General technical approval Z-30.3-6 The general technical approval Z-30.3-6 of 5th
December
2003 [1] from DIBt (Deutsches Institut Für Bautechnik) deals with “Products, joining materials and components of corrosion-resistant steels”. The determinations contained in this approval are binding according to building law and may only be breached in exceptional cases for good reason. Table One of Z-30.3-6 contains 15 different steel types
according to DIN EN 10088. Table Two contains 13 different steel types for joining materials according to DIN EN ISO 3506. With the resistance classes against corrosion also defi ned in both tables and the given typical application examples, the architect and the structural engineer have the possibility to select the suitable material from an abundance of available corrosion-resistant steel types. Worthy of note here is the remark that at least the steel types of resistance class III/medium (V4A, e.g. 1.4404) must be used for inaccessible constructs, meaning constructs whose condition cannot be inspected or can only be inspected under diffi cult conditions, and which can only be repaired with a great degree of effort, even without appreciable content of chlorides and sulphur dioxides.
Examples of damage Cases of damage again and again show that the previously
described cases are not merely theoretical. This will be illustrated with one example. While restoring the roof of an aluminium foundry in the north-east of the Netherlands, the joining materials were also replaced. The approximately 20-year old roof consisted of aluminium trapezoid profi les joined with the substructure with screws of material group A4 (1.4401). There were no signs of corrosion attacks on the screws. The new roof construction, also made of aluminium trapezoid profi les, was fastened to the substructure with screws of material group A2 (1.4301). All of the screws had to be replaced after less than 2 years due to corrosion. Many of the screws were already broken as a result of the considerable corrosion damage. The screws of the material 1.4301 were not suited for the corrosion stress existing in this case.
The aluminium trapezoid profi les could be lifted by hand
Some screws were already broken due to corrosion damage
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