Abstract: Leakage occurs frequently at the dilution steam pipe elbow of the cracking furnace of certain ethylene plant. Through fracture analysis, it was found that the wall thickness of the elbow was reduced seriously and the leakage point was in the heat affected zone of the weld. This paper adopts macroscopic inspection and metallographic analysis methods to analyze the reasons for the leakage of dilution steam pipe elbow. It is found that the leakage is caused by the thinning of pipe elbow resulting from gas-liquid scour on the elbow by the dilution steam and the alkali stress corrosion at the weld resulting from the concentration of Na⁺in the process medium in the heat-affected zone of the weld. Aiming at the above problems, the paper proposes optimization suggestions and preventive measures.

Key words: ethylene plant, elbow, leakage, dilution steam