IV2014 - How would you model his cutout?

[hfds006]

Here is my situation:

38.0" OD x 1.0" WT length of pipe.

Centered inside it at one end is a 26.0" OD x 1.0" WT length pipe that bent along a 130 ft. bend radius.

See attached file which illustrates the basic premise.

I need to make a cutout in the side of the 38" pipe that will allow the bent 26" pipe to pass thru it.

Assume 1/2" clearance per side so the cutout is 27" nominal.

The cutout will be flame or plasma cut, so ideally the cut edge would perpendicular to the OD of the pipe at any given point. I hope the makes sense.

This is a little out of my normal realm so any advice on how to model the cutout would be greatly appreciated.

Thanks in advance,

Richard in Houston

 ETA: Just realized it 4pm and Friday so this problem has solved itself. Until Monday at least. Have a great weekend everyone.

[graemev]

With the bold assumption that you're looking to make a wrap-around template for the shop...

Make an IDW, placing the flattened version of the file at 1:1 scale with hidden lines shown.  Edit the view and turn on Tangent Edges.  Highlight the view and create a sketch.  Project both penetration shapes, then offset each by your desired amount (1/2".)  Print at full scale (mind your plotter's scaling error) and voila: a wrap-around template for the shop to use.  Note that they must cut along the outermost profile at all times in order to have the interior of the pipe clear the elbow.

If you wish for the 1/2" clearance to be as an offset of the outer surface of the elbow, simply adjust the size of the sketched circle in the revolved surface feature instead of ofsetting the profiles on the drawing view.

[hfds006]

You are correct Graemev, the ultimate goal is to produce a wrap-around pattern for the shop.

For that pattern the intersection at the outside of the larger pipe is all that is needed. So, I assumed "flattening" the part would be the route to take even though that is not a method we ever had a reason to use before.

That discussion led to my reason for posting here which is more for curiosity sake than actual need.

If you needed to, how would you model the cutout as descibed?

Signed,

Curious in Houston

[johnsonshiue]

Hi! I took a quick look at this model. If I undestood the requirement correctly, the simplest way to do it based on the current model state is the following.

Edit Revolution2 -> select the inner circular profile -> change operation from Join to Cut -> OK.

.

Is it what you are looking for?

Thanks!

[mrattray]

Model as surfaces and thicken.

[graemev · Accepted solution]

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@hfds006 wrote:

You are correct Graemev, the ultimate goal is to produce a wrap-around pattern for the shop.

For that pattern the intersection at the outside of the larger pipe is all that is needed. So, I assumed "flattening" the part would be the route to take even though that is not a method we ever had a reason to use before.

If you needed to, how would you model the cutout as descibed?

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Are you SURE you only need the intersection at the outside of the pipe?  You will have an interference as the curved pipe comes past the interior surface towards the "concentric end," hence the complicated version I posted.

If you're model is to include bevelling, the methods posted by others will work well.  If you're looking to model what teh shop wil produce - cutting perpendicular to the pipe's surface - you're opening up a nasty can of worms.  How nasty?  Look at the equations used in the attached.  They generate interior and exterior intersections for branched pipe (lateral at any angle up to a tee of 90°, any centerline offset up to exterior tangency.)  I've done one for a structural support pipe's end cut for the back side of an elbow.  Nasty.  One could be done for an elbow "consumed" by a pipe per your example, I suppose.  Equation curves would be a better solution, I suppose, but I wasn't that much of an expert at the time and haven't felt like revisiting that particular headache just yet. 

[hfds006]

Correct again gremeav. I finally got a chance to look at this a little closer.

Doing a straight (perpendicular to the large pipe centerline) "extrude cut" based on the intersection at both the OD and ID works out pretty well. 

Since Friday the discussion has changed from cutting a "clearance hole" around the elbow to cutting a "tight fit hole" so it could be seal welded on the OD.

If that comes to pass it will complicate matters a bit.

At this point we are just quoting to a major oil company, so typically the plan will change a few dozen times between now and actually building anything.

I remember back in the BC (before CAD) days doing patterns for odd pipe on elbow intersections. NASTY or at the very least TEDIOUS is a good way to describe those.

Thanks to all for all the peplies.

[graemev]

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@hfds006 wrote:

At this point we are just quoting to a major oil company, so typically the plan will change a few dozen times between now and actually building anything.

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Oil & gas are my bread & butter.  As a general heads up, you will likely wind up needing the hole as I described with a reinforcement pad to boot, if not worse.  Welding the elbow to the pipe will involve a full penetration groove weld with fillet cap where you can and a fillet weld where you can`t with a the repad fitting just outside of the weld toe.  Strongbacks may be needed through the intersection area depending on the design pressure.  Good luck, and happy hunting.