| 摘要 |
PROBLEM TO BE SOLVED: To attain both excellent construction properties and excellent corrosion resistance by a method wherein an initial adhesion of coating is made to be a specified value, an adhesion after immersion in specific hot water for prescribed days to be the specified value of the initial adhesion or above and a cathodic peeling length of the coating after impression of a specific potential at a specific temperature for prescribed days to be a specified value or below. SOLUTION: A polyethylene coated steel pipe is prepared by coating the outer peripheral surface of the steel pipe with a chromate coat layer, a primer layer, a modified polyethylene adhesive resin layer and a polyethylene coating resin layer sequentially from the lower side. By setting the gelation time of a primer and the characteristics of modified polyethylene adhesive resin in specified ranges respectively, the steel pipe is made to have an initial adhesion of 3.5 Kgf/cm at the temperature of the steel pipe on the occasion of coating being lower than softening temperatures of the adhesive layer and the coating layer, which facilitates execution of construction, and is also made to have such an excellent hot water-resistant secondary adhesion as to hold 90% or more of the initial adhesion even after immersion in hot water of 80 deg.C for 30 days and such an excellent property of resisting to cathodic electrolytic peeling that the cathodic peeling length of the coating after impression of a potential of -1.5 V VS SCE at 60 deg.C for 30 days is 15 mm or less. |
