Cracking Analysis on Three-way Pipe of Continuous Catalytic Reforming Unit
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Graphical Abstract
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Abstract
Cracking reasons of the three-way pipe mixing hydrogen and naphtha of continuous catalytic reforming unit were analyzed by macroscopic appearance observation, scanning electronic microscope observation, energy spectrum analysis, determination of electrode potential and galvanic current. The results indicate that the cracking was near welding joint connecting three-way pipe and adapter bonnet, and the main reason for cracking was galvanic corrosion on the basis of cavitation erosion and corrosion of Cl and S. The potential difference between the cracking three-way pipe made of Cr5Mo steel and the welding seam made of chromium nickel stainless steel reached up to 60 mV, which formed galvanic corrosion. The three-way pipe near welding joint became constantly thinning and finally cracking, because it was the anode of galvanic couple that could be accelerated corrosion because of its more negative potential.
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