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By Barry Messer, Fluor Canada, Inc.
Presented at SSPC 2015; Session: Bridge Painting and Protection; Session chair: Mark Hudson, The Sherwin-Williams Company
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Inorganic zinc coating was previously applied to partially fabricated low alloy, 2-1/4 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 coating was removed to below 1 PPM to mitigate known embrittlement and weld cracking that can occur after welding and PWHT. Typical blasting and etching procedures were unable to effectively remove the coating. The need for complete coating removal led to the development of a novel, environmentally friendly method to remove the inorganic zinc to trace levels. The success of this novel development is the first-known method of inorganic zinc silicate coating removal to trace levels below 1 PPM. This method can be utilized in restoration projects of bridges and structural steel where abrasive blasting is not practical or environmentally unsafe. This presentation will discuss the chemical mechanism of this new coating remover, method of application and testing, the validation program utilizing X-Ray Fluorescence (XRF) analyzer Energy Dispersive X-Ray spectroscopy (EDX) calibration, and effective field implementation.
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