Tecnoseal Answers - The Cathodic Protection of Port Structures
After the digressions of the last few weeks, in today's Tecnoseal Answers we return to talk about cathodic protection. The last article dedicated to this category was that of the aluminum anodes on hulls of the same material. To do this, we have chosen a topic that we have briefly mentioned on several occasions in the past: the cathodic protection of port facilities.
Before we start, I remind you that at the following link you can find a thematic index of all the Tecnoseal Answers released until today.
Example of immersed metal port structures
Which Cathodic Protection To Use
If you remember the Tecnoseal Answers dedicated to the bases of cathodic protection (otherwise you will find it here), you can easily guess that any type of port structure, completely or in part, metallic that is immersed or otherwise in contact with water, it will be at risk of galvanic corrosion and will therefore need to be protected. Tackles, poles, mobile bridges, cranes, etc... there is no exception to what has just been said.
As for the naval transport sector, also in the port facilities, cathodic protection can be either active or passive. In both cases it is necessary to perform a calculation of the anodic mass required to protect the structure, taking into account the main regulations (ie the DNV-RP-B104). In the first case, impressed-current systems are used, but must be created and developed together with the port structure because they include the introduction of cable ducts and power points inside the same. In the second case sacrificial anodes are used which are modeled according to weight and appropriately distributed, according to what is the distribution of the electric fields and of the contact surfaces. In this case different anchoring systems are used, but the simplest and most common is to use anodes with insert which are welded to the structure. Other solutions are those of using extensions (called clamps) welded to the structure or anodes fixed with bolts.
Which Anode Alloy To Use
The choice between passive or active cathodic protection is very free and depends on few external factors linked to the structure. The same cannot be said, instead, for the choice of anodic alloy. Here there are few doubts and we always prefer to use sacrificial anodes in aluminum alloy. This is due to two reasons. The first is of logistic nature. The anodic masses that are usually installed, although depending on how much surface is to be protected, are always very large and aluminum, notoriously lighter, makes installation management much easier.
The most important reason why aluminum alloy is preferred, however, is the second and is a reason of environmental nature. As is known, in fact, the zinc alloy contains Cadmium and, as far as this isn't normally a problem, having to install large quantities of anodic mass in a restricted marine environment, such as that of a port structure, there would be a very high dispersion and a concentration of residual cadmium in the water which could give problems to the present marine fauna, as well as to the whole marine ecosystem in which the port structure is located.
Another example of port facilities at risk
The Importance of Maintenance
Another very important thing to remember is that, even if the calculation of the anodic mass is done for a very long time (we talk about a minimum of 5 years), it is vital to make periodic inspections to verify the state of cathodic protection of the structure. This, in fact, in the course of the five years foreseen, could be in situations such that the consumption of sacrificial anodes is altered. For example, port basins are often protected. Inside this large boats are built and if welds are used, these could alter the installed anodic mass and no longer make it fit within the calculation parameters.
The above is even more true for structures protected by impressed current systems. In these cases maintenance must be very accurate because there is a risk that, if a power supply is broken without we realize it, we can find ourselves in a situation such that the structure is not protected even if we believed it was. For this, together with the active cathodic protection system, must always be provided a maintenance program carried out by specialized technicians which periodically: go to the site, check the condition of the power supplies, measure the potentials and take certain decisions regarding the adjustments of the system supply voltages and currents.
A photo with many examples of river port facilities
Summarizing the above, therefore, the three important things to do if you want to protect a port structure from galvanic corrosion are:
- The choice of anodic alloy (which as we have seen is obvious).
- The calculation of the anodic mass necessary to guarantee the cathodic protection of the structure.
- A periodic maintenance program to constantly verify that everything is working properly and there are no anomalies or failures.
One last note before concluding today's article. The above applies to any port structure, even the lacustrine or fluvial ones. In fact, although usually in fresh water the technical standards would indicate as an anodic alloy ideal to use the magnesium one, in these specific cases (for the reasons listed above) it is still preferable to use aluminum alloy. In any case, if you have any doubts, the best solution is always to contact someone expert in the sector to ask for advice.
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Tags: welding, Tecnoseal, Weld-on Anode, Aluminum, tecnoseal answers, Alloys, cathodic protection, anodic mass, Cadmium, Bolt-On Anode, sacrificial anodes, ICCP system, active cathodic protection, Impressed-current cathodic protection systems, port facilities, port structures