A smart maintenance plan starts with a good design: corrosion
Corrosion is an undesirable chemical or electrochemical deterioration of a material. What is beautiful turns ugly, structures become unusable, leakage occurs, etc. with corresponding associated costs. In construction, we mainly talk about corrosion of steel. Rust is what we observe visually in case of corrosion of steel: a brown colour and in advanced cases, a peeling crust. Copper for example will turn green in the case of corrosion, silver will turn black.
Corrosion is a complicated process. The principle can be traced to the law of conservation of energy: the metal wants to return to its natural state in which it needs the least energy. Corrosion is therefore a purely natural process. In the case of steel, the minimum energetic state can be found in iron ores: bonds between iron and oxygen, hence the brown colour of rust. That is why the term oxidation is sometimes used.
There are many types of corrosion, each with a specific underlying mechanism, but essentially three elements are required: oxygen, moisture or water and the metal itself. And all three elements are almost always present. Moreover, there are still a lot of parameters that play an additional role and that make it very difficult to predict which form of corrosion will occur and how quickly this will happen: temperature, contamination, stresses.
Protecting a structure against corrosion is therefore not that obvious, certainly not in the maritime environments where locks and weirs are located. There are so many parameters affecting each other and the corrosion process, that a good combination of underlying mechanisms, theoretical insights and practical experience is required.
Many methods have been developed to protect metal objects and structures. They are not all equally relevant for use in civil structures due to the size of the structures and the often highly corrosive environments they are located in. The most common applications in hydraulic engineering are therefore paints, metallic coatings, cathodic protection and the use of stainless steel.
These methods each have their advantages and disadvantages and ideally, they are combined. Because although it may sound easy to use stainless steel, this would lead to a very expensive design that is not necessarily better. In addition to a few technical disadvantages, stainless steel is also very expensive. These disadvantages can be remedied with the right choice of stainless steel, but this only adds to the cost. Paint systems are cheap but can get damaged quickly and require regular maintenance. Metallic coatings on the other hand are difficult to apply on a large scale without going over the budget. Finally, cathodic protection is only possible in specific cases and is very specialised work.
SBE is experienced with this problem due our speciality in the maritime infrastructure sector. As a result, we know that corrosion prevention is not only a task of adequate maintenance such as regular painting. Optimal prevention starts with the design:
- material selection,
- geometry of the structure and smart detailing,
- proper definition of the environment regarding corrosion-loading parameters,
- selection of an appropriate preservation system and
- prescribing the correct method of execution of both the steel structure itself and the application of the preservation system
All these steps are essential and just as critical to achieve good corrosion prevention.
Maintenance works on the Pierre Vandamme Lock
The prevention of corrosion is crucial in minimising maintenance costs during the life cycle of the lock. This is proved by the recent maintenance works on the Pierre Vandamme Lock in the Port of Zeebruges.
The lock was built in 1984 and acts as the crucial access to the inner port of Zeebrugge. There are two lock heads and 4 rolling gates, which were in need of a thorough renovation. Flanders decided to invest about 120 million euros in a phased renovation, which must be completed by the summer of 2023. SBE is offering technical advice during the maintenance works of both the lock gate and the gate chamber.
For the last couple of months, the seaside gate chamber of the lock has been put in dry conditions. During a spectacular lifting operation, the fourth lock gate was removed out of the chamber and renovated onshore. A single lock gate weighs more than 2,300 tons and measures 66m x 11m x 25m. The images below show details of corrosion which have been restored.
For more information about the Pierre Vandamme lock, click here.