Corrosion Resistance of Stainless Steel acc CRC Classification

Corrosion Resistance Classification of Stainless Steels for Structural Applications

According to EN 1993-1-4, stainless steel grades are classified according to their corrosion resistance, depending on the environment in which they are to be used. The environmental conditions are assessed using three Corrosion Resistance Factors (CRF). Based on the resulting CRF value, stainless steel grades are assigned to a Corrosion Resistance Class (CRC) from I to V. The higher the class, the greater the corrosion resistance.

The Corrosion Resistance Factor (CRF) is calculated as follows:

CRF = F1 + F2 + F3

F₁       Risk of exposure to chlorides from salt water, seawater or de-icing salts.

F₂        Risk of exposure to sulphur dioxide.

F₃        Cleaning or washing by rain.

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F₁ – Risk of Exposure to Chlorides from Salt Water, Seawater or De-Icing Salts

M is the distance from the sea.

S is the distance from roads where de-icing salts are used.

F₁ categories

–1         Internal, controlled environment

–0         Low exposure risk: M > 10 km or S > 0.1 km

-3         Medium exposure risk: 1 km < M ≤ 10 km or 0.01 km < S ≤ 0.1 km

-7         High exposure risk: 0.25 km < M ≤ 1 km or S ≤ 0.01 km

-10       Very high exposure risk: Road tunnels where de-icing salts are 

_____    used and where de-icing salts may be carried into the tunnel by

             vehicles

-10       Very high exposure risk: M ≤ 0.25 km from the North Sea coast 

____      of Germany and all Baltic Sea coastal areas

-15       Very high exposure risk: M ≤ 0.25 km from all other EU coastal

__         areas_____

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F₂ – Risk of Exposure to Sulphur Dioxide

In European coastal environments, sulphur dioxide concentrations are generally low. In inland environments, concentrations are typically low to moderate. High concentrations are generally found at heavily industrialised sites or in specific environments such as tunnels.

Sulphur dioxide concentrations can be evaluated according to the method specified in ISO 9225.

F₂ categories

-0           Low exposure risk: < 10 µg/m³ average gas concentration.

-5           Medium exposure risk: 10–90 µg/m³ average gas concentration.

-10         High exposure risk: 90–250 µg/m³ average gas concentration.

F3 – Cleaning or Washing by Rain

F3 relates to the cleaning regime or washing by rain. The following applies:

If F1 + F2 ≥ 0, then F3 = 0.

F₃ categories

–0           Fully exposed te rain.

-2           Specified cleaning regim.

-7           Not exposed to rain or subject to a specific cleaning regime.

Calculation of the CRC

The required Corrosion Resistance Class (CRC) for a given environment is determined by first calculating the Corrosion Resistance Factor (CRF) by adding F1 + F2 + F3.

The resulting CRF value is then used to assign the stainless steel grade to one of the five corrosion resistance classes.

Corrosion Resistance Factor (CRF)      Corrosion Resistance Class (CRC)

—-_—CRF = 1                                                                I

_0 ≥    CRF > -7                                                              II

-7 ≥    CRF > -15                                                           III

-15 ≥  CRF ≥ -20                                                          IV

——_-CRF > -20                                                          V

I                   1.4003 | 1.4016 | 1.4512

II                 1.4301 | 1.4307 | 1.4311 | 1.4541 | 1.4318 | 1.4306 | 1.4567 | 1.4482

III                1.4401 | 1.4404 | 1.4435 | 1.4571 | 1.4429 | 1.4432 | 1.4162 | 1.4662

—————1.4362 | 1.4062 | 1.4578

IV                1.4439 | 1.4462 | 1.4539

V                 1.4529 | 1.4547 | 1.4565 | 1.4410 | 1.4501 | 1.4507

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The corrosion resistance classes (CRC) according to EN 1993-1-4 are intended only for the stainless steel grades listed above and apply exclusively to structural applications.

Source: EN 1993-1-4.

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Despite every effort being made to ensure the accuracy of the information presented above, no guarantee is given regarding its completeness or accuracy. For design purposes, the applicable edition of the relevant standards should always be consulted.