Cause analysis and preventive measures of pipeline corrosion and leakage accident in alkylation unit

Abstract

Owing to the corrosive, flammable, and explosive properties of pipeline materials in alkylation units, corrosion failure may result in leakage, fire, and explosion accidents. A bursting accident occurred in the 90° elbow of an alkylation unit pipeline. Failure analysis was performed by macroscopic analysis, metallographic analysis, chemical composition, corrosion form analysis, and corrosion product analysis. Finite element software was used to analyse the flow velocity, turbulence intensity, pressure, and wall stress distribution. The fault tree was combined with the analytic hierarchy process to realise the transformation of the structural importance-judgement factor-judgement matrix and to weight the events that may cause device corrosion failure. The results showed that uniform corrosion and stress corrosion of hydrofluoric acid occur in the pipeline and uniform corrosion is the dominant effect. Hydrofluoric acid corrosion leads to severe thinning of the pipe wall, making its strength drop below the bearing strength and rupture occurs. Quality of internal anticorrosion coating, water content of the medium and working temperature are the key factors to prevent pipeline leakage in alkylation unit.