Coatings filiform corrosion

Filiform corrosion is characterised by the formation of a network of threadlike filaments of corrosion products on the surface of a metal coated with a transparent lacquer or a paint him, as a result of exposure to a humid atmosphere. This phenomenon first attracted attention because of its formation on lacquered steel, and for this reason it is sometimes referred to as underfilm corrosion, but although it is most readily observed under a transparent lacquer it can also occur under an opaque paint film or on a bare metal surface. Filiform corrosion has been observed on steel, zinc, magnesium and aluminium coated with lacquers and paints, and with aluminium foil coated with paper. Surface treatment of the metal by phosphating or chromating lessens the tendency for filiform corrosion to occur, but it is not completely... 

This appears as a random non-branching white tunnel of corrosion product either on the surface of non-protected metal or beneath thin surface coatings. It is a structurally insensitive form of corrosion which is more often detrimental to appearance than strength, although thin foil may be perforated and attack of thin clad sheet (as used in aircraft construction) may expose the less corrosion resistant aluminium alloy core. Filiform corrosion is not commonly experienced with aluminium, as reflected by the insignificance afforded it in reviews on the phenomena (Section 1.6). 

A patchy form of rust that attacks paint films from underneath, can be caused by sweaty hands, residues from fluxes, etc. Examples of the latter include residues from phosphating and soluble salts (including those from unsuitable rinsing water) and they can manifest themselves on steel in the form of a creeping filiform corrosion, i.e. as progressing threads of rust which loosen the coating. This can be followed visually through transparent films. It occurs, however, only when the relative humidity of the surround-... 

Even small traces of certain corrosion stimulants, notably soluble chlorides and sulphates, can maintain a continuing corrosion process under a paint film because the salts accelerate the initial dissolution of ferrous iron (and other metal ions) but are not immobilised in the hydrated oxide corrosion products. Filiform corrosion is the most spectacular example of this phenomenon, but progressive spread, preceded by blistering, is also observed from scratches or other breaks in a coating, for example during salt spray tests. 

Filiform Corrosion a form of corrosion under paint coatings on metals characterised by a thread-like form advancing by means of a growing head or point. 

D 2803 1982 (1987) Test method for filiform corrosion resistance of organic coatings... 

Figure 1. The assignments of FTIR-RA spectra of unaged epoxy free and coated films on steel have been given previously ( ). It should be noted that this aged specimen exhibited extensive filiform corrosion after 7 months exposure. Figures 2 show the spectral changes at different exposure periods. These spectra have been normalized for the baseline shift resulting from the reflection change of the steel substrate due to exposure and corrosion.

Sease C, Selwyn LS, Zubiate S, Bowers DF, Atkins DR (1997) Problems with coated silver whisker formation and possible filiform corrosion, Stud Conserv 42 1-10271. 

Anodic Delamination (Filiform Corrosion) on Coated Aluminum... 

Filiform corrosion on epoxy-coated 1045 carbon steel was investigated with SKPFM [111]. Under coatings of 150 and 300 nm thickness at 93% relative humidity, samples were studied under air. Separation of active anode and cathode locations in the head of the filament could be identified. Microscopic and even submicroscopic aspects of electrochemical delamination have been studied with SKPFM [99]. 

CORROSION, FILIFORM - Corrosion that occurs under organic coatings on metals as fine wavy hairlines. 

Filiform corrosion is observed under thin organic coatings on aluminum, steel, aircraft structures exposed to humid atmosphere, beverage cans, flanges, gaskets, dis-bonded... 

Filiform corrosion is observed under thin organic coatings (typically 0.1 mm) on aluminum and steel exposed to a humid atmosphere. It has been observed in aircraft structures, beverage cans, flanges, gaskets, and weld zones [111—113]. Corrosion-resistant alloys of stainless steel, copper, and titanium are not susceptible to fihform corrosion. Metals with thin organic coatings are in contact with water from the humid atmosphere. 

D2803—09 Standard Guide for Testing Filiform Corrosion Resistance of Organic Coatings on Metal... 

G. Williams and H.N. McMurray, Poly aniline inhibition of filiform corrosion on organic coated AA2024-T3, Electrochim. Acta, 54, 4245-4252 (2009). 

A further advantage of polyaniline dispersion coatings and complete coating systems including interlayers and topcoats is its applicability to metal substrates other than steel. Aluminum is subject to so-called filiform corrosion, which can be effectively beaten by suitable products, in this case CORRPASSIV 4901 (a different kind of primer and top coat) the performance was tested by an independent institute (see footnote 7). In the meantime, the same primer was also successfully tested in various applications on magnesium. 

Phosphate surface treatments and chromate prime coats of paint serve to limit filiform corrosion, but apparently do not prevent its occurrence. Wholly adequate remedies have not yet been found. 

Filiform corrosion A type of corrosion that occurs under coatings on metal substrates characterized by a definite thread-like structure and directional growth. Baboian R (2002) Corrosion engineer s handbook, 3rd edn. NACE International - The Corrosion Society, Houston, TX. Uhlig HH (2000) Corrosion and corrosion control. John Wiley and Sons Inc., New York. 

Filiform corrosion resistance The ability of a coating to resist that type of corrosion of metal substrates characterized by a definite... 

Filiform corrosion under organic coatings is common on steel, aluminum, magnesium, and zinc (galvanized steel). It has also been observed under electroplated silver plate, gold plate, and under phosphate coatings. 

Filiform corrosion, identified by threadlike strands, is formed under finishes such as powder-clear-coated aluminum [77]. 

ASTM Standard D 2803 Standard Guide for Testing Filiform Corrosion Resistance of Organic Coatings on Metal, Anmuil Book of ASTM Standards, Vol. 6.01, ASTM International, West Conshohocken, PA, 2001. 

Coyle, J., Fortier, M., and McKeon, J., Studying Filiform Corrosion of Powder-Clearcoated Aluminum Wheels, Powder Coating, March 1997, pp. 22-35. 

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