During the hydraulic fracturing phase of petroleum well production, temporary sealing is a key technology achieved by interventionless fast-dissolving Magnesium (DM) tools. They can maintain integrity during operation but “disappear” to allow formation production afterward in the most efficient way. Therefore, this sealing technology needs to exhibit the following characteristics: (1) excellent protection for 6-24 hrs.; (2) disintegration to expose DM for dissolving; (3) low thickness and high wear resistance for part assembly; (4) flexibility for various downhole fluid conditions; (5) low cost for mass production. Even though ordinary polymer coatings have been proven effective and broadly utilized as temporary coatings in low and middle-temperature range, it fails to protect these tools effectively at higher temperatures (>140℃ [284℉]) where dissolvable Mg alloys fail due to stress corrosion cracking (SCC) instead of general corrosion. Over 5 years, we have initiated a program to test almost all the major commercial coating technologies, including various polymer coatings, conversion coatings, metal coatings, Chemical Vapor Deposition (CVD) coatings, Plasma Electrolytic Oxidation (PEO) coatings, etc., without success. In this work, we systematically analyzed the failure mode of these industrial coatings and illustrates our technical route to achieve the temporary seal that finally satisfies our unique requirement.