On-line monitoring of corrosion

One of the maj or ways of protecting oil and gas production and operating systems against corrosion is by applying corrosion inhibitors. The corrosion inhibitors are evaluated in order to determine if the corrosion preventive measures applied are necessary, and if the required lifetime can be achieved with a particular inhibitor, as the effective life of corrosion inhibitors varies with the quantity of water intrusion. The purpose of this chapter is to evaluate the on-line monitoring of corrosion and corrosion inhibitor effectiveness under different conditions. 

The concept of corrosion monitoring has developed from two distinct areas, plant inspection techniques, and laboratory corrosion testing techniques, with the original aim of assessing or predicting corrosion. 

Corrosion monitoring data are used for following purposes  

Corrosion and Materials Selection A Guide for the Chemical and Petroleum Industries, First Edition. Alireza Bahadori. 2014 John Wiley Sons, Ltd. Published 2014 by John Wiley Sons, Ltd. 

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In Situ and High Resolution Experimental Probes The active support now given to the development of probes to measure corrosion processes in situ and with the spatial resolution needed for studying local corrosion phenomena should be continued. Of particular importance is the use of probes where possible as sensors for on-line monitoring of corrosion of components in technologically important systems. 

ASTM G 96, Practice for On-Line Monitoring of Corrosion in Plant Equipment (Electrical and Electrochemical Methods)—This standard outlines procedures for online corrosion monitoring in operating systems. The test methods described in this standard are used to determine the cumulative metal loss (electrical resistance method) or instantaneous corrosion rates (electrochemical method). Reference 15 provides a summary of electrical resistance and polarization resistance theory. 

G 96, Guide for On-Line Monitoring of Corrosion in Plant Equipment (Electrical and Electrochemical Methods)... 

There are many other techniques for measuring corrosion. Some of these may rely on chemical solution analysis or physical measurement of metal loss. One widely used additional technique is provided by ASTM G 96, Practice for On-Line Monitoring of Corrosion in Plant Equipment (Electrical and Electrochemical Methods). This guide covers two basic procedures. In one, a sample of the material, usually in the form of a continuous wire, is immersed into the environment of interest (liquid, air, solid, or multiphase). The electrical resistance through the wire is determined. As corrosion consumes the cross section of the wire, the resistance increases proportionately. The second procedure uses the polarization resistance technique described in ASTM G 59 to determine the corrosion rate in the environment. 

Continuous, on-line corrosion monitoring can be used to operate FGD systems at optimal efficiency while avoiding high corrosion rates. Conventional corrosion monitors are designed for use in bulk liquids and do not function satisfactorily in the thin condensate films that form on the surfaces of FGD ducts. Recent EPRI research has made use of an advanced electrochemical method of corrosion surveillance developed by the Corrosion and Protection Centre Industrial Services (CAPCIS) in England [30]. This method allows on-line monitoring of corrosion activity in either thin condensate films or bulk liquids. EPRI introduced the CAPCIS system to the U.S. electric utility industry in 1985, sponsoring several field demonstrations. 

Attributes of LPR probes are rapid data collection and ability to sense process excursions. These attributes allow them to be used as a process control and for on-line monitoring of corrosion rate. 

LPR testing is typically done in accordance with ASTM Standard G 96. Yeske [154] measured the corrosion rates of carbon steels in alkaline sulfide environments using the LPR technique and described the use of the silver/silver sulfide reference electrode. These techniques were develop>ed further by Crowe and Yeske [755] and used with real mill liquors for on-line monitoring of corrosion rates. The corrosion rates were found to be related to liquor composition with a strong flow effect. Crowe [156] also used LPR testing for on-line corrosion monitoring in white liquor clarifiers. Leinonen et al. [757] used the LPR method to monitor corrosion in a batch digester. 

Standard Guide for on-line monitoring of corrosion in plant equipment (Electrical and electrochemical methods). Annual Book of ASTM Standards. Philadelphia, Pa. American Society for Testing of Materials, 2001 03(02) G 96-90. 

Asher, J., Conlon, T. W., Tofield, B. C. and Wilkins, N. J. M., Thin Layer Activation-A New Plant Corrosion Monitoring Technique , Proc. Conf. On-Line Surveillance and Monitoring , entitled On-Line Monitoring of Continuous Plants, Ellis Horwood, London (1983)... 

Polarization resistance of the corroding sample may also be monitored over an extended duration. Thus, AC impedance may be used for online monitoring of a corrosion system such as on-line determination of corrosion inhibitor performance, as depicted in Figure 1.31. 

Over the past decade, a revolution has occurred in the field of electrochemistry with the development of in situ and ex situ surface analysis techniques capable of resolving important phenomena on both microscopic and short time scales. These techniques should be adapted and utilized to characterize local physicochemical corrosion events in situ. In addition, in situ techniques should be extended to provide on-line monitoring of real-world systems where reliability often requires detecting the onset and progress of corrosion phenomena (e.g., pit depth and crack length) as a function of time. 

Y. Schiegg, L. Audergon, B. Elsener, H. Bohni, On-line monitoring of the corrosion in reinforced-concrete structures , Eurocorr 2001, Associa-zione Italiana di Metallurgia, Milano, 2001 (CD-ROM). 

Robinson, M. J. and Strutt, J. E., (1988) The assessment and prediction of plant corrosion using an on-line monitoring system. In On-Line Monitoring of Continuous Process Plants, Ed. Butcher, D. W., SCI/EIlis Horwood, Chichester, pp. 79-94 (1988)... 

Protection of Austenitic Stainless Steel from Polythionic Acid Stress Corrosion Cracking During Shutdown of Refinery Equipment Collection and Identification of Corrosion Products Initial Conditioning of Cooling Water Equipment On-Line Monitoring of Cooling Waters... 

Development of the monitoring techniques is necessary to ensure sound and efficient operation of the FUJI-MSR. Fortunately, the reactor system does not require continuous monitoring of the major fuel constituents such as Li, Be, Th, F and U [XXX-36]. Therefore, electrochemical on-line monitoring of the redox potential has been developed it is only the U /U ratio, which responds to the corrosive atmosphere and to the distribution of fission... 

Finally it deals with monitoring internal corrosion. It provides guidance for on-line monitoring of internal corrosion in plants associated with the oil, gas and chemical industries, and guidance on laboratory monitoring and evaluation of corrosion inhibitors. The book also covers experiments on the corrosion behaviour of high-alloy tubular materials iu inhibited acidizing conditions. 

Electrochemical On-Line Corrosion Monitoring On-line corrosion monitoring is used to evaluate the status of equipment and piping in chemical process industries (CPI) plants. These monitoring methods are based on electrochemical techniques. To use on-line monitoring effectively, the engineer needs to understand the underlying electrochemical test methods to be employed. This section covers many of these test methods and their applications as well as a review of potential problems encountered with such test instruments and how to overcome or avoid these difficulties. 

Are there on-line monitors installed, for example, for the measurement of biofilm, scale, or corrosion Do they work What do they tell you What value is placed on this equipment by the operators Could this equipment be used to provide independent information in any subsequent trial ... 

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