| 摘要 |
<p>The present invention relates to a passive state film type coated steel pipe comprising: a step of three-layer coating epoxy powder, adhesive modified polyethylene, and polyethylene resin subsequently in a powder fusion method after heating an outer surface of a steel pipe at 220-280°C; and an inner surface coating layer consisting of one either polyurethane or epoxy secondarily by forming a passive state film on a metal surface corroded layer by chemical reaction by primarily injecting a passive state film type primer before an inner surface of a pipe main body is coated with polyurethane or epoxy. A powder fusion method polyethylene coated steel pipe have gone through a step of cooling a pipe by using water to coat an inner surface by being sequentially coated with epoxy powder, adhesive modified polyethylene, and polyethylene resin after heating an outer surface of a steel pipe at 220-280°C in a coating step. In this case, peeling of Inner coating is performed by decreasing adhesive force even if being coated with polyurethane or epoxy by having residual rust after coating by generating rust in the inner surface of a steel pipe due to instantaneous oxidation when moisture is in contact with the inner surface of the steel pipe due to coolant. To solve the problem, hygiene and durability of a water pipe is improved by being secondarily coated with one either polyurethane or epoxy secondarily after forming a passive state film by chemical reaction on a metal surface corroded layer by primarily injecting a passive state film type primer before the inner surface of a pipe main body is coated with polyurethane or epoxy.</p> |
