This paper reviews the application of electrochemical noise (ECN) corrosion surveillance techniques in a large sour gas processing plant operation. The ECN technique has been employed on a real-time basis in several process unit operations for over two years with extremely interesting results. A sulfinol contactor tower where the solvent was contaminated by air is investigated. The use of electrochemical noise in an on-line, real-time basis has positively identified localized pitting attack. The corrosion data when converted to meaningful information and then coupled with real-time plant process information derived from the distributed control system (DCS) provide the corrosion engineer with the requisite tools to look at both the mechanism of corrosion as well as those factors controlling it. It is relatively safe to assume many similar sour gas plants haven?t yet considered some form of real time surveillance, since the technology is only emerging and widely considered as unproven, Electrochemical noise when used on-line in real-time will reliably benefit the end-user by providing meaningful information, which is in the realm of near-absolutes, and not merely generalities. The confidence achieved from ECN surveillance will directly impact pressure equipment life and mandatory inspection frequencies.
Electrochemical noise has been known for some 20 years but its use in industrial applications has only been more common in the last five-to-six years. Even rarer has been the use of the technique on an on-line, real-time basis as opposed to obtaining data on a random spot-check basis. Adopting an integrated asset management philosophy, AEC West Ltd. of Calgary, Alberta incorporated the electrochemical noise technique as part of a comprehensive corrosion and vibration surveillance portfolio intended to extend pressure and rotating equipment safety and service life?.
Since the technique was a relatively new and unfamiliar corrosion assessment tool for the writer, no preconceived biases, positive or negative, were formulated about the anticipated performance of the tool. Rather, the reliance upon more conventional electrochemical techniques such as linear polarization resistance (LPR) was expected to be the primary source of corrosion data from this new gas plant. From the commissioning of the plant in November 1995, it was rapidly apparent the corrosion rate data being stored in the Mentor database for LPR versus electrochemical noise (ECN) were in most instances, very different. The differences are inherent in the respective techniques employed; the LPR method provides an estimation of the general corrosion rate while ECN tends to provide an insight into localized (pitting) rates. Over the period of the eight months (November, 1995 through June 1996) following plant commissioning the ECN data were tracked but not given their full credit, simply because the technique was new, unfamiliar and above all unproved in any sour gas plant application in Canada. What was to emerge following visual and/or NDE inspection at a June, 1996 turnaround and subsequent operation of the ECN technique has been an overwhelming appreciation (through visual and other NDE inspection protocols) for the precision of the technique, its reliability and its highly sensitive capa
