In normal mechanical and structural engineering design materials are selected primarily for their mechanical properties-corrosion is not an important criteria. The systems are generally protected against corrosion by surface coatings. Most machines are located indoors and are accessible for inspection and maintenance. The exceptions to this are machines used for construction and agriculture. These machines may well be used in corrosive environments but they are generally regularly maintained and some level of corrosion is acceptable.
In process engineering corrosion is a very important design factor and material are selected primarily on their corrosion resistance properties. Surface coatings are often not considered because of the risk of contaminating the process stream.
Metal Corrosion Properties – Non Chemiscal Environments
Ratings 0 = Unsuitable, 1 = poor, 2 = Fair, 3 =Fair to Good, 4 good, 5 = good to excellent, 6= excellent.
| Fresh Water | Sea Water | Steam | Steam Cond’te | Air | |
| Metal | Static/Turb | Static/Turb | Dry | Wet | City/Indust |
| Grey Cast Iron- Plain or Low Alloy | 4/3 | 4/3 | 4 | 4 | 3 |
| Ductile Iron (High Strength ) | 4/4 | 4/2 | 4 | 4 | 3 |
| Cast Iron Ni_Resist. (14% Ni, 7% Cu, 2% Cr bal Fe) | 5/5 | 5/5 | 5 | 5 | 4 |
| Ductile Iron Ni_Resist. (24 % Ni, bal Fe) | 5/5 | 5/5 | 5 | 5 | 4 |
| Mild Steel- Low Alloy steels | 4/3 | 4/2 | 4 | 4 | 3 |
| Stainless Steel Ferritic (17% Cro) | 4/6 | 1/4 | 6 | 5 | 3 |
| Stainless Steel Austenitic (18% Cro ,8% Ni ) | 6/6 | 2/5 | 6 | 5 | 4 |
| Stainless Steel Austenitic (18% Cro 12% Ni, 2.5% Mo ) | 6/6 | 3/5 | 6 | 6 | 6 |
| Stainless Steel Austenitic (20% Cro 29% Ni, 2.5% Mo,3.5% Cu ) | 6/6 | 4/6 | 6 | 6 | 6 |
| Hastelloy Alloy (55% Ni, 17% Mo,16% Cr, 6% Fe, 4% W) | 6/6 | 6/6 | 6 | 6 | 6 |
| Inconel (78% ni,15% Cr, 7% Fe) | 6/6 | 4/6 | 6 | 6 | 6 |
| Copper Nickel alloys (Up to 30% Ni) | 6/6 | 6/6 | 5 | 6 | 5 |
| Monel 400 (66% Ni, 30% Cu, 4% Si) | 6/6 | 6/6 | 6 | 6 | 5 |
| Nickel Commercial (99% Ni) | 3/5 | 6/6 | 6 | 6 | 4 |
| Copper and Silicon Bronze | 6/5 | 4/1 | 5 | 6 | 5 |
| Aluminium Brass | 6/6 | 4/5 | 5 | 6 | 5 |
| Bronze (88% Cu,5% Sn,5% Ni,2% Zn) | 6/6 | 5/5 | 5 | 6 | 5 |
| Aluminium Alloys | 4/5 | 0-5/4 | 2 | 5 | 5 |
| Lead (Chemical or antimonial) | 6/5 | 5/3 | 0 | 2 | 5 |
| Silver | 6/6 | 5/5 | 5 | 6 | 6 |
| Titanium | 6/6 | 6/6 | 5 | 6 | 6 |
| Zirconium | 6/6 | 6/6 | 5 | 6 | 6 |
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