Corrosion Information on Stainless Steel
Stainless steels are not indestructible materials, or resistant to corrosive attack. However, the family of stainless steels are excellent combatants of corrosion. With the correct selection of alloy and application of good design elements the few problems associated with corrosion in stainless steel can be conquered.
General Corrosion
General corrosion is an attack of the entire metal surface. It is the least dangerous because rates of corrosion can be gauged and predicted. The general corrosion rates are low in many aggressive environments.
Galvanic Corrosion
Galvanic corrosion occurs when two different metals are in electrical contact and submerged in the same corrosive solution. Stainless steels are grand metals and therefor seldom suffer increased corrosion rates as a result of galvanic corrosion.
Errosion / Abrasion Corrosion
Erosion / abrasion corrosion is a combination of mechanical and corrosive attack. Abrasive particles in suspension, or high velocities, uncover fresh metal surfaces which then suffer high rates of corrosion. Stainless steels offer a high resistance due to the secure and sturdy passive film on their surface.
Intergranular corrosion
Intergranular corrosion is due to the formation of chromium carbides at high temperatures (generally between 45° - 85° C)
These form preferentially at the grain boundaries therefore reducing the chromium content and resulting in a path of lower corrosion resistance around the grains. with correct selection of material such as "L" or stabilised grades and caution during fabrication this form of corrosion should not occur.
Pitting Corrosion
Pitting Corrosion is a dangerous limited form of corrosion which results in small pits or perforations through the material, but with little general metal loss. The chloride ion, which can break down the passive chromium rich oxide film, is usually responsible for pitting corrosion, especially in acidic solutions at high temperatures. Stainless steels alloyed to resist pitting corrosion can be selected for environments
Embedded iron may also increase pitting corrosion. This is one of the most common forms of corrosion seen on stainless steel. Iron particles deposited on the surface of stainless steel through mechanical contact with, usually carbon steels, quickly corrode and form a rust stain. If chloride ions are present this can increase an environment likely to cause pitting corrosion in the basic grades of stainless steel (see picture on previous page). Stainless steel fabricators are cautioned against using the same tools on stainless steels and carbon steels.
Crevice / Shielded Corrosion
Crevice / shielded corrosion occurs where the surface of stainless steel is Shielded therefore preventing the free access and availability of oxygen to the surface. The passive film tends to break down in these areas. Any conditions which give rise to a "crevice" should be avoided.
Micro-Biologically Induced Corrosion (MIC)
MIC results from the attraction and adherence of bacteria to the surface of metal. A condition similar to a CreViCe is thereby produced. Certain bacteria develop aggressive metabolic products which aggravate the situation.
Stress Corrosion Cracking
Both pitting and crevice corrosion can lead to stress corrosion cracking under certain conditions. Stress corrosion cracking is a brittle fracture occurring in an otherwise ductile material. The austenitic crystal structure is prone to stress corrosion cracking whereas the ferritic crystal structure prevents its development.
For stress corrosion cracking to develop it requires the following three factors:
- The presence of tensile stress. This can either be applied or residual stress occurring as a result of the metal forming, fabrication and welding procedure.
- A minimum temperature. Generally stress corrosion cracking does not occur under 60 degrees ceicius.
- The presence of a particular ion, eg. the chloride ion. It is often hard to quantify the exact chloride concentration needed, but localised concentration of chlorides will often initiate stress corrosion cracking.
Eventually the progress of attack reaches such a degree that the yield stress of the material is exceeded due to the lack of residual sound material.
High resistance to stress corrosion cracking 15 obtained by use of duplex stainless steels, stainless alloys and super ferritic stainless steels.
Corrosion Chart on Stainless Steel
R Indicates that the material is resistant to the named chemical up to the temperature shown, subject to limitiations indicated below.
