A Fitness-for-Service evaluation was conducted on a tank for a brewery. The evaluation was conducted in accordance with API 579-1/ASME FFS-1 2007 and good engineering practice.
The evaluation showed the stresses in the bottom head in the area of the supports are significantly greater than the allowable stress limit. Considering the corrosion of the tank was less than 0.0625 inches yet still had stresses greater than the allowable limit, it is suspected that the original design calculations did not consider the effects of the supports on the tank. This is evident in that the maximum allowable working pressure (MAWP) would be greater than the operating pressure if the areas of the supports were ignored.
Other analyses were performed, and it was concluded that the tank in its current condition no longer met the current industry accepted safety margins and should be removed from service.
– Fitness For Service
– (PDF) “Weld Defects and Failures: Quantifying Fitness For Service – How Finite Element Mathematical Simulations can Mitigate Risk, Cut Costs and Improve Overall Safety”
– Publications – Heat Exchangers, Pressure Vessels, Welds and Other Applications, Fatigue, Elevated Temperature