Research On The Interface Microstructure Of Bimetallic Seamless Steel Pipe

Bimetallic seamless steel pipe (BSSP) applied in oil and gas field is composed of innercorrosion-resistant alloy and outer carbon steel, which has been widely used abroad anddomestic offshore oil and gas field exploit, for its excellent corrosion resistance but lessexpensive price. Metallurgical bonding interface composite pipe owns privilege be chosen inlarge-scale application of oil and gas field exploit, because of its good mechanical propertiesof the interface. Perfect interfacial bonding of BSSP is the prerequisite to ensure the stabilityof pipe serving. Metallurgical bonding interface composite pipe produced by the conventionalmethod failed to achieve complete metallurgical bond, there is still exist some interspace, andcrucially the space is probably the starting of corrosion and cracking.Especially the hot-rolled method on BSSP, by virtue of its high reliability andadaptability of species, dash out from the fierce competition of composite pipe productioncrafts. Application Market of BSSP in oil and gas field exploit is much too broad, who ownsgreat significance towards the research, production and application of BSSP to be furtherdemonstrated on indicators including microstructure, precipitated phase and elementsdiffusion across the interface, while large-scale investment meet the needs in future.In this paper, interfacial bonding and microstructure get by external heating field(diffusion annealing) of BSSP (10MnVNb/12Cr) have been analyzed and researched.Design a suitable casting gating system for BSSP,10MnVNb/12Cr, and analyze itsdefect positions may occur, then set the casting on the piercer for hot rolling, normalizing thenair cooling. Both of the two metals beside the interface of BSSP obtained by this method hasbeen largely in combined state, there are only a few partial unfusion zone, which make itpossible to attain an fully integrated interface through the diffusion annealing process. Find aproper temperature range of bonding after the diffusion annealing in different temperatures(10001250℃) towards the BSSP after hot rolled piercing. It can be concluded that at atemperature from1100℃to1150℃, the interface obtained with good, reasonablemetallographic structure, fine carbide particles, uniform distribution on both sides, from laterinterphase structure observation, second phase particles analysis and micro-hardnessdistribution test. Micro-hardness value locate on the interface is just between the ones of twometals near the interface; meanwhile provide convenience for the coordination of thebimetallic tube deformation.Significantly, make reasonable assumptions combinning with Fick ’s second law whichbased on interface diffusion theory, after the selection of a suitable basic model, then find theinitial conditions accord to the assumptions. The element diffusion of chromium and nickelnear the interface are calculated and analyzed under different annealing temperature. Both theformula and its fuctional solution in connection with interface elements diffusion for BSSP are found, the possible causes of error between the measured and calculated values areconcluded.