Abstract
In 2005, a 60 kt/a alkylation (ALK) unit began to resume production in the Second Oil Refinery Plant of Beijing Yanshan Petrochemical Company. There have been many leak cases from pipeline welds, valve body, flange, etc. After a half-year period of operation, production process is stable. However, the operation of the hydrofluoric (HF) acid ALK unit has been suffered from corrosion problems. There are no clear answers and references to the following problems. What types of corrosion are currently in the main equipment for HF acid ALK unit? What does cause equipment corrosion? What are the main influencing factors for corrosion? What measures can be taken to reduce the corrosion of HF acid? In this paper, considering the acid-related conditions of the ALK unit, the damage mechanism and damage rate analysis were carried out to calculate the safety risk of the static equipment of the ALK unit. Based on the damage mechanism and failure history, the material suitability of the ALK unit was investigated. The anti-corrosion measures and recommended materials for important corrosion parts of the ALK unit were proposed. It is meaningful for reducing the number of shutdowns of ALK units and maintaining safe and stable operation of the unit.
Highlights
An alkylation (ALK) unit was set up in a Beijing petrochemical refining plant in 1988
The operation of hydrofluoric (HF) acid ALK unit has been suffered from corrosion problems
Three consecutive HF leakage accidents occurred in equipment of HF acid ALK units abroad in 2009
Summary
An alkylation (ALK) unit was set up in a Beijing petrochemical refining plant in 1988. 2. Risk Source Analysis of Static Equipment in HF Acid ALK Unit 2.1. Most of the equipment materials involved in the acid system are carbon steel and Monel alloy for the HF acid ALK unit When it contacts with high concentration acid, for example water content less than 3%, a stable iron fluoride layer is formed inside the equipment. Corrosion leakage of acid-related heat exchanger is one of the common failure modes in HF acid ALK units. The leakage of the flange sealing surface is one of the typical failure modes for HF acid ALK unit. Corrosion leakage of instruments and their connections is one of the main failure modes for static equipment in HF acid ALK unit. Through calculating the correction factor, the failure probability of the vessels or pipelines can be determined
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