Assystem UK have a long track record of providing cutting-edge substantiation techniques within Energy and Infrastructure using the latest Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD) tools.
Our expertise and knowledge in this area has brought us very close to key customers who see the advantages in using our expert knowledge in using modern methods to provide life extension to existing plant and improved safety margins for new products.
Recently, Dr Adam Towse and Dr David Griffin, two world renowned experts from Energy & Nuclear’s Sunderland based Centre of Excellence for Stress presented a selection of these advanced analysis techniques at the prestigious American Society of Mechanical Engineers (ASME) conference in Toronto, Canada.
Our specialists presented a total of five papers to the conference, four of which were the result of collaborations with UK–based engineers from Rolls-Royce Marine Power on business critical areas such as performing life extension and optimisation of new plant design.
The papers were:
- Justification of extended plant operations by performing non-linear thermo-mechanical analysis of thermal shock loading in a valve using strain-life fatigue methods. The existing stress-life methodology was unable to provide justification for extended operation, but combining CFD (for improved flow and heat transfer characteristics) and non-linear FEA (accounting for material hardening with repeated cycling using a Chaboche material model) it was possible to provide justification for the required life extension period.
- Justification of the defect tolerance of defects postulated to occur at the root of high integrity threaded connections within the plant. The bolts were sufficiently important to the safety of the plant that a defect tolerance assessment was required. Due to the very complex geometry and large scale difference between the structural elements and the very small defects, a novel analysis methodology was required to determine the stress intensity factors for the fracture calculation.
- Design optioneering / optimisation of a large nozzle entry into a pressure vessel. Design of experiments techniques were used to quantify the effect of geometric changes to the nozzle on the outputs from the analysis. These variations were fitted to a series of polynomials (meta-models) which were delivered to the customer to allow what-if studies and design trade-offs to be understood and quantified (eg thicker nozzles good for primary strength, but bad for secondary thermal stress range).
- Use of limit load analysis for primary strength assessment. This paper supported previous papers by Rolls-Royce concerning the use of non-linear analysis to reduce excessive conservatism in the ASME Boiler and Pressure Vessel Code primary strength checks. Three different example structures were analysed and the influence of linear and non-linear geometry effects (i.e. geometric weakening or strengthening) were shown.
- Impact analysis of a nuclear encapsulation vessel including a simulated internal blast of the contents on impact. The customer required Assystem to design, substantiate, build and proof test a small transport flask containing an internal nuclear product can, this can could be pressurised and fail should the flask be dropped. Explicit dynamic analysis methods were employed to simulate the event (duration approximately 40ms) including the internal blast to monitor the seal movement and bolt strains during impact to ensure leakage was not possible. Multiple design iterations were undertaken analytically ensuring that the physical tests, carried out at Assystem premises, were successful first time.
The conference and the associated publications demonstrate once again, the expertise that Assystem UK and our Engineers possess in the field of design substantiation. Our experts showed how that knowledge can be applied to real business issues and provide customers with effective solutions to challenges they face in optimisation, safety justification and life extension.