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• FEATools is an automated CAESAR II model modifier that can solve stress and rotating
equipment problems automatically with almost no input from the user.
• FEATools is not a solution for every problem. There are certain piping model geometries as pointed out in WRC 329 that respond very favorably to the use of more applicable flexibility and stress intensification factor data. FEATools is designed for those problems. One objective of this webinar is to help the user identify these types of problems.
• FEATools is a proprietary suite of programs designed for use with CAESAR II using approaches identified in 1987 with WRC 329, implemented in ASME Section III, and verified in the PRG lab using experimental methods updated from B31.J and WRC 346.
• FEATools provides a standard application of approaches identified by WRC, EPRI, ASME
Section VIII Div 2 Part 5 and PRG. The unique quality of FEATools is that the process of application is automated by a company that has been doing the same thing since 1990, and the FEATools software development team is headed by the same person that was the original author of the CAESAR II pipe stress program.
• When k-factors are large and the system is stiff the affect on the calculated result can be large, where “large” can be a maximum of around 10. Generally the result is smaller and between 20 and 200%. Small errors are more important when there is rotating equipment in the model, large errors are also important when changes in the pipe routing or supporting have an economic impact on the project.
• When the d/D ratio is between 0.5 and 1 as stated in Note 11 of B31.3 Appendix D
the stresses may be half of what they should be.
• When the d/D ratio is less than 0.5 the i-factors in the run pipe can be highly overestimated by more than 2 as the D/T ratio gets larger.
• For B31.3 the torsional i-factor is not 1 and increases as the D/T ratio gets larger.
When D/T > 35 check the i-factors and k-factors for the system using the FEATools PRGiK spreadsheet. When the system is classified as “severe cyclic” check i-factors and k-factors. Check the following configurations for most systems:
a)Largest d/D for the largest D/T. b)Largest (d/D)(D/T)0.5. c)Largest D/T when d/D ~ 0.5 d)Largest D/T when d/D < 0.25 e)Largest D/t when d/D ~ 1
Compare the B31 i- and k-factors to ST-LLC 07-02 i- and k-factors. Where they agree then perform the stress as usual. Where they do not agree then take extra precaution.
C2-Translator
Decide where the system is looped and/or stiff. If the stresses or the loads are high and a problem due to stress or rotating equipment then run the FEATools C2-Translator to see if the real answers are better.
Severe Cyclic Conditions: Markl: ireal (M/Z) > 0.4 x 490 N -0.2 ;ksi, range PVP 2008-61871: ireal (M/Z) > 0.4 x 1894 N – 0.335 ;ksi, range
Notes: 1) 0.4 = 0.8 x 0.5. At 7000 cycles, the allowable stress is approximately
equal to 1/2 of the mean stress to failure. The curves for the mean stress to failure from Markl and Hinnant (PVP2008-61871) are known as 490N-0.2 and 1874N-0.335 respectively.
2) ireal is the actual stress intensification factor. When it is known that the stress intensification factor used in the pipe stress analysis is too low, it must be increased by the difference, or multiplied by the largest 07-02 and B31 i-factor ratio.
3) The percentage of the allowable used is based on the allowable from a typical pipe stress program that is based on 6 x N-0.2 [ 1.25(Sc+Sh)]
D/T = (30-0.5)/0.5 = 59 d/D << 0.5 The D/T ratio is greater than 35 – and so we want to take a look in the PRGiK spreadsheet to see if there’s any difference between more applicable data and the Code values that will be used. The d/D ratio is << 0.5 and so we know that run side i-factors are going to be very overconservative – and so we want to take a look at this too.
Without considering the branch connection flexibility of the 12x30” fabricated tee at point 15 the out-of-plane (Z) bending moment at point 15 is 372,000 in.lb. Including the branch connection flexibility reduces the bending moment to 41,832 in.lb., a reduction of 8.8.
Conclusions: 1)There are three very nice, relatively independent tools available in FEATools. There is a CAESAR II file converter that incorporates more applicable i and k-factors. There is an i-K spreadsheet that lets us evaluate more applicable data that may be needed for our pipe stress analysis, and there are several stand alone finite element programs that are very easy to use for typical configurations. 2)The WRC 329 recommendations for the B31 Piping Codes an be checked easily to see if they apply to our system using the PRGiK spreadsheet. 3)Severe cyclic service can be interpreted to mean a system where the maximum stress is greater than 0.8x0.5 = 40% of mean failure stress at the given number of cycles. A chart with the equations for use is given in the slides so that the user can define equivalent severe cyclic service. 4)Where there are multiple operating cases, the load history processor should be used. 5)It is easy to convert one CAESAR II model into a more applicable CAESAR II model and see if an improvement in the loads or stresses results. In the examples we went through, there were substantial changes both due to more applicable (corrected) k-factors and i-factors.
Through the course of these webinars we hope to continue showing practical examples where more accurate analysis approaches can save time and money while providing a uniform, Code intended safety. Thank you for your time.