Help w/ Piping Flexibility Example, Piping Handbook

[recoveringEngineer]

I have read many posts from regarding piping stress analysis and recently purchased a couple of recommended books, specifically "Piping Handbook" 5th Edition edited King and "Process Piping" second edition by Charles Becht IV. I would like to aquire the Kellogg

I am just learning to "crawl" regarding flexibility analysis and am attempting various examples.
King has a Simplified Procedure for Desk Computation in chapter Four by John E. Brock he refers to as the Hao Hsiao Method (page 4-103 Table 11). I am working through that and am stumped and unable to follow the arithmetic in calculating the reaction force ranges. Specifically, line item (6) in the last section, Reaction Force Ranges is allegedly the sum of line item (5) + (8). This does work mathematically. Is this example updated in a later edition of the Handbook or is there something else I am missing?

Thanks,

don

 

[Frank1344]

hi,
are you trying to do the analysis manually without using any computer software?
and if yes, may i ask why?
Faraz

 

[recoveringEngineer]

Well, um, yes I am.

Because:
1) as a mechanical engineer, I think I should be able to understand the technique well enough to analyze a simple system without the aid of FEA and I understand that per ASME B31.3 paragraph 319.4.1, "A formal flexibility analysis does not mean a computer stress analysis. It can be by simplified, approximate, or comprehensive methods." "Process Piping, The complete Guide to B31.3", Charles Becht.

2) I am doing this on my own and can't justify purchasing a computer program as a learning experience.

3) even with computer analysis, I would expect, the engineer should be able evaluate the resonableness of a solution. I beleive in bracketing or approximating solutions to complex problems using simplifying assumptions of methods usually before I delve into rigorous analysis.

don

 

[StressGuy]

Guess I came to the game just a little too late. My edition of the Piping Handbook is the 6th and I can't find a reference to the method you're describing in this one. So, I'm afraid I can't be of much direct help on the method you are trying to use.

I do congratulate you for trying to build a feel for how these systems should behave by doing some manual work. There are still plenty of problems that can be reasonably solved w/o having to dig into Caesar. I still routinely use the Kellogg Guided Cantilever method to check simple systems

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

 

[recoveringEngineer]

Well I could use some help on the guided cantilever method also. I have not been able to find an affordable copy Kellogg's (apparently) classic volume.

A paper by Peng Engineering

http://www.pipestress.com/papers/QuickFlex.pdf

demonstrates the guided cantilever method of a simple two-dimensional pipe system with two 24-foot 6 inch pipes at right angles. Figure 7 (b) notes that the stress is 8226 psi.

I calculate a reactions of Fx = 407, Fy = -407 and maximum bending moment 4884 ft-lbs for a bending stress of only 6092 psi using a generalize method of determining integral in my Seventh edition of Mark's Standard Handbook of Mechanical Engineering (pages 5-82- 5-89). I assumed straight sections(mitered?), neglecting the curved elbow.

Using the formula given in referenced paper, I obtained a stress of only 6073 psi for a expansion of 0.874 inches (alpha 7E-6 inches/inch/F) using the provided formula. This is good agreement. This method neglects any stress intensification at the elbow. Is this the difference?

That would imply a SIF of only 1.35 whereas in-plane bending SIF for an Elbow is more typically 1.85!

As you can see, I am at the fundamental stage in analysis.

don

 

[StressGuy]

Ah, but you're not checking the stress at the elbow, you are checking it back at the anchor point.

What you have here is the basic case from strength of materials of bending a cantilever beam (i.e. anchored at one end and free at the other). In this case, it is modified to assume that the "free end" where the deflection/load is applied is free to deflect, but not rotate.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

 

[stanier]

To help you get into the computer analysis you may be able to get a demo copy from Algor (Pipepak) or Autopipe. The computerised analysis is the way forward as it allows you to focus on the design not the maths.

I am unsure about the method by King. Some publications , and software, have had their errors in the past.

Oher references you may find are

Piping Design and Engineering ITT Grinnell Industrial Piping
Piping Engineering by Tube Turns

Try the website

http://www.pipingdesign.com.

They have some technical papers on the subject.

NASA did have publications and I believe some software that you can download, if you are an American resident.

You might try the local chapter of ASME or other institution. Try to get on to a retired piping engineer and ask if they would be your mentor. Even try the large design and construct companies and ask if there is anyone who can help. They probably have these books in their attic. If you were in Sydney Australia you could borrow mine. Most engineers like to impart their knowledge to anyone eager to learn.

Good Luck

 

[recoveringEngineer]

StressGuy wrote, "Ah, but you're not checking the stress at the elbow, you are checking it back at the anchor point. "

Correct me if I am wrong. I went out the storage last night and found my copy of Roark. For a guided cantilever, there is a no (vertical) reaction at the guide, only a moment. This must represent the elbow(?). For the fixed end, there is a reaction force equal and opposite of the load and moment equal and opposite of the guided moment. This must represent the anchor(?). So the bending moments are the same magnitute and so are the bending stresses.

Granted, there is additional stress in the elbow side wall due to flattening which is accounted for with a stress concentration or stress intensity factor.

Thanks for the above responses,

Can anyone recommend the ASME short courses on B31.1 or 31.3? I would need the English on-line version. The Spanish version did not seem unreasonably priced.

don

 

[Frank1344]

have you tried

http://www.asme.org