An overview of Eurocode recommendations is presented 9 for the protection of aluminum building structures against corrosion.
1 Eurocodes 9
Standard EN 1999 considering the requirements for Aluminum constructions strength, serviceability, durability and fire resistance
Standard EN 1999-1-1 - the first part of standard EN 1999 - defines the basic rules for the structural design of the wrought aluminum alloys, and, to a limited extent, for use in the construction of aluminum castings.
2 Durability aluminum alloys Eurocode 9
Eurocodes 9 It connects the durability of building structures with their resistance to climatic influences of the environment, first of all, corrosive influences. All aluminum alloys, that Eurocode 9 Recommended for use in structures, are divided by durability into three classes: A, B and C. Class A corresponds to the highest durability, the lowest - With Class. These classes are used to determine the need for protection against corrosion of these alloys, as well as the extent of this protection.
design, which include several aluminum alloys, including the additive metals in the welds, durability class is set at the lower of the components of classes of durability.
3 Types of aluminum alloys to corrosion
The technical documentation for the manufacture of building designs should describe the type and scope of protection against corrosion of aluminum materials. Type corrosion protection must comply with the basic mechanisms of corrosion of aluminum articles, such as:
- surface corrosion,
- galvanic corrosion,
- crevice corrosion and
- Corrosion of interaction with other building materials.
Crevice corrosion can occur in any type of gap, including, between the metal and plastic. Corrosion can be triggered by specific conditions of construction, for example, if the copper roof is installed by aluminum elements.
When choosing the correct corrosion protection, the following considerations must be taken into account:
- Organic coatings (liquid and powder) can be repaired to some extent by touch-up or cleaning.
- Anodized parts require very careful handling during transportation and construction. Therefore, they need to use protective films.
- Anodic oxidation of organic coating and in most cases are equivalent to each other as protective coatings. Selecting one or another protective coating in any particular circumstances will depend on the type of the corrosive effects of the environment, for example, an acidic or alkaline.
- As a short-term protection against corrosion or corrosion protection in areas with relatively clean atmosphere apply surface passivation of aluminum products and parts, for example, Chemical oxidation of aluminum.
4 Recommendations for the protection against corrosion of aluminum construction
Table 3 recommendations on corrosion protection for these three classes of durability - A, B and C - depending on the environment of their operation
0 Usually there is no need for protection against corrosion
Pr usually required corrosion protection, except for special conditions (see. P. 5)
(Pr) The need for corrosion protection depends on the specific conditions (see. P. 5)
NR immersion in seawater is not recommended
1) For alloy 7020 It requires corrosion protection HAZ
welding, if post weld heat treatment was not
2) If the heat treatment of the alloy 7020 after welding is not carried out, the
the need for protection against corrosion welding heat affected zone must
check for special conditions (see. P. 5)
5 Special conditions for the purpose of corrosion protection
Local conditions may occur with more severe or more mild corrosive effect on the whole structure or part of it. Therefore, in determining the degree of corrosive attack in Table 3 you need to carefully examine their operating conditions for compliance with paragraphs 5.1-5.3 this section.
5.1 When selecting the corresponding column in table 3 for this atmosphere it is necessary to take into account the possible existence of local differences within that region. it happens, that some regions have different local "microclimates", that are substantially different from the ambient medium characteristics, typical of the region as a whole. So, region, designated as "rural", may have areas, wherein external air is greater closer to the industrial atmosphere, If it is close to the industry, or the wind often blows from their side of these enterprises.
Similarly, lot, located close to the sea, but next to the onshore facilities, can, at the appropriate prevailing winds, have characteristics most industrial, rather than the marine atmosphere. Moreover, environment for design, inside the structure, It will not necessarily be the same, for construction, located outside.
5.2 The occurrence of corrosion is dependent not only on the susceptibility of the material thereto and common climatic conditions. In practice, the appearance of corrosion often defined period of time, during which the environmental moisture is present in combination with the accumulation of contaminants on the structural elements and corrosive substances. Those elements or design details, on which these contaminants accumulate or delayed, They are more critical from the corrosion point of view, than those parts, rain that cleans the surface, and the wind quickly dries her. It means, that should be avoided in structures closed niches, which are poorly ventilated. It is also necessary to avoid the formation of various "pockets", in which water can remain, or such pockets should have an efficient drainage.
5.3 In determining the need and the extent of the necessary corrosion protection should take into account the expected life of the building structure service. For structures with short term
service is possible to do less stringent measures or none at all.
Often the occurrence of corrosion can be detected in the early stages as a result of a routine inspection or maintenance, which makes it possible to take appropriate measures in time. In such cases, the initial level providing protection against corrosion can be was low. In the same time, there, where inspections is practically impossible, and signs of corrosion attack can not be detected, the initial level of protection should be higher.
6 Chemical oxidation protection against corrosion
There, which uses hollow aluminum structural members, for example, hollow aluminum profiles, should consider the need for protection against corrosion of the internal cavity. Since such stain is difficult to design elements, it would be better to use a chemical conversion coating, for example, which is used to prepare the surface of aluminum profiles before powder coating.
If the inner cavity is protected from water and moist air, or, If the cavity is working reliable water drainage and ventilation, the protection against corrosion such a cavity may not be necessary.
Source: European standard EN 1999-1-1: 2014