Spyros A. Karamanos, Ph.D. Department of Mechanical Engineering

Title:	STRUCTURAL INTEGRITY OF STEEL OIL & GAS PIPELINES WITH LOCAL WALL DISTORTIONS
Sponsor:	Ministry of Education
Program:	HRAKLEITOS - Funding of PhD dissertation research
Investigator:	Aglaia E. Pournara - PhD candidate
Objective:	The present research aims at estimating the residual structural capacity of oil and gas transmission pipelines of steel grade X52, which contain wall defects in the form of wall wrinkling (i.e. local buckling) or denting (Figure 1 & 2). The necessity of inspection and examination of pipe wall deformations, caused by external forces, is crucial especially for old pipeline networks, in order to safeguard their structural integrity and the unhindered flow of energy resources. Experimental and numerical research is being carried out in order to investigate the residual structural integrity of buckled steel tubes. A series of experiments on steel tubes will be carried out, where steel tubes of diameter-to-thickness ratio equal to 30 will be buckled or dented first using the appropriate mechanical equipment, and subsequently, the deformed tubes will be subjected to further monotonic and cyclic (bending and pressure) loading in order to estimate their residual strength and remaining fatigue life (Fig. 4). Furthermore, a series of small-scale tests on 30cm-long longitudinal strips extracted from the X52 pipes will be performed towards the thorough investigation of the cyclic behavior along the compression fiber of a dent/buckled region. Non-linear numerical analysis is already in progress in order to simulate the formation and the cyclic behavior of local buckles and dents (Fig. 5) according to the full and small-scale experimental procedure. Furthermore preliminary numerical analysis has been conducted in order to provide preliminary estimations about the stress-strain concentration factor at the critical region of buckled and dented pipelines under cyclic bending conditions. Further numerical investigation (Fig. 6) will be conducted in order to simulate the experimental procedure for each type of deformation and loading case in order to verify the experimental results and estimate the level of residual stress and strain distributions around the deformed area of the pipe wall. The ultimate objective of this present research emphasizes on the utilization of the experimental and numerical results for the development of design guidelines and methodologies, which will be employed for the inspection, estimation and possible repair of hydrocarbon steel pipelines with structural damages in the form of wall wrinkles.
Principal Investigator:	Spyros A. Karamanos
Budget:	45,000 Euros
Duration:	36 months (2010 - 2013)
Figures:	Figure 1 - Figure 2 - Figure 3 - Figure 4 - Figure 5 - Figure 6