Impact against empty and water-filled X65 steel pipes – Experiments and simulations

Eur. Phys. J. Spec. Top.

Hopperstad

2016

Abstract. Anchors or trawl gear occasionally impact offshore pipelines, resulting in large local and global deformations. Impact velocities are typically less than 5 m/s, but local strain rates may be very high. In this study strain rate effects in an X65 offshore material was characterised by split Hopkinson bar tests, while the cross-section homogeneity and possible anisotropic behaviour were determined by quasi-static material tests. Further, dynamic impact tests at prescribed velocities were carried out on simply supported full scale X65 steel pipes. Next, deformation-controlled quasi-static tests with the same boundary conditions were conducted. The level of deformation in the quasi-static tests were set to be equal to what was attained in the dynamic tests. Finally, an assessment of the differences between the dynamically and quasi-statically loaded pipes was made in terms of force-displacement response, energy absorbed, and fracture. An optical light microscope and a scanning electron microscope were used to investigate fracture surfaces arising from the various tests.

Section: Component Tests 31 Setupmentioning

confidence: 99%

Dynamic versus quasi-static loading of X65 offshore steel pipes

Kristoffersen

Eur. Phys. J. Spec. Top.

Hopperstad

2016

“…These pipes have been empty, filled with a variety of different media or pressurized. Impact against submerged pipelines has been studied by Longva et al (2013) and Kristoffersen et al (2013b;2014). However, none of these studies have investigated the impact properties of pipe fittings with a deviation in quality.…”

Section: Introductionmentioning

confidence: 99%

Influence of sigma-phase precipitation on the impact behaviour of duplex stainless steel pipe fittings

Marken

Ships and Offshore Structures

Rørvik

et al. 2014

In this study, the effect of sigma phase precipitation in duplex stainless steel (grade 2205) pipe fittings collected from top-side process systems offshore was investigated under realistic loading conditions. This was done by conducting quasi-static and dynamic impact tests on 3" fittings with nominal outside diameter of 88.9 mm, nominal wall thickness of 3.05 mm and D/t-ratio of nearly 30. The fittings had a sigma phase level between 0 and 15 vol.%, and were loaded by a massive steel indenter with a hemispherical nose of 25 mm radius. In the quasi-static tests, the loading rate was 2 mm/min, while in the dynamic tests the impact velocity was varied between 5 and 10 m/s.A few dynamic impact tests on 2" fittings with an increased wall thickness and low sigma phase levels were carried out for comparison, while some 3" fittings were pre-charged with hydrogen before dynamic testing to examine the effect of sigma phase on cathodic protected subsea components. When the sigma phase level was low (i.e., 5 vol.%   ), no evidence of fracture was found in any of the pipe fittings, whereas at higher sigma phase levels

“…8, is largely a recreation of the experimental setup, and this has been done using the commercially available finite element solver ABAQUS [36]. Even though the material 220 exhibits strain rate sensitivity [44], this effect is omitted as the tests herein are quasi-static. With a fairly time consuming experimental procedure involving contact, the optimal numerical setup is not immediately obvious.…”

Section: Numerical Simulationsmentioning

confidence: 99%

“…The material constants are taken from a study using the exact same pipe material [44], and are listed in Table 1 where ν is the Poisson ratio and ρ s is the density. Bridgman's analysis [45] and an empirical relation [46] were used to obtain the equivalent stress from the measured major principal stress, and a least squares approach was employed to fit the constants σ y , R 0 and n to the Bridgman corrected data.…”

mentioning

confidence: 99%

“…Using an Eulerian mesh to this end is not necessary, as this technique is mostly intended for problems like fluid flow or liquid sloshing [69]. If, however, the change in volume during deformation alters the pressure, using some kind of fluid-structure interaction is helpful [44]. Another approach is to 515 mesh only the interior of the pipe with a mesh that is able to follow the deformation of the pipe (arbitrary Lagrangian-Eulerian method), thereby reducing the number of required fluid elements.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Combined three-point bending and axial tension of pressurised and unpressurised X65 offshore steel pipes – Experiments and simulations

Kristoffersen

2018

Marine Structures

Self Cite

Subsea pipelines are occasionally struck and hooked by objects such as anchors or trawl gear. The initial denting, followed by potential hooking and displacement of the pipeline, give rise to a complex load and deformation history. Transverse displacements cause a simultaneous increase in tensile axial forces, further complicating the load sequence. This study examines the effect of applying one of three different axial loads (zero, constant, and linearly increasing) to a pipe while simultaneously deforming it transversely. The three tests were repeated with an internal pressure of 10 MPa (100 bar), and all tests were recreated numerically in finite element simulations using both iterative (implicit) and non-iterative (explicit) approaches. As expected, adding an axial load increased the pipe's resistance to bending in terms of force-displacement, and the same can be said of including internal pressure. However, a more localised dent was observed in the pressurised pipes, which in turn could affect the onset of failure. The experimental results were well captured by the finite element simulations.