THESSALONIKI – SKOPJE CRUDE OIL PIPELINE AT FAULT CROSSINGS – VERIFICATION STUDY V.K. Koumousis, C.J. Gantes, G.D. Boukovalas, C.K. Dimou and M. Ε. Lemonis Department of Civil Engineering National Technical University of Athens, GR-10682 Athens, Greece 1. SUMMARY This paper summarizes the results of a verification study of the effects of an eventual fault rupture on the Thessaloniki to Skopje Crude Oil Pipeline. Two cases are analyzed, one corresponding to a normal fault and the other to a strike-slip fault. The study is carried out using a nonlinear displacement-based finite element formulation. The analysis is based on two models; one employing pure beam elements and one employing shell and beam elements that can also consider internal pressure effects. The analysis results, including displacement and stress/strain distributions along the pipeline, are used to carry out strength and serviceability verifications and to formulate construction recommendations. 2. PIPELINE GEOMETRY AND MATERIAL At the specific locations of active faults crossings, heavy wall NPS 16 (Nominal Pipe Size 16” outside diameter) line pipes with a wall thickness of 8.74mm will be installed [1], made of API-5LX60 steel with Specified Minimum Yield Strength (SMYS) equal to 413.68MPa. The pipeline steel is modeled with a typical API-5LX60 tri-linear stress-strain curve [2]. Strain-stress points for the tri-linear model are: (2.25‰, 465.4MPa) and (4%, 515.7MPa), whereas the corresponding moduli of elasticity are E 1 =206.84GPa and E 2 =1.33GPa. The design pressure follows the guidelines of ASME B31.4 [3] and equals 10.2MPa. No special construction techniques are employed, but conformance to recognized codes of practice (DIN, BS, ASME, API and Greek Specifications) for construction, transportation, storing, placement, and backfilling is required. The nominal backfill cover varies from 0.6m in rocky areas to 0.90m in cross-country areas and 1.20m under major roads [1]. 3. FAILURE CRITERIA An upper strain limit of relative ground movements caused by fault rupture is specified and loading is displacement-controlled, exerted on the buried pipe by the displacement of its surrounding soil. Pipelines resist the imposed displacements mainly through axial (tensile or compressive) strains, thus it is more meaningful to talk in terms of strains than stresses. Pipeline steel can withstand tensile strains in excess of 4% without undergoing ductile rupture, but this limit is not acceptable for girth welds due to metallurgical alterations induced