Ettore Anelli

Development of High Strength 100 ksi Seamless Weldable for Deepwater Riser Application

The deepwater and ultradeepwater production and exploration technical demands are increasing on a daily basis. The benefit of having pipes with high strength and reduced wall thickness is very well recognized by all the oil community. In order to develop a high strength seamless 100 ksi weldable riser, a Joint Industrial Development Program (JIP) was launched in 2003. This paper describes the results of the first phase of this JIP, devoted to the development and production of seamless 100 ksi pipes. A detailed metallurgical analysis, including the role of chemical composition and quenching and tempering process conditions on the microstructure and precipitation was performed. The influence of the type of microstructure on strength, toughness and fracture mechanics behavior was studied in detail for both laboratory and industrial materials. The 100 ksi grade was accomplished for seamless pipes with wall thickness of 16 mm and 25 mm. The second phase, devoted to evaluate field weldability of this new product, is in progress.Copyright

Seamless Pipes of High Strength 100 KSI Grade

A joint industrial program (JIP), termed “Seamless 100 ksi weldable” was launched in order to address the complex design issues of high strength Q&T seamless pipes for ultra deep water applications. The JIP was split in two main phases, the first one devoted to the development and production of seamless pipes, with minimum yield strength of 90 ksi (620 MPa) to 100 ksi (690 MPa), and the second one to evaluate their field weldability. Phase I was recently completed. The role of chemical composition and Q&T process conditions on microstructure and precipitation was analyzed, together with relevant effects on strength and toughness, for both laboratory and industrial steels. The main microstructural features which control the strength-toughness combination of these high strength Q&T steel grades were identified and results were exploited for the set-up of a production route for pipelines and risers. The 100 ksi grade was achieved in 16 mm (0.630 in) and 25 mm (0.980 in) WT pipes. Phase II is in progress.© 2006 ASME

Sour Resistant High Strength Seamless Pipes for Risers

In case of a Weld On Connector’s riser using ASTM A182 F22 forged joints, high strength (SMYS of 80 ksi) steel pipes for sour service (hardness below or equal to 250 HV10) suitable for welding to the connectors are required. Welding is challenging because of the Post Weld Heat Treatment (PWHT) needed to reduce the hardness in the F22 HAZ while maintaining the required strength in the pipe. Theoretical evaluations were performed by means of metallurgical models and a potential solution was identified in grade P22-like steel (2¼ Cr - 1 Mo), with minor modifications with respect to the standard ASTM A335 and supplied in Q&T condition. A trial heat was cast and hot-rolled into pipes. After water quenching, the response to tempering was assessed by means of laboratory heat treatments and subsequent mechanical testing, together with metallurgical examination. Simulated PWHTs were also performed on Q&T material. 80 ksi grade P22 seamless pipes were finally produced and qualification involved mechanical testing before and after simulated PWHT: SMYS of 80 ksi and HV10 ≤ 250 requirements were met. The material also exhibited excellent toughness and resistance to HIC and SSC cracking.Copyright

Austenite Stabilization by Quenching and Partitioning in a Low-Alloy Medium Carbon Steel

Innovative treatments like quenching and partitioning (Q&P) have been recently proposed to improve the combination of strength and ductility of high strength steels by stabilization of significant fractions of retained austenite in a microstructure of tempered martensite. The decomposition of austenite into bainite and carbides precipitation are the two main competitive processes that reduce the content of retained austenite achievable at room temperature. A medium carbon low-silicon steel (0.46% C and 0.25% Si) has been studied to identify in which limits the austenite can be enriched in C and stabilized by Q&P, although a silicon content well below 1.5%, commonly used to retard cementite precipitation, is adopted; indeed, high Si contents are detrimental to the surface quality of the product due to the formation of adherent scale in high temperature manufacturing cycles. The heat treatments have been carried out with a quenching dilatometer, investigating the carbon partitioning process mainly below Ms, where cementite precipitation is not activated. The dilatometric curves show the progressive enrichment of carbon in the untransformed austenite and the occurrence of austenite phase transformation during the isothermal holding below Ms. A range of temperatures and times has been found where a content of about 10% of retained austenite can be stabilized at room temperature, a percentage much lower than the theoretical maximum achievable with the carbon content of this steel.

Bends for Critical Line Pipe Projects: Advantages of the Off-Line Full Quenching and Tempering

Recent trends for linepipe projects reflect a sustained increasing complexity: Sour Service (SS), High Temperature & High Pressure (HT/HP) field conditions, deep and ultra-deep water oil and gas transportation, Artic and Artic “alike” areas. This reflects into stringent requirements for manufacturing and testing of the concerned products, which are not only the straight pipes but also a number of accessories, among which bends are the ones presenting the most complex combination of critical issues. As long as a whole chain reliability standpoint is assumed as the main concern, the design, production and supply of the bends have become a key stage within a linepipe project. Bends for linepipe projects are produced in general by hot induction bending (HIB). Two different fabrication routes can be clearly identified: HIB followed by Stress Relieving (SR) and HIB followed by off-line full quenching and tempering (QT X60 to X70 steel grades, different bending and post-bending heat treatments conditions and mother pipe chemistries. For each analysed item, the final bend, the corresponding mother pipe and samples taken in as-bent / as-quenched (TR / QT) conditions were fully characterised in terms of mechanical properties, hardness profiles and microstructure features. As a result, a much better performance was found for the bends produced by the off-line full Q&T method, principally due to the better quenching efficiency with respect to the in-line system. Production of bends through out the traditional method can be seen as a reliable option for bends which are not going to face hard conditions in the field, and therefore the corresponding specification requirements are no stringent as well (i.e. X52 grade or lower, Charpy tests required at 0°C or higher temperature, no corrosion tests required, etc.). If either stringent conditions are required or X60-X80 steel grades are involved, the off-line quenching tank route becomes the reliable option.Copyright

