pipeline re routing by avoiding 90 degree bends to 45 degree bends

[JoseEnb]

Dear Seniors,

I have been doing a fine tuning in pipeline re routing by avoiding 90 degree bends to 45 degree bends.
My question is for a 36 inch X70 11.8 mm WT pipeline what are are the advantage and disadvantage of uising 45 degree bend vs 90 degree bend.

Thanks
Joseph

 

[pennpiper]

JoseEnb,
You have not given us enough information.
Example:
How far apart are the 45 degree bends?
Will this line be pigged?
What is the commodity?
Is the pipeline all above ground, all underground or a combination?

Sometimes its possible to do all the right things and still get bad results

 

[dicksewerrat]

The size of the thrust block on the bends.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[JoseEnb]

Dear Pennpiper,

Below are the info you have asked for

1) 90 Degree crossing has 56 to 60 meters
2) 45 Degree Crossing has 80, 88, 112, 135, 151 and 192.
3) Yes the line will be pigged.
4) Dilute Bitumen.
5) All Underground.

Thanks for your time

Regards
Joseph Anthony

 

[pennpiper]

dicksewerrat,
Butt welded steel pipe does not need Thrust Blocks.


JoseEnb,
Bitumen!! Will these lines be Heat Traced to prevent them setting up?

Sometimes its possible to do all the right things and still get bad results

 

[JoseEnb]

Dear Pennpiper,

It will not be Heat Traced.

Thanks
Jose

 

[zdas04]

Are you talking fittings or induction bends? The numbers above all seem to be talking about fittings. I've never used fittings on a pipeline and don't understand why anyone would.

I can't see any benefit of a 8D radius 45 induction bend over an 8D radius 90 induction bend. Your 30 inch welds are kind of expensive and using 2 45's to turn 90 is going to add a bunch of costs.

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

 

[JoseEnb]

Dear Zdas04,

I was talking about 45 degree induction bend vs 90 degree induction bend.
What are the advantage of pipeline routing by 90 degree vs 45 degree (eg crossing pipeline corridor).

Thanks
Jose

 

[zdas04]

You always want to cross a pipeline corridor as close to right angles as humanly possible. People who cross at some other angle cause no end of trouble. Given that, I generally find that some combination of a field bend and an induction bend is required line up properly. Use whatever it takes to hit the corridor square.

In a situation where you are trying to offset a pipeline laterally and keep the two sections parallel, either a 45 or a 90 will work, it just depends on why you are offsetting the pipeline which is best.

Changing overall direction you want to minimize the number of welds (i.e. don't use 2 45's to make a 90).

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]

Why let a good bending machine sit idle; make field bends.
As Zdas says, don't make a 90 with 2x45.
If you need a 45 use a 45, 90 a 90.

A 90 will anchor your pipeline slightly better against axial stress than will a 45. You may want to do that, you may not.

You didn't mention the design temperature.

 

[JoseEnb]

Thanks Zdas04 for your valuable suggestion

Regards
Jose

 

[JoseEnb]

Dear Biginch,

The design temperature is 65 degree centigrade.I am trying to eliminate induction bend and to replace with field bend,and also i am looking for field bend from 1.2 degrees per axial bend to 1.4 degrees per axial bend in oder to eliminate my induction bend angle degree between (20 to 30).

Please corect me if i am wrong

(Thanks Biginch for your valuable suggestion)

Regards
Jose

 

[BigInch]

Per the ASME B31.4 & .8 codes you can bend as much as 1.5 degrees per each length equaling an outside diameter using a minimum bend radius of 40 x OD = 100ft.
Provided that your total longitudinal stress remain within allowable with such a bend. Check that with your stress engineer. 65C might work. 80C+ can get critical quickly. A 90 deg turn will tend to convert axial thermal and pressure stresses into bending stress. A large diameter cold bend will pick up bending load slowly. A tight 90deg induction bend has a much higher stress concentration factor and will pick up bending load much quicker than that large cold bend radius will. Axial stress in the straight run is usually reduced, depending on the joint moving a little bit to alleviate some of that axial load. In an induction bend, the remainder of the axial load is picked up by bending stresses usually developed in the 1/2 length to full length of the next pipe after the induction bend.

Say a minimum of 40 ft joint length - 2 tangents of 2 diameters length each = maximum of 30ft length of bend.
So that allows 30ft/2.5ft = 12 ODs for bending
12 ODs x 1.5 Deg/OD = 30 deg

So you can cold bend each 40ft joint of pipe like this,
1 beginning tangent of 5ft
30 feet of bending length at 1.5 deg/OD = 30degrees
1 ending tangent of 5ft

It will take two of those to make 45deg

First Pipe
1 5ft tangent
30 ft of bend (30deg)
1 5ft tangent remaining

Second Pipe
1 5ft tangent
15ft bend (15deg)
1 20ft tangent remaining

I assume you can work out the 90deg geometry.

