Stress & Dynamic Analysis

EPRI Research Program: DEI has more than 30 years of experience in welding simulation and recently led a multi-year EPRI research program to validate residual stress models for dissimilar metal welds in nuclear components. As documented in EPRI reports MRP-316 and MRP-317 (3002005498 and 3002005499), DEI’s contributions to this effort included:

• Development of finite element analysis models for predicting residual stresses in dissimilar metal welds, including consideration of different component and weld geometries, material properties, weld parameters and thermal and structural models
• Comparison to independent models developed by others, including the NRC Office of Regulatory Research
• Model validation using residual stress measurements performed on various weld mockups using neutron diffraction, deep hole drilling, x-ray diffraction, hole drilling and ring core, and contour method

This project improved the understanding and quality of residual stress models for dissimilar metal welds. In addition to the research effort highlighted above, DEI also authored ASME Code Case N-899, which provides standardized welding residual stress distributions for use in flaw growth calculations.

Dynamic Response Analysis: For more than 15 years, DEI has supported design of the Hanford waste treatment plant as a key technical consultant, evaluating the risk and consequences of hydrogen accumulation and potential detonation when processing transuranic (TRU) waste streams. DEI contributions to this project have included:

• Over 70 calculations and technical position papers advancing the state of the art in understanding and analysis of response of piping systems and components to the effects of internal hydrogen deflagration, detonation and deflagration-to-detonation transition (DDT)
• Development of custom quantitative risk assessment software for analyzing hydrogen risks and failure modes to nuclear safety-related quality assurance standards (ASME NQA-1 2000, Subpart 2.7)
• Dynamic analysis of other system transients including from shock waves associated with waste processing activities and from gas build-up and acceleration of waste slugs with Bingham rheological properties
• Experimental evaluation of explosions and other transients to validate and qualify modeling and simulation results

DEI has presented technical findings and recommendations to the US DOE and the US DNFSB.

Root Cause Investigation: The line which feeds liquid hydrogen to space shuttle main propulsion systems includes a flexible joint which accommodates relative motion between the space shuttle structure and main engine. Cracks were detected in Inconel 718 flow liners in this joint for several space shuttles, including Atlantis, Discovery and Endeavor. In support of investigation of the issue by NASA’s Langley Research Center, DEI completed a root cause investigation of this issue. Specific assistance and insights provided by DEI in this investigation included:

• Modeling and finite element analysis of the flowliner flexible joint, and stress intensity and fracture mechanics calculations
• Identification of the cracking root cause as flow-induced alternating stresses during operation, combined with high tensile residual stresses from production welding

These results contributed to NASA’s resolution of the issue, which included identification of appropriate inspection intervals and the development of a high resolution surface replication technique for precise detection of crack initiation locations.