**5. Conclusions**

The purpose of this study is to ensure that in case of an extreme event, such as a water-hammer, the pipeline system will perform its intended function: position retention (the pipeline does not fall), leak tightness (the pipeline does not leak), and operability (the pipeline system delivers and regulates flow). However, when the pipeline is suspended, other constraints should be taken into account, due to the serious risk of damage by pipe buckling due to too high bending.

Based on existing pipeline damage, the structural flaws of the suspending oil pipeline were modelled using a finite element method. The suspending pipeline was calculated for two different combinations: ULS1-maximum overloading and ULS3-live. For the first, the structure fulfilled the safety conditions, unlike the ULS3 combination, where the standard design specifications failed in all aspects: (i) maximum pipeline bending stress; (ii) maximum deflection at mid-span; (iii) maximum acceptable stress; and (iv) damping limit. By using a moving point load in ULS3, the maximum mid-span achieved in the simulation results (*i.e*., 702.40 mm) are validated with the *in situ* measurements (*i.e*., ~750 mm).

The structural model can be used for simulating real extreme events where the maximum pressure is lower than the critical pressure (*i.e*., when extreme conditions are guaranteed). Thus, assuming here the water–hammer event as the maximum point load that moves along the pipeline, the results obtained give a good approximation of the real case and can be adopted by engineers and designers to meet pipeline protection standards.

**Acknowledgments:** This research was funded by the Portuguese Foundation for Science and Technology (FCT) through the Doctoral Grant—SFRH/BD/68293/2010 of the first author. Also, thanks to CEris (Civil Engineering Research and Innovation for Sustainability) of the Department of Civil Engineering, Architecture and Georesources, Instituto Superior Técnico (IST), Universidade de Lisboa.

**Author Contributions:** Mariana Simão simulated the accident according to the data, kindly lent by Igor Orynyak; Helena M. Ramos and Jesus Mora-Rodriguez analyzed the data; All authors contributed reagents/materials/analysis tools; Mariana Simão wrote the paper. Helena M. Ramos and Jesus Mora-Rodriguez reviewed the manuscript.

**Conflicts of Interest:** The authors declare no conflict of interest.
