Laying piping in trenches

[hlyada001]

For laying a 36" NB pipe (thickness 0.472") and 40 ft length sections, I need to find the maximum radius of curvature that the pipe would bend to under it's own weight. The pipe is to be placed in a trench and so i need to know what allowable curvature the trench can be for the pipe to follow the curvature under it's own weight.

 

[BigInch]

You need to find out the minimum{/b] radius that the pipe will bend under its own weight without overstress.

Bending_Stress = Bending_Moment / section_modulus
Set Maximum bending stress = the max allowed longitudinal stress
and calculate the max bending moment.
Be sure you limit the maximum bending stress to the yield stress.

Calculate moment of intertia, I,
find E, Young's modulus
curvature = M/EI = d²y/d²x
from that curvature you can calculate the minimum radius it can bend to while still avoiding overstress.

Hold that radius as a minimum and it doesn't matter how it is deformed, by it's own weight, or by any kind of bending during the lowering operation, it simply cannot be overstressed by bending.


If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[bimr]

Use of the standard deflection formula for steel pipe allows the designer to calculate the bending stress and drive the minimum radius of curvature.

Welded steel pipe design manual:

http://www.steeltank.com/LinkClick.aspx?fileticket=Mj3tZdJ5OwA=&tabid=94&mid=452

Contractors use a rule of thumb to calculate the minimum radius of curvature.

The pipe radius in inches, multiplied by 100 gives the radius of curvature in feet. An NPS 12 pipeline will have a minimum radius of curvature of 360 m (1200 feet).

Design radii can be longer than the minimum, the rule of thumb is presented as a planning guideline.

 

[CPENG78]

hlyada001,
Also, ensure that you check with the agency in jurisdiction and what the pipe will be used for. For instance, some sewer districts reduce the allowable manufacturer or calculated bending radii as a safety factor since it will be utilized to convey sewer.

 

[BigInch]

Safer would be to increase the bend radius.

If it ain't broke, don't fix it. If it's not safe ... make it that way.