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How to model flexible tubes (metal hoses) in CAESAR? 3

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jgilrod

jgilrod

Mechanical
Dec 22, 2023
3
Good afternoon, I would like someone to help me with the following situation. I am modeling a piping system in CAESAR where the connections to the equipment are made with flexible hoses (a tight corrugated stainless steel tube with or without braided stainless steel mesh suitable for operating within a wide range of temperatures and pressures, capable of compensating for a variety of movements with excellent anti-corrosive properties. They are of annular type and manufactured according to ISO 10380 standard and their end fittings according to ISO 10806 standard).

What would be the best way to model this in CAESAR? Typically, where I work, they don't usually do it assuming that the flexible does not load the connection, so the model ends at the flexible connection flange instead of ending at the equipment connection. However, here is the detail of how I model that connection to be as realistic as possible. I was thinking of modeling it as an expansion joint and inputting the axial and transverse stiffness coefficients without adding the effective diameter, but the flexible supplier tells me they do not have the stiffness coefficients as they are very low and considered negligible, loading very little. What do you recommend I do?

"Attached are images of the flexible hoses. There are hoses for cryogenic service that are vacuum insulated, and others for gas, drains, and lubricating oil that are basically the same."
NATURAL_GAS_aux9x9.png

cryogenic_service_dvojrs.png
 
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OP said:
What do you recommend I do?
Click to expand...

Listen harder to what the guys at work are telling you.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."
 
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First, you probably won't get full stiffness values for the hoses from the manufacturer, at least I've never been able to get any when asked by clients.

Second, yes, the hose does have some theoretical stiffness similar to engineered expansion joints. However it will be such a low value compared to rigid piping, nozzles, and/or other devices that it won't matter.

More importantly is that the hose is installed properly. See the install guide at the back of any hose catalog - typically I end my model at the inlet of the hose and use the Caesar II output to determine the movements and size the loop/hose properly.
Hoses_yqr5q1.png
 
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And BTW don't tell your client how you are burning through the engineering budget.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."
 
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I would just model it as a free end tbh.

The thing you need to check is the movement, especially axial as hose hate being stretched or compressed or bent outside their accepted radius.

How are these being used?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
 
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Thank you all very much for your contribution, especially to user 1503-44 who helped me a lot with his answers. Greetings.
 
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That was truly my best advice. I meant it with all the best intent. Sorry it was more professional advice than the technical advice you were looking for, but that's the way it is in some cases.

Now I am encouraged, so I will tell you the whole story.
Generally only calculate what you need to calculate to get the required answer at the time the question was asked. The opportunity to investigate details will follow as necessary, if such is required. As you gain experience, you will generally make fewer and fewer calculations. Until then, listen. Ask questions and learn what works. You have to get on the fast track to move up. That's it. Doing detailed calculations for everything puts you in a holding pattern with a slightly downward spiral. Steeply downward, if your colleagues think calculations are not necessary. Do not reinvent the wheel. Do enough of them when you need to to be happy with the result and move on to the next problem. You will likely move up too. Save the detail work for when your boss asks you to investigate further, or for homework and self study time. When in doubt, ask someone with experience if they think calculations to a higher level of detail might reach a better solution and discuss if its "worth the attempt".

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."
 
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Always remember you're modelling it. It will never be perfect or match what actually happens in reality, but you'll be within 25% hopefully. so don't waste time chasing down the last 5% of anything. It won't make any appreciable difference.

There are time when a free end analysis is the right thing to do and this, IMHO, is one of them. I've had the opposite at the end of pipelines where people insisted on modelling a buried pipeline and above ground piping as two separate things which I refused to accept because they would be joined together and exert significant forces and resistance to movement and a free end would give wildly unrealistic results.

A flexible pipe has very little strength or resistance to movement, but as noted above, needs to be used in such a way that you don't end up stretching it or inducing buckling or tight radius.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
 
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jgilrod

Your piping system termination at the flex hose would have to be properly supported and restrained to meet the movement allowance at the flex joint. You can't model a flex joint properly of any use.

Mike
 
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