The general aim of this research is to generate specific know-how concerning the development and possible safe and reliable use of spiral welded pipes in demanding onshore and offshore applications, requiring good performance under the application of large strains. The outcome of this research can also be used as technical basis for improving existing international standards and guidelines for oil and gas pipelines, addressing the design and safety of spiral-welded pipelines.
Spiral welded pipes have become an accepted and very competitive alternative to longitudinal welded pipes for gas and oil pipelines. In the field of onshore pipelines, spiral welded pipes have gained large market shares. Recently, spiral welded pipes have become attractive for off-shore pipelines as well because production limitations with respect to wall thickness have been overcome. The increasing demand for gas requires reliable and economical transportation options from remote regions to the final market. In this scenario, High-Pressure/Large-Diameter transmission pipelines, made of High Strength Steel appear to be the most efficient solution, combining technical feasibility, cost effectiveness and reliability over the entire pipeline lifetime span. Nevertheless, those pipelines may pass through harsh and hostile terrains, and therefore, the effects of different geo - hazards must be faced.
This research combines experimental testing, analytical effort and numerical simulations to evaluate the strain capacity of large-diameter spiral-welded pipes subjected to bending and axial loads with or without the presence of internal/external pressure. Furthermore parameter studies will be performed to quantify the various influences on the load deformation behaviour within the range of practical geometries and steel grades for spiral welded pipes. Based on the results of FE numerical analyses, the validity of several existing formulae, developed to predict pipeline local buckling resistance is examined, considering pipeline material and geometrical parameters. Numerical modelling of the material behaviour during the spiral-welded pipe manufacturing process and numerical determination of the residual stresses will be conducted taking into account the Bauschinger effect and imperfections (in particular out of roundness, e.g. near spiral welds and girth welds).
The results of this research indicate that an integrated investigation that combines full-scale testing and numerical analyses constitutes a powerful tool to support the strain-based design of large-diameter spiral-welded pipelines.

Daniel Vasilikis
Spyros A. Karamanos

In Conference Proceedings

• G. Demofonti, A. Lucci, A. Fonzo, J. Ferino, C. M. Spinelli, P. Pappa, Vasilikis, D. and Karamanos, S.A., “Bending Strain Capacity of Large-Diameter Steel Pipes”, Rio Pipeline Conference, Rio de Janeiro, Brazil, September 2013.