Sulfur pits that house molten sulfur from the hydrocarbon refining process are subject to an extremely harsh environment each day. The corrosive nature of sulfur can cause the concrete sulfur pits to erode and leak, which presents a problem to operations. A major refining company in the South began to experience degradation to their below-grade sulfur pit when water began to enter the pit through cracks. When the water mixes with the sulfur, it creates sulfurous acidic compounds that are extremely damaging to concrete. Producing 425,000 barrels per day, the refinery needed the sulfur pit returned to its original operating condition to ensure plant operations could continue.

With extensive experience in sulfur pit repairs, Structural Preservation Systems (SPS) was brought in to assess the condition of the sulfur pit and then implement a repair. The main goals of the repair were to stop all of the water intrusion, seal the cracks and restore the structural integrity of the concrete walls. Before work began, SPS performed a condition survey and evaluation of the sulfur pit to determine the extent of the damage. The pit was in poor condition and had last been repaired in 1995. To begin the repair process, SPS removed all loose and delaminated concrete from the pit. Leaking cracks were sawcut, impacted with lead wool and covered with hydraulic cement - a process known as chinking. This process prevents water from entering the pit.

Once the water intrusion was stopped, SPS continued the structural restoration of the sulfur pit walls by installing mechanical anchorage and wire mesh that helps the new repair material bond to the existing substrate and reduce shrinkage cracking. Stainless steel reinforcing and anchors were used because of the corrosive nature of sulfur pits. Once the repair cavity was properly prepared, SPS installed a 4-inch thick concrete durability liner to all four walls of the sulfur pit, essentially creating a "pit within a pit." Special concrete incorporating sulfate resistant cements were used, hand-mixed and placed with a pump. The project required more than 25 pallets of material. The durability liner was installed in one continuous placement, which ensured that the material was monolithic and did not have any joints that could allow for water intrusion.

Completed during a planned plant shutdown, schedule was of the utmost importance for this project. The repairs needed to be complete in 14 days, so crews worked around the clock. Proper planning was crucial to the success of this project to ensure deadlines could be met and the project was properly staffed.

Special safety procedures were taken because of the harsh environment. The walls of the pit were hydroblasted before crews entered the pit to eliminate some of the problems associated with sulfur. In addition, crews wore harnesses and full-face respirators when they were in the pit.  Confined space-hole watches and continuous air monitoring were additional safety measures that were in place since this project was completed underground.

The owner was extremely pleased with the outcome of the project and hired SPS to perform the exact repairs for a sister pit located at the refinery. The project was completed on time, which ensured that the refinery could get back online when planned.

Seven years after the repairs were completed, the refinery scheduled another unit shutdown and requested that SPS return to the sulfur pit to inspect the repairs and determine if any additional repairs were needed. Once the sulfur pit was drained and cleaned out, a representative of SPS entered the pit and performed an inspection. It was noted during the inspection that all four walls were in remarkably good shape and the durability liner repairs showed no structural damage. There was only slight erosion due to sulfate attack but the special concrete held up as expected. During the inspection, the owner's inspectors visited the pit and remarked how impressed they were at how the liner held up. In fact, one of the inspectors at the facility noted that they were impressed at the quality of work SPS does and would be referring others to SPS based on this repair. This project is a true testament of SPS's preplanning and attention to detail.