Antonio Lucci

Experimental and Numerical Investigation of Pressurized Pipe Elbows Under Strong Cyclic Loading

The present work examines the behavior of pipe elbows subjected to strong cyclic in-plane bending loading in the presence of internal pressure. In the first part of this work the experimental procedure is presented in detail. The tests are conducted in a constant amplitude displacement-controlled mode resulting to failures in the low-cycle fatigue range. The overall behavior of each tested specimen, as well as the evolution and concentration of local strains are monitored throughout the testing procedure. Different internal pressure levels are used in order to examine their effect on the fatigue life of the specimens.The above experimental investigation is supported by rigorous finite element analysis. Using detailed dimensional measurements and material testing obtained prior to specimen testing, detailed numerical models are developed to simulate the conducted experiments. An advanced cyclic plasticity material model is employed for the simulation of the tests. Emphasis is given on the local strain development at the critical part of the elbow where cracking occurs. Finally, the results of the present investigation are compared with available design provisions in terms of both ultimate capacity and low-cycle fatigue.Copyright

Ultra Heavy Wall Linepipe X65: Ratcheting in Severe Cyclic Straining

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 pipe models. 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 full scale testing program, including both pipe and girth weld. Both investigations are mainly addressed to basic understanding of impact on design criteria from interaction between severe loading and aggressive environment. Two papers have been already presented on this project, [2] and [3]. The present paper deals with the study, carried out in cooperation with Saipem Energy Services, aimed at setting up a tool for the prediction of ratcheting extent for the pipeline in pressure subjected to axial cyclic, even plastic, straining. In such conditions, ratcheting may develop in the circumferential direction, as a consequence of both material cyclic performance and bi-axial plastic flow. So, detailed characterization of material is required, as well as calibration of plastic performance parameters, particularly in relation to relevant modeling. The final objective of the study is to establish a threshold for the plastic strain development at peak load, beyond which circumferential ratcheting may develop. A numerical model was set up, on-purpose developed and implemented on commercial software, where reverse yielding is modeled by kinematic hardening referring to Von-Mises yield criterion. Use of relevant parameters describing/approximating the actual material response has been made, based on laboratory Multi Plastic Straining Cycling (MPSC) of pipe full thickness samples. Full scale testing of pressurized X65, 10 3/4″ OD × 46 mm WT linepipe has been performed including plastic axial and cyclic straining. A huge measurement campaign allowed to establish the relevant parameters that characterize the response from numerical modeling, facilitating the validation of the set up by comparing the actual ratcheting exhibited by the heavy wall pipe with predictions obtained by the model. Limits of current tools for numerical modeling are also shown, with some degree of dependence on applied straining sequence. Possible paths of numerical modeling improvement are then envisaged.Copyright

Pressurized Flanged Joints Subjected to Bending Cyclic Loading: Tests and Finite Element Analyses

Temporary ground deformations produced by strong seismic activity can result in severe cyclic loading applied to piping, fittings and components such as flanges, elbows, tee joints etc. The integrity of the piping system in such condition is of critical importance for the safety of petro-chemical plants or refineries. Among various reasons of failures under earthquakes, the accumulation of plastic strains due to cyclic bending loading of pressurized piping sections containing bolted flanged joints, have to be carefully considered. This paper reports the results of the experimental full scale tests performed within the RFCS INDUSE Project [1] on PN40 and PN63 piping sections containing bolted flanged joints subjected to monotonic and cyclic bending load, in presence of internal pressure. On the basis of the experimental results, a FE model adopting Lemaitre-Chaboche nonlinear kinematic hardening rule for the pipe material has been developed, allowing to extend the results of the tests by performing a study on the main parameters affecting resistance of the joint.Copyright

Strength and stability of High-Strength Steel tubular beam-columns

The present work examines structural strength and s tability issues for steel tubular beamcolumns made of high-strength steel. The tubular be m-column elements are widely used in a variety of structures such as buildings, off-s hore templates, masts, towers and cranes. The research focuses on the analysis of such member s for better understanding the benefits of using high strength steel in tubular structures. Extensive numerical work has been conducted on CHS high strength steel beam-columns of two cross sections and various values of member length. First, considering initial out-ofstraightness imperfection, structural member stabil i y curves are calculated. Subsequently, an extensive beam-column analysis takes place and i nteraction diagrams are provided as a result. The numerical results are compared with the predictions of the current Eurocode 3 provisions.

Ultra Heavy Wall Linepipe X65: Double Joint Girth Weld Performances for Severe Applications

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.© 2011 ASME