Development of 3D clad bend fabricated from large diameter heavy wall X65 TMCP pipe

ABSTRACT

Increasingly challenging conditions especially with respect to corrosive oil and gas properties lead to an increase in demand for pipes and related products serving in transportation with outstanding corrosion resistance. The selection of most suitable material that is both technically and economically viable is a key issue in pipeline projects.

While carbon steel produced in thermo-mechanically controlled process (TMCP) has well documented mechanical properties including very good toughness alongside excellent weldability it does have certain limits concerning corrosion resistance. These can be overcome by utilising corrosion resistant alloy (CRA) material which, in case of large diameter products, is used as clad layer to protect the carbon steel that supplies the load carrying capacity. Production of TMCP clad bends requires additional dedicated experience and know-how to retain mechanical properties after induction heating as well as quenching and tempering of the mother pipe.

This investigation presents the results of a development of X65 clad bends with an outer diameter of 24". The plate, that had a lean chemistry that is typical for a line pipe product, was produced by thermo-mechanical rolling followed by accelerated cooling (TMCP). It had a heavy wall of 39mm as is often used in deepwater projects. The plate material was explosion welded using a CRA plate of Alloy 625 with a thickness of 4mm. The clad plate was formed into a pipe in a JCO process and welded with a multilayer welding technique. Subsequently, a 3D bend was made by induction bending process. The paper presents a detailed description of each production step alongside the evolution of relelvant properties throught the process. The investigation proved the feasibility of producing a heavy wall bend that had undergone a full body quenching and tempering (QT) process stemming from a TMCP plate.

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