NR Indicates that the material is not recommended
ND Indicates that no data is available
1 - Not if chlorides present
2 - Limited Data
3 - Depending on the acid
4 - Acid fumes dry, attack may occur of moisture builds up
5 - Anhydrous
6 - Depending upon Concentration
7 - May discolour with time
8 - In Strong solutions only when inhibited
9 - Pitting possible in stagnate conditions
10 - Possibility of pitting
11 - May cause stress corrosion cracking
12 - When free of SO2
13 - May cause contamination of product
14 - Dilute hypochlorites can be used to sterilise some stainless steel with extreme care
15 - General corrosion may become excessive
|
18/8 |
MOLYBDENUM |
DUPLEX |
3CR12 / 5CR72 |
| TEMPERATURE Cø |
20ø |
60ø |
100ø |
20ø |
60ø |
100ø |
20ø |
60ø |
100ø |
200 |
60ø |
100ø |
| Aldehydes |
R1 |
R1 |
R1 |
R1 |
R1 |
R1 |
R1 |
R1 |
R1 |
R1 |
R1 |
R1 |
| Acetic Acid (10%) |
R |
R |
R |
R |
R |
R |
R |
R |
R1 |
R |
R |
ND |
| Acetic Acid (glac. & anh.) |
R |
R |
NR |
R |
R |
R |
R |
R |
NR |
ND |
ND |
ND |
| Acetic Anydride |
R2 |
NR |
NR |
R |
R |
NR |
R |
R |
R1 |
R2 |
NR |
ND |
| Ketones |
R |
R |
R |
R |
R |
R |
R |
R |
R1 |
R |
ND |
ND |
| Acetylene |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
ND |
ND |
| Acid Fumes |
R3 |
R3 |
R3 |
R3 |
R3 |
R3 |
R4 |
NR |
NR |
NR |
NR |
NR |
| Alcohols |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
| Alphatic Esters |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
ND |
ND |
| Alkyl Chlorides |
R5 |
R5 |
R5 |
R5 |
R5 |
R5 |
R |
R |
R |
R5 |
ND |
ND |
| Alum |
R |
R6 |
NR |
R |
R |
NR |
R |
R |
NR |
ND |
ND |
ND |
| Ammonia |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
| Antimony Trichloride |
R5 |
NR |
NR |
R5 |
R5 |
NR |
R |
R |
NR |
NR |
NR |
NR |
| Aromatic Solvents |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
Atmospheric
- Industrial |
R7 |
ND |
ND |
R |
ND |
ND |
R |
ND |
ND |
R7 |
ND |
ND |
| - Marine |
R7 |
ND |
ND |
R |
ND |
ND |
R |
ND |
ND |
R7 |
ND |
ND |
| - Rural |
R |
ND |
ND |
R |
ND |
ND |
R |
ND |
ND |
R7 |
ND |
ND |
| Ascorbic |
R1 |
R1 |
R1 |
R |
R |
R |
R |
R |
R |
R1 |
ND |
ND |
| Benzoic Acid |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
| Boric Acid |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
| Brines, saturated |
R8 |
NR |
NR |
R8 |
NR |
NR |
R |
R |
R |
NR |
NR |
NR |
| Bromide (K)soln. |
R9 |
NR |
NR |
R9 |
R9 |
R9 |
R |
ND |
ND |
NR |
NR |
NR |
| Bromine (+ aqu.) |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
| Butyl Acetate |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
| Calcium Chloride |
NR |
NR |
NR |
R8 |
NR |
NR |
R10 |
R10 |
R10 |
NR |
NR |
NR |
| Carbon Disulphide |
 |
R |
ND |
R |
R |
ND |
R |
R |
R |
R |
R |
R |
| Carbonic Acid |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R9 |
NR |
| Carbon Tetrachloride |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
| Caustic Soda & Potash |
R |
R |
R6 |
R |
R |
R6 |
R6 |
R6 |
ND |
ND |
R6 |
R6 |
| Cellulose Paint` |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
| Chlorates of Na, K, Ba |
R1 |
R1 |
R1 |
R1 |
R1 |
R1 |
R |
R |
R |
ND |
ND |
ND |
| Chlorine, dry |
R |
R |
R |
R |
R |
R |
R |
R |
ND |
ND |
ND |
ND |
| Chlorine, wet |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
