Corrosion Protection - Durable and Environmentally Friendly
Steel structures designed for long service life require reliable corrosion protection. The old reinforced coating system, in which several layers of paint (organic substances based on polymers, etc.) are applied to the steel, loses its protective effect over the years. The layers of paint peel off and enter the environment unnoticed, polluting flora and fauna. After 15 to 20 years, corrosion protection is often no longer given and must be renewed. There are different approaches that need to be weighed up. Bridge parts are elaborately dismantled, brought with a lot of planning and logistical effort to a corrosion protector to be recoated there. Alternatively, a mobile solution at the bridge can be considered on site. In some cases, it is already too late or simply expensive to carry out maintenance. A new bridge is manufactured, the old one dismantled and disposed of at great expense.
The impetus for our current pilot project was provided by the Hamburg Port Authority - port manager, public institution and modern service provider, who says about himself that he wants to help advance the Port of Hamburg economically with innovative concepts and environmentally friendly technologies. Mr. Marbes, project manager at Hamburg Port Authority, is committed to breaking new ground in the maintenance of port bridges. The bridges should be made more durable, and as environmentally friendly as possible. Can't do it? We have proof that it can be done!
Thermal spray galvanizing is not a novelty. For many years, this process has been successfully used as corrosion protection, especially in the offshore sector. Wind farms are exposed to extreme weather conditions, which is why zinc alloy was used here early on for corrosion protection and is now indispensable. The process has not changed significantly to date: zinc wire is melted by an electric arc in a spray gun, and the molten particles are applied to the surface with pressure. The process is independent of the component size and can therefore be carried out both in the factory and on the construction site. There is no heat load on the component.
In our pilot project at the Grevenhofschleusenbrücke in Hamburg, we carried out a new coating with thermally sprayed zinc mobile for the first time. Environmental protection was already in the foreground during construction site equipment and decoating. The entire bridge was rebuilt with a suspended scaffolding, the building material of which is 100% reusable. In small construction phases, the contaminated old coating was then removed in a recycling process in accordance with the applicable technical rules for hazardous substances. The steel gravel used here is collected, cleaned and reused so often after a work step with suction systems until the grain size is too smooth and only then disposed of. This saves material, reduces the disposal volume and thus conserves resources.
In protective clothing and with a mobile spraying system, the zinc alloy is applied to the steel after blasting. The arc spraying system for corrosion protection from OSU-Hessler and the wire material used for this project from Grillo are the basis for the optimal corrosion protection layer, which were provided especially for this application.
An advantage of thermal spray galvanizing is that there are no drying times. The zinc is directly firmly bonded to the substrate. Thickness measurement is possible during the coating process with standard measuring devices. If a too low layer thickness is detected, it can be reworked directly. The handling of the corrosion protection system is suitable for the construction site. The wire to be processed on spools is located on an intermediate carriage and is placed near the execution site. A second skilled worker guides this trolley and changes the coils if necessary.
In terms of sustainability, the coating process takes place in a closed recycling process. After spray-galvanizing, the excess zinc dust is collected and cleanly recycled it can be used for the production of new zinc wire.
For the Grevenhofschleusenbrücke project, the Hamburg Port Authority chose a 200 μm thick layer of zinc alloy for lifelong corrosion protection. A duplex system, i.e. the further color coating of the spray layer, which in this case would only involve an optical change, was deliberately omitted for environmental reasons, according to the motto "environment before optics".
The topic of sustainability has arrived in all industries today, which is why each individual must think about how he can contribute to a more environmentally friendly action in his daily working. We as Muehlhan Deutschland GmbH have gone this way together with Hamburg Port Authority, the Metall Unternehmertisch e.V. (MUT) and Grillo-Werke AG, have dealt intensively with the process and together found a solution to make corrosion protection sustainable and mobile implementation.
To demonstrate this process, the Metall Unternehmertisch e.V. invited representatives of authorities and specialist planners from all federal states to two dates each on 09.08. and 18.10.2022. As part of an inspection of the construction site, a visit to the spray-galvanized bridge and an open round of questions, special concerns were discussed. The hope is that more authorities will switch to this procedure for new construction and maintenance and thus make their contribution to the environment and the future.