Protection of aluminum against corrosion in contact with metals (Eurocode 9)
standard EN 1999, which is also called "Eurocode 9", It applied in the European Union with the design of structures made of aluminum alloys for buildings and civil engineering structures. This standard is consistent with the principles and requirements for safety and serviceability of structures fitness, source data for their design and checks, indicated in a more general construction standard EN 1990 - Basics of structural design.
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.
- See. Eurocodes 9: building wrought aluminum alloys
- See. Eurocodes 9: use in construction of aluminum castings
- See. Eurocodes 9: general protection against corrosion of aluminum structures
Below is an overview of the recommendations of Eurocode 9 for the protection of aluminum building structures against corrosion, which occurs in the compounds of aluminum with other metals: slot and galvanic. In construction, these "metals" are mainly:
- Various alloys of aluminum,
- Cink Steel,
- painted steel and
- stainless steel.
Corrosion of aluminum in the compounds
When designing aluminum building structures, it is necessary to separately consider the issues of aluminum corrosion under the following conditions:
- all aluminum contacts in joints with different materials with the formation of gaps to prevent crevice corrosion;
- all contacts in the aluminum compounds with metallic materials or metal washers, galvanic corrosion - which resulted in the electrochemical reaction may occur therebetween.
Protecting the contacts of the crevice and galvanic corrosion
The contact surfaces of aluminum and aluminum compounds or other metals require additional corrosion protection, in addition to general protection against corrosion of aluminum structures. The degree of total protection against corrosion of aluminum structures is dependent on the climatic conditions of operation. This also applies to the contact surfaces in the compounds, made bolt, rivets, and welding using a high-friction screw clamps.
Guidelines for such additional protection against crevice corrosion and galvanic aluminum building structures in various environmental conditions are presented below in Tables 1-3:
- table 1 - for non-marine atmosphere of various pollution;
- table 2 - for maritime atmosphere and a variety of pollution
- table 3 - For designs, that operate in conditions of immersion in water, water or sea.
More detail on measures to protect against corrosion of aluminum building structures set out in EN 1090-3. Measures for protection against corrosion of contacts of sheet material for roofs and outer cladding are set out in the standard EN 508-2:1996.
If building components are assembled, which have been subjected to prior staining or corrosion protection, in the construction of technical documentation necessary to provide additional insulation for the contact surfaces, including the type and procedure of such isolation. These measures should take into account the estimated useful life of the aluminum structure, external factors, and the degree of protection of such components pre-protected.
Corrosion protection of the compounds in constructions
Usually there is no need for any treatment for protection against corrosion.
Method 0 / X
The need for treatment for protection against corrosion is dependent on the design features. Small contacting surfaces, and the surface, which dry quickly and naturally from moisture can be installed without any sealing (see. method X)
Both contact surfaces have to be assembled in such a manner, to leave no gaps, in which water may penetrate. The two contact surfaces, including holes for bolts and rivets, before mounting structures must be free, preprocessed and are single layer of primer must be applied, as specified in EN 1090-3, or sealant, so that it extends beyond the contact surface. The surfaces to be joined together, while primer layer is still wet.
If you collected prestained or components with corrosion protection, contacting the sealing surfaces may not be necessary, depending on the ink composition or method applied corrosion protection, as well as the expected life of the structure and environmental features.
Complete electrical isolation between the two metals and all fasteners. Is provided by the installation of non-absorbent and non-conductive films, washers and gaskets, to prevent metal contact between materials. It may require application of additional coatings or sealants.
If application of the method requires Y, and load is transmitted through the point contact, and this prevents the application of the insulating material, then the compound must be assembled without the use of insulating materials, but with the implementation of a complete external insulation of the entire assembly, to prevent moisture penetration of the elements of compound. Methods for such isolation should be established by agreement between the parties concerned.
Bolts and rivets
Usually, No additional processing is not required.
Between the bolt heads, nuts, washers and the joined materials should be installed gasket of inert material or adhesives, compound to seal and prevent ingress of moisture at the contact surface between the construction components and fasteners.
Measures should be taken to, applied to gaskets and sealants in the compound does not adversely influence the load transfer through the connection.
- (1) In case, If the compound does not have a surface layer of paint or other coating, the bolt heads, nuts and rivets, as well as nearby areas joined materials, They must be protected, at least, one coat of primer (see. EN 1090-3). Particular attention should be given to sealing all cracks.
- (2) In case of using galvanized bolts, protection of the aluminum compound is not required.
- (3) When using aluminum bolts or rivets, protection of the aluminum compound is not required.
- (4) When using stainless steel bolts to connect aluminum or galvanized steel parts, the nearby galvanized joint area should have similar protection (i.e.. it is. protected by at least one coat of primer).
Additional protection against corrosion
In those cases,, when in the compound can collect dirt or moisture-retaining, and adjacent to the compound of the metal parts have not been painted for some reason, it may be necessary to protect them with a suitable paintwork
May require additional protection galvanized construction parts in general,.
Protecting the contacts “metal-metal” from crevice corrosion and galvanic
The symbols in the tables 1-3:
- M - metal (metal), B - bolt, R - rivet
- Methods of protection against corrosion of metals 0, 0/X, X, Y and Z - sm. section 4.1
- Methods of protection of bolts and rivets 0, 1 and 2 - cm. section 4.2
- Additional methods of protection and a z - cm. section 4.3
- When assigning protection methods in brackets (), it is necessary to take into account the special conditions for general corrosion protection (see. Total protection against corrosion of aluminum constructions, section 5)
Crevice and galvanic corrosion in normal atmosphere
Table 1 – Methods for protecting metal-to-metal compounds from crevice and galvanic corrosion in a normal (non-marine) atmosphere – rural and industrial
Crevice and galvanic corrosion in the marine atmosphere
Table 2 – Methods for protecting metal compounds of metal and slotted on galvanic corrosion in marine atmosphere - rural and industrial
Crevice and galvanic corrosion in water - fresh and sea
Table 3 – Methods of protecting compounds from the metal-metal crevice and galvanic corrosion under operating conditions in water - fresh and sea
Source: European standard EN 1999-1-1:2014