Ultra Heavy Wall Linepipe X65 for the Most Stringent Applications: Metallurgical Design and Industrial Development

Offshore industry has evolved to meet numerous challenges, e.g. deep water, high currents, high pressure and high temperature (HPHT), and sour reservoirs, facing deepwater exploration. The trend in flowline specifications for deepwater offshore fields is a consequence of complex oil-gas field conditions, such as HPHT and developments in design criteria (i.e. limit state design), welding and laying technologies. The technological evolution exhibits a trend towards an increasing wall thickness (WT) to provide sufficient resistance for the very high operating pressures. Furthermore, the pipelay operations, especially when linepipes are installed by means of the reel laying method, cause repeated plastic bending and straightening deformation cycles. These cyclic loads affect final material stress-strain properties. Reeling is currently applied to an increasing range of pipe geometries, being the present limit given by pipes with 16″ outer diameter (OD) and 30 mm wall thickness (WT). Other pipeline installation techniques, for example, J-lay, S-lay and steep S-lay also introduce plastic strain. All previous factors mentioned before and adding one more variable when exploring and producing in regions alike to the Artic where low temperatures implied several material challenges calls for high performance seamless pipes tailored to the specific application required by the oil and gas industry. In this paper, a description is given of the results of latest fundamental studies on high-strength heavy-wall steel materials manufactured by Q&T processing. This work is part of an on-going development program on high performance heavy wall seamless pipes for special applications such as HPHT, low temperature design criteria, sour requirements and studying the material under the strain based design criteria involving metallurgical modeling, laboratory tests, industrial trials and advanced metallographic examinations. The most recent findings and overall conclusions are reported hereafter, these results have been exploited by Tenaris to manufacture a limited production seamless pipes in a wall thickness range from 40 mm to 48 mm in steel grade X65 Sour Service.© 2009 ASME

Development of High Steel Grade Seamless X100 Weldable

The technological evolution in the offshore sector points out a trend towards an increasing use of high strength steels (grade 80ksi and higher), for both pipelines and risers. Pipeline specifications for deepwater offshore fields demand developments in design criteria (i.e. limit state design), welding, installation, and laying technologies. As long as the market goes deeper in offshore exploration and production, the market trend is to use heavier pipes in steel grade X65/X70 and some technological limits from several fronts are faced and more attractive becomes for the market to have a lighter high strength 100ksi seamless steel grade. The joint industrial program (JIP), termed “Seamless 100 ksi weldable” launched by Tenaris in order to address the complex design issues of high strength Q&T seamless pipes for ultra deep water applications has been finalized. The 100ksi steel grade has been achieved in two wall thickness 16 mm and 25 mm. The main results from both phase I devoted to the development and production of seamless pipes with minimum 100ksi and phase II devoted to evaluate the high strength seamless pipe weldability will be addressed in this paper. Main microstructural features promoting the best strength-toughness results obtained from phase I and the results from phase II, where the heat affected zone (HAZ) characterization made using stringent qualifying configuration such as API RP2Z and the promising results after qualifying the girth welds simulating a typical offshore operation and the Engineering Critical Assessment for installation will be addressed. The results from this development are of interest of all oil & gas companies who are facing as an output from the design project analysis the need to have high strength seamless pipes.© 2008 ASME

Effect of Reel-Laying Simulation on Mechanical Performance of Flowlines

In this work, major efforts were devoted to a full understanding of the effect of the plastic deformation pattern which is typical of reeling on the in-service mechanical performance of quenched and tempered (Q&T) seamless pipes. This was performed by both laboratory multiple plastic straining cycle (MPSC) tests and full-scale reeling (FSR) trials. Different steel grades were investigated with and without aging after single deformation and MPSC/FSR. All materials showed similar deformation behavior. In MPSC tests and FSR trials, the direction of the last deformation step influenced the mechanical behaviour. Finishing with compression gave a slight reduction in YS, whereas subsequent aging gave a YS value similar to that in the as-received condition. Leaving the last step in tension, an increase in YS was observed and subsequent aging gave a further increase to a level similar to that of conventional tensile straining plus artificial aging. In terms of toughness properties (CVN energy, 50%FATT, CTOD) there was no significant effect of reeling plus aging process. Also girth welds were tested: no significant effect of reeling plus aging process was pointed out with respect to the as-received situation for both HAZ and weld metal. The behavior of deformed and aged material was explained in terms of work-hardening, Bauschinger and bake-hardening effects.Copyright