TPi January 2019

match “real-world” conditions and preferably checked by an experienced engineer. The user should ask four important questions: 1. Are my boundary conditions to my structure, equipment or vessels correctly modelled? 2. Are the support locations, types and behaviour defined properly? 3. Are the weights and components’ linear or non-linear behaviour modelled accurately? 4. Are the loadings like temperature, pressure, seismic and wind applied across the correct components in the model? The old saying “garbage in equals garbage out” must be carefully considered, because accurate results only come from trusted software and logical input data. Advances in interoperability like pipe/structural interaction provide a convenient and more accurate way of defining boundary conditions by extending the piping model to include the actual restraint stiffness. Building up confidence in results, using simple models and benchmarks, and utilising AutoPIPE in the stress analysis of piping systems with its superior interoperability will help design safer systems and improve future plant safety. References [1] Roark’s Formulas for Stress and Strain 7 th Edition, Table 8.17 case 1a [2] Roark’s Formulas for Stress and Strain 7 th Edition, Table 8.17 case 1a [3] ASME B31.3 2010 Process Piping. Appendix S Piping System Stress Examples [4] QA111 through QA117 – Benchmark Problem No. 1 through No. 7 contained in NUREG/CR-1677, Vol. 1 (8/80). To compare AutoPIPE frequency, response spectrum and modal combination methods results [5] QA109A, QA109B and QA109C – Benchmark Problem No. 1, 2 and 3 contained in NUREG/CR-6049. To compare AutoPIPE uniform support motion response spectrum results obtained by the Grouping and Double Sum modal combination methods, independent support motion response spectrum results obtained by using Grouping modal combination method between SRSS Combination Across Groups and AutoPIPE Modal Time History Analysis Direct Integration [6] QA110 – Benchmark Problem No. 2 contained in NUREG/CR-1677, Vol. 2. AutoPIPE multiple support response spectrum results obtained by using SRSS combination method between SRSS Combination Across Groups [7] QA58 – To compare the results obtained by AutoPIPE buried piping and simulated soil spring models to values published in ASME B31.1 – 2012 Appendix VII buried piping example [8] QA93 – To compare the results obtained by AutoPIPE buried piping model to published results from “Buried Piping – An Analysis Procedure Update” paper by EC Goodling et al [9] The Art of Checking Pipe Stress Computer Programs, LC Peng © 2018 Bentley Systems Incorporated Bentley, the ‘B’ logo, and AutoPIPE are either registered or unregistered trademarks or service marks of Bentley Systems, Incorporated, or one of its direct or indirect wholly owned subsidiaries. Other brands and product names are trademarks of their respective owners.

Figure 5

The stress, force and moments results from these three example models are all within 0.5 per cent of the averaged results presented in Appendix S. The only exception is the vertical anchor load at node 50 of S301, which is 1.6 per cent. This exception is because of the unit conversion; with imperial units, this load is within 0.5 per cent. Closely matching loads provides confidence that AutoPIPE is producing the correct static results. Additionally, AutoPIPE uses more than 600 regression models, backed up by around 2,000 MathCAD worksheets and hand calculations, to validate the program’s calculations both statically and dynamically. New features and code updates are accompanied with new test models and worksheets, continuously added to the test plan to ensure changes are working as expected. AutoPIPE’s development and testing procedures follow the most rigorous rules of ASME NQA-1; US Code of Federal Regulations 10CFR50/10CFR21; ISO 9001; and ANSI/ASME N45.2. Moreover, AutoPIPE’s quality assurance procedures have been, and continue to be, successfully audited by major users since the 1990s. Included in these regression models are other industry benchmark models to provide additional confidence that the most accurate results are produced. [4, 5, 6, 7, 8] These benchmark models investigate the more advanced analysis features, such as dynamic analysis of piping systems that represent piping from advanced boiling water reactors and buried pipe analysis. This investigation shows that the program results match with the published results. LC Peng’s paper offers some further references to benchmarks. [9] He explains how easy it is to get results from a computer program, as it is the task of all software vendors to make their program “user friendly”. But, Peng warns, “To ensure a good analysis the analyst has to have at least a clear picture of what the program functions are. He or she should also be able to spot the inconsistencies when they occur.” The confidence you deserve Having an extensive range of benchmarks for pipe stress analysis programs like AutoPIPE is critical to building trust in these important design calculations and providing confidence in the long-term reliability for years of safe operation. Equally important is that the modelling assumptions are valid to

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TUBE PRODUCTS INTERNATIONAL January 2019

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