Development of Optimized Temperbead Techniques for Dissimilar Metal Welds

Dissimilar metal overlays and welds are commonly used in the Power Generation, Oil and Gas, and Petrochemical industries. The most common joints consist of low alloy steel and/or stainless steel components joined or overlayed with Ni-base or stainless steel filler metal. These weldments typically require a PWHT to temper the martensite that forms in the steel HAZ, so that the hardness is reduced and the impact toughness is improved.

Several phenomena occur during welding and PWHT that can potentially lead to failures in service: 1) carbon migration from HAZ to fusion boundary region during PWHT results in a formation of a hard and brittle band along the fusion boundary; 2) loss of mechanical properties in HAZ due to over-tempering; 3) hydrogen embrittlement in fusion boundary region, due to high hardness created by carbon migration. In addition to these potential failure issues, PWHT in the field is time consuming and often impractical.

A temper bead procedure – in which the base metal HAZ is tempered by subsequent welding passes - that eliminates the need for PWHT will be developed. Ideally, the temper bead procedure could be optimized to meet specified hardness and impact toughness requirements. This project will result in the development of efficient temper bead welding to replace PWHT, resulting in reduced production cost, improved resistance to hydrogen embrittlement, toughness, and service reliability of DMWs. The main deliverable of this project is a methodology for development of temper bead welding procedures that replace PWHT, as well as a finite element model to determine the proper welding parameters to achieve the desired final weld properties.

Industry Sponsor: EPRI, AZZ

Faculty: Boian Alexandrov (OSU)

Graduate Students: Matt Forquer (former student), Jeffrey Stewart

Industry Contact: Steve McCracken, Darren Barborak