solutions have also made it possible to actively involve plant personnel on a real-time basis. This feature brings a new paradigm where they can view real-time process and corrosion data together. The benefits of this real-time process control approach are three fold:
· Data capabilities allow better correlation of periods of process corrosivity to specific changes in process variables.
· Corrosion upsets can be handled and mitigated before substantial damage has occurred.
· Better process control and reduced corrosion during production allow for extended run time and reduced allocations for inspection and repair.
Experience has shown that these benefits, in turn, have the potential to impact overall operational issues in three important ways:
· Increase system/unit run time
· Reduce inspection downtime
· Increase system utilization and productivity.
Furthermore, from a technical standpoint, these advances in corrosion monitoring technology have also resulted in B value corrected corrosion rates for increased accuracy (see Appendix II), and have made it possible to separately trend pitting corrosion tendencies in addition to the more commonly used general corrosion. Another key point in automated measurement systems is that it is now possible to achieve data sharing between process operators and corrosion specialists to track corrosion and process variables as key performance indicators (See Figure 1). This has led to the ability to increase system integrity and reliability of performance while extending the life of pipeline and plant assets.
MONITORING METHODS FOR MULTIPHASE ENVIRONMENTS
This investigation utilized modern multi-technique electrochemical monitoring instrumentation ? SmartCET® (1) ? incorporating automated, on-line measurements for:
· Linear Polarization Resistance (LPR) for general corrosion measurements
· Harmonic Distortion Analysis (HDA) for measurement of B value (Stearn-Geary Constant) for correction of LPR corrosion rates, and
· Electrochemical Noise (ECN) for evaluation of pitting tendencies.
· Nine additional variables and statistical parameters
Further background on these techniques has been published previously [1-19]. A summary of the three primary field techniques utilized (LPR, HDA and EN) are provided in Appendix I.
FIGURE 1 ? Representation of Modern Corrosion/Process Control Monitoring Scheme
This field instrumentation was employed to investigate and characterize the corrosive conditions in multiphase environments containing brine, oil and gas phases, in combina
