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A Sulfuric Acid Alkylation [SAA] unit in a refinery converts olefins and butane to high octane alkylate using highly concentrated sulfuric acid as a catalyst. The function of this Sulfuric Acid Regeneration [SAR] unit is to regenerate spent sulfuric acid from alkylation process into clean sulfuric acid of 99.2% concentration, which is then recycled back into the SAA unit. The process of SAR can be classified in to following four steps:
• Formation of SO2 by the decomposition of Spent acid and combustion of H2S.• Cooling and Purification of the SO2• Conversion of SO2 to SO3• Absorption of SO2 in H2SO4
In Sulfuric Acid Regeneration [SAR] Unit, the spent sulfuric acid [H2SO4] from Alkylation Unit is regenerated to produce a clean Sulfuric Acid of 99.2%. As part of regeneration process the spent acid is decomposed to sulfur dioxide (SO2) at 1066oC [1950oF]. After cooling and purification the conversion of SO2 to Sulfur trioxide (SO3) occurs with the presence of Oxygen in the Convertor section of the unit. The conversion process is an exothermic reaction in nature and the converted Hot gas is used to heat the inlet cold gas to the 1st Converter in Hot Gas-Gas Plate type heat exchanger. The metallurgy of the plates is UNS S30400 [SS304] and the operating temperature is around 620oC [1150oF]. During operation, a leak from this exchanger was observed and while carrying out the repair a metal sample was retrieved for analysis. As part of metallurgical analysis, chemical compositional analysis, Optical Microscopy, XRD analysis of the scale, SEM and EDS were conducted. This paper explains the probable reason for the failure of heat exchanger plates and mitigation measure for the same.
Additive manufacturing (AM) techniques are being studied widely for producing intricately shaped parts and structural components with superior mechanical properties and corrosion resistance. Several detailed studies have been performed on selective laser melted (SLM) stainless steel 316L (SS316L) alloys which describe the effects of process parameters, anisotropy and heat treatments on the corrosion behavior of these alloys. These studies have revealed various pit morphologies and passive films formed on the alloys in various solutions.
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Drag Reducing Agents (DRA) usage in liquid petroleum pipelines has increased over the past few decades, as they improve the mechanical efficiency of flow systems, but their potential impact on different aspects affecting corrosion management has not been fully evaluated. For example: DRA may a) decrease mass transfer and velocity near-wall, reducing flow induced localized corrosion or erosion-corrosion; b) introduce changes in the oil/water interface, affecting water-in-oil stratification and water-oil phase inversion point; c) affect the function of corrosion inhibitors by adsorbing to surfaces or direct chemical interaction.
The potential effect on water accumulation was not included in the model developed for the Pipeline Research Council International, Inc (PRCI) or in other models that are typically used6 for the indirect inspection step of the Liquid Petroleum Internal Corrosion Direct Assessment methodology (LP-ICDA).
About a month after commissioning, a decrease in pH of the cooling water in the plant was observed. This meant that CO2 has leaked into the cooling water in one of the coolers. Two months after commissioning, about 15% of tubes in one cooler downstream of the reactor were plugged after inspection results showed that they have leaked.