PURPOSE: To make it possible to surely effectively and hermetically seal the metallic hermetic sealing regions by forming zinc foundation layers in these hermetic sealing regions and forming alloy coating layers consisting of ductile nonferrous elements thereon, then heating the layers under specific conditions.
CONSTITUTION: The surfaces of the parts to be screwed of a pipeline consisting of steel pipes for collecting petroleum, etc., are subjected to a pretreatment, such as degreasing to deposit the zinc layers. After these surfaces are subjected to a first heat treatment at 150 to 200°C, the parts are cooled and are further subjected to a second heat treatment for a short period of time at the temp. above the m.p. of the zinc. The metallic coatings are thus deposited on the metallic hermetic sealing regions and/or threaded regions to be impressed with the high surface pressure. At this time, the foundation layers (total layer thickness of max. 50μ in a region of 5 to 50g/qm) made of the zinc or contg. the zinc are first formed in the hermetic sealing region and the threaded regions. One of the ductile nonferrous elements (for example, lead) or the alloy thereof is deposited by electrolysis to form the coating layers. The treated regions are heated for 1 to 10 seconds at the temp. above the m.p. of the zinc.
BUERUNAA FURIIE
BUIRUHERUMU SHIYUBUENKU
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