PURPOSE: To prevent properly the stress corrosion cracking (SCC) of a tank containing a liquid, etc., by forming a metal coating of prescribed thickness by melt- spraying a welded zone with a metal in alternate orthogonal directions several times.
CONSTITUTION: After blasts of quartz sand or pulverized Al are blown on the above-mentioned welded zone, the 1st layer I is melt-sprayed with Zn and then part II with Zn in the advance direction parallel to it. In this case, an overlap is made one third as wide as melt-spraying width W and until required width is obtained, melt-spraying of several processes is carried out to form the 1st layer. Next, melt-spraying I' is carried out nearly at right angles to those of melt-spraying processes IWIII, process II' is done while overlapping with I' by one-third W width, and similarly III' is performed to form the 2nd layers in sequence. Then while alternate melt-spraying directions are made orthogonal, a thin film or approximately 200μm in thickness is formed of normally about four layers. This coating improves the effect of anticorrosion of the welded zone, etc., and even in periodic inspection, etc., SCC can easily be detected by a means of magnetic powder inspection without peeling the coating.
YAMAZAKI HIROSHI
KAWAHARA MINORU
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