PSI - Issue 5

Rui F. Martins et al. / Procedia Structural Integrity 5 (2017) 640–646 Author name / StructuralIntegrity Procedia 00 (2017) 000 – 000

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Fig. 3. (a) Maximum principal stress distribution at the welded joint between the exhaust pipe and the intermediate supporting ring considering the use of AISI 316L stainless steel (SS) in all the structural parts; (b) Maximum principal stress distribution at the welded joint between the exhaust pipe and the intermediate supporting ring considering the use of 445M2 SS in all the structural parts; (c) Maximum principal stress distribution at the welded joints between the lower flanges and the exhaust pipe considering the use of AISI 316L SS in all the structural parts; (d) Maximum principal stress distribution at the welded joints between the lower flanges and the exhaust pipe considering the use of 445M2 SS in all the structural parts.

4. Conclusions

The following main conclusions could be drawn:

• The current exhaust system ’s design led to thermal fatigue crack initiation and propagation, because the thermal expansion on the exhaust system is highly constrained by the existing reinforcement ribs and support rings and due to the big thickness difference between the plates of the exhaust system; • The use of a 445M2 ferritic marine type stainless steel resulted in lower induced stress at the critical regions, which could lead to an increase in the fatigue life of the exhaust systems under study. These results are mainly influenced by the lower thermal expansion coefficients of the ferritic stainless steel in comparison to the austenitic stainless steels; • The uniformity of the plate s’ thicknesses at the critical regions of the exhaust systems under study also induced stress reduction; • Frequent surveys during service should be carried out in order to prevent crack propagation from the weld toes, and hence aiming to increase the overall fatigue life of the exhaust systems. Also, high quality fabrication is required in order to avoid the presence of initial defects in the structure.

Acknowledgements

The authors would like to thank the Portuguese Foundation for Science and Technology through project ref. UID/EMS/00667/2013.

References

ASM Specialty Handbook  – Stainless Steels. In: J. R. Davis and Davis & Associates, editors. ASM International  – The Materials Information Society; 1994