Pressure Thrust 3

[PhilEduard]

I thought quickly this could be easy but it seems to give me a bit of confusion. Where you realized a pressure thrust exist, you simply multiply the inside crossectional area of the pipe with its operating pressure and, that is if the change in direction is 90 degree. How do you evaluate this figure if the chage in direction is other than 90 deg, (less than 90 degree)? Thanks for any help.

Phil

 

[rconner]

The formula for thrust at bend is 2PAsin(Theta/2), where P is the pressure (e.g. in psi), A is the effective cross-sectional area (e.g. in inch^2), and Theta is the change in direction of the pipeline effected by the bend (e.g. in degrees). [I believe one can derive this for oneself if one wishes, e.g. by drawing a free body diagram with force arrows PA e.g. pushing from both axial directions on the bend, and then with trigometry or vector addition determining the direction and magnitude of the resultant of these two forces.]

 

[PhilEduard]

rconner, thank you so much for a quick reply. More power to you.

Phil

 

[jte]

Phil-

Another way to look at it is that the pressure thrust is that force which needs to be applied over the cross sectional area to create the longitudinal stress. In essence, reverse deriving the forumula for longitudinal stress. So calculate your longitudinal stress (PR/2t) and multiply by the cross sectional area of the metal of the pipe (~pi*D*t).

jt

 

[BigInch]

Since the OP asks about change of direction, I assume its a pipeline and not a simple (but bent) closed-end vessel with 1 end fixed and 1 sliding support, so its better to use the P/A method. Reverse engineering using longitudinal stress could be complex, since [σ]l can be anywhere from 0 and (1-[ν])* P*r/2/t, depending on the degree of anchoring around the bend and the regidity and location of longitudinal pipe restraints, so [σ]l can vary significantly from segment to segment, esp. if multiple restraints are present (still not including any temperature effects).

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[PhilEduard]

I thank you all guys for refreshing me on this subject. It's been a while (35 years) since I grauated my college and it's interesting to meet incidentally pressure thrust on piping system other than 90 degree. I have confirmed all your mentoring from the hydraulic books. Funny because I asked a lot of MEs and I have not heard anyone knowing the formula on change in direction other than 90 degree. This is the very first time I am using this formula.

Regards,