A survey showed that corrosion on the outside of the reducer led to gas formation. The bubblejets are caused by escaping gas, possibly through a small hole to the inside of the reducer, owing to the combination of decreasing wall thickness and mechanical deformation of the reducers.

There are two possibilities for repairing the functionality of the reducers:

1. Repairing the reducers by inserting new aluminium parts locally at the location of the corroded sections

2. Replacing the existing reducers by removing them and inserting new reducers

The reducers will be repaired from the outside (the concrete route) by removing the concrete. The decision on whether to only carry out local repairs of the damaged sections of the reducers or to completely replace the reducers depends on the condition of the reducers, which will be determined during the inspection, after the surrounding concrete has been removed.