Renovation of the coating of a metal structure

Study of the composition of paint layers on a metal structure

During a renovation or painting work, it is important to have a good knowledge of the composition of the existing paint system on which the work will be carried out.
In this expertise, the client wishes to carry out a renovation on a metal structure with several layers of paint.
The demand is therefore to know what is the different chemical structure (s) intervening on the surface of its complex in order to have the best possible renovation and to guarantee the best compatibility with the renovation.

The old paint on this metal structure was peeling off, revealing several layers.
The client therefore took a representative sample of all the layers in order to allow analysis and identification on the layers of interest.

Concerning the structural identification, a structural analysis by Pyrolysis / GCMS was carried out on the surface layers in order to identify the polymeric matrix (s) and organic adjuvant (s) present (s). ), which allows us to have an estimate of the ratios of the constituents .

In addition, the customer suspecting the presence of lead within the initial layer (in contact with the metal support), we also carried out an analysis by SEM/EDX in order to have a photo and an elementary analysis on sample to have a complete atomic inventory focusing on the presence of lead to affirm or not the hypothesis of its presence in the first coating layer.

Conclusion

Structural analysis revealed that the paint surface layer matrix was an alkyd resin , with some traces of vinyl polyester most likely coming from the bottom layer.

SEM/EDX analysis demonstrated a significant presence of lead on the first layer, representing approximately 45%w total elements
This lead suspicion hypothesis was also confirmed by the cartography , visible thanks to the white coloring on the photo.
Concerning the other layers, only the one in contact with the first layer contains lead in small quantity, probably due to a migration of this element on the layer in contact with the first.
Thanks to these analyses, the customer is able to proceed with the renovation of the structure by taking into account the structural information of the last coat of paint as well as the previous coats.