Guidelines for the selection of the correct stainless steel grade in structural applications according to the service environment: Euro Codes 1 to 4 provide a procedure for selecting the appropriate grade of stainless steel for the service environment of structural members. The environment is assessed using Corrosion Resistance Factor (CRF) and the stainless grades are placed in Corrosion Resistance Classes (CRC) I, I, III, IV & V according to CRF value.
Calculation of Corrosion Resistance Factor (CRF)
The Corrosion Resistnace Factor is comprised of three elements: F1, F2 & F3.
F1 rates the risk of exposure to chlorides from salt water/sea water or de-icing salts
F2 rates the risk of exposure to Sulphur Dioxide
F3 rates the cleaning regime or exposure to washing by rain
Calculating F1: Risk of exposure to Chlorides
M is distance from sea
S is distance from roads where de-icing salts are used
|1||Internal, Controlled Environment |
|0||Low Risk of Exposure: M.10km or S>0.1km|
|-3||Medium Risk of Exposure: 1km<M<10km or 0.01km<S<0.1km|
|-7||High Risk of Exposure: 0.25km<M<1km or S<0.01km|
|-10||Very High Risk of Exposure: Road Tunnels where de-icing salts used|
|-10||Very High Risk of Exposure: M<0.25km: North sea coast of Germany & All Baltic Coastal Areas|
|-15||Very High Risk of Exposure: M<0.25km - InclAll other European/UK Coastal Areas|
Calculate F2: Risk of exposure to Sulphur Dioxide
Note: In European coastal environments the SO2 value is usually low. For inland environments the value is either low or medium. High values are usually associated with heavily industrialised locations or sepcific environments such as tunnels.
In the table the deposition values are given in the units micro-grams per cubic metre
|0||Low Risk of Exposure: 10 average deposition|
|-5||Medium Risk of Exposure: 10-90 average deposition|
|-10||High Risk of Exposure: 90-250 average deposition|
Calculate F3: Cleaning or Rain Washing
F3 relates to either the Cleaning Regime or the expsoure to Washing by Rain.
NB: If F1 + F2 = 0 then F3 = 0
|0||Fully exposed to washing by rain|
|-2||Specified cleaning regime|
|-7||No washing by rain or specified cleaning regime|
Calculation of CRC
The Corrosion Resistance Class (CRC) required for the given enviroment is given by first calculating the Corrosion Resuistance Factor (CRF) through adding F1+F2+F3.
|0 to Under -7||II|
|-7 to Under -15||III|
|-15 to Under -20||IV|
CRC by Grade
An appropriate stainless steel garde for the environment can now be chosen from the table below showing the CRC for the various commonly available grades.
|I (Ferritic)||1.4003 / 1.4016 (430) / 1.4512 (409)|
|II (Standard 18/8 Austenitic)||1.4301 (304) / 1.4307 (304L) / 1.4311 / 1.4541 / 1.4318 / 1.4306 / 1.4567 / 1.4482|
|III (Mo-Austeniic & Lean Duplex)||1.4410 / 1.4404 / 1.4435 / 1.4571 / 1.4429 / 1.4432 / 1.4578 / 1.4462 / 1.4362 / 1.4062 / 1.4162|
|IV (Super-Austentic & Duplex)||1.4439 /1.4539 / 1.4462|
|V (Super-Austentic & Duplex)||1.4565 / 1.4529 / 1.4547 / 1.4410 / 1.4501 / 1.4507|