7 ALL TYPES OF BACKGROUND RADIATION HAVE INCREASED SO DRASTICALLY AND SO QUICKLY IN THE LAST FIFTY YEARS THAT WE CAN NO LONGER HOPE TO COPE WITH THEM.
8 STRAY CURRENT CORROSION ELECTROMAGNETIC FIELDS NATURAL PROCESSESELECTRIC AND MAGNETIC COMPONENTSTHERMAL SIDE EFFECT
9 THE CORROSION OF THE UNDERGROUND STEEL PIPELINES TECHNOLOGICAL AND INDUSTRIAL DEVELOPMENTPRODUCTION AND CONSUMPTION OF ELECTRICITYELECTROMAGNETIC POLLUTIONTHE CORROSION OF THE UNDERGROUND STEEL PIPELINES
11 The first mobile laboratory specialized in investigating and determining the dispersion in DC currents(Los Angeles, 1910)
12 Stray currents may originate from cathodic protection systemelectrical welding machinesgrounded dc electric sourcesstreet railway systems, etc
13 Stray current corrosion DC traction systemStray current corrosionIn this case rails act as primary current return path and the surrounding ground acts as a conductor that can carry stray currents. There is a fundamental tendency for the return current in the rails to flow from the train to the substation. Because the tack is not perfectly insulated from the ground, there is a tendency for the current to flow in the ground in the same direction. Here the stray current will be picked up by the pipeline near the train and discharge near the substation.
14 The corrosion resulting from stray currents (external sources) is similar to that from galvanic cells (which generate their own current) due to the fact that the corroding metal is again considered to be the anode from which current leaves to flow to the cathode.Soil and water characteristics affect the corrosion rate in the same manner as with galvanic-type corrosion.Despite the apparent similarity, stray current strengths may be much higher than those produced by galvanic cells and thus corrosion may be much more rapid. Moreover, seeking the path of least resistance, the stray current from a foreign installation may travel long distances along a pipeline causing severe corrosion where it leaves the line.
15 Accentuated degradation of the fastened elements in the Budapest’s subway The corrosion of the gas pipes due to the stray DC currents which originate in Bucharest’s tram and subwayDamages of the pipeline in Cluj-Napoca
16 Stray current corrosion prevention Eliminate or reduce stray currentActing on the source instead on the consequencesIncreasing the global circuit resistance
17 an external current that reduces or inverses the anodic current. CATHODIC PROTECTIONsacrificial anodesimpressed current/voltage anodesCURRENT DRAINAGERSvarying the boosting DC voltagechanging the resistance of the direct connectionbringing the galvanic potential of the metal to a level where the anodic reactions are impossible for the given circumstancesan external current that reduces or inverses the anodic current.possible when the sources of the stray currents are accessiblethe connection is made unidirectional, such that current can only flow from the buried structure to the negative pole of the DC source, thus rounding the electrolyte (the soil)