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Reaction forces on Drainage Pipe

Reaction forces on Drainage Pipe

Reaction forces on Drainage Pipe

(OP)
Hello everyone,

This is my first actual post on this website, but I've being using it as a reference for a few months now. :P

I was hoping you guys could help me out with my "simple" project I've been trying to complete at work. I've been asked to add some drainage piping off a steam header to a building drain. The piping (1.5" diameter) will be socket welded (as per in-house spec) to the y-style globe valve and will drop vertically down by ~1ft, then run straight to the drain ~9ft away. I added a flange connection, so the last section of the pipe is removalabe so there is better access for other equipment near by. The entire section of pipe is very close to the ground, approx. 3" above the concrete.

VERY rough sketch :)
http://files.engineering.com/getfile.aspx?folder=b901cfc8-1d45-4e02-a5d1-4196417c2d07&file=rough_sketch.jpg  

The steam header process conditions are ~9200kPa and ~306 deg C. Doing some quick calcs (F=PA; A=flow area), I calculated a reaction force in the y-direction of 2358 lbsf or 10.488kN.

Now here is my issue.... because of the small section of vertical pipe into the drain, isn't all the reaction forces in the y-direction? Isn't the pressure change boundary right at the end of the pipe? ...i.e. the velocity changes there, creating the force? I used a pipe reaction force calculator (http://www.engineeringtoolbox.com/forces-pipe-bends-d_968.html), and it says with a pipe bend at 90deg, the reaction force in the x-direction (my z-direction) is the same as the y-direction, thus you need to use the resultant Force, ~ 14 kN. I was going to use a u-style clamp, bolted down to two HDI Hilti anchor pins, but I guess I can't do this if I need to account for z-direction forces... What do you guys think?

Another question...I know it's just drainage piping, but what kind of sch do you guys recommend? When I first started this project an experienced colleague recommend just simple sch 80, threaded connections. But, after doing some homework, I decided to stay with the same spec as the header (sch 160; no threaded connections, 1500#), which is probably grossly over-designed (it's basically a gun barrel with sch 160!) I just keep thinking, what happens if that piping ever becomes plugged? Our plant runs pretty dirty boiler feed water, and the steam header is only 80% quality, so condensate will be coming out of this line.  

I really appreciate all your thoughts on this! Thanks!    

RE: Reaction forces on Drainage Pipe

Continuous jointed pipe (welded or glued) pick up change of momentum and other forces, by transferring those forces through the welds to equal and opposite reactions of axial force, shear and moments on the attaching pipe.  How those forces are distributed between the two ends of the elbow depend on the relative flexibility of the pipe configuration attached to each end of the elbow. Pipe configurations that are relatively rigid in comparison to more flexible configurations, will carry a higher percentate of the axial, shear and moment stresses.  Once the stresses are transferred to the attaching pipe, they are carried further along until they reach support, guides and anchor points.  So each X,Y,Z force and X,Y,Z moment at a joint will be distributed to reaction points according to the flexibility and rigidity of the pipe in each of the planes.  It could be that its a 50-50 distribution or 90-10. The flexibility matrix of the pipe configuration must be known in order to determine exactly how forces are distributed throughout.

The temperature might suggest that your thermal expansion forces could be more to worry about than your change of momentum forces.

Something sounds wrong about using screwed connections with those wall thicknesses and pressure ratings.  You should always use the same specification as the pipe you attach to, unless you provide some method of pressure control and safety relief device between the two.  Then you create a "specification break", a point where the pipe design specification is changed and note that on the plant piping drawings.    

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch
http://virtualpipeline.spaces.live.com/

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