Industrial Structure Repair Case Study: Structural Assessment and Repair Prioritization

Industrial structures in oil refineries face unique challenges. Aside from the highly corrosive environments typically found within refinery processing units, the equipment supported by the structures can pose serious risks of fire. For example, many vessels containing flammable hydrocarbons operate in excess of 900 degrees Fahrenheit (482° C). Furthermore, no new major refineries have been built in the United States for over 30 years and many structures are nearing or exceeding the end of their design life throughout our nation’s refining infrastructure. All of these factors are contributing to a widespread need for structural rehabilitation. Another issue that is becoming more prevalent throughout the industry is damage caused by fireproofing deterioration on structural steel members. In the event of a fire, steel structures need adequate protection from high heat until emergency responders arrive. Protection is generally provided by concrete cast in place around critical structural steel members. This method provides adequate fire ratings; however, if not applied and maintained correctly, concrete fireproofing may result in significant structural deficiencies and safety hazards in the long term. This case study will focus on the rehabilitation of a fluid catalytic cracking (FCC) unit at a Midwest refinery and is targeted at structural design, analysis, and inspection professionals. A structural assessment of the 12-story braced frame structure was performed in response to a connection failure resulting from corrosion due to moisture trapped in the mastic fireproofing material. Because of the size of the structure and the extents of deterioration, a systematic approach was required to develop a long-term rehabilitation strategy. A detailed field inspection of the structural members was performed in conjunction with the development of a full structural model. In pairing the results of the field investigation with the utilization ratios obtained from the model, a practical rehabilitation strategy was developed.