Corrosion monitoring cathodic protection

A large percentage (57%) of mains and services (46%) is metal (steel, cast iron or copper), and corrosion is a major issue. For distribution pipe, external corrosion is of primary importance, although internal corrosion has been noted in some cases. The methods of monitoring corrosion on cathodically protected pipe are similar to those in the transmission pipeline sector, including pipe-to-soil potential and coating surveys. One difference is that in distribution systems, leak detection is an acceptable method of monitoring for these pipelines without CP (nearly 15% of the steel mains). 

Recognize corrosion problems in materials used at the site and make monitoring a normal part of the operation. Sour oil and gas operations are often conducted under high pressure and corrosive conditions. Therefore, in addition to temperature and pressure considerations, system designs for the wellhead, downhole equipment, and pipeUnes must have features to minimize the effects of corrosion and prevent an accidental release of H2S. Corrosion-inhibiting fluids can be used to prevent internal corrosion and cathodic protection can be used to prevent external corrosion. Also, during extended periods of shut-in and injection into pipelines, inhibitor applications may be beneficial. 

Monitoring cathodic protection is emphasized by ASME B31-11, which recommends testing at two month intervals or less of all cathodic protection rectifiers and connected protective devices. Erosion-corrosion of slurry pipelines may be reduced using special corrosion inhibitors, by avoiding sharp corners and short elbows, and providing some lining such as HDPE, rubber, or polyurethane. Monitoring of the pipeline on a yearly basis and at intervals that do not exceed 15 months is recommended by B31.il. Areas prone to more rapid localized erosion-corrosion should be monitored more frequently as dictated by experience. Corrective measures should be established on the basis of bis torical leaks. 

Monitoring cathodic protection systems and corrosion damage to pipelines (and other structures) under their influence is a highly specialized subject. This material is therefore presented separately from the general corrosion monitoring chapter, although readers should be able to identify some overlap in basic concepts. 

The Handbook of Corrosion Engineering was designed entirely in collaboration with Martin Tullmin. In fact, Martin is the sole author of many sections of the book (corrosion in concrete, soil corrosion and cathodic protection) as well as an important contributor to many others. My acknowledgments also go to Robert Klassen who contributed to the atmospheric corrosion section as well as for his study of the fiber optic sensors for corrosion monitoring. 

An alternative means of avoiding the hazard from fire is to bury the vessels or to employ the increasingly popular method of mounding. In either case, acknowledgment of the reduced hazard is indicated by the reduced separation distances (see Table 20.4). Since both burial and mounding preclude the possibility to monitor continuously the external condition of the vessels, very high-quality corrosion protection needs to be applied, often supplemented by cathodic protection, depending on soil conditions. 

Willis, A. D., New Monitoring Methods of Cathodic Protection Systems , Anti-Corrosion, 27, 6, April (1980)... 

McKenzie, S. G., Techniques for Monitoring Corrosion of Steel In Concrete , Seminar Corrosion In Concrete-Monitoring, Surveying and Control by Cathodic. Protection , Global Corrosion Consultants, Telford (1986)... 

When the bottom plates are welded together, the coating is partially destroyed. Research and field work showed that protection can be achieved using volatile corrosion inhibitors under the tank [688]. This works alone or in combination with cathodic protection. Double tank bottoms for leakage monitoring are often specified for new tanks. However, the same problem of coating destruction occurs. Volatile corrosion inhibitors are an excellent solution from both a technical and an economic standpoint. This type of corrosion inhibitor... 

Monitoring of the pipelines, (inspections, pigging, corrosion, cathodic protection, helicopter survey, etc.)... 

Monitoring of the electrochemical potential of steel reinforcement in concrete is a well established technique for assessing the severity of corrosion and for controlling cathodic protection systems. A reference electrode is the electrochemical device used for measuring these potentials. The reference electrode is either placed on the concrete surface during the measurements or permanently embedded in the concrete in close proximity to the steel. The latter technique enables remote long-term monitoring. 

Most of the reference electrodes embedded in concrete are used for control of cathodic protection (CP) systems. Potential stability is then less important, compared to corrosion state monitoring. Control of CP systems requires only short-term stability, maximum 24 hours. Corrosion rate measurement, like linear polarisation resistance (LPR) measurements, also requires short-term reference electrode stability. However, regardless of application, a reference electrode which is to be permanently embedded in the test solution, e.g. concrete, must have a long life when exposed to this environment. 

