PIPE SADDLE SUPPORT DESIGN

[RLC32681]

I was requested to design a replacement of an existing pipe saddle support inside a tunnel. The pipe diameter is 900mm and spacing is 7.50m. Does anyone have a guidelines/ procedure on how to design this support.Any opinions are highly appreciated.

Thanks,

Rhie

 

[pennpiper]

You do not need to "Design" one just go here and buy them.

http://www.pipingtech.com/products/ptpcat/pipeshoes/nofw/fig2000.htm

Here are more types:

http://www.reliablesprinkler.com/pdfs/products/Erico 12 - Pipe Supports,Guides,Shields,Saddles.pdf

 

[RLC32681]

i am refering how to size the thickness and width of the saddle.

 

[BigInch]

Flange bending.

Look at your pipe + water test load and distribute it equally on the bearing surface below the saddle. Calculate bending stress on the saddle's flange as a canteliver from the edge back to the web considered as the fixed point. Make sure the bending stress in the falnge is less than 22 ksi.

Web bending

Take about 30% of the weight applied at the bearing flange and calculate bending on the web from bottom of flange to height of the web. Again limit that to 22 ksi.

 

[stanier]

Suggest you could contact Paulin and invest in their software.

 

[BigInch]

Might be a good idea for a vessle, or a critical length of pipe in a nuclear plant, but Paulin's stuff looks like overkill for a pipeline saddle.. IMO.

 

[RLC32681]

Thanks guys for your opinions. To give you a more detail scenario of the above topic, i am planning to design a saddle 120 degrees cut from a carbon steel pipe and supported by a W8x31.

BigInch,

I agree to consider weight of water and pipe. But how about the effect of the vibration since the pipe is pressurized.

I am also curious how did you arrive with 22ksi. I appreciate if you can explain it further.

 

[C2it]

If you want to design support saddles from scratch, there is an excellent section in 'Pressure Vessel Design Manual' by Dennis Moss. It provides a complete procedure for complex stiffened web vessel supports, easily adapted to piping. You can download the entire book as a pdf.

 

[BigInch]

You have vibration on the pipe? You need to offset your supports to unequal spacing or provide intermediate supports as you've probably got some kind of natural frequency and flow velocity interferences. I doubt it was designed for cyclic vibration fatgue.

Mild structural steel ASTM A36 has a 36 ksi yield stress. 22 is 60% yield, which is commonly used as a local flange bending maximum stress.

For this type of application, I wouldn't use anything other than the old Blodget's text, "Design of Welded Structures". More than adequate.

Note that some pipeline codes, B31.8, do not allow direct welding of any kind of support directly to the pipe.

 

[stanier]

AWWA M11 has design information.

 

[RLC32681]

Thank you.

 

[sigma1525]

RLC32681

You did not mention the thickness of your pipe. Even though the saddle may work structurally the pipe may fail locally. The maximum local stress usually occurs just above the tips of the saddle. Regular pipe stress analysis software do not check local stress.

 

[stanier]

Authors Roark & Young or Timoshenko have the formulae for checking local stresses in cylinders in their classic books.

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His Holiness the Dalai Lama.

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