| Chlorides of Na, K, Mg, Ca, Ni, Nh4, Alm Sn, Zn |
R10 |
NR |
NR |
R9 |
R11 |
R11 |
R |
R |
ND |
R5 |
NR |
NR |
| Chlorosuphonic Acid |
NR |
NR |
NR |
NR10 |
NR |
NR |
ND |
ND |
ND |
ND |
ND |
ND |
| Chromic Acid (80%) |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
| Citric Acid |
R6 |
R6 |
R6 |
R |
R |
R6 |
R |
R |
R |
NR |
NR |
NR |
| Cres lic Acids (50%) |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
|
18/8 |
MOLYBDENUM |
DUPLEX |
3CR12 / 5CR72 |
|
(304, 304L, 321) |
(316, 316L) |
(2205) |
|
| TEMPERATURE Cø |
20ø |
60ø |
100ø |
20ø |
60ø |
100ø |
20ø |
60ø |
100ø |
200 |
60ø |
100ø |
| Detergents, synthetic |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
| Emulsifiers |
R |
R |
R |
R |
R |
R |
R |
R |
R |
ND |
ND |
ND |
| Esters and Ethers |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
| Fatty Acids (>C/6) |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
| Ferric Chloride |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
| Fluorinated Refrigerants, Aerosols e.g. Freon |
R5 |
R |
R |
R5 |
R |
R |
R |
R |
R |
R5 |
R |
NR |
| Fluorine, dry |
R |
ND |
ND |
R |
ND |
ND |
R |
R |
ND |
ND |
ND |
ND |
| Fluorine, wet |
NR |
NR |
NR |
R |
ND |
ND |
ND |
ND |
ND |
NR |
NR |
NR |
| Formic Acids |
R |
NR |
NR |
R |
R |
ND |
R |
R |
ND |
NR |
NR |
NR |
| Fruit Juices |
R12 |
R |
R |
R |
R |
R |
R |
R |
R |
R13 |
NR |
NR |
| Gelatine |
R1 |
R |
R |
R1 |
R |
R |
R |
R |
R |
R1 |
R1 |
ND |
| Glycols |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
| Hydrobromic Acid (50%) |
NR |
NR |
ND |
NR |
NR |
ND |
NR |
NR |
ND |
NR |
NR |
NR |
| Hydrochloric Acid (10%) |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
ND |
NR |
NR |
NR |
| Hydrochloric Acid (conc.) |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
ND |
NR |
NR |
NR |
| Hydrocyanic Acid |
R |
R |
ND |
R |
R |
ND |
R |
R |
ND |
R |
ND |
ND |
| Hydroflouric Acid |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
| Hydrogen Peroxide (30%) |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
ND |
| Hydrogen Sulphide |
R5 |
R5 |
R5 |
R5 |
R5 |
R5 |
R5 |
R5 |
R5 |
R5 |
R5 |
R5 |
| Hydrochlorite (Na 12 - 14ø/a) |
R14 |
NR |
NR |
R14 |
NR |
ND |
R14 |
ND |
ND |
R14 |
ND |
ND |
| Lactic Acid (100ø/0) |
R |
NR |
NR |
R |
R |
NR |
R |
R |
ND |
NR |
NR |
NR |
| Lead Acetate |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R6 |
| Lead Perchlorate |
R1 |
R1 |
R1 |
R |
R1 |
ND |
ND |
ND |
ND |
NR |
NR |
NR |
| Lime (CaO) |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
| Manganate. Potassium (K) |
R |
R |
R |
R |
R |
R |
R |
ND |
ND |
R6 |
ND |
ND |
| Meat Juices |
R |
R |
ND |
R |
R |
ND |
R |
R |
R |
R7 |
NR |
NR |
| Mercuric Chloride |
NR |
NR |
NR |
NR |
NR |
NR |
R |
R |
R |
NR |
NR |
NR |
| Milks and it's products |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
| Molasses |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
| Monoethanolamine |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
| Naphthalen |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
| Nitrates of Na,K, Nh3, Ag |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
| Nitric Acid (<25%) |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R15 |
NR |
