No abstract

The present research focuses on the investigation of an in situ hydrogen charging effect during Crack Tip Opening Displacement testing (CTOD) on the fracture toughness properties of X65 pipeline steel. This grade of steel belongs to the broader category of High Strength Low Alloy Steels (HSLA), and its microstructure consists of equiaxed ferritic and bainitic grains with a low volume fraction of degenerated pearlite islands. The studied X65 steel specimens were extracted from pipes with 19.15 mm wall thickness. The fracture toughness parameters were determined after imposing the fatigue pre-cracked specimens on air, on a specific electrolytic cell under a slow strain rate bending loading (according to ASTM G147-98, BS7448, and ISO12135 standards). Concerning the results of this study, in the first phase the hydrogen cations’ penetration depth, the diffusion coefficient of molecular and atomic hydrogen, and the surficial density of blisters were determined. Next, the characteristic parameters related to fracture toughness (such as J, KQ, CTODel, CTODpl) were calculated by the aid of the Force-Crack Mouth Open Displacement curves and the relevant analytical equations.

No abstract

Large-diameter thick-walled steel pipes during their installation in deep-water are subjected to external pressure, which may trigger structural instability due to pipe ovalization, with detrimental effects. The resistance of offshore pipes against this instability is affected by local geometric deviations and residual stresses, introduced by the line pipe manufacturing process. In the present paper, the JCO-E pipe manufacturing process, a commonly adopted process for producing large-diameter pipes of significant thickness, is examined. The study examines the effect of JCO-E line pipe manufacturing process on the external pressure resistance of offshore pipes, candidates for deepwater applications using nonlinear finite element simulation tools. The cold bending induced by the JCO forming process as well as the subsequent welding and expansion (E) operations are simulated rigorously. Subsequently, the application of external pressure is modeled until structural instability (collapse) is detected. Both the JCO-E manufacturing process and the external pressure response of the pipe, are modeled using a two-dimensional (2D) generalized plane strain model, together with a coupled thermo-mechanical model for simulating the welding process.

The current thickness limit of the HFI technique is about 20,6mm for grades up to X80. It is mainly governed by the necessary forming load, the coil edge formability and above all the optimisation of the power/heat input requirements on the weld seam area. The availability of hot rolled coils in thicknesses up to 25mm has made possible the exploitation of the HFI limits to such thicknesses. Following the successful industrial HFI welding production of 609,6mm (24″) × 25mm thick wall pipes at the CPW-Thisvi mill, the current paper deals with the development of the process regarding forming, welding, process automation and NDE inspection techniques for thicknesses up to 25mm. The latter made possible the broadening of the HFI process limits, currently for grades up to X60. Details of the technology used are described along with the investigation of the influence of welding and post-weld heat treatment (PWHT) cycles on the microstructure of the welding zone (WZ) and heat affected zone (HAZ) of the hot-strip micro-alloyed high strength low alloyed (HSLA) steel chosen. Mechanical testing of the pipe body and weld seam was used to characterise their performance. The dimensional tolerances of the pipe products are also described. Results of the study showed properties which were uniform and satisfied API 5L requirements. The above research demonstrates that the HFI technique has a clear potential to provide the energy market with lower cost-options for the construction of heavy wall pipes.

The recently constructed Bord Ga´is E´ireann, Curraleigh West to Midleton pipeline runs due north from the Midleton compressor station near the city of Cork in Southern Ireland. The 47.5 km, 610mm outside diameter pipeline, comprises over 30 km of 9.5 mm and 17 km of 19.1 mm wall thickness L450MB (X65) grade pipe. The pipe for the project was produced by Corinth Pipeworks (CPW), at its state of the art HFW pipe mill at Thisvi, Greece and represents a first in terms of the quantity of 19.1 mm L450MB (X65) HFW pipe produced by the mill for a specific project. The paper outlines the engineering approach adopted for the pipeline before describing in detail the production challenges faced by the pipe mill in successfully completing this demanding pipe order. Production of the 9.5 mm wall thickness pipe was not anticipated to present any particular difficulties. However, the principal concern associated with the manufacture of the 19.1 mm pipe was that the combination of wall thickness and strength level was toward the upper end of the commercially supplied wall thickness-strength combinations for HFW produced linepipe, particularly as the actual strength of the starting coil was well above the minimum specified level for L450MB (X65). In addition, to accommodate the demanding drop weight tear test (DWTT) toughness requirement the chemical composition of the 19.1 mm coil strip was above the permitted limits of the parent pipe standard EN 10208-2 [1] for the elements Cu & Ni, and the yield to tensile ratio was also above the 0.87 maximum level required by EN 10208-2 for L450MB (X65) grade pipe. Potential risks were therefore identified prior to production and mitigated by several methods detailed in the paper, including for example; increased initial production test frequency, close monitoring during pipe production, duplicate testing to verify mill results, identification of potential construction issues and weldability testing. A summary of production experience including statistical data for the production of both 9.5 mm and 19.1 mm pipe is presented. Also covered are the results of a supplementary investigation which makes a further assessment of the influence of the welding and heat treatment cycles on the final pipe properties. The paper concludes by referring to the overall successful construction phase of the project.

No abstract

No abstract