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UGIGRIP® - Corrosion resistance

UGIGRIP® is "stainless to the core", and there are therefore no worries about durability over time and no worries concerning metal cutting locations.

The passive layer:

Stainless steels produce a very thin oxide on the surface, consisting of chromium oxides and hydroxides a few Angströms thick. This oxide, commonly called the passive layer, protects the stainless steel from external attacks and provides it with properties ensuring the corrosion resistance of these alloys. The passive layer forms an intrinsic part of the material, unlike the zinc deposited by galvanization on steels, which explains why stainless steel has essential advantages. Once formed, this layer is perfectly stable, because its thickness remains constant. The passive layer inhibits any exchange between the metal and the outside: in the event of an incident on the material (scratch, cutting, impact, drilling, deformation, etc.), it is reformed spontaneously. This self-restructuring is also called "repassivation".

Choosing the most appropriate grade:

Only by choosing the appropriate grade for the operating environment can the durability of structures be increased depending on the areas of exposure. European standard EN 206-1 defines the five main exposure classes of concrete structures. Depending on the environment to which the part of the structure is exposed, Ugitech recommends using the following grades of stainless steel, irrespective of the quality (porosity and permeability) of the concrete used.

Exposure classRecommendation TYPE GRADES
DUPLEXConventional grades AISI
Class XC (carbonation)XC1.4062304
Class XD (chlorides other than marine chlorides, including road salt)XD1 & XD21.4062304
XD31.4632316
Classes XS (marine chlorides)XS11.4362316
XS2 & XS31.4462*
Class XF (freezing/thawing with deicing agent)XF1 & XF21.4362316
XF3 & XF41.4462*
Class XA (chemical attacks) XA11.4362316
XA2 & XA31.4462*

 Properties of our stainless steel grades

UGIGRIP® - Galvanic coupling

Galvanic coupling

Stainless steel and carbon steel can be in electrical contact, which could cause risks of galvanic corrosion, even though concrete is not very conductive.

So long as the two materials are in a passive state (of non-corrosion), the potentials acquired by the two materials are not very different in these alkaline environments; the potential difference of the "battery" thus formed is very low, and there is not enough energy to create a corrosion current.

Accordingly, the two materials can be coupled in the case of a new structure: stainless steel in areas with a risk of chloride infiltration into the concrete and mild steel in areas more protected against external attacks.

If the carbon steel is corroded and the stainless steel remains passive, then there is a corrosion rate due to the galvanic coupling between the two materials; to answer this question, some authors have carried out experiments with concrete test specimens (water/cement ratio = 0.5) containing, for example, 5 bars in carbon steel and two shorter bars in 316 steel. After one month of concrete "setting", the test specimens undergo a cyclic test: two days in a solution of NaCl 165 g/l (3M) + Ca(OH)2 and five days drying in air. The main tendency is as follows: the measured corrosion current is 15 times weaker in the case of a repaired composite structure (mild steel which is corroded/stainless steel) than for the reference structure consisting entirely of carbon steel.

The risk of galvanic corrosion, accelerating the corrosion of carbon steel in the presence of stainless steel, is eliminated.