AM-93-62 CRUDE UNIT CORROSION CONTROL: UNDERDEPOSIT CORROSION CONTROL FOR EXTENDED EQUIPMENT LIFE

Description:

Failures of overhead equipment often occur at a much higher rate than probe measurements predict. This can be due to accelerated underdeposit pitting rates which are about twenty times the general rates. Underdeposit corrosion is primarily caused by iron sulfide deposits rather than neutralization salts as is commonly believed. The corrosion mechanism that leads to failures is the formation of a differential potential cell between the clean or lightly covered areas and the heavily deposited areas. Equations have been derived which show that the solubility of iron sulfide is dependent on pH and the concentration of sulfides present. These equations define the maximum pH at which a system can operate and remain free of iron sulfide deposits. Data are included which show that new generation inhibitors can control corrosion in the pH range necessary to prevent deposits. The goal of any program designed to minimize equipment failures should be to prevent the formation of deposits and the ensuing underdeposit pitting corrosion.