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Inorganic zinc (IOZ) silicate coating was previously applied to partially fabricated low alloy, 21/4 Cr-1MoV, high temperature, hydrogen, reactor vessels for long-term storage corrosion protection prior to final welding and post weld heat treatment (PWHT) at 690-720°C (1274-1328°F). The need for complete coating removal to mitigate the known embrittlement and weld cracking that can occur after welding and PWHT led to the development of a novel, environmentally friendly method to remove IOZ to trace levels below 1 ppm.
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Case histories will illustrate failures that occurred in components that were made of different brass alloys in water and steam systems. Recommendations will be made to mitigate the damage that occurred in each case.
In this article, we will be presenting some background about the zinc‐in‐immersion technology itself while addressing some of the important questions where the two opposing sides commonly clash. A discussion over failure modes; reasons for failure; and alternate technologies will be discussed. Additional information will detail what factors and features are needed to develop a good lining to protect steel water tanks. The paper will conclude by discussing alternative coating options that exist (including “greener” versions) and expected performance levels these coatings are anticipated to provide.
Liquid Metal Embrittlement (LME) phenomenon occurs when the certain molten metals wet the specific alloys, causing drastic ductility reduction that normally is associated with the formation of an intergranular crack that is sudden and brittle in nature. High tensile stress is also known to promote cracking; however, cracks may develop merely by contacting molten metal with a susceptible alloy as there is only a small amount of low-melting-point metal required to cause LME.
Corrosion is a natural phenomenon, and thus can never be completely eliminated; however, it is a misconception nothing can be done. Estimates show 25-30% of steel corrosion could be eliminated if proper corrosion protection methods were employed. Corrosion can simplistically be viewed as the tendency for the metal, after production and shaping, to revert back to its lower, more natural energy state of ore. This tendency is known as the Law of Entropy.
Two-Coat zinc-rich primed systems with a fast-dry topcoat were evaluated for their potential to replace the conventional three-coat zincrich/epoxy/polyurethane bridge coating systems for rapid field deployment.
In 2003, the City of Anoka, Minnesota completed the reconditioning of its 400,000-gallon legged water storage tank. A 2-year warranty inspection followed in 2005. The project was introduced in the May 2007 issue of the Journal of Protective Coatings. Its significance was that reconditioning of interior surfaces, above the high waterline, were treated with a trial application of three coating system solutions.
A review of research work in the literature to date for both laboratory and field evaluations, toward identifying technically relevant situations where the use of sacrificial anodes may or may not be a practical option for reinforcement protection in concrete structures.
Zinc and its alloys are used as sacrificial anodes because zinc is an active metal. Carbon steel can be coated with zinc to protect against corrosion. These metals are known as galvanized steel. In this work, microbiologically influenced corrosion (MIC) of pure zinc and galvanized steel caused by a sulfate reducing bacterium was investigated. After 7 days of incubation in 125 mL anaerobic vials with 100 mL culture medium and 1 mL inoculum, the sessile cell count on the galvanized steel was slightly higher than that on pure zinc. The abiotic weight loss for pure zinc was 1.4 ± 0.1 mg/cm2 vs. 4.6 ± 0.1 mg/cm2 for galvanized steel after 7 days of anaerobic incubation at 37oC. The weight losses for galvanized steel and pure zinc were 31.5 ± 2.5 mg/cm2 and 35.4 ± 4.5 mg/cm2, respectively, which were 10X larger than the previously reported carbon steel weight loss in the same SRB broth. Electrochemical corrosion tests confirmed the severe corrosion of these two metals. The corrosion current densities of galvanized and pure zinc were 25.5 µA/cm2 and 100 µA/cm2, respectvely at the end of the 7-day incubation with SRB, confirming that pure zinc was more prone to SRB MIC than galvanized steel. In both cases, the corrosion product was mainly ZnS. Three MIC mechanisms were possible for the severe corrosion. Extracellular electron transfer MIC is thermodynamically favorable for Zn. Furthermore, the detection of H2 evolution in the vials suggest that proton attack and H2S attack occurred against Zn in the SRB broth with neutral pH after passive film damage by the SRB biofilm.