Center to End Dimensions for Elbows Other Than 45, 90 and 100.

Hi All,

I need the method to calculate the center to end dimensions for long radius elbows with elbow angles other than 45, 90 and 180 Deg. Information provided in some sources I found on the internet( link copied below) is bit confusing. Kindly also provide the basis for your answers.


For example if I want to calculate the center to end distance "B" for a 45 Deg elbow. If I use the formula mentioned then

B = Tan (45/2) * 1.5* D

for a 2" 45 Deg LR elbow

B = Tan(45/2)*1.5*2 = 1. inches = 31.56 mm

The value from the standard dimensions chart, link copied below, for 2" elbow says

B= 35 mm.


I want to know how.

If I understand this, I want to calculate the center to end dimension "B" for an elbow angle of 24.76 Deg for my project.


Thanks and Regards,

Pavan Kumar. The "2" in that table is the pipe size, not the radius. The radius is given for the A value of the 90 degree elbow.

I don't see where 1.5 comes from.

Tan(theta/2) = the straight end distance / radius of the bend at the center of the elbow.

The formula given was because the elbows are not in the table by radius; only by setback. So if all you know is setback, then you need to divide by the tangent(theta/2) to get the original radius. ASME B16.9 section 6.2.4 implies that dimension B is different if you cut the elbow.

SO if you get one made use that formula, but if you cut a 45 elbow you won't get the same dimension.

At least that's my reading of it...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it. Hi3DDave,

I have given an example of a Long radius 45 Deg elbow. For a LR elbow r=1.5 D. for a 2" 45 Deg LR elbow

As per ASME B16.9 Section 6.2.4, the "B" dimension for segmented elbow is given by

Bs= A x Tan(Θ/2)

where is A is the dimension A for the 90 Deg elbow from which the segmenting is being done

A) With this lets says we are cutting a 45 Deg C elbow from a 2" 90 Deg LR elbow

A for 2" LR 90 Deg elbow = 76 mm

Theta = 45 Deg

Therefore Bs = 76 * Tan(45/2) = 76 * 0. = 31.48 mm.

Per the table below the B dimension for 45 Deg elbow is 35mm. That was my question.


B) Lets say I want to cut a 2" elbow with 24.76 Deg C angle what would be the "B" dimension?.

is it Bs = 76* Tan(24.76/2) = 16.68 mm ?

Thanks and Regards,
Pavan Kumar
6.2 4 is not easy to interpret but at the start it says "factory made segments.."

Now I read that to means that the B dimension is somehow an odd dimension.

B16.9 provides 45 and 90 factory made elbow dimensions. It doesn't say that you can cut either and get the same thing. So in your B this would be the dimension if you forged a 25 elbow , NOT if you cut it out of a 45 elbow. At least that's my interpretation.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it. I would talk to a shop that does pipe bending, and get them to make the custom bend, cut the ends to whatever it is they can cut them to, and weld that section of pipe in. Alternatively do a double 90 or 90 & 45 offset if you can take the elevation/dimensional change in your assembly. Hi 3DDave , LittleInch ,TBP ,KevinNZ ,

I am modeling an existing pipe from a distillation tower overhead to the overhead condenser in CAE Pipe software to do the Pipe Stress Analysis. I have to enter the dimensions in this model. I need the "B" dimension for a bend that has an elbow angle of 22.8 deg to input the value in the model. I need the correct way to calculate this "B' dimension. I was using a 45 deg elbow as an example to verify the formula given in B16.9. An accurate input would help me model correctly. This is an existing bend. I am NOT fabricating new one now.

I downloaded a free copy of B16.9 from internet. I will avoid posting it next time.

Thanks and Regards,
Pavan Kumar
The standard radius for that 45 degree fitting is 84.5 mm; for the 90 degree fitting the radius is 76 mm.

It seems like the off-standard fitting could be either one of those or some other radius. If it is a highly stressed area you may have to either make an accurate measurement from the installation or to try likely limits on different runs of the analysis.

When I apply that given:B, find:radius, formula to the 3D version of the 45 degree 2 inch fitting, I get the same radius as the 90 fitting (152 mm); I don't know why the standard for smaller radii don't have consistent radii. Do you want (need) a uniform bent elbow, or one with a variable inlet and outlet tangent (straight) length?
Are you placing the specialized pipe bend as a macro (assembly) with an original at the workpoint on the bend's centerline arc, at the inlet CL, or on the point of rotation? For the analysis I would just use whatever figure ASME B 16.9 calculates.

If this is going to impact your results by 3mm on a 2" elbow I think you've got other problems.

Sometimes there is no perfect answer, so you need to state your assumption (following the calculation in B16.9), stick the dimension in and then run the analysis.

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

how to find piping elbow  3.9 D elbow radius

Link to JIANZHI

90° Long radius elbow center   ÷ 90° short radius elbow center

Example 

अगर किसी एल्बो का सेंटर डाइमेंशन 600 mm है तो उसका हम कैसे पता करेंगे वह कौन सा D है

If the center of an elbow dimension is 600 mm, then how do we know which D it is?

Elbow size 6 inch

Elbow center dimension  600 mm

6″ × 25.4 = 152.2 mm

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600 ÷ 152.2 = 3.9 D elbow

अगर किसी एल्बो का सेंटर 800 mm है तो उसका हम कैसे पता करेंगे वह कौन सा D है

If the center of an elbow is 800 mm, then how do we know which D it is?

Elbow size 6 inch

Elbow center  dimensions 800 mm

6″ × 25.4 = 152.2 mm

800 ÷ 152.2  = 5.2  D elbow