As energy demands increase, the size of LNG and LPG carrier markets has considerably increased. However, as these ships dangerous cargo carring ships increase, issues regarding impact and fire safety evaluation also became to draw attention. Especially, as ships exposed to fire become bigger and automatized even small fire can cause big accident such as explosion, sinking, stranding etc.. Therefore, ships require perfect preparation system for fires and this makes fire fighting equipments of the ships more important. Among these fire fighting equipments, sprinklers are important in extinguishing fires automatically in ships carrying dangerous cargos. When fire occurs temperature becomes to rise than the fire detector, then, pressurized water move to sprinkler header which pours water to extinguish fire. Because it works automatically it is installed in ships, building, parking lots and dangerous facilities.
For this test the materials are cut into optimum size by grinding in order to expose 1cm² surface and 1cm × 1cm insulation tape is attached to the side which will be tested. For measuring potential of test piece connects applicate copper, after connecting insulate coat with epoxy resin. Based on the test piece 3% NaCl solution measured natural potential also by the results of electrochemical polarization measuring test and galvanic current understood the properties of corrosion.
According to the experimental results, the corrosion mechanism of pitting of pipe expansion joint for sprinkler head is analyzed as the following content.
First, when the sprinkler's pipe is appendant natural potential (Ecorr) result (STS > CU >> Fe > Fe(Zn)) galvalume steel pipe which results the lowest potential, by reaction prevents STS steel pipe and copper steel pipe corrosion, preferentially corrode itself. Also, when plated galvalume side is all consumed by corrosion, pipe which has lower natural potential than STS steel pipe and copper pipe that same of zinc will surface. Especially, at this point corrosion products like Zn(OH)₂made from galvalume side's corrosion and Fe(OH)₃ made from steel pipe's corrosion is stacked inside the sprinkler's pipe.
Through this experiment, find out what is best for the inner parts of pipes, sprinkler's corrosion state and also to find the best material and measures to prevent corrosion and pitting.