Detection of Corrosion

One of the most important aspects of an inhibitor test is the actual measurement of changes that reflect the degree of corrosion. In all cases, the metal of interest comprises the specimen, but the actual changes measured may not necessarily involve the metal directly  

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Detection of corrosion and defects under a layer of protective coatings, rust and foulings to 8-10 mm in thickness. 

This technique is based upon the detection of corrosion products, in the form of dissolved metal ions, in the process stream. A thin layer of radioactive material is created on the process side of an item of plant. As corrosion occurs, radioactive isotopes of the elements in the construction material of the plant pass into the process stream and are detected. The rate of metal loss is quantified and local rates of corrosion are inferred. This monitoring technique is not yet in widespread use but it has been proven in several industries. 

Electrochemical sensors with a liquid electrolyte are widely used for the detection of corrosive or toxic gases in the workplace. Portable monitors are used in short time measurements of exhaust gases as well. These sensors work amperometri-cally - an external voltage supply is connected with the electrode on both sides of the measuring cell. 

The choice of the technique used in monitoring or detection of corrosion depends upon many factors such as the size of the sample, the particular features of the defect, accessibility, sensitivity of the technique, the limitations of the techniques, knowledge and skills of the operator and the availability of the instrument. The following is a general guide for the application and suitability of the technique in the detection of discontinuity.52... 

Fig. 9.61 Schematic drawing of approach to detection of corrosion fatigue cracks [226].

E. Tada, Detection of corrosion fatigue cracking through current responses induced by cyclic stressing, Corros. Sci. 49 (2007) 248—254. 

Other methods include use of intelligent pigging as well as corrosion prediction models developed by C. De Waard and some other modifications that have been published and commercialized by several other investigators. However, after prediction and/or detection of corrosion incidents inside the pipelines, the most cost-effective method of control is the use of corrosion inhibitors. These are usually amine based and are thus water dispersible. They are usually blended with vapour phase inhibitors and probably some flow enhancers. 

Conductivity measurements are also used in monitoring neutralization and precipitation reactions where the conductivity has its minimum at the equivalence point. Processes where soluble electrolytes are washed from insoluble materials are conveniently monitored by measuring the conductivity of the washing solution. Detection of corrosion and leaks in process heat exchangers are widely monitored by measuring the conductivity of... 

E. J. Madras et al., Application of terahertz radiation to the detection of corrosion under the... 

FIGURE 21. F scans of amplitude ratio BLEl/FWE for detection of corrosion attack and debonding. 

In addition to the major techniques used for evaluation of corrosion of the reinforcing steel described above, non-destructive techniques such as computed tomography, impact echo and magnetic field disturbance, electrochemical noise and other techniques have also been used for inspection and detection of corrosion of reinforcing steels. Reference on these techniques along with the references on major techniques are cited at the end of this chapter. 

Bertocci, U., A Comparison of Electrochemical Noise and Impedance Spectroscopy for the Detection of Corrosion in Reinforced Concrete, in Kearns, J. R., ully, J. R., Roberge, P. R., et al. (eds.). Electrochemical Noise Measurement for Corrosion Applications, ASTM 1277, Montreal, American Society for Testing and Materials, 1996, pp. 39-58. 

The phase relationship of water in oil wiU invert between 25-40% water. After inversion, equipment will be water-wet and corrosion may occur. The following is suggested as one procedure for early detection of corrosion ... 

A period prior to the detection of corrosion while the metal is in contact with a corrodent. 

D. Xia, S. Song, W. Gong, Y. Jiang, Z. Gao 2012. Detection of corrosion-induced metal release from tinplate cans using a novel electrochemical sensor and inductively coupled plasma mass spectrometer. Journal of Food Engineering 113,11-18. 

A technical application of potential measurements is the detection of corrosion damages of underground metal constructions like gas or water pipes. Two electrodes are put to the wet ground, one of them changes place to detect sites of intense dissolution currents and the related ohmic drops. These sites are the locations of corrosion damage. 

Leak detection and monitoring Detection of corrosion of storage structures and tools... 

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