ABSTRACT

The present research proposed a metallurgically bonded corrosion resistance alloy/carbon steel bimetal pipe. The interfacial bonding behavior, and the corrosion and mechanical behavior of bimetals was investigated using various heat treatment technologies. It can be inferred that the cohesion strength, corrosion resistance and strength were attributed to the diffusion behavior of Chromium in terms of interfacial diffusion behavior and the precipitation of carbides. Additionally, the welding technique for the bimetal pipes with particular composite structure, as well as its recent application in the oil and gas field development, was illustrated in the present research.

INTRODUCTION

Bimetal composite pipes composed of carbon steel and corrosion resistant alloys have attracted increasing attention for the applications in the fields of transferring pipes, downhole tubes, reservoirs and heat exchangers. It shows superior properties such as corrosion resistance of the corrosion resistant alloys and formability, and mechanical properties of carbon steels, which satisfy the requirements of both anti-corrosion and mechanical properties applied in oil and gas filed with an affordable price[1-7].

A series of manufacturing methods for the fabrication of bimetal composite pipes, including mechanical bonding method, welded pipe using the clad plate and inner surfacing welding clad pipe, have been applied in recent years [8-11]. For instance, in recent years, mechanically bonded S31603/X65 composite pipes have been applied as transferring pipes in onshore and offshore fields [12-13]. However, failure induced by corrosion, collapse, bulge or crack is occurred at the interface of the bimetal pipe due to a low interface bonding strength (usually 2∼15 MPa). Since there is a difference in the thermal expansion coefficient and low interfacial bonding strength, the elbow and triplet manufacturing method can not be solved presently. Moreover, welded pipes using clad plate are developed recently, realizing metallurgically bonded interface with a high interfacial cohesion strength [14]. However, the wavy bonding interface between the carbon steel and corrosion resistant alloys that formed during the explosive cladding process leads to micro defects such as micropores or microcracks for the clad plate. In addition, the diffusion of elements and related complex microstructures along the straight welding joint increases the risk of weld corrosion during servicing. It is worth noting that the inner surfacing welding technique for the composite pipes is also developed. Due to a low efficiency, as well as a poor performance between welds, the inner surfacing welding technique could be more widespread for the manufacturing of the composite pipes [15].

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