Below-Grade Sulfur Storage Pits in Oil Refineries: A Review

The analysis of subsurface structures has always remained a challenge for construction engineer, especially the below-grade sulfur storage pit. A sulfur pit temporarily accommodates elemental sulfur extracted from oil refineries through a Sulfur Recovery Unit (SRU) and conveyed further to different transportation systems such as railcars, trucks or barges via a pumping system. The storage pit ensures that the elemental sulfur remains in its molten state, and further, the surrounding soil environment is protected. The operating temperature of below-grade sulfur storage pits range from 250 °F (121 °C) to 300 °F (149 °C) at which molten sulfur is kept in fluid form using submerged heating coils located at the pit base. The hazardous, corrosive and highly acidic environment causes severe concrete deterioration in the sulfur pit. The extensive concrete deterioration reduces the life span of the sulfur pit to even less than 10 years. The sulfuric acid formation is mainly responsible for the corrosive environment in the pit. The progression occurs from crack formation to delamination to spalling of concrete cover to corrosion, which finally degrades the structural durability and integrity. The heavily affected areas within the pit include the soffit of the roof slab and the walls in the headspace regions. This research paper presents the review of the various mechanisms in sulfur pit deterioration supported by industrial case studies and the absence of long-term durability performance in current industrial sulfur pit repair approaches.