PSI - Issue 3

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J.L. González et al. / Procedia Structural Integrity 3 (2017) 33–40 Author name / Structural Integrity Procedia 00 (2017) 000–000

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Fig. 7. Von Mises stress distribution of the coke drum skirt cracked and misaligned at the skirt junction, calculated by finite element analysis.

3. Rehabilitation The common sense would suggest welding the cracked line as the first rehabilitation method. Independently of the technical difficulty to realign the skirt junction, to machine the bevel butt joint and to stress relieve the weld, this certainly is not a permanent remedial action, since the drum movements and thermal expansions that caused the skirt junction cracking will be still present and active, thus causing the same cracking again, and perhaps in a shorter time. Other remediation methods that involve reestablishing the continuity between the skirt and the drum shell may suffer similar damages, i.e. cracking and bulging. The authors of this paper propose that a better solution is a reinforcement of the skirt, without welding the circumferential crack, designed in such way that the effects of the lateral and vertical movements of the drum, as well as the misalignment are mitigated. This reinforcement can be in the form of an orthogonal stiffened ring in the skirt and a stiffening ring with tripping brackets in the shell side, as depicted in figure 8. This solution will give a very high vertical stability to the skirt, provide a wider contact surface for the shell support, make an even distribution of the vertical load, even if there is a large lateral displacement, and will restrict the tilting movements of the drum.

Fig. 8. Conceptual design of a reinforcement to rehabilitate the coke drum skirt without welding the junction crack.