Pipe Stresses

[Hclrag123]

I am supposed to calculate the Stresses on the Key parts of the Pipe Bending Machine called as Benders henceforth.

Pleae see the attachment. This is used on the Offshore pipes bending.
The Pipe is initially rested on a Table whch is pivoted.
There is a Die whch is curved to some angle and there is a clamp in the end to hold the pipe firmly.

The Table is lifted and the pipe is pressed against the Die. Then the Table tries to rotate at the PIvot and the front end moves up. Due to this the Pipe starts bending against the Die.

Now i m supposed to calculate the stresses on the die and its strength requirements.
Per my understanding the Die is in Compression as well as bending in the entire operation. Please help me.

 

[desertfox]

Hi Hclrag123

Nice photo but we need more information ie pipe size your bending and dimensions of the machine, we can't see enough of that bender to tell you anything.
Start by working out the force to bend the pipe to the right shape.

desertfox

 

[Hclrag123]

Thanks Desert Fox for your response.
I have calculated the Force required to bend the Pipe From the Cylinders Specs I calculated that it is exerting 3000PSi on the Pipe, the Force comes to 3Million Pounds.
The distance i know from the Pressure exerting end to the Centre of the Die and with this i calculate the Bending Moment to be 505500000 Inch Pound.

The Die material Yield stress is 100 KSi and Tensile is 110 Ksi.

How do i proceed to claculate the stresses on this Die? What formulas i should be using?

Thanks in advance.

 

[desertfox]

Hi Hclrag

Can you please post your calculations and some drawings or sketches of the machine, where are these cylinders positioned on the machine, you still haven't provided any information about the pipe or the machine that we could possibly provide help on.
Rather than we spend the next four or five posts extracting what information is in your posession can you please just upload everything you have.
Normally once you work out the forces to bend a pipe you hire/buy a bender capable of those forces, talk to the manufacturer of the bender and see if he can give you any guidence, not sure why your tasked with calculating the dye stresses.

desertfox

desertfox

 

[chicopee]

To bend such pipe, you'll need a mandrel, otherwise,it will flatten on the outside and kink on the inside of the curve.

 

[Hclrag123]

HI, ACtually I am a contractor to this firm and cannot really share much information. Hope you understand my situation.

I have attached a handsketch here. I am new to this forum and do not really know how it works.

In such a scenario i look upon the help on what kind of loads are acting on the Die and what formulas to be used to calculate the Forces and stresses. I assume it is combined compressive and bending only, but not sure.
Similarly the Forces on the Clamp.

 

[desertfox]

hi Hclrag

There is no attachtment

 

[Hclrag123]

OOPS! Sorry, Forgot to attach.

 

[desertfox]

Hi Hclrag123

Well from what I can see from your sketch the die would be in compression but I can see no bending on it.
Just behind the die there is what I would assume is a clamp? now if that is holding the tube or pipe rigid then as I see it, you have a cantilever beam with a support ie the die and a force applied at the end of the pipe via the table cylinder.
To analize the forces involved in the position shown in your sketch, I would treat it as a cantilever beam with the span length starting at the clamp and a intermediate support (the die) acting part way along the beam with the load applied at the table as a distributed load, the beam is statically indeterminate so you need to use superposition to get the die reaction.
The pivot point on the table will also have to react against a shear force during the bending operation.
From the die reaction you need to look at compressive stress of the die and how the reaction force on it affects its supports.
The clamp end will be taking a moment and a direct shear force.
From the cylinder pressure and force you have posted it seems a very large cylinder to me, I calculate the cylinder ID to be 3ft is this correct?
Also to achieve the bending moment as quoted I get a distance of 168.5" again is this correct?
I tried looking at different pipe benders but couldn't find any calculations that would help.
I cannot help any further as you still haven't given:-

pipe size or material to be bent.

Distances and conformation of pivot position, die position, clamp position.

Without a lot more information I cannot go any further.

desertfox

 

[Hclrag123]

Thanks Desertfox.
The Pipe to be bent is a 60" Dia X70/80.
There are 6 cylinders used. the distance 168.5 is the dist of the pivot from the cylinder centre.
The pipe is pushed and held firmly against the die through another set of cylinders at the pivot point itself.
The other end of pipe is held tight on a clamp 15" Width
I will give the length spans shortly.
The pipe does not extend beyond the Table as in picture.

Do you think the Force on both ends of pipe is the same with this kind of arrangement?
If not how do i calculate the force on the clamp end?

 

[desertfox]

Hi Hclrag123

I have looked high and low on the net to try and find force diagrams for pipe benders without any luck sadly.
From what I have seen though its quite a complex calculation to do, from your earlier sketch I made a sketch showing how I think the forces should and what theory to use ie superposition theory to calculate deflections.
I am a contractor myself so I do understand where your coming from but the best advice I can give you, is you need to talk to someone at your place of work, if these benders are what they produce then someone should be able to guide you particularly if this is not your field of expertise.
My sketch by the way is just before the pipe yields and starts to bend so the deflection I am talking about is the elastic deflection, one other point is if the pipe diameter is large ie 60" compared to its length then this beam theory is not valid.

 

[Hclrag123]

Thank you Desertfox.
The Pipe diameter is 1/8th length of Pipe.

I am considering the Dist for calculating the moment to be the distance from the Pivot poin to the Point of Force. One of my friend is arguing that the distance should be from the die to the Force point (end of pipe). Can you please help me interpret this correctly? Thanks inadvance.

 

[lisa247]

I don't mean to sound rude, but should your company not have hired a Stress Engineer to do this job?

 

[rb1957]

i reckon they think they did ...

 

[Hclrag123]

Hello lisa247,
Thats a different story. For now i have taken it up voluntarily.

 

[dhengr]

Hclrag123:
I think we have seen this question and problem before. Look at thread404-315538, and really study it. With these two threads, I think we’ve taught you most of what we can from here, given your level of understanding of the subject. I really think you are in over your head on this problem, and that you need some engineering help right at your side, to guide you as you progress. Dig out some of the text books suggested earlier, and enlist the help of a senior engineer where you work. If they don’t have a senior engineer to help you, they should certainly not be asking you to tackle this problem alone. And, we can’t do your design for you, from here either.

 

[Hclrag123]

Thank you all for your time and help.
I think i solved the problem. will get back if i need any further guidance.