After Mexico City Earthquake, the PEMEX (Petroleos Mexicanos) Refiney located in Salina Cruz, Oaxaca, Mexico required a shut down to inspect some vapor lines connected to turbines, steel structures and foundation. This system has been operating for 40 years without any problems.
After a visual inspection on the lines, it was found out that several spring supports are not working or are not set properly. In order to design and size the springs, a Piping Stress analysis was performed. The calculation shows several elements overstressed and the loads on nozzles exceding the allowable loads.
For safety requirements, the operator has decided to replace all the spring supports based on the stress analysis results.
As stress engineers, how can we justify that this system is failing according to Autopipe but it has worked for over 40 years without any issues?