about the protection from the corrosion of steel
1. Introduction: damage due to the pipes corrosion.
It is common knowledge that, all the steel underground conduits conveying gas, water, mineral oil, and so on as well as the big tanks and their connected big metal masses, are cheap and environmental.
2. The active cathodic protection.
Their corrosion is generally due to electric currents coming from the ground, called "stray currents".
The phenomena of corrosion of methane pipe-line, aqueducts, oil pipe-line systems, etc., caused by stray currents are particularly important and happen very quickly nearby electric railways, tram-ways, undergrounds, industrial settlements, stations supplying electricity, etc.
The simple shrewdnesses of covering the pipes with insulating sheets, plastic sheathings, bituminizes, etc. or rather of setting them with particularly careful modalities, don't guarantee at all the indemnity of the pipes from the attack of the electric corrosion.
The tecnique of the active protection on this system of pipes by means of dispersors has been applied profitably for ages. Till some years ago they were of the "horizantal" type, that's to say placed on the surface at a distance of about 100 metres from the pipe to protect. such a technique is today surpassed by the fulfiment of dispersors of the "vertical" type, because this technique shows the following advantages:
3. Economic estimations.
- possibility to carry out the dispersors also nearby the pipes that must be protected (3 + 5m), with a smaller occupation of the ground, and without interfering on grounds belonging to a third party;
- better reliability with the passing of time, for a term at an average of 12-15 years of steady protection;
- better dispersion and yield, because the grounds where the anode is placed don't feel the effects of the variations of dampness and resistance, because of their depth (from 100 to 40 metres under the countryside ground).
This technique of "cathodic protection" is practised now all over the world by the greatest Conveyance Companies of gas, mineral oil and water. In Italy the greatest users of such a technique are: SNAM, AGIP, ITALGAS, METANO CITTA', DALMINE, etc. and TELECOM ITALIA (telephones); Municipalized Companies too.
There are some of the references of the company group FOREX-SONDITALIA, that are specialized in the application of system of cathodic protection "keys in your and" since 1970.
The American Argent and Shilton have esteemed that the expenses met to prevent the corrosion of new pipes are between 5% and 12% of the total cost of the construction.
It's important to realize that, if at first sight the cost of the cathodic protection sounds high, the damage suffered by the unprotected pipes are higher, because of:
- the lost product and its non-sale;
- the environmental damages and the tort and criminal liabilities;
- the repairs of the conduits and the superficial area that must be restored.
Finally, it's useless to remember that a conduit that has been well-protected by means of the cathodic process will keep its commercial value with the passing of time.