Leakage currents corrosion

In the USA, interest has been particularly concentrated on leakage currents from inter-urban and street railway tracks, and the 1921 Report of the American Committee on Electrolysis summarises the problem and the methods of controlling electrolytic corrosion applied both in America and in memy European countries. 

In nearly all known cases of stray-current corrosion the damage is caused by direct currents, but leakages of alternating currents at industrial frequencies have been suspected of causing corrosion of buried metallic structures. The mechanism of corrosion caused by a.c. is not clearly understood and fresh studies are being made. However, the corrosion caused is much less severe than with stray d.c. and experiments indicate that stray a.c. at 50Hz will produce less than 1 % of the corrosion caused on most buried metals by an equivalent d.c. 

All samples primed with type B primer showed visible corrosion at a very early date. Within one week of water submersion, all of these samples showed some signs of deterioration. In each case, the side of the pattern maintained at positive potential was the first to discolor and then corrode. In contrast none of the samples primed with type 4 material showed visible deterioration at day 60. With the exception of the type B samples, all of the other samples failed to show any noticable deterioration until one month into the test. At this time, most of the types A, B, and C primed samples showed discoloration and debonding. Correspondingly their leakage currents, at day 30, were an average of 35 times greater than those samples primed and encapsulated with the self-priming elastomer types 4, 5, and 6. 

Electrical leakage currents, cathodic corrosion protection In electrically conductive equipment stray or leakage currents can flow as reverse currents to electric generators (in particular in the area of electric trains and major welding equipment), if, for example, conductors like rails, pipes and cable liners laid on or in the earth reduce the resistance of the reverse path, due to earth contact in faulty electrical equipment, due to induction (e.g. in the vicinity of electrical equipment with high currents or high frequencies), due to lightning. Potential equalization, respectively additional electrical override required... 

Reduction of the resin content and quantity of activators simultaneously diminishes the risk of leakage current, electro-migration and corrosion. 

The major failure modes of adhesives include loss of adhesion, high thermal impedance, loss of electrical contact, and corrosion. To a lesser extent, failures may occur because of metal migration causing high leakage currents and even electrical shorting. Sloughing of particles from the... 

Leakage currents can be short circuited [64] or biased by placing an opposite current via electrodes placed in the piping [40] or reacted at sacrificial electrodes located in the manifolds [65]. These concepts have been used in the manifolds of MBC electrolyzers of Chlorine Engineers and also in the design of the CME and BiTac cells. Corrosion of catalytic cathodes used in bipolar water electrolyzers during shutdowns is prevented by cathodic protection [9]. 

Active metal targets in electrolyte headers can intercept leakage currents and prevent corrosion of piping and equipment. Leakage can also be prevented at its source by installing current breakers that actually disrupt the continuous stream of liquid (Fig. 8.10). 

Purified brine often is heated and acidified before entering the cells, the pH usually being 1-3 at temperatures up to 75-80°C. Materials must be chosen to prevent corrosion under these conditions and must not contribute harmful impurities to the brine. To avoid damage by leakage currents, steel-based pipelines are cathodically protected by properly grounded target anodes. 

Moisture and humidity cause corrosion, reduce the dielectric strength, and lower insulation resistance. Pressure variation, shock, and vibration can cause mechanical damages (seal cracks, etc.) that result in electrical failures. It is interesting to note that for electrolytic capacitors three parameters, namely, capacitance, leakage current, and the equivalent series resistor Resr are considered as the basic ones, and the failure of the capacitor after a test is established comparing the values of these parameters with the specified ones. 

Electrical and electronic systems are extremely susceptible to corrosion by the aggressive automobile environment [29-3i], Pitting, crevice and galvanic corrosion, and corrosion product creep are all important mechanisms, and in many cases these mechanisms are accelerated by leakage currents, which impose a potential bias on the materials. Fretting and coatings failure are also failure mechanisms. 

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