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In this paper the development of a welding procedure for the joining of steel type UNS S32760 (Super duplex F55) for use in the off-shore application is described. The joint was realized by means of the TIG (GTAW) manual process for the first passes and by a manual filling process with stick electrode (SMAW), in order to obtain the combination of mechanical and microstructural characteristics desired by the customer. The results obtained from the tests on the joints must provide proof of successful completion of all the tests to be part of the joint in accordance with the contractual requirements and stabilized the base for actual use in the production. The particularity of the case, in addition obviously to the inherent difficulties posed by the type of steel chosen, consisted in the request by the customer of a combination of mechanical and microstructural characteristics to the limit of the possibilities of a welding procedure suitable for use in production mode and times compatible with the internal market and production requirements. It was therefore necessary to design the welding procedure and choose the most suitable process parameters to achieve the required results. The evaluation of the joints to achieve in production and the characteristics to be obtained, has led to decide to perform welding with welding processes previously mentioned and in the welding position-frontal plane (PB/2G). The main problems to be considered in the design phase of the welding procedure, are to be found in the value of the maximum heat input, interval of interpass temperatures to be observed and the type of shielding gas to use with which material can be welded to avoid the formation of intermetallic microstructure phases of the joint and sappers of corrosion resistance. [ABSTRACT FROM AUTHOR]

Presently, many economical and technical efforts are made by pipeline industry aimed to satisfy the needs to transport gas from far away regions to the final market and to set new solutions in terms of both design criteria and new high performance materials. Due to the fact that easy Oil and Gas is largely exploited and new fields will be more and more in deeper water (it means water depths greater 305 m), that means higher pressures and temperatures and more corrosive environments, material requirements are increasing. In this situation low-alloy carbon steels tend to be structurally satisfactory, but lack in terms of corrosion resistance. On the other hand stainless steels and nickel alloys resist to corrosion environments but are lack in terms of strength or extremely costly. Clad pipes, low-alloy carbon steel with a thin layer of a corrosion-resistant alloy, is presently considered, more and more, a suitable solution to the most demanding requirements of strength, corrosion resistance and cost-effectiveness. In a cladded pipe, the (generally) unalloyed carbon steel outer pipe handles the internal and external pressure, while the high-alloy cladding provides the corrosion protection. The paper describes the pipes and fittings production starting from metallurgical clad plates. In particular the experience developed by Allied Group is described. The developed products and components represent the ideal candidate for the most severe offshore and subsea applications typical of the Oil&Gas sector. [ABSTRACT FROM AUTHOR]