The objective of this project was to reduce potentially significant schedule delays by identifying optimal forming practices for Alloy 625 in several critical CVN 78 Class components as well as evaluating the corrosion performance of the Alloy 625-to-HSLA (high strength, low alloy) steel welds.
Alloy 625 was chosen to be used for intake/discharge ducts because of its compatibility with titanium, seawater and its excellent self-passivating properties. The issues for using the alloy are associated with the manufacturability and material design because the alloy work hardens easily and the designs are expected to require bend radii as tight as 1T, with wall thickness from ½ to 1-inch.
The technical scope of work included a material property trade-off study for various material processing routes, completion of processing and structural analyses and evaluation of the performances testing of selected fabrication systems.
The primary benefit of this project was to develop the necessary forming practices to enable Newport News Shipbuilding to successfully form several complex shapes on the first attempt. The project results minimize the risk of cracking this very expensive material, which could result in significant schedule delays and costs to re-form these shapes.
Fabrication of these components was planned very early in the production cycle for CVN 78 Class, which made it necessary to accelerate the development of the required forming practices in this project. The forming practices were transitioned to NGSB-NN in July 2008, which was in sufficient time to support the production schedule for these critical components. The specifications and procedures developed during this project directly translated into NGSB-NN procurement specifications, drawing callouts, tooling design, and process instructions to support the fabrication of these components for CVN 78 Class.
Naval Sea Systems Command (NAVSEA)
Newport News Shipbuilding
PMS 378 Future Aircraft Carriers