Abstract

Crude Corrosivity issues manifest themselves at locations where fluid flow rates and velocities are relatively high in atmospheric distillation units, vacuum distillation units, transfer lines, valves, baffles, heat exchangers, and side cut piping in refinery systems. The heavy vacuum gas oil fraction of the vacuum distillation plant is the crude fraction which usually has the highest total acid number (TAN) due to high concentration of naphthenic acids close to their boiling points. This mechanism of non-aqueous corrosion in the presence of crude oil or oil fractions with high quantities of organic acids and sulfur compounds is termed as high-temperature naphthenic acid and sulfidic corrosion.

This paper will describe naphthenic acid corrosion behavior and corrosion rates of multiple alloys (C1018 carbon steel, A182-F5 5Cr-0.5Mo low alloy steel, A182-F9 9Cr-1Mo alloy steel, AISI 410 stainless steel, and AISI 304L stainless steel) stemming from a comprehensive Joint Industry Program (JIP) conducted to quantify influence of crude oil chemistry on naphthenic acid corrosion, contributions of reactive sulfur chemistry to protectiveness and FeS scale formation, and the ability to resist naphthenic acid corrosion utilizing beneficial sulfur speciation within the context of operational parameters of temperature and wall shear stress.

Introduction

In the petroleum industry, much greater attention has been focused on more highly sour and acidic oil resources due to the gradual depletion of conventional sweet oil resources. In addition, reducing crude oil costs have forced to look for opportunity (alternate) crudes, usually low-quality corrosive crude oils with high concentrations of naphthenic acids and sulfur compounds.1 The main constituents in the crude that cause corrosion are sulfur compounds, organic and inorganic chlorides, salt water, organic and inorganic acids. Processing of these highly acidic and sulfur-containing crudes at high temperatures in refineries has promoted significant corrosion problem in hot oil distillation units and associated piping systems.1-8

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