Umbilicals are important tubes assembly essentially used for subsea equipment controlling functions and fluid injection. Super duplex stainless steel 2507 (UNS 32750 / EN 1.4410) has been the historical grade used for its corrosion resistance and mechanical properties. The Oil and Gas industry is gradually working on the exploration and exploitation of offshore and deep offshore resources. These operating conditions lead to new philosophy in the design of subsea umbilicals, which are evolving to answer the needs of new functionalities. Recent years development supported by O&G operators, have seen innovative super duplex stainless seam welded tube solution being used for their high mechanical characteristics (YS0.2≥ 750 MPa; UTS≥ 900 MPa), tight dimension tolerances, and their ability to generate cost saving during installation. The specific metallurgical manufacturing route for the 2507 strip together with an efficient roll forming process and NDT control allows to obtained tubes for umbilicals which push the usual boundaries of utilization of this super duplex grades. In this paper, Hydrogen Induced Stress Cracking (HISC) behavior, possible failure mode of the super duplex stainless steel tubes exposed to cathodic protection in the termination unit, was extensively studied. A stress load of 110% YS0.2 was applied using a dead weight bench and the tubes performance was characterized after 500h of exposure in synthetic sea water under cathodic protection. Crevice corrosion is also a reported failure mode for umbilical tubes. Corrosion resistance of the 2507 seam welded tubes was also assessed in natural sea water in crevice conditions at open circuit potential (OCP). No failure was observed during the HISC testing in synthetic sea water after 500hours of exposure and no micro-crack was detected on the tubes after characterization. The metallurgical microstructure of the laser weld is not preferential initiation zone for crevice corrosion.

Offshore and deep offshore applications are coming more and more demanding regarding number of functionalities and water depth for umbilicals and especially regarding tubing. Oriented to new resources, the future developments (i.e. ultra deep offshore or abrupt margins) will be more difficult to operate leading to more and more stringent requirements for tubes. Thanks to its high mechanical properties and appropriate corrosion performances, super duplex stainless steel (SDSS) grade 2507 is already commonly adopted by main players of the O&G industry for a wide range of conditions. With a strong collaboration with one of the Majors, an innovative SDSS seam welded tube solution has been developed, exceeding the standards characteristics and opening new perspectives.An extensive program of qualification, here presented, has been built in collaboration between Oil Companies, Umbilical manufacturers and the tube supplier, to confirm the expected potentialities of the product. Based on more than 11000 results, this paper is presenting the performance of the product in terms of mechanical and corrosion properties. The associated innovative and robust process, here described, is able to guarantee tight manufacturing tolerances combined with a high quality level, offering attractive potential cost savings.

Since the last five years, an innovative technology for umbilical’s seam welded super duplex stainless steel tubes (grade 2507, UNS S32750) has been developed in order to meet new technical challenges. An extensive program of qualification, based on 4 dimensions covering the full manufacturing range, i.e. internal diameter and wall thickness, has been set. More than 11000 test results demonstrated the efficiency and the stability of the manufacturing process. The results were also confirming the expected properties of the tubes, in term of mechanical characteristics, corrosion resistance and manufacturing tolerances. At the end of this qualification phase, a Type Approval Certificate was delivered by an independent and official certifying authority demonstrating then, the suitability of the product for offshore static applications. The next step was to confirm the fatigue performance of the product to meet the requirements of umbilicals for dynamic applications. This paper describes how a dedicated fatigue test protocol has been jointly defined between a Major O&G player and the tube supplier. This protocol has been built in order to test the 3 dimensions already produced during the first step of the qualification, considering tube samples with and without orbital weld. Fatigue test programs are known to be very sensitive to the test parameters, i.e. temperature, test frequency and dimensional properties of the samples. As a consequence, special attention is paid to the description of the testing methodology, the selection of the acceptance criteria and the definition of the testing parameters. Finally, the results of this program are presented and discussed in order to assess the capability of the product with respect to the defined acceptance criteria.