Obviously, very stable and long life embeddable reference electrodes are a must for this type of application (long-term corrosion monitoring). However, for cathodic protection control applications the stability requirement is not that important. It is surely desirable for the reference electrode to have a long embedded life . More reports on held experiences with embeddable reference electrodes for concrete would be highly appreciated. 

P. Pedeferri, G. Mussinelli and M. Tettamanti, Experiences in anode materials and monitoring systems for cathodic protection of steel in concrete , in Corrosion of Reinforcement in Concrete, edited by C. L. Page, K. W. J.Treadaway and P. B. Bamforth, Elsevier Applied Science, London, UK, 1990, pp 498-506. 

If materials selection depends on corrosion control by process-related measures (such as chemical treatment), these should be indicated on the MSD. Indicate the intended injection points and the type of chemical to be injected. Examples include corrosion inhibitors, scale inhibitors, biocides, pH control chemicals, wash water, etc. Also indicate the location of proposed corrosion monitoring and sampling sites. If anodic or cathodic protection is to be part of the corrosion control design, the MSD or its Notes section should indicate the piping and/or equipment to be protected. 

The ohmic drop exerts a sensible influence on the evaluation of the electrochemical parameters as well as on the definition of the reaction scheme that is most suitable for describing the behaviour of a metal in a given environment. It also determines the success of many operations, such as cathodic protection by means of sacrificial anodes or impressed current and corrosion rate monitoring. 

R. B. Polder, Cathodic protection of reinforced-concrete stmctures in the Netherlands — experience and developments , in Corrosion of Reinforcement in Concrete - Monitoring, Prevention and Rehabilitation, Papers from Eurocorr" 97, J. Mietz,... 

An important aspect of cathodic protection is the means to monitor the effectiveness and the criteria for protection. Criteria recommended by NACE (RP0169-96) for the CP of steel and cast iron piping are given in Table 4 [24]. Although several criteria are described for CP of steel structures, the most commonly used criterion is that the steel structure to be protected should be maintained at a potential more negative than —0.85 V versus Cu/CuSOr reference electrode. The primary disadvantages of this criterion are no connection of the potential of the steel to the corrosion rate, and a large difference in protective... 

A large percentage of mains (57%) and services (46%) are metallic systems (steel/cast iron/copper), and corrosion is a major problem. For distribution pipe, external corrosion is the primary problem and internal corrosion has also been observed in some instances. The methods of corrosion monitoring on cathodically protected piping are similar to the methods used in the case of transmission pipelines... 

The effectiveness of cathodic protection can be accomphshed by monitoring the pipeline potential using the close interval potential survey (CIPS) method or by using direct current voltage gradient (DCVG) or IR coupon techniques. Also, physical and electrochemical methods can be used to estimate the corrosion rates of a cathodicaUy protected system. 

Cathodic protection (CP) is described in Section 10.4. The simplest and most important method for monitoring structures protected by CP is potential measurement. This is used to check that the potential is below a certain limit at which the corrosion rate is assumed to become significant (see Section 10.4). As described earlier (Chapter 3) the potential is measured with a voltmeter with high internal resistance. One terminal on the voltmeter is connected to the reference electrode, which is held close to the actual part of surface of the structure to be monitored. The other terminal on the meter is connected to flic structure. 

Cathodic and Inhibitor Protection and Corrosion Monitoring -ISBN 978-0-8493-8247-5... 

Underground pipelines are essential requirement of any developed country. Transportation of crude oil, gas, and many hydrocarbons are carried out through underground CCPs, as they are one of the safest modes of transportation, causing minimum disturbance to mankind. Since the material of construction of pipelines is steel, which is prone to severe corrosion, both from inside and outside, safety of pipelines depends upon a foolproof system of corrosion protection. All three major techniques of corrosion protection, namely, coatings, inhibitors, and cathodic protection, are used to protect pipelines. Protection of pipelines alone is not enough it is also important to monitor... 

After a cathodic protection system is installed, the system needs to be monitored. The systan should be evaluated periodically to ensure that it is providing corrosion protection to the metallic structure. Criteria have been developed to determine if adequate corrosion protection is being achieved on the structure in question. For example, some of the indications of a cathodic protection problem include changes in operating conditions of the rectifier output and any noted corrosion increase in the structures. 

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