Abstract
Duplex stainless steel alloys are widely used by the upstream oil and gas industry for line pipe applications as per API(1) 5LC and DNV(2) OS F 101 standards. Among the various duplex grades available the superduplex grades are gaining wider acceptance because of increased strength and corrosion resistance. Line pipes are conventionally made of seamless or longitudinally welded pipes supplied in the wrought form. An alternative process for the manufacture of a seamless pipe is the centrifugal casting process. The development of centrifugally cast 25% Cr superduplex line pipe of 25 mm wall thickness, corresponding to a modification of the UNS(3) S32520 composition has been reported. Mechanical testing, corrosion testing and microstructure checking of these pipes has been done and the properties achieved are compared with those necessary as per currently used industry standards. Detailed microstructural studies have been carried out on the as-cast state and the heat-treated state (solution annealed condition) using high resolution scanning electron microscopy (HRSEM) coupled with energy dispersive x-ray spectroscopy (EDS) analysis. It is shown that the centrifugally cast superduplex alloy pipe meets the property requirements of the industry standards.
