minimum thickness and MAWP calculation for pipe bends

[Mr. P]

Dear All,

I need your assistance on the minimum thickness and MAWP calculation for pipe bends based on ASME B31.3 clause 304.2.1;

The minimum required thickness of a bend after bending in its finished form is calculated by:

t-min = (PD)/2[(SEW/I)+PY]

where at the intrados (inside bend radius)

I = [4(R1/D)-1]/[4(R1/D)-2] @ Example : I = [4(76.2/60.3)-1]/[4(76.2/60.3)-2] @ ANSWER is 1.33

and at the extrados (outside the bend radius):

I = [4(R1/D)+1]/[4(R1/D)+2] @ Example : I = [4(76.2/60.3)+1]/[4(76.2/60.3)+2]@ ANSWER is 0.86

To complete the equation;
t-min = (1689*60.3)/2[(20000*1*0.86/I)+(1689*0.4]

Problem - Unsure the value of I?

Secondary, how to calculate the MAWP for pipe bends?

Your advice is highly appreciated and advance thank you for your support.

 

[XL83NL]

B31.3 doesn't recognize or define the therm MAWP.
If you do the math for I[sub]int[/sub] and I[sub]ext[/sub], you will find its a dimensionless number.
What units are you using in the eq., and are they consistent? It seems you use mm for pipe dia, but for pressure and stress it looks like psi, is that correct?

The temperature seems to be 1100°F in this case, correct?

Huub
- You never get what you expect, you only get what you inspect.

 

[Mr. P]

Thank you for highlighting and just realised the unit mixed up.

I have corrected according to as in below;

I = [4(R1/D)-1]/[4(R1/D)-2] @ Example : I = [4(3/2.37)-1]/[4(3/2.37)-2] @ ANSWER is 1.32

and at the extrados (outside the bend radius):

I = [4(R1/D)+1]/[4(R1/D)+2] @ Example : I = [4(3/2.37)+1]/[4(3/2.37)+2]@ ANSWER is 0.85

To complete the equation;
t-min = (244.9687*2.37)/2[(20000*1*0.86/I)+(244.9687*0.4]

So, How do I get the value of I?
Do I need to calculate separately? as the example below?
t-min = (244.9687*2.37)/2[(20000*1*0.86/1.32)+(244.9687*0.4]
t-min = (244.9687*2.37)/2[(20000*1*0.86/0.85)+(244.9687*0.4]

or Maximum I value of 1.32 instead 0.85?
t-min = (244.9687*2.37)/2[(20000*1*0.86/1.32)+(244.9687*0.4]

Secondary, since B31.3 doesn't recognize or define the therm MAWP.

How to calculate the maximum of remaining thickness?

 

[LittleInch]

The equation gives you the calculation for the minimum bend thickness based on the radius for inner and outer extremes.

That's it. Use that to specify or measure your bend. Normally then you want thicker pipe to start with so that when bent, the bend remains within the min thickness calculated.

This appears to be a very tight bend (3in radius for a 2.37in diam pipe).

B31.3 doesn't use MAWP, it uses design pressure.

I'm not really understanding your problem / issue here.

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

 

[marty007]

So, How do I get the value of I?
Do I need to calculate separately? as the example below?
t-min = (244.9687*2.37)/2[(20000*1*0.86/1.32)+(244.9687*0.4]
t-min = (244.9687*2.37)/2[(20000*1*0.86/0.85)+(244.9687*0.4]

The intrados/extrados calculations will result in three different required thicknesses for the pipe after bending.
[ol 1]
[li]Internal surface of the bend: t-min = (244.9687*2.37)/2[(20000*1*0.86/1.32)+(244.9687*0.4] = ti (t-internal)[/li]
[li]External surface of the bend: t-min = (244.9687*2.37)/2[(20000*1*0.86/0.85)+(244.9687*0.4] = te (t-external)[/li]
[li]Sidewall surface of the bend: t-min = (244.9687*2.37)/2[(20000*1*0.86/1.00)+(244.9687*0.4] = ts (t-sidewall)[/li]
[/ol]

So, if you measure the pipe wall thickness after bending, you'll have three different thickness criteria depending on where you're doing your measurement. You need to communicate these requirements to your bending contractor to ensure they can meet the required thicknesses AFTER bending.

Cheers,
Marty

 

[Mr. P]

Dear marty007,

Highly appreciate your explanation and it's really thoughtful for better understanding.

With regards to a maximum pressure of the bends, I understood the formula to calculate as in below;

((2*t*S*Ej*W/I)/(OD-2*t*Y))*6.894757 = XXXX KPA

Question: The I should be?

where at the intrados (inside bend radius)
I = [4(R1/D)-1]/[4(R1/D)-2] @ Example : I = [4(3/2.37)-1]/[4(3/2.37)-2] @ ANSWER is 1.32

and at the extrados (outside the bend radius):
I = [4(R1/D)+1]/[4(R1/D)+2] @ Example : I = [4(3/2.37)+1]/[4(3/2.37)+2]@ ANSWER is 0.85