Bend Classifications 3D vs 3R 2

[CanOkie]

I have been told that a pipeline 3D bend is equivalent to a bend with a radius of 3 x the outside diameter of the pipe, hence 3D. I have also been told that a 3R bend means the same thing as a 3D bend. They are both 3 x the outside diameter of the pipe. A lot of people get confused about the R in 3R. Does it stand for radius? If it does then how can a 3D and a 3R be equivalent?

Can anyone shed some light on the background of these two terms?

 

[Gator]

I would only expect to see "R" (radius) specifically mentioned on a fabrication drawing as a hard dimension, since the bend radius can theoretically be anything while the "D" (nominal pipe diameter) is obviously fixed.

Piping Design Central

 

[CanOkie]

I come from an inline inspection pigging background. We always refer to bends as 1.5D or 3D, etc. A lot of field maintenance or pipeline construction personnel refer to them as 1.5R or 3R. I have always been curious why they use R instead of D.

 

[BigInch]

Radius "R" = 3 x "D"
Not much else you can say about that.

you must get smarter than the software you're using.

 

[zdas04]

Yeah there is. We are talking about two different centerlines. The "D" is the diameter of the pipe (usually nominal, but sometimes OD). The "R" is the radius of the bend relative to the pipe centerline. So "3D" is leaving out the "Radius" and "3R" is leaving out the pipe diameter. I always specify "3D radius" because I really hate to see pipe fabricators ciphering. A "3D (nominal)" pipe bend in 10-inch pipe would have a bend radius (relative to the centerline of the pipe) of 30 inches. Relative to the inside of the bend it would be 5-3/8 smaller (24.625 in radius) and relative to the outside of the bend it would be 35.375 inch radius.

Like so many things, it is very simple when you use all the words, but "common" shortcuts are only common to insiders. We so often do ourselves a disservice by failing to fully specify what the heck we're talking about.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

 

[BigInch]

"Insiders" = those that know what they are doing and those others that can manage to read a fitting catalogue.

you must get smarter than the software you're using.

 

[LittleInch]

I like the last para. The same applies to bend angles. We all know a 15 degree bend means 15 degrees away from straight ahead or straight pipe, but others have quoted this as a 165 degree bend, which logically it also is as this is the inside angle of the bend.

I've never heard of anyone calling a 3D radius bend a 3R bend before now.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[zdas04]

BigInch, or maybe "bother to read the catalog".

I often see manufactured elbows referred to as "3R" even though it doesn't really communicate. In field bends, some surveyors have really odd designations. I've only seen the 165° terminology on one alignment sheet--I sent it back and had the draftsman use the 15° terminology, I had visions of pipe bent back on itself. The draftsman said "but you can measure the angle my way, your way you have to measure to a virtual line". He was right, but running counter to custom and I wasn't going to let that cat out of the bag.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

 

[Gator]

LittleInch, your example is only 15 degrees away from a 180!

Piping Design Central

 

[zdas04]

Gator, that was his point. I'm not sure I get yours?

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

 

[Gator]

The ohnosecond was when I realized that I wrote 180 but wanted 360.

Piping Design Central

 

[BigInch]

Deviation from straight line is used because pipelines are staked out using a transit, not a *&%&^*&# protractor!

you must get smarter than the software you're using.

 

[BigInch]

Measure a virtual line? What's more virtual than the vertex of an interior angle.
Anyway it's easy enough to figure out, the interior angle is simply 2 x the deflection angle.

you must get smarter than the software you're using.