Monitoring corrosion

A test water box was installed during a 2-week trial to monitor corrosion and fouling in a utility cooling water system. A baffle plate from the test box was removed after the test. Small, hollow incipient tubercles dotted surfaces (Fig. 3.28). Small amounts of carbonate were present atop and around each tubercle. Each tubercle capped a small depression no deeper than 0.005 in. (0.013 cm) (Fig. 3.29). This indicated local average corrosion rates were as high as 130 mihy (3.3 mm/y). 

Implement scheduled nondestructive testing at key points to monitor corrosion as part of a mechanical integrity program... 

The severity of weather in arctic regions, especially in winter months, presents difficulties. They can be in monitoring corrosion, inspection of equipment. 

Install and monitor corrosion and hydrogen probes in key areas,... 

Fig. 9.11 Sentinel hole method of monitoring corrosion of a pipe wall...

Where a solid corrosion product is formed, meaningful results are only obtained after a conditioning period for a new measured element. Even so, the conditions under which the scale is laid down may not be the same as that for the original equipment. This objection applies equally to coupons or spools, and points to one of the basic objections of using anything other than the plant itself to monitor corrosion rates. 

The advantages of this type of monitor are that it can be automated to produce print-outs of corrosion rate at regular intervals and that it can be used to monitor corrosion in any type of corrodent, e.g. gaseous, non-ionic liquid or ionic electrolyte. Such monitors are in wide use, especially in refinery applications. 

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. 

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)... 

Methods. To observe that corrosion testing in the laboratory frequently fails to predict what happens in real-world environments is to admit that the mechanisms controlling corrosion in such environments are not understood, even at this late date of study. Mechanism-based test methods for monitoring corrosion are needed that will provide reliable and rapid prediction of service life for corrosion-susceptible systems. It is expected that statistical analysis will play a... 

Fig. 10.2 Various monitoring devices (1 to r) corrosion/fouling/ biofouling mesh coupons, LPRM monitor, corrosion rack, deposit monitor, membrane filter on poured plate, and dip-slide... 

One of several different types of equipment used for monitoring corrosion in a cooling system, often on-line and real time. Best known example is the Corrator , which uses a probe and instrument to provide a direct... 

Some applications of ultrasonics are inspection for flaws in forgings, flat-rolled products such as strips, sheets and plates, castings, extrusion billets, rolling blooms or slabs, bar stock, pipes, welded joints, bonded joints, monitoring cracks, measurement of thickness, measurement of fluid levels, microstructural features and monitoring corrosion. 

Corrosion may be monitored by measuring changes in thickness with time using ultrasonic thickness gages. An automated ultrasonic inspection system has been devised and used in monitoring corrosion in nuclear waste containers and typical variations in ultrasonic indications in corroded and uncorroded areas have been recorded successfully. Major types of equipment inspection by ultrasonic technique has been done in mill components, power equipment, jet engine parts, aircraft components, railway materials, automotive components and other machinery components. 

Periodic inspection of equipment or plant for detection and monitoring corrosion should be followed by a written report, detailing all the observations and the necessary actions to be taken in future maintenance so that unexpected premature failures can be avoided. It is also necessary that all personnel involved are aware of the observations in the periodic inspection report on corrosion detection and monitoring in order to avoid future premature failures. 

Operation Inspection, testing Nondestructive testing, condition monitoring, corrosion monitoring, malfunction detection, plant degradation audits Plant safety audits... 

Electrochemical evidence. Conventional techniques such as variation of corrosion potential and corrosion rates at different periods. Noise electrochemical techniques should be very fruitful for monitoring corrosion evolution. (Little)5... 

The most common method of identifying and monitoring corrosion is visual inspection. Evidence of leakage, staining, or a change in surface appearance can be an indication that some type of corrosion is taking place. Experience with certain types of equipment and processes may help dictate inspection intervals and areas on which to focus the inspection. Records of vessel operation, maintenance, and repair can be helpful in establishing a pattern of performance that will improve predictability and minimize down time. 

In areas where general corrosion is the expected form, a simple ultrasonic thickness gage can be utilized to determine the extent of corrosion, based on baseline readings made at installation or previous inspections. The entire unit need not be examined. Attention can be focused on those areas most likely to corrode, such as liquid levels, mixing zones, or areas of high turbulence. Corrosion probes, which can be placed in process equipment or pipelines, can monitor corrosion conditions by measuring an actual corrosion current, or other process parameters known to be related to general corrosion rates. These data can be constantly monitored and recorded to predict equipment wear, or as an alert to upset conditions. 

An effective method to monitor corrosion in buried structures is to measure the pipe/soil potential along its span. With horizontal pipelines this is technically feasible however the access to data on the local CP performance in well casings is very limited and can only be obtained using expensive logging tools. 

Corrosion studies. It is equally essential to monitor corrosion rates at this stage, although ideally, these analyses should have been initiated during the previous phase of laboratory studies. 

ENEA (Comitato Nazionale per la Ricerca e per lo Sviluppo dell Energia Nucleare e delle Energie Alternative) in cooperation with CISE (Centro Informazione Studi e Esperienze) developed an advanced automatic corrosimeter for monitoring corrosion in power plants, consisting of two modules the first one acquires data from the probes, and the second one (an IBM personal computer) controls the first module and performs all the required calculations. Several probes can be connected to a single corrosimeter [12]. 

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