This called for de-rating of the vessel as well as providing an external support system which would be capable of carrying the design wind load. Hence, the available section modulus in shell ring # 3 was not sufficient to carry out the design wind loading for the vessel. The shell ring # 3 (from bottom) had corroded from original thickness of 0.375” to a thickness of 0.135” and shell ring # 2 (from bottom) had corroded from original thickness of 0.500” to current thickness of 0.270”. Fitness for service evaluation was performed for a tall vessel which had severe corrosion for two courses of shell rings.Using the pressure drop guidelines specified by these set of calculations, the plant increased the safe operating time before the next shut down.
#Structural analysis examples for reading code
At this pressure drop, the code allowable stress criteria were not satisfied and the structural components start to yield. The maximum allowable pressure drop for the failure case was specified to be 158 psig. At this pressure drop, all the design criteria were satisfied and this pressure drop was safely permissible. The maximum allowable pressure drop for the upset case was specified to be 138 psig. The design pressure drop through the reactor bed was 100 psig. For each of these cases, the limiting pressure drop for the three distinct structural beams and the associated grating support was calculated. These structural calculations were automated using MathCAD to calculate the maximum allowable pressure drop through the bed for design case, upset case and failure case. The structural calculations (per AISC code) were performed to check the stresses in the beams, welds and the beam support grating. The intent was to shut down the reactor before the pressure drop reaches a scenario causing the structural failure of the bed. This was causing significantly higher pressure drop on the bed leading to very high stresses in the beams. The bed was getting plugged during operation. The packed bed had 3 distinct stainless steel fabricated beams. Fitness for service evaluation was performed for the top bed of a stainless steel reactor with the intent to calculate the maximum permissible pressure differential allowed by the structural capacity of the bed.A few examples of Structural analysis performed by Pressure Equipment Engineering Services, Inc.