Cokers play a vitally important role to refineries. Generally, coke drums need to be repaired every seven years and the cones and skits need to be replaced every 14 years. The cones and skirts of a coking structure located at a refinery in the South needed replaced because of fatigue cracking and stress cracks. In addition, the concrete structure was heavily deteriorated because of the thermal cycles during daily cutting of the coke. Large pieces of concrete had been falling off the octagon faces and created safety hazards. Having worked with this refinery along the Gulf Coast in the past, Structural Preservation Systems (SPS) was contracted to perform the repairs during a turnaround because of their experience working during time intensive turnaround projects. Originally slated for a turnaround in 1999, the repairs were delayed due to a fire in the unit before the turnaround began. The goal of the repair project was to restore the more than 40-year-old coker octagon structures to their original capacity, upgrade and replace the anchor bolts, and restore the coker sluiceway.

Before the work began, the repair team discussed a total replacement of the sluiceway, but ultimately decided that there was not enough time during the turnaround to prefabricate the necessary pieces and perform a total replacement. Instead, a partial repair plan was selected that joined four contractors together to perform the repairs. For the coker sluiceway, crews repaired the eight concrete sections surrounding the nozzles and the concrete corner of the sluiceway. The top of the sluiceway was then resurfaced and the steel plates were grouted after installation. Repairs then began on the four coker octagons. The coke drums were lifted in place with a shoring system, and the coke drum cones and skirts were removed from the structure. SPS then installed a work platform to the soffits of the octagons. SPS removed the deteriorated concrete, augmented the rebar, installed mechanical anchors, abrasive grit blasted, installed passive cathodic protection, formed the repair areas, mixed and placed a shrinkage compensated repair mortar, removed the formwork, and finally removed the prefabricated work platform. The work area was then turned over to the general contractor to install new cones and skirts. SPS's subcontractor then cored out 64 deteriorated anchor bolts and SPS installed new corrosion-resistant mechanical anchors. Crews prepared the surface and placed new cementitious grouts under the coke drum base ring.

Just a few days into the turnaround, a large crane that was going to be used to life the derricks and coke drums collapsed. At this point, the work for the coker octagons could not proceed as it was outlined in the current plan. Work stopped and the owner, general contractor and the SPS team brainstormed ideas and re-engineered a new repair strategy. One octagon was repaired in phases in our typical on-line scenario. SPS performed the engineering to determine how many faces could be repaired at a given time. These repairs were done while the shoring system for the drums was being engineered and constructed. The remaining three octagons were repaired monolithically similarly to the original plan.

For the coker octagon repairs, a special work platform was designed and built that hung from the bottom side of the concrete soffits. The platform was comprised of steel I-beams and wood decking. The system was pre-fabricated and installed during the turnaround. The pre-engineering work platform was quicker to install than standard scaffold systems and also functioned as the soffit formwork for our repairs. 

This repair project provided the owner with a more durable structure that can withstand the coke cutting cycles for more than 20 years. In addition, it restored the load carrying capacity to withstand the additional forces of delta valves.