Cathodic Protection Current
Calculate the current needed for cathodic protection, I = current density × area ÷ 1000, multiplying the required protection current density (mA/m²) by the metal surface area to protect (m²). The result, in amperes, sizes cathodic protection systems — impressed current or sacrificial anodes — that protect pipelines, buried tanks, ship hulls and offshore structures by polarizing the metal to a corrosion-immune potential. The required density depends on the medium and the coating. Enter the protection current density and the area to protect.
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Cathodic protection current
Cathodic protection is one of the main defences against corrosion of buried or submerged metal structures — pipelines, storage tanks, ship hulls, offshore platforms, foundation piles. The idea is to force the metal to behave as the cathode of an electrochemical cell, polarising it to a potential at which the corrosion reaction (dissolution of the metal) comes to a halt. Doing that requires injecting current into the surface, and the amount needed is I = current density × area ÷ 1000, multiplying the required protection current density (in mA/m²) by the total area of metal to be protected (in m²), with the result expressed in amperes. The required density depends heavily on the environment (soil, fresh water, seawater) and, above all, on the quality of the coating: a well-painted structure draws very little current, since the paint is already the first barrier and cathodic protection only has to cover its defects, whereas bare metal demands a great deal more. Once the total current is known, the technology is chosen: impressed current (a rectifier feeds inert anodes) for large demands, or sacrificial anodes (zinc, aluminium or magnesium, which corrode in place of the structure) for smaller ones. Enter the protection current density and the area to protect.
Related Tools
Sacrificial Anode Life
Calculate the life of a sacrificial anode, life = (mass × capacity) ÷ (current × 8760), from the anode mass (kg), the material's current capacity (A·h/kg), the protection current drained (A) and the 8760 hours in a year. The result, in years, shows how long the anode (zinc, aluminium or magnesium) will provide protection before being consumed and needing replacement — essential in designing galvanic cathodic protection of tanks, pipelines and marine structures. Enter the mass, the material capacity and the current.
Tafel Overpotential
Calculate the activation overpotential by the Tafel equation, η = a + b × log₁₀(i), from the Tafel constant a (V), the Tafel slope b (V/decade) and the current density i. The result, in volts, is the overpotential — how far an electrode's potential departs from equilibrium — needed to sustain a given current density in an activation-controlled electrochemical reaction. The Tafel relation is central to electrode kinetics, corrosion (extrapolation to obtain the corrosion current) and electrolysis. Enter the Tafel constant, slope and current density.
DC Motor Stall Current
Calculate the stall current of a DC motor, I = V ÷ R, from the applied voltage V and the armature resistance R. The result, in amperes, is the maximum current the motor draws when the shaft is locked (zero speed, no back-EMF) — far higher than normal operating current. It is the most dangerous current: it can burn the motor and driver if sustained, so systems include stall protection. It also corresponds to the maximum (stall) torque point on the torque-speed curve. It is essential for sizing fuses, drivers and power supplies. Enter the voltage and the armature resistance.
Injection Capacity (PS Equivalent)
Convert a machine's nominal injection capacity (always specified in polystyrene, PS, density ~1.05) to the equivalent capacity in another material by multiplying by the density ratio. Since the barrel has a fixed volume, the mass it injects changes with the plastic's density — denser materials yield more grams per shot. Essential to size the machine for the real material. Enter the nominal PS capacity and the material density.
Approach Surface Height
Calculate the height of an approach surface (or other obstacle limitation surface) at a given distance, h = (gradient ÷ 100) · distance, from the ramp gradient (%) and the horizontal distance from the surface origin (m). Obstacle Limitation Surfaces (OLS) are imaginary inclined planes projected from runway thresholds and around runways, defined by ICAO, delimiting the airspace that must stay clear of obstacles for safe landing and takeoff. The approach surface, for example, rises at a typical 2% (1:50) gradient from the runway strip end; any object (building, antenna, tree, terrain) penetrating it is an obstacle to be removed, lowered, marked/lit or, ultimately, leading to operational restrictions. This calculation gives the maximum allowed surface height at each point, to compare with the actual height of existing or proposed obstacles around the airport — the basis of land-use control in airport protection zones and the assessment of new developments. Enter the gradient and the distance.
Larson-Skold Index (Water Corrosivity)
Computes the Larson-Skold index, the ratio between the aggressive and the protective anions in a water: chloride plus sulphate divided by alkalinity, all converted to milliequivalents per litre with the equivalent weights 35.45 for chloride, 48.03 for sulphate and 50.04 for alkalinity expressed as CaCO₃. The reading is direct: below 0.8 alkalinity dominates and the carbonate film protects carbon steel; between 0.8 and 1.2 corrosion stops being negligible; above 1.2 chloride and sulphate break the film and the localised corrosion rate takes off, the typical scenario of cooling tower makeup water running at many cycles of concentration. Unlike the Langelier index, this one does not say whether the water will scale — it measures only the corrosive power of the anions, which is why the two readings complement each other rather than compete. Total alkalinity was adopted as the input, instead of separate bicarbonate and carbonate, because that is what a routine laboratory reports, and converting it through the CaCO₃ equivalent returns exactly the sum of the two in milliequivalents per litre. Enter the chloride, the sulphate and the total alkalinity.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.