ASME B31.3 - 304.2.1 Pipe Bends 1

[flare9x]

In calculating the radius, R[sub]1[/sub]:

Long radius = 1.5 * Pipe Diameter

Is the diameter the outside diameter OR the values taken from ASME B16.9 which are the inside diameter.... or the stated nominal pipe size.

Which diameter is used?

 

[racookpe1978]

Nominal pipe diameter for bend start-stop position calculations.

 

[flare9x]

outside or inside?

 

[racookpe1978]

No. NEITHER ID nor OD!

Nominal OD is a diameter DEFINITION of a specific range of pipe sizes, each of constant standardized OD and a different ID. ALL 6 inch pipe have the same OD - which is NOT 6.00 inches, ALL 10 inch pipe have the same OD - which is NOT 10.00 inches, ALL 4 inch pipe have the same OD - which is NOT 4.00 inches.

(Same for equivlient metric 25 mm, 50 mm, 100 mm, 150 etc. ID is NOT PNOM is NOT OD for pipes under 12 inch PNOM.

 

[flare9x]

right i get that.... 14" NPS = 14" OD...

where NPS 4" = 4.5 OD

So what do i use to work out the radius....

Long radius = 1.5 * pipe diameter...

again which diameter to use?

Or there are values stated:

lets take 2"..

If you do: 1.5 * NPS = 3

if you do 1.5 * OD = 3.5625

For B31.3 pipe bend purposes... which is the correct radius to use, calculated from OD or the tables in ASME B16.9?

 

[LittleInch]

Well it's something I had never checked before but for all the sizes < 14", B 16.9 appears to use the exact nominal OD X 1.5.

So it is 1.5 x nominal diameter in inches.

The radius referred to is the mid point of the bend or bend centerline.



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

 

[flare9x]

Ok In API 579 - the lorenz factor for pipe bends:

NPS 12 * 1.5 = 18

 

[flare9x]

@racookpe1978

Approx ID = OD - 2Tnom

 

[LittleInch]

Strictly speaking, I believe the section listed above in the OP is for when you take normal pipe, heat it up and then bend it, usually to 3D or 5D. There can be some notable bend thinning when this occurs a those sorts of Radii.

The elbows are usually forged and therefore there is no bend thinning as the forging has the same thickness as the pipe.

So be careful not to mix up bend and elbow.

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

 

[flare9x]

@LittleInch

ok but isnt hoop stress same in bend and an elbow ie we design to the stress and the the fabrications methods are independent of each other?

 

[LittleInch]

No because a bend has different wall thickness depending on if its the inside or outside of the bend whereas the elbow is the same wt all the way through

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

 

[flare9x]

Not what im getting at....

Hoop stress acting on a bend stresses the ID, crown and OD etc... hence minimum wall thickness requirements and the differences in the calculations.

If after bending it needs to be n thickness on the ID, crown and OD to adequately handle the hoop stress (governing stress).

So the minimum thickness requirements are independent to how the bend is formed..... as the stresses acting on a bend are similar to an elbow due to geometry.

 

[david339933]

This is a confusing post.....
Based on OP:
R1 is the midline Radius...equal to Dimension A from B16.9....which is based on NPS not ID as all 2" LR elbows have the same A dimension, regardless of schedule.
D is OD of the pipe...d is ID of pipe.

 

[KevinNZ]

Fig 304.2.1 is about making your own bends. The radius can any number you like.