When we say the SCS process makes ordinary hot-rolled black rust-inhibitive without the need for oil or coatings, we’re often asked ‘Just what is the shelf life of SCS? How long can I store it before signs of corrosion will appear?’ Good questions for which there is no definitive answer because it depends on the specific storage conditions.

The more easily answered question is ‘How does SCS compare to P&O in its ability to inhibit rusting?’  That can be reliably determined with through controlled testing, and we recently enlisted the help of St. Louis Testing Laboratories to perform such a test. The test used samples of bare SCS, samples of P&O that had been pickled in a continuous in-line process and samples of P&O that had been batch (immersion) pickled. Three samples of each group were used in the testing with both sets of P&O samples retaining the protective oil coating that is routinely applied right after pickling.

All samples were placed in a high humidity environment  – 98% relative humidity at 100°F. At regular intervals, the samples were removed and visually inspected for signs of rust formation. If no rust was observed, they were returned to the high humidity chamber for further exposure.

Through approximately 200 hours, no samples showed any sign of rust. At the 312 hour inspection interval, both the continuous P&O and the batch P&O samples began to show slight levels of reddish-colored corrosion. The SCS samples did not. At the 384 hour inspection, the batch P&O samples showed pervasive rust spots, while the continuous P&O samples began showing noticeable edge rust (see photos
at right). Again, no signs of rust on the SCS samples.

Signs of rust began to appear on the SCS samples at the 504 hour inspection (see photo). But the rusting was limited to the edges of the samples that had been cut on a shear. This pattern indicates that the impact of the shear blade disrupted the SCS’ thin layer of polished scale, thus diminishing its ability to resist rusting in that specific location.

A complete synopsis of this comparative humidity testing is available at this link and clearly documents the SCS advantage: SCS samples achieved 60% greater exposure before developing rust than oil-protected P&O samples. Had the SCS sample edges not been sheared, the exposure levels may well have been even higher.

We hope this result gives you, the reader, a clearer idea of what is meant by the statement SCS is ‘rust-inhibitive’ and how that can translate into a shelf-life advantage and a scrap reduction advantage when you replace your P&O with SCS.