Corrosion testing instruments

Most of the corrosion problems in power transmission can be reliably detected and assessed using conventional and well-established corrosion testing instruments, practices, and methods. The data, from field or laboratory, are essential information for the implementation of ameliorative measures. The corrosion control technology available today can, in a cost-effective way, protect reliability, performance, and safety of transmission hnes. 

The war itself also drove the development of improved and miniaturised electronic components for creating oscillators and amplifiers and, ultimately, semiconductors, which made practical the electronic systems needed in portable eddy current test instruments. The refinement of those systems continues to the present day and advances continue to be triggered by performance improvements of components and systems. In the same way that today s pocket calculator outperforms the large, hot room full of intercormected thermionic valves that I first saw in the 50 s, so it is with eddy current instrumentation. Today s handheld eddy current inspection instrument is a powerful tool which has the capability needed in a crack detector, corrosion detector, metal sorter, conductivity meter, coating thickness meter and so on. 

Apart from the instruments described in previous paragraphs, there are others that, while not directly connected with cathodic protection as such, are extremely useful tools to a corrosion engineer. They include pH meters. Redox probes, protective-coating test instruments and buried-metal-location instruments. 

Miller, M. C., Portable Testing Instruments for Corrosion Mitigation Testing , Proceedings Appalachian Underground Short Course, W. Virginia University, USA (1959)... 

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. 

Other Start-up Shut down Relief system Power/service failure Corrosion/erosion Materials of construction T oxicity/asphyxia Maintenance (provision of isolation, etc.) Double valves (trapped liquids) Valve access Provision for testing instruments, trips, alarms Fire Static electricity Noise Thermal radiation Ionising radiation Sampling Spares Anything else ... 

Electrochemical methods have been used in corrosion testing ever since the electrochemical nature of corrosion processes was discovered. In the present age electrochemical measurements involve the use of sophisticated black boxes which are invariably blamed for any pitfalls which occur. Hence the European Federation of Corrosion Working Party on Physicochemical Methods of Corrosion Testing felt it desirable to remind research workers, students and instrument designers of the more fundamental aspects of the measurements. 

Another important electroehemical corrosion test method is the measurement of current between an area with dominating cathodie reaction and an area with dominating anodic current. This is done by separating the two areas, using two specimens, and then connecting these specimens to each other via a currentmeasuring instrument. To avoid a potential drop in the instrument, a zero-resistance... 

Engineering the test assures that materials, equipment, instrumentation, personnel, and supporting services are available and used in a timely and effective manner. The test plan must be examined with a clear understanding of problems that may arise to thwart its successful completion. Critical supplies, equipment, and schedule steps must be identified options developed tasks simplified resources allocated and adequate time allotted. The cost and effort of this step is usually recouped in a more efficient, trouble-free corrosion test. 

Dean, S. W., Jr., "Planning Instrumentation and Evaluation of Atmospheric Corrosion Tests and A Review of ASTM Testing, Atmospheric Corrosion, W. H. Ailor, Ed., John Wiley and Sons, NY, 1982, pp. 195-216. 

FIG. 1—Typical atmospheric corrosion test yard at Middletown, Ohio, showing exposure racks and instrumentation. Reprinted with permission of Armco, Inc. [s/c]... 

There are several other aspects of atmospheric characterization which, if measured, can provide pertinent information related to the performance of materials. Probably the most important and universal is the determination of the TOW, described earlier. ASTM G 84, Practice for Measurement of Time-of-Wetness on Surfaces Exposed to Wetting Conditions as in Atmospheric Corrosion Testing, describes instrumentation and techniques for measuring TOW. This parameter can most easily (and adequately) be estimated from weather bureau records. It is generally accepted that metal atmospheric test specimens are wet when the temperature is above freezing and the relative humidity is above 80 %. There are indications that corrosion can occur under arctic conditions down to 0°F if... 

Standard Test Method for Total Immersion Corrosion Test for Aircraft Maintenance Chemicals Standard Test Method for Pitting or Crevice Corrosion of Metallic Surgical Implant Materials Standard Test Method for Corrosion of Surgical Instruments Standard Test Method for Sandwich Corrosion Test... 

Electromagnetic NDT instruments allow to increase the test records reliability. They are most efficient for detection of the rope durability loss as a result of loss of metallic cross-sectional area (LMA) localized faults (LF) like broken wires, localized corrosion etc. 

Reference Book On Instruments for Electrolysis Corrosion and Cathodic Protection Testing, American Gas Association, New York (1951)... 

Rowlands and Bentley have provided an account of the possibilities for continuously monitoring corrosion rates by polarisation resistance measurements, and they also describe the development of a commercial instrument, which uses low-frequency square-wave current to polarise the test specimens. 

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