Study with the objective to characterize the emissions generated by welding coated metal sheets in ship construction

Status:

completed 12/2000

Aims:

In shipbuilding, coated metal sheets are increasingly used which are welded and cut for confectioning. Mostly, those components are coated for the purpose of corrosion protection. The coatings consist of binding agents, fillers and pigments. When welding and cutting coated components, the thermal stress generates gaseous pollutants and polluting particles the chemical composition of which depends on the material type and coating type. Due to reasons of quality and occupational health, it is recommended that, prior to welding, the coating be removed in the welding area. However, in most cases, coating residues remain which then, during welding, will thermally decompose (pyrolysis). Particularly coatings containing organic binding agents will generate a variety of substances as decomposition products which possess varying hazard potentials.

It was the objective of the campaign to assess the pollutants and thence the hazard potential. In particular the pollutants stemming from the coating (residues) were to be assessed here.

Activities/Methods:

The method of metal inert-gas welding was selected by way of welding five metal sheets having different coatings. Contrary to the usual procedure, the complete coating was welded over (deposition welding) within the framework of the studies, in order to observe the "worst case scenario" of a high evaporation rate of the coating. Coating types were selected which are representative for the majority of the shipbuilding sectors (epoxy resin, urethane-modified alkyd resin, epoxy tar, alkyd resin and vinyl/epoxy resin (tar-containing)). The pollutant emission was examined to detect the total amount of dust, aromatic hydrocarbon BTX, aldehydes, phenol/cresols, and acrylates. In parallel, samples of polycyclic aromatic hydrocarbons (PAH) were taken. Furthermore, a qualitative analysis of gaseous substances applying gas-chromatography/mass spectrometry was performed (GC/MS).

Results:

The examination of the emissions generated by deposition welding of metal sheets with organic coating show that a multitude of emission products is created. The emission rates are lying between 7,7 mg/s and 24 mg/s. The larger part (more than 73 %) of the particulate substances is respirable. Apart from aliphatic hydrocarbons, also aromatic hydrocarbons and cyclic hydrocarbons and terpenes were found.

The results of the studies on emissions created by deposition welding of coated metal sheets in shipbuilding show that the qualitative determination of such complex pollutant compounds is not sufficient to make a sufficient quantitative determination of the hazard potential. In order to be able to make a quantitative statement on the hazard potential, further studies to determine the emission products are necessary. The results introduced in the present project are to be considered "worst case", as the coatings in the welding area were not removed here. This fact shall be taken into account under any circumstances when implementing those results into practice.

Last Update: