Furnace Coil Failure Analysis Case Study

Problem

The client hired KHE to determine the root cause of an unacceptably high rate of ethylene furnace coil tube failures and to provide an assessment of the entire process side of the furnace system.

Solution

Using the integrated systems approach, KHE first developed a pipe stress model of the coil system and then analyzed an initial heat and mass transport model. After reviewing the process procedures, we developed a 2-D Computational Fluid Dynamics model of the firebox and tube. This provided a comprehensive view of the process, mechanical, and material interactions and established a baseline for subsequent work. A review of the process procedures found good descriptions for changeovers and decoking, but did not specify ramp conditions with detailed control parameters. The coil counterweight system, modified from original design, could allow accelerated creep to occur with the elevated temperatures being the driving factor. The decoke procedures needed more control variables for changeovers and decoking. The coil was highly sensitive to the process flow rate, to the coke layer, and to the coke layer conductivity. CFD results indicated that the circumferential temperature differences along the coil may have affected the structural stability. All of these factors contributed to the likelihood of tube failure during operation. Detailed recommendations were given to improve performance and reliability.

Results

New operating procedures were developed and implemented, resulting in more efficient and reliable production.