Testing for Iron and Stainless Steel Contamination
American standards ASTM A380 and A967 outline iron contamination tests.
Some of the tests simply look for rust stains from contact with water or high humidity environments, but for detection of the 'cause' ie free iron on the surface, rather than the 'effect', which is the resulting rust stains, then the 'ferroxyl test' is probably the better method. This will detect either free iron or iron oxide and is sensitive enough to detect small levels of contamination.
ASTM A380 outlines the procedure in section 7.3.4.
Nitric acid is added to distilled water, followed by the potassium ferricyanide. The 'recipe' is shown in the table.
| Distilled water |
94 weight % |
1000 cm3 |
| Nitric acid |
3 weight % |
20 cm3 |
| Potassium ferricyanide |
3 weight % |
30 grams |
Preparation of the solution must be done using equipment where no iron or steel comes into contact with the reagents. It should be applied to the stainless steel surface preferably using an atomizer spray.
A blue stain, appearing in about 15 seconds, indicates the presence of iron. The solution has to be removed from the surface as quickly as possible after testing using either water or 5-20% acetic acid (or vinegar) and scrubbing with a fibre brush, finally rinsing with the solution used, several times. The standard notes that potassium ferricyanide is not toxic but that the fumes may become toxic if the solution is heated.
Iron Contamination and Rust Staining on Stainless Stee
Avoiding Iron and Stainless Steel Contamination
Testing for Iron and Stainless Steel Contamination
Removing Iron and Stainless Steel Contamination
Cleaning methods for Stainless Steel
|
