Induction Bending of Clad Pipes made by the 'Liquid Interface Diffusion Bonding Technique' (L.I.D.B.)

摘要

Over the past decade, an alliance of metallurgists, engineers and fabricators has developed seamless clad joints, of a corrosion resistant alloy metallically bonded inside a carbon steel substrate, primarily aimed at steel catenary risers, line pipe for rigorous physical environments and piping on offshore structures. One major problem was to match the temperature requirements of both the cladding corrosion resistant alloy (CRA) and the carbon steel (CS) substrate. This was achieved in two steps; raising the allowable maximum CS temperature to 1100 deg C by the design of a new, unique chemistry and secondly, by invention of an activator material that provided metallic bonding in the required temperature range for co-extrusion of the product. The temperature is several hundred degrees below the usual forge bonding temperatures. When seamless clad hollows are reduced in wall thickness, and elongated in length by the extrusion process, all of these seamless products are clad with the CRA material having a true bonding between the CRA and the CS. The local bond line shear strength is 400 N/mm~2 or greater, higher even than either of the two primary materials. This paper discusses two distinct carbon steels. One is as designed for subsequent induction bending. The second is as designed for straight pipe usage in the "as-extruded" state. Our final step will be development of the induction bending process for this second composition. Both carbon steels are very weldable. Ductile to brittle transition temperatures are below - 40 deg C. A special inerting technique was invented to eliminate oxygen and other detrimental contamination from the bond line. These results in a bond line impact strength typically of 95J and with essentially no effects from fatigue phenomena. The new CS is sour service compatible and is suited for the slow strain rate of the extrusion process and merely requires spray quenching down from the extrusion temperatures. There is full retention of the corrosion resistant alloy properties after processing. Because of the temperature and cooling rate options allowable with induction bending, the carbon steel properties of bends are especially good.