Consideration of Safety Factors in the Life Extension Modelling of Components Operating at High Temperatures

2009 ◽  
pp. 20-20-14
Author(s):  
KM Nikbin
Keyword(s):  
High Temperatures ◽  
Life Extension ◽  
Safety Factors

scholarly journals Probabilistic and Risk-Informed Life Extension Assessment of Wind Turbine Structural Components

Energies ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 821
Author(s):  
Jannie Sønderkær Nielsen ◽  
Lindsay Miller-Branovacki ◽  
Rupp Carriveau
Keyword(s):  
Fatigue Life ◽  
Wind Turbine ◽  
Wind Farm ◽  
Assessment Method ◽  
Economic Feasibility ◽  
Life Extension ◽  
Structural Components ◽  
Safety Factors ◽  
Original Design ◽  
Partial Safety Factors

Reassessment of the fatigue life for wind turbine structural components is typically performed using deterministic methods with the same partial safety factors as used for the original design. However, in relation to life extension, the conditions are generally different from the assumptions used for calibration of partial safety factors; and using a deterministic assessment method with these partial safety factors might not lead to optimal decisions. In this paper, the deterministic assessment method is compared to probabilistic and risk-based approaches, and the economic feasibility is assessed for a case wind farm. Using the models also used for calibration of partial safety factors in IEC61400-1 ed. 4, it is found that the probabilistic assessment generally leads to longer additional fatigue life than the deterministic assessment method. The longer duration of the extended life can make life extension feasible in more situations. The risk-based model is applied to include the risk of failure directly in the economic feasibility assessment and it is found that the reliability can be much lower than the target for new turbines, without compromising the economic feasibility.

Reliability Based ECA Flaw Acceptance Criteria and Safety Factors of Risers and Flowlines

2017 ◽  
Author(s):  
Yohann Miglis ◽  
S.-H. Mark Chang ◽  
Xinhai Qi
Keyword(s):  
High Stress ◽  
Fatigue Performance ◽  
Life Extension ◽  
Unstable Fracture ◽  
Safety Factors ◽  
Acceptance Criteria ◽  
Project Cost ◽  
Critical Flaw ◽  
Fatigue Loads ◽  
Girth Welds

Risers and flowlines are an integral part of deepwater oil and gas field developments around the world. Risers, which serve as the interface between floating platforms and subsea flowlines, are subjected to low-stress high-cycle fatigue loading due to platform motions and vortex induced vibration (VIV). Flowlines are increasingly required to withstand high-stress range fatigue due to high pressure and high temperature (HP/HT) conditions causing lateral buckling along the flowline. Risers and flowlines are generally made by steel tubulars which are joined by girth welds for most subsea applications. Therefore, the quality of the girth welds is critical to the fatigue performance of risers and flowlines. Fatigue design of risers and flowlines is based on the SN fatigue approach. However, that approach does not address the potential for weld flaws to affect performance. Fracture mechanics based engineering critical assessments (ECAs) provide the technical basis for Non-Destructive Evaluation (NDE) and critical flaw acceptance criteria (FAC). The FAC should address maximum allowable flaw sizes at the fabrication stage to ensure that initial girth weld flaws do not grow excessively and cause unstable fracture or through wall failure over the entire service life. Where there is variability and/or uncertainty, ECAs use conservative assumptions and safety factors. However, as HP/HT developments are becoming more common, FAC resulting from ECA tend to be smaller. The specification of FAC plays an important role in the success of the project in terms of quality, cost and schedule. A more stringent FAC will have more weld rejections, which results in slower fabrication and higher cost, or may even become too small to be detected using automatic ultrasonic testing (AUT). In addition, weld repair will adversely affect the quality and increase probability of failure as girth weld failures are often found initiated at weld repairs. The result is questions about assumptions and safety factors applied. As part of this reliability-based assessment, this paper considers two design examples to address reliability based ECA flaw acceptance criteria and safety factors of risers and flowlines. The first example is a deepwater steel catenary riser (SCR) subjected to fatigue loads due to vessel motion, wave fatigue and riser VIV. The second example is a subsea flowline subjected to thermal fatigue loads. This paper offers valuable insights into a balanced approach for inputs selection in ECA by deriving a reliability based FAC and comparing it with the approach outlined in DNV-OS-F101 (Reference 1). It demonstrates FAC can be significantly increased by using reliability based ECA, and as such it will result in faster fabrication and reducing the project cost and schedule. This is of particular interest when considering fatigue performance and life extension of risers and flowlines, asset integrity management, and their relationships with project cost and schedule. Instead of the fit-for-purpose ECA which calculates fatigue life with known girth weld flaws, this paper discusses how to determine allowable initial flaw sizes to satisfy riser and flowline fatigue requirements by deriving a probability density function of the critical flaw acceptance criteria using a reliability based Monte-Carlo approach. This paper provides an approach which is beneficial not only for detailed design but also for tendering purposes during the very early stages of projects, with less conservatism.

In situ REM imaging of surface processes on ceramic bulk crystals from 300 to 1670 K in a conventional TEM

1991 ◽  
Vol 49 ◽  
pp. 660-661
Author(s):  
Z. L. Wang ◽  
J. Bentley
Keyword(s):  
High Temperatures ◽  
Image Resolution ◽  
Atomic Processes ◽  
Crystal Surfaces ◽  
Beam Radiation ◽  
Surface Areas ◽  
Transmission Electron ◽  
Reflection Electron Microscopy ◽  
Gas Reactions

Studying the behavior of surfaces at high temperatures is of great importance for understanding the properties of ceramics and associated surface-gas reactions. Atomic processes occurring on bulk crystal surfaces at high temperatures can be recorded by reflection electron microscopy (REM) in a conventional transmission electron microscope (TEM) with relatively high resolution, because REM is especially sensitive to atomic-height steps.Improved REM image resolution with a FEG: Cleaved surfaces of a-alumina (012) exhibit atomic flatness with steps of height about 5 Å, determined by reference to a screw (or near screw) dislocation with a presumed Burgers vector of b = (1/3)<012> (see Fig. 1). Steps of heights less than about 0.8 Å can be clearly resolved only with a field emission gun (FEG) (Fig. 2). The small steps are formed by the surface oscillating between the closely packed O and Al stacking layers. The bands of dark contrast (Fig. 2b) are the result of beam radiation damage to surface areas initially terminated with O ions.

Life Extension of Nuclear Power Plants: World Situation and the USA Case

2010 ◽  
pp. 50-56 ◽  
Author(s):  
Pablo T. León ◽  
Loreto Cuesta ◽  
Eduardo Serra ◽  
Luis Yagüe
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Life Extension ◽  
The Usa

Campaign Life Extension of Blast Furnace Offgas System

2020 ◽  
Author(s):  
C. Lopes ◽  
C. Van der Woude ◽  
H. Ghorbani ◽  
J. Luiz de Oliveira ◽  
M. Al-Dojayli ◽  
...  
Keyword(s):  
Blast Furnace ◽  
Life Extension ◽  
Campaign Life
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