Induction Bending of Alloy 825 Overlays on Low-Alloy Carbon Steel

Cracking of corrosion-resistant nickel-base alloy overlays on low-alloy carbon steel has been experienced in the Oil and Gas industry during the induction bending process while trying to reduce cost by using Alloy 825 filler metal instead of the more commonly used Alloy 625.  Optical microscopy, microhardness mapping, SEM fractography, and EBSD traverses have been performed in order to understand the nature and mechanism of this cracking. An FEA model of the dissimilar metal interface was produced using Abaqus CAE to understand how the mismatch in coefficient of thermal expansion changes the strain throughout the pipe. Additionally, Thermocalc has been used in conjunction with EBSD data to generate pseudo-binary dual-alloy phase diagrams to more fully understand what phases could be present throughout the weld overlay region, particularly in the transition region between the two materials. Theories have been developed about crack nucleation and propagation. A Gleeble™ test to simulate the induction bending process has also been designed, based on the Strain-to-Fracture test. Results show cracks similar to those observed in pipes bent in the industry. These Gleeble simulations are being used to develop an optimal process parameter window (including temperature, total strain, and strain rate) that will produce successful bends of pipes clad with Alloy 825.

Industry Sponsor: Exxon Mobil

Faculty: Boian Alexandrov (OSU)

Graduate Student: Rex Alexandre

Industry Contacts: Matt Rondon, Desmond Bourgeois