| Nitric Acid (50%) |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R15 |
NR |
| Nitric Acid (90%) |
R |
NR |
NR |
R |
NR |
NR |
R |
NR |
ND |
R |
NR |
NR |
| Nitric Acid, fuming |
R |
R2 |
R |
R |
R2 |
R |
R |
NR |
NR |
ND |
ND |
ND |
| Oil, Diesel, Petroleum, Spirits |
R |
R |
R |
R |
R |
R |
R |
R |
ND |
R |
R |
R |
| Oils, Essential |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
|
18/8 |
MOLYBDENUM |
DUPLEX |
3CR12 / 5CR72 |
|
(304, 304L, 321) |
(316, 316L) |
(2205) |
|
| TEMPERATURE Cø |
20ø |
60ø |
100ø |
20ø |
60ø |
100ø |
20ø |
60ø |
100ø |
200 |
60ø |
100ø |
| Oil. Lube with aromatic adds |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
| Oils, Vegetable and Animal |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
ND |
| Oxalix Acid |
R6 |
NR |
NR |
R6 |
R16 |
NR |
R |
R |
R |
NR |
NR |
R |
| Perchloric Acid |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
NR |
R |
| Phenol |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
NR |
| Phosphoric Acid (20%) |
R |
R |
R |
R |
R |
R |
R |
R |
R |
NR |
NR |
NR |
| Phosphoric Acid (50%) |
R |
R |
NR |
R |
R |
R |
R |
R |
R |
NR |
NR |
ND |
| Phosphoric Acid (95%) |
R |
R |
NR |
R |
R |
NR |
R17 |
R17 |
R17 |
NR |
NR |
NR |
| Phosphorous Pentoxide |
R |
R |
R5 |
R |
R |
R5 |
R |
R |
R |
ND |
ND |
NR |
| Pyridine |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
NR |
| Sea Water |
R9 |
NR |
NR |
R9 |
NR |
NR |
R |
R |
R |
NR |
NR |
NR |
| Slicic Acid |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
| Sodium Peroxide |
R16 |
NR |
NR |
R6 |
R16 |
R16 |
R |
R |
R |
NR |
NR |
NR |
| Sodium Silicate |
R |
R |
NR |
R |
R |
NR |
R |
R |
NR |
R6 |
R6 |
NR |
| Sodium Sulphide |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
NR |
| Starch |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
ND |
| Sugar. Syrups, Jams |
R12 |
R |
R |
R |
R |
R |
R |
R |
R |
R12 |
R12 |
NR |
| SulphamicAcid |
R1$ |
NR |
NR |
R |
R19 |
NR |
R |
R |
NR |
NR |
NR |
ND |
| Sulphates (Na, K, Mg, Ca, AI, Fe) |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R5 |
| Sulphates |
R |
R |
R |
R |
R |
R |
R |
R |
R |
NR |
NR |
ND |
| Sulphar Dioxide, dry |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
NR |
| Sulphar Dioxide, wet |
R |
NR |
NR |
R |
R |
NR |
R |
R |
NR |
NR |
NR |
R6 |
| Sulphar Dioxide, aqua. Soln. (96%) |
R |
NR |
NR |
R |
R |
R |
R |
R |
R |
NR |
NR |
NR |
| Sulphar Triochide |
NR |
NR |
NR |
R5 |
R5 |
R5 |
R5 |
R5 |
R5 |
NR |
NR |
R |
| Sulphuric Acid (<50%) |
NR |
NR |
NR |
R16 |
NR |
NR |
R |
R |
NR |
NR |
NR |
ND |
| Sulphuric Acid (70%) |
NR |
NR |
NR |
NR |
NR |
NR |
R |
NR |
NR |
NR |
NR |
NR |
| Sulphuric Acid (95%) |
R |
NR |
NR |
R |
NR |
NR |
R |
NR |
NR |
R16 |
NR |
NR |
| Sulphuric Acid, fuming |
R |
R2 |
NR |
R |
R |
NR |
R |
R |
NR |
R2 |
R2 |
NR |
| Tannic Acid |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
| Tartaric Acid - |
R |
R |
R |
R |
R |
R |
R |
R |
R |
NR |
NR |
R |
| Trichlorethylene |
R5 |
R5 |
R5 |
R5 |
R5 |
R5 |
R5 |
R5 |
R5 |
R5 |
R5 |
R |
| Urea (30%) |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
| Water, pure |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
NR |
| Yeast |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
R |
NR |
