Sulfur Storage Pits in Petrochemical Plants: Deterioration Mechanism, Materials Selection, and Repair

To mitigate concrete sulfur storage pits deterioration, it is important to understand the mechanisms leading to concrete deterioration. The Claus chemical process is the industry standard for obtaining sulfur from hydrogen sulphide gas (derived from natural gas). The deterioration of concrete pits can be from both environmental factors and chemical effects of the Claus process. This may take the form of corrosion, sulfation, acidic attack, thermal expansion, or polymerization. Corrosion occurs as a result of sulfuric acid formation. Reactions occur because of Claus products presence, ingress of water through the concrete matrix or from leaks in steam coils. Sulfation occurs mainly from catalyzing some of Claus products by concrete or its admixtures. An acid environment lowers the pH value of the concrete and leads to impacting the passive film protecting the reinforcing rebars. Effects of thermal expansion and polymerization are also discussed in this paper. Selection of the proper materials is crucial in the construction of a durable sulfur pit. Low porosity concrete prevents ingress of gas/liquid species inside the concrete and hence mitigates destructive chemical reactions inside the structure. Cementious materials that will lower the diffusion of gas and liquid such as silica will improve the durability of the sulfur pits. In addition, because of the pozzolanic reaction associated with the use of silica fume the Ca(OH) content will be reduced. Concrete with mineral additives such as silica fume will result in higher compressive strength, lesser permeability and higher corrosion and sulfate resistance. To assure the structure durability, designers need to understand and envision the operational conditions of sulfur pits. Utilization of wrong materials and construction practices can significantly shorten the expected service life of sulfur pits. Finally, repair of deteriorated sulfur pits needs also to be evaluated and conducted by specialized personnel. This repair can take many forms and scenarios including crack repair, structural members repair, durability liner, and structural liner. A proper strategized and engineered repair should be implemented to ensure the repair’s effectiveness and durability.