The Use of Finite Element Analysis in the UK Gas Industry. Keith Wright Structural Integrity Assessments Ltd, Melbourne, Derby, United Kingdom

Transcription

1 Industry Sector RTD Thematic Area Date Power & Pressure Systems Durability and Life Extension Nov-01 The Use of Finite Element Analysis in the UK Gas Industry Keith Wright Structural Integrity Assessments Ltd, Melbourne, Derby, United Kingdom Summary A brief overview of some of the uses of FEA in the UK Gas Industry is described along with a summary of suggested possible future activities of FENet that would be of real benefit to the UK Gas Industry.

2 Advantica Technology A leading provider of technology and engineering services to customers in gas, pipelines and associated industries internationally. Heritage going back over 30 years. Formerly BG Technology Ltd with origins in the research, technology and engineering arms of British Gas. An 80 million turnover with operating experience in over 30 countries. Part of the Lattice Group Organisation that was demerged from BG Group in Lattice Group has annual turnover of over 3 billion Lattice Group has operating profit of over 1 billion

3 Some Uses of FEA include: Buried pipeline modeling Design by analysis (DBA) component modeling, eg branched connections Flaw assessment of components

4 The UK National Transmission System (NTS) km of pipeline from St Fergus, Scotland to the south coast of England Typically 36 inch (914 mm) or 42 inch (1067 mm) diameter pipe Maximum operating pressure of 75 bar

5 Design and Construction of NTS Late 1960s through to early 1980s Institution of Gas Engineers Recommendations on Transmission and Distribution: IGE/TD/1 (1977) Steel Pipelines for high pressure gas transmission IGE/TD/9 (1975) Offtakes and pressure-regulating installations (7 to 70 barg) IGE/TD/12 (1985) Pipework stress analysis for gas industry plant Method of Pipework Stress Analysis Used for NTS A computerised flexibility analysis of piping model Forces and moments obtained at component locations Pressure and system load stresses combined using design-by-rule equations Stress concentration factors applied

6 A Typical System Compressor Station

7 The Pipeline Model Compressor Station Simple pipe elements ANSYS or CAESARII

8 Close Up View: Range of pipe sizes Above and below ground Buried pipeline modeling

9 Buried Pipeline Modeling: Soil stiffness NL springs Node spacing important

10 Design By Rule Assessment of Uprated NTS Above methods still similar to original design basis Therefore increased pressure causes violation of acceptance criteria Sustained Limits Shakedown Limits Fatigue So How is Conservatism Being Removed? Detailed 3D FE Models. Main advantage over design by rule method: Maximum SCFs do not occur at same co-incident location

11 Sweepolet - 12 on 48 pipe

12 Weldolet (3 ) on 36 Pipe

13 Forged Tee - 30 x 18

14 Forged Tee - 36 x 24

15 Forged Equal Tee

16 Split Tee Equal 18

17 Split Tee 24 x 6

18 Split Tee

19 Benefit of Component Assessments using FEA Existing NTS components justified to be operated at uprated pressure Avoiding the replacement of components has meant saving several $Millions IGE/TD/12 being revised to include option for Design By Analysis (DBA) Design by Analysis Collapse due to tensile instability (sustained loading) Progressive Deformation (shakedown) Fatigue WHAT ABOUT ASSESSMENT OF FLAWS?

20 High Pressure Gas Storage Vessels Used to smooth out diurnal pressure fluctuations.

21 High Pressure Gas Storage Vessels Typically 3m Diameter Length of 55m to 75m Manufactured between 1968 to 1972

22 Flaw Assessment Procedures BSI PD6493 (First published 1980) Guidance on methods for assessing the acceptability of flaws in fusion welded structures BSI PD6493 (Second edition 1991) BS7910 (1999) Guide on methods for assessing the acceptability of flaws in metallic structures Also: R6 SINTAP API 579

23 High Pressure Gas Storage Vessels Inlet/Outlet nozzle.

24 HPSV Nozzle FE Model Inlet/Outlet nozzle Protruding design

25 HPSV Nozzle FE Model Inlet/Outlet nozzle

26 HPSV Nozzle FE Model Includes area compensation pad.

27 HPSV Nozzle FE Model Flush design.

28 Nozzle Flaw Assessment The uncracked body through wall stress distribution are input to: CRACKWISE3 or R6

29 Nozzle Flaws

30 Future Nozzle Flaw Assessments 3D cracked body FE analysis crack tip elements Existing Guidance NAFEMS - How to Undertake Fracture Mechanics Analysis API 579 Section B The Problem How to use results from 3D cracked body analysis with a BS7910 two parameter Failure Assessment Diagram (FAD)

31 Brief Insight Provided Into Some Uses of FEA including: Buried pipeline modeling Design by analysis (DBA) component modeling, eg branched connections Flaw assessment of components Other Uses Not Discussed Include: Vibration analysis of pipework (modal superposition) Non Linear Analysis of Dented Pipes Residual Stress predictions

32 Suggestions For Future FENet Activities Benchmarks for verification and validation Particularly for flaw assessment of pressure vessel nozzles Guidelines for application of 3D cracked body FE analysis Application of Design-By-Analysis (DBA) to 3D FE models Note a DBA Manual was published in 1999 Guidelines for Dynamic Fracture Propagation Modeling