Corrosion-monitoring systems

The aforementioned limitations are not problems with the probes or the monitoring systems but occur when information is desired that cannot be measured direc tly or which requires extrapolation. Many of the problems that are encountered with corrosion-monitoring systems and probes are related to the use to which probes are put. 

The type of probe, its materials, and method of construction must be carenilly considered in designing an effective corrosion-monitoring system. Since different types of probes provide different types of information, it may be necessary to use several types. 

A Btu meter may be used in the fuel-quality system as an aid in determining turbine system efficiency. A water capacitance probe is used for detection of water in the fuel line. A water-detecting device can be incorporated into the corrosion monitoring system. This monitoring device is based on detection of changes in the dielectric constant of unknown fluid components... 

Errors in design and changes in operation will occur which increase the risk of corrosion. Corrosion-monitoring systems give advance warning and enable remedial measures to be worked out and adopted. 

A factor which previously limited installation of automatic corrosion monitoring systems was the cost of cabling between sensors and control room instrumentation-this was particularly relevant to the electrical resistance (ER) systems. Developments to overcome this have included transmitter units at the probe location providing the standard 4-20 mA output (allowing use of standard cable) for onward transmission to data systems or the use of radio linkage which has been successfully used for other process-plant instrumentation. 

Computers and programs are also important in corrosion monitoring systems, such as an automated constant rate extension system (A Cert) shown schematically in Figure 5.5. This system may be used for conducting corrosion and cracking evaluation tests. The system is capable of initiation and conducting tests as well as data acquisition and analysis. There is very little human intervention and the system is capable of corrosion evaluation in environments which are difficult to simulate. This system is a... 

The use of an on line corrosion monitoring system in power plants is currently possible due to the marked technological improvements in both probes and measuring instruments. The addition of an Expert System provides the operator with easy to use informations. 

There is also a NACE Standard Recommended Practice RP0187. The 1987 edition has been re-issued in 2006 while undergoing revision at the time of writing. It mentions stray current induced corrosion and corrosion monitoring systems which the other standards do not and has short paragraphs covering the same topics as ACT 222.3R-03. 

Corrosion monitoring systems (Chapter 5) are gaining acceptance and use around the world with the continued reduction cost of electronics and the increase in computing power it is easier to collect and analyse data. There is considerable research on wireless systems in the United States. 

Niblock, T., H.S. Surangalikar, J. Morse, B.C. Laskowski, M.H. Castro-Cedeno, and A. Wilson. 2002. Development of a commercial micro corrosion monitoring system. Proc SPIE Int Soc Opt Eng 4934 179-189. 

Also, NACE Standard Recommended Practice-Design Considerations for Corrosion Control of Reinforcing Steel in Concrete (RP0187) contains recommendations for corrosion monitoring systems for steel in concrete. 

More recently, a full-spectrum, relatively low-cost EIS corrosion monitoring system has been developed, which is wireless, small (5 cm diameter, 1.2 cm height), requires nominally 10-mW power during its 200-second measurement period, and has an electronic identifier. 

In an idealized corrosion control program, inspection and maintenance would be applied only where and when they are actually needed, as reflected by the maintenance on demand (MOD) concept. In principle, the information obtained from corrosion monitoring systems can be of great assistance in reaching this goal. Conceptually, the application of a monitoring system essentially creates a smart structure, which ideally reveals when and where corrective action is required. 

The first requirement can be met with real-time corrosion monitoring systems, provided that the monitoring techniques selected are sufficiently sensitive to respond rapidly to changes in the process conditions. Corrosion monitoring techniques (such as coupons) that yield only retrospective, cumulative corrosion damage data are not suitable for this purpose. 

The first application area arises from the fact that many corrosion-prone areas of aircraft are difficult to access and costly to inspect. Typically, these areas are inspected on fixed schedules, regardless of whether corrosion has taken place or not on a particular aircraft. Unnecessary physical inspections could be eliminated and substantial cost savings could be realized if the severity of corrosion damage in inaccessible areas could be determined by corrosion sensors. Several prototype on-board corrosion monitoring systems have already been... 

On-board corrosion monitoring systems can facilitate the testing and evaluation of aircraft materials and corrosion control methods under actual operating conditions. Sensitive techniques make such evaluations possible in short time frames. 

Strain relaxation Atmospheric monitoring Currently being tested as an on-board corrosion monitoring system on an aircraft... 

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