PR-186-073508-R01 Environmental and Stress Factors that Produce SCC in Existing Ethanol Facilities

The potential exists for stress corrosion cracking (SCC) of carbon steel pipelines transporting fuel grade ethanol (FGE) and FGE- gasoline blends. The objective of SCC 4-3 Phase 2 was determine if inhibitors are effective in preventing SCC growth under more realistic field conditions than those found in the slow strain rate (SSR) tests performed previously. The results of the research demonstrated that: 1. Un-notched SSR test results generally correlated well with the results of the crack growth tests using precracked CT specimens, although the latter test technique was somewhat more aggressive. 2. The notched SSR test technique was so aggressive that it was not useful for screening SCC inhibitors. 3. E-50, prepared with a simulated FGE was consistently more potent as a cracking agent than SFGE. 4. Some commercial inhibitors were effective in inhibiting ethanol SCC under many of the test conditions. 5. The commercial inhibitors, in general, were less effective in E-50 than in SFGE. 6. Ammonium hydroxide, at a relatively low concentration, was by far the most effective inhibitor evaluated. 7. For one commercial inhibitor, a higher concentration was needed to inhibit SCC in one lot of corn based FGE than in SFGE. 8. Water inhibited, but did not completely arrest, SCC in the crack growth tests in SFGE. 9. Sustained crack growth was observed in SFGE in which no chloride was added. 10. Evidence of loss of inhibition, at low concentrations, was observed in an inhibition scheme for batching of FGE with gasoline in which a high initial dose, followed by a low maintenance dose was used.