H5
The Failure Test

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08:35
conference time (CEST, Berlin)
Defining Safe Operating Limits for the Inlet Tee of the Steam Reformer by Level 3 Fitness-for-service Assessment
26/10/2021 08:35 conference time (CEST, Berlin)
Room: H
O. Kwon, E. Griffiths, H. Duncan (Quest Integrity Group, NZL); D. Osuna (Incitec Pivot Ltd., AUS)
O. Kwon, E. Griffiths, H. Duncan (Quest Integrity Group, NZL); D. Osuna (Incitec Pivot Ltd., AUS)
The ammonia plant experienced increased process inlet gas temperatures, triggering a review of asset integrity. The initial fitness-for-service (FFS) work suggested that the critical location identified was the inlet “tee” and conservatively set their operating limits. The conservatism in the initial assessment, such as creep relaxed stress at 40,000 hours instead of fully relaxed stress and surface point failure criterion, was relaxed to determine realistic remnant creep life consequently providing more reliable operating limits. The creep damage indicated by the metallurgical replications allowed the material properties to effectively be calibrated. The material calibration process involved estimating creep life fraction based on the replication results and matching the FE predicted life at the replicated locations by adjusting creep material properties. Full creep stress relaxation behaviour was modelled by simulating the creep stress evolution behaviour from commissioning up until 2023, and a creep failure criterion based on net section stress was considered to reduce the conservatism associated with the surface stress failure criterion. In order to acquire a through-thickness stress distribution for the creep life assessment, reference stresses were calculated with guidance from API-579. Linearised membrane and bending stress components were calculated based on von-Mises stresses extracted from the FE model through the section of the tee. Three critical locations were selected and analysed. Given the operating temperature data, and the reference stresses determined from the FE analysis, the creep life consumption at the start of 2020 was calculated to be up to 52%. Given the 2020 creep life consumption of 52% calculated, future creep life consumption until 2023 was calculated based on various operating combinations of temperature and pressure scenarios. A correlation of operating conditions with remnant life was established, which enable to define integrity operating window. In addition, the safe operating envelope for the inlet tee achieving 100,000 hours of further operation was determined.
fitness-for-service, Inlet Tee, operating limits, creep remnant life, failure criterion
08:55
conference time (CEST, Berlin)
A Contribution to the Analysis of Structural Failure of Sandwich Structures Under Localised Load
26/10/2021 08:55 conference time (CEST, Berlin)
Room: H
S. Diana Zimmermann (Hochschule Mittweida, DEU); D. John (Westsächsische Hochschule Zwickau, DEU)
S. Diana Zimmermann (Hochschule Mittweida, DEU); D. John (Westsächsische Hochschule Zwickau, DEU)
As efficient lightweight components, sandwich elements are becoming increasingly important in machine tool design and automotive industry, based on the combination of a very high ratio of rigidity and flexural rigidity to weight. Bending and shear loaded fasteners such as bolts, rivets and screws are used most frequently to connect the often semi-finished parts. A major challenge in the design of screw connections is the absorption of load and moments, usually supported by various reinforcement structures. Therefore, both the geometry and the reinforcement principle must be considered. A local, precisely placed load introduction element for composite sandwich structures is analysed and validated as a purely mechanical and form-fitting solution using experimental and numerical investigations in several iteration steps. The sandwich structures, made of carbon fibre reinforced plastic face sheets and a phenolic resin-impregnated Nomex random fibre paper honeycomb core, with screw connection are prone to failure due to this geometry discontinuity and the material transition caused by the direction of load and bending moments. The analysis considers an appropriate modelling approach of the failure mechanisms occurring during a pull-out test according to the ESA insert design handbook of a developed insert connection using explicit simulation codes and special algorithms. For this, extensive preliminary investigations were carried out to determine the necessary, relevant parameters for the simulation. The presented work focuses on the material-specific design and the direction-dependent elasto-plastic material behaviour using a suitable material model to depict buckling and strength failure which depend significantly on the semi-finished fibre product used and the matrix system and manufacturing imperfections like cracks, pores and resin conglomerations in corners. A specific example illustrates the non-linear method considering the material behaviour, contact conditions and occurring failure mechanisms. The global load-displacement curve from experiment and calculation shows a good coincidence. The mapping of the successive failure and the resulting failure modes enables a targeted improvement of the insert connection design.
sandwich structure, CFRP, structural failure, explicit simulation
09:15
conference time (CEST, Berlin)
New VDI Guideline "Strength Assessment of Plastic Components" - A Contribution to the Democratization of Structural Simulation
26/10/2021 09:15 conference time (CEST, Berlin)
Room: H
W. Korte (PART Engineering GmbH, DEU)
W. Korte (PART Engineering GmbH, DEU)
The strength assessment of plastic components is a problem in practice. In the field of material modeling and failure behavior of plastics, there are numerous scientific studies - however, there is a lack of structured compilation and useful presentation of the already existing knowledge. The democratization of simulation in the sense of CAD-integrated simulation and the increase in the user-friendliness of simulation software is progressing. This leads to the increased use of simulation in early design phases by non-simulation experts. Typically, a good product knowledge can be assumed here, but no profound knowledge of numerical methods and material mechanics. In this respect, it is important for the beneficial application of simulation to achieve a good trade-off between the simplest possible modeling approaches (material model, strength assessment) and sufficient fidelity of the simulation results. As a rule, the supposedly simple question "Will the component hold?" cannot be answered easily on the basis of a simulation. Neither directly by the simulation software and often not even by a simulation expert. In practice, different, non-standardized simulation and assessment approaches are used, or experience-based, subjective procedures are employed. In addition to the uncertainty of such approaches, the comparability of different analyses is not given. These are major obstacles to the democratization of structural simulation, especially in the plastics processing industry. This is where the new guideline VDI 2016 "Strength Assessment of Components made of Thermoplastics" (VDI = The Association of German Engineers) comes in. The guideline is currently being developed within a working group of 14 industrial and university organizations. The guideline is based on the use of simple isotropic material models and its applicability even with a "thin" data basis with the material information usually available in the public domain. The aim is to ensure a balanced ratio of effort and accuracy, so that even non-simulation or material experts can carry out a plausible and reproducible strength assessment of plastic components using "on-board" tools. This paper gives an overview of the content of the guideline, the methods used and the expected benefits for the simulation community.
plastics, strength assessment, democratization
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