During last decade, customers’ requirements of Line Pipes and accessories became more and more stringent. This process is led by the exploitation of fields with more severe conditions of pressure, environment and temperature. For this reason, heavy wall products (both straight pipes and bends) need to be developed. A development program was carried out in order to satisfy more stringent requirements and higher wall thickness. The metallurgical approach to steel design aimed to improve the combination of strength and toughness and increase the control of hardness after quenching and tempering, preserving adequate weldability. Industrial trials were performed to manufacture 60 mm thick hot induction bends in grade X65. Characterization was carried out after various post bending heat treatments (quenching, tempering and post welding). The new low-C steel showed promising results. The full characterization of off-line Q&T bends at various locations (tangent length, transition zone, and bend body) confirmed the achievement of X65 grade, with hardness HV10 < 240, Charpy V-notch transition temperature < −60°C, Crack Tip Opening Displacement > 0.7 mm at −45 °C, and very good HIC and SSC resistance.
Tenaris and Centro Sviluppo Materiali (CSM) are carrying out a Joint Industrial Project aimed at developing heavy wall line pipes. The suitability for very severe applications, involving high service pressures and temperatures, the latter causing large strain fluctuations, in presence of an aggressive sour environment, is analyzed both theoretically and experimentally, including small and full pipe models and tests. The full project program aims at developing a new generation heavy wall product, supported by a comprehensive laboratory analysis of the material response under severe mechanical loading in aggressive environment and a full scale testing program, including both pipe and girth weld. Both investigations are mainly addressed to basic understanding of impact on design criteria of interaction between severe loading and aggressive environment. Four papers, [2], [3], [4] and [5], have been already presented, in previous OMAE conferences, on this project. The present paper focusses on the full scale testing performed on strings of pipeline consisting of different pieces of pipe. In particular, two full scale testing have been performed applying the severe straining sequence defined as extreme in term of resistance against ratcheting, also involving plastic straining, as deduced in a previous work inside the project. The loading sequence was applied in global strain control, averaged on the whole string length, but necessarily the local distributions of strain differs in the three pieces of pipe. Analytical considerations are done about the expected straining behaviour and experimental results confirmed the theoretical considerations. The high strain hardening capability of the X65 steel pipes, metallurgically designed for strain based applications, guaranteed a good recovery of any non-homogeneity in straining, both during cycling that in larger axial deformation of the string. During severe cycling in elastic-plastic regime in presence of pipe internal pressure, the strings demonstrated good resistance to ratcheting. In fact, due to the material capability to redistribute the cycling strains along the whole sample length, any section experienced limited ratcheting with unreversed circumferential expansion, during cycling, well within limits of tolerability. It is worth noting that, even in presence of severe cycling conditions, both on-shore type girth welds (SAW for double joint) and off-shore type (GMAW in Narrow Groove Bevel Preparation) preserved their integrity with no cracking or other damage.
Tenaris and Centro Sviluppo Materiali (CSM) launched a Joint Industrial Project aimed at developing heavy wall line pipes. The suitability for very severe applications, involving high service pressures and temperatures, the latter causing large strain fluctuations, in presence of an aggressive sour environment, is analyzed both theoretically and experimentally, including small and full scale pipe models. The full project program aims at developing a new generation heavy wall product, supported by: comprehensive laboratory analysis of the material response under severe mechanical loading in aggressive environment; and full scale testing program, including both pipe and girth weld. Both investigations are mainly addressed to the basic understanding of impact on design criteria from interaction between severe loading and aggressive environment. Three papers have been already presented, in previous OMAE conferences, on this project. In the present paper, main outcomes of laboratory testing activities of the above program on girth welds for double jointing (fill passes by Submerged Arc Welding) are reported. A fitted for purpose special testing program, including mechanical and SSC laboratory scale testing, has been executed. Full thickness longitudinal specimens were extracted crossing girth weld to apply severe strain cycling. The strain cycling has been defined as extreme in terms of resistance against ratcheting for the pressurized pipeline, as deduced in a work reported in one of the previously mentioned papers. The girth welds exhibited very satisfactory performance during severe cyclic straining. Furthermore, mechanical and stress-corrosion properties of the As-Weld girth joint have been compared with the corresponding properties after severe straining and ageing. This comparison highlighted high level of mechanical and SSC resistance, even after the application of severe straining and ageing.
Tenaris and Centro Sviluppo Materiali (CSM) carried out a Joint Industrial Project aimed at developing heavy wall line pipes. The suitability for very severe applications, involving high service pressures and temperatures, the latter causing large strain fluctuations, in presence of an aggressive sour environment, is analyzed both theoretically and experimentally, including small and full pipe models and tests. Five papers have been already presented on this project, in previous OMAE conferences. The present paper focusses on Lined Heavy Wall Pipes for the adoption in presence of extremely aggressive conveyed fluids. As in-service large strains are involved in the JIP envisaged scenarios, the risk of liner buckling is necessarily concerned. To evaluate the suitability of lined heavy pipes in presence of in-service severe straining, a finite element study has been performed aimed at quantifying the limits for pipe deformability without occurrence of liner buckling. Two full scale tests on lined pipe strings have been also performed, imposing the very severe straining sequence previously determined as extreme for pipeline resistance. The sequence has been applied both in pure axial (tensile / compressive) loading and in bending conditions. The latter has been performed in very low internal pressure conditions to conservatively verify the resistance to liner buckling. In both cases, the lined heavy wall pipe resisted the severe straining sequence without any liner buckling, pipe excessive ratcheting or any other damage compromising the serviceability of the pipe.
Oil and Gas industry in the last decades has increased the use and need of heavy wall thickness line pipes, in particular for onshore / offshore high pressures and high temperatures (HP/HT) and offshore deep water / ultra-deep water applications. The paper presents the results achieved by Tenaris on seamless line pipes in grades X65/X70, according to API 5L / ISO 3183, with wall thickness in a range from 40 to 60 mm and diameter between 6 5/8” and 16”, produced by hot rolling process followed by quenching and tempering. Such line pipes are able to withstand very demanding conditions, like sour environment, very high pressure and wide temperature range. In this publication, the main outcomes of laboratory testing activities on the mentioned materials will be presented as part of heavy wall line pipe qualification. For this purpose, a special testing program, including mechanical and corrosion tests, has been executed. Material demonstrated an excellent behaviour, exhibiting both mechanical, toughness and stress corrosion properties suitable for the envisaged harsh applications.
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