Requirement and Calculation of Corrosion Allowance for Piping and Valves in the Oil and Gas Industry

Abstract

“Acid Gases” refer to two of the undesirable by-products of oil and gas, namely CO2 and H2S$$.$$ The reaction of H2S and other sulphur compounds with water increases the degree of “sour corrosion” by forming sulphuric acid. CO2 corrosion of carbon and alloy steels is designated as “Sweet Corrosion” which is defined as the deterioration of metal components resulting from contact with gas or solutions including both CO2 and water. CO2 corrosion is an important problem in the oil and gas industry due to metal loss and its severe effects in terms of localized corrosion. Accurate prediction and modelling of CO2 corrosion rates for carbon and alloy steel pipes are vital tasks at the basic design phase of oil, gas and petrochemical projects in order to determine whether to consider additional wall thickness for the pipes and valves defined as “Corrosion Allowance (CA)” or to change the pipes’ or valves’ base materials to “Corrosion Resistance Alloys (CRA)”. Other corrosion mitigation approaches such as injecting the corrosion inhibitors and glycol or methanol can reduce the metal loss and CO2 corrosion. This paper proposes a practical model to calculate and select the corrosion allowance for piping and valves in oil and gas industry. Different process parameters such as scaling, fugacity, pH, glycol and corrosion inhibitor injection, water cut, operating pressure and temperature as well as CO2 partial pressure have been applied in the model.