The objective of this work is the evaluation of hydrogen effects on the martensitic transformation and strain hardening in Duplex Stainless Steels (DSS) SAF 2205 (UNS S32205/S31803). DSS are two-phase alloys (austenite and ferrite), which are used for applications requiring high mechanical strength, in corrosive environments. Therefore, it is necessary a better understanding of the phenomena involved on the hydrogen embrittlement. For this, in situ measurements of X-ray diffraction were made during tensile test in H 2 cathodically charging DSS 2205. The hydrogen charging reduces the stress relaxation, reducing the ductility and suppressing the hydrogen-induced austenitic to martensitic transformation. In addition, it also reduces the strain hardening (dislocation multiplication) in austenite. The strain hardening seems to have a higher influence than martensitic transformation on fracture process, even in absence of hydrogen.
Oil production in offshore areas has increased in recent years, especially with deeper water creating new challenges to be overcome. In this scenario, the mooring systems of floating units need to withstand higher operating loads. The mooring system is designed to keep the FPSO (Floating Production Storage and Offloading) properly positioned. Being fundamental to the integrity of risers and the platform itself, the failure can cause the overloading of other lines and generate the collapse of the whole mooring system in an extreme environmental situation, so the design and material selection are essential to the success of the venture. This work presents the investigation of the premature failure in some lines of the mooring system for an FPSO, in this case links in class R3. There were flaws in the weld between the link and the stud, with the subsequent complete failure of link. Some analyses were performed to understand the problem, including chemical composition, microstructural evaluation, hardness, corrosion potential, numerical analysis and fatigue tests. Finally, we concluded that the use of materials from different links to the stud generated a localized corrosion leading to increased local tensions and the failure by fatigue.
Design of steel catenary risers (SCRs) requires the use of connection hardware to decouple the large bending moments induced by the host floater at the hang-off location. Reliability of this connection hardware is imperative, especially in those applications involving high pressure and temperature fluids. One option for connection hardware is the metallic tapered stress joint. Because of its inherent density, strength and stiffness, steel is not well suited for these applications as it would result it excessive length and weight for deepwater applications. Titanium grade 29 (Ti 29) has been identified as an attractive material candidate for demanding stress joint applications due to its unique mechanical properties including greater flexibility, excellent fatigue performance, and high resistance to sour fluids. Industry has successfully used this technology in over 60 SCR applications. Titanium stress joints (TSJs) for deep-water applications are typically not fabricated as a single piece due to titanium ingot/billet volume limitations, thus making an intermediate girth weld necessary to satisfy length requirements. Fracture and fatigue performance of these welds in the presence of cathodic potential in seawater and galvanic potentials in sour production fluids that may produce hydrogen embrittlement effects must be assessed to ensure long term weld integrity. This paper describes a joint industry project (JIP) performed to qualify titanium stress joints welds for ultra-deep water applications under harsh service and environmental conditions. Fatigue crack growth rate (FCGR) results for Ti 29 1G/PA gas tungsten arc welding (GTAW) specimens in air, seawater under cathodic potential and sour brine environments under galvanic potentials are presented and compared to vendor recommended design curves.
Design of a steel catenary riser (SCR) requires the use of connection hardware to decouple the large bending moments induced by the host floater at the hang-off location. Reliability of this connection hardware is essential, particularly in applications involving high pressure and high temperature fluids. One option for this connection hardware is the metallic tapered stress joint. Titanium (Ti) Grade 29 has been identified as an attractive material candidate for demanding stress joint applications due to its “high-strength, low weight, superior fatigue performance and innate corrosion resistance”2. Titanium stress joints for deep-water applications are typically not fabricated as a single piece due to titanium ingot volume limitations, thus making an intermediate girth weld necessary to satisfy length requirements. As with steel, the potential effect of hydrogen embrittlement induced by cathodic and galvanic potentials must be assessed to ensure long term weld integrity. This paper describes testing from a joint industry project (JIP) conducted to qualify titanium stress joint (TSJ) welds for ultra-deepwater applications under harsh service and environmental conditions. Corrosion-fatigue crack growth rate (CFCGR) results for Ti Grade 29 1G/PA gas tungsten arc welding (GTAW) specimens in seawater under cathodic potential and sour brine under galvanic potentials are presented and compared to vendor recommended design curves.
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