 

[LittleInch]

Joseenb,

This thread is going all over the place.

first - "I have been doing a fine tuning in pipeline re routing by avoiding 90 degree bends to 45 degree bends. " Err why??, who told you / asked you to do this? What do you think is the reason?

Then the issue of crossings appears? Where does this link into the first point?

pluses and minuses? - I've seen 2 x 45degree used, as BI says, if the stress on a 90 is too big and you need to effectively spread it out a bit, but at 65C doesn't seem likely.

Practicality could be key here. Without knowing your radius (3D?, 5D?, 8d?) its difficult to calculate but a 36" 90 degree bend can be really quite difficult to transport on a standard flatbed - you do the maths and work it out....

Otherwise 2 45's will cost you a lot more than one 90 plus an extra weld.

Then you're trying to change induction bends for cold bends. Then it comes down to space on your route and again practicality of bending this size of pipe. work out what the actual geometry is for a bend angle of X for a 36" pipe. You rapidly find yourself with a significant sized none straight thing to move around.

So I don't know where you're going with this post - if you can elaborate a bit more you might find some answers.

BTW, your pipe is pretty thin for the diameter - D/t of nearly 80 doesn't give much room for manoeuvre.

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

 

[dicksewerrat]

Pennpiper, I only work with water mains and sewers. Welding pipes is outside my area. Is this forum only for high pressure lines?

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[JoseEnb]

Dear Biginch,

Thanks a lot for sharing your knoweldge and giving your valuable time to educate young engineers like me.

Regards
Jose

 

[JoseEnb]

Dear Littleinch,

Apologize for not providing a big picture to my question.

I am trying to elimnate 90 degee induction bend (which looks like a ladder throughout my pipeline alignment sheet climbing up and down )I am trying to straigtened up pipeline route by replacing with field bends or 45 degree bends. As per my upper management they have asked me to reroute pipeline for cost effective

Bend radius for IB is 6D and for the field bend is 1.2 degree per bend to 1.5 degree bend(48D to 55d)
These are my question while straightening my pipeline
1)Why we need to cross pipeline corridor by 90 degree why dont we cross by 45 degree and what are the advantages and disadvantages crossing 90 vs 45?
2)is it effective to provide field bends or it will take more rooms in routing?
4)All the existing pipeline are strainght and my pipeline in zig zag manner?

My wall thickness is thin i know it, but my management saying i am using very stringent design and increasing the steel tonnage, i dont have any reference to show them that D/T should be less than 80.

My point is to straightened up the pipeline route.

Thanks
Jose

 

[pennpiper]

dicksewerrat,
Re: your question: "Is this forum only for high pressure lines?"
No, this forum is for all piping, low pressure and high pressure, low temperature and high pressure, Steel pipe, Cast Iron and nonmetallic, butt welded and mechanical joint.

You have a long history on this forum and over 1700 replies on Eng-Tips.com. I think you are doing a very good job helping others, please keep it up.

I think you would agree with me, it would help if the original post gave the right/complete information so the readers recognize the real situation and are able to give the right answers.



Sometimes its possible to do all the right things and still get bad results

 

[JoseEnb]

Dear Biginch,

I cant understand the calculation. Can you please elaborate little more.

Say a minimum of 40 ft joint length - 2 tangents of 2 diameters length each = maximum of 30ft length of bend.
So that allows 30ft/2.5ft = 12 ODs for bending (From where do we got 2.5ft?)
12 ODs x 1.5 Deg/OD = 30 deg (I am getting 18 degree.)

I am confused on the second pipe calculation too.
So you can cold bend each 40ft joint of pipe like this,
1 beginning tangent of 5ft
30 feet of bending length at 1.5 deg/OD = 30degrees
1 ending tangent of 5ft

It will take two of those to make 45deg

First Pipe
1 5ft tangent
30 ft of bend (30deg)?
1 5ft tangent remaining?

Second Pipe
1 5ft tangent
15ft bend (15deg)?
1 20ft tangent remaining?

Thanks
Jose

 

[BigInch]

OK 2xOD for 36" actually equals 6' tangents
I tend to use the lowest of either 2xOD, or 5ft.

I see that you could also set a minimum tangent length if you were working with small diameter pipe. Say maybe 24"?