pipethrust allowance?

[marcoh]

Simple question probably but I have little experience in designing piping systems.

I have a 500mm pipe attached to the side of a building on brackets. The pipe run is fairly simple and essentially a 'Z' shape with 2 right angle bends. The pipe is to be pressure tested to 1000kPa and maximum water velocity is 3m/s.

The pressure thrust (278kN) and velocity thrust (2.5kN)calulation at each bend is simple but will the pressure thrust be transferred to the building at each bend or is the piping system essentially self restrained?

 

[BigInch]

With welded (or glued) piping, there is basically no pressure or velocity thrust that leaves the pipe. Thrusts acting on the interior of the bends is immediately counterbalanced by an equal and opposite axial tension load in the x-sectional area of the pipe. The forces remain internal to the pipe.

Expansion due to pressure and temperature is another matter. The pipe will contract longitudinally due to Poisson's effect from the hoop stresses developed from the pipe's internal pressure and the pipe will either expand or contract due to a temperature change from the pipe's original installation temperature. If there are no physical guides or anchors on your "Z", the only means of transmission of expansion/contraction loads to the building is through the static and dynamic frictional forces of the weight of pipe and contents acting on the supports, as the pipe starts to expand and begin to move. Those expansion loads, in addition to the weight of pipe and contents, wind loads, seismic loads etc. will be transmitted from pipe to the pipe supports and onwards to any structure holding them.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[GregLamberson]

BigInch

A somehwat related question, what about liquid slugs and slug catcher designs? How is that pressure surge calculated and designed for?

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[BigInch]

Its pretty much the same way, as long as you have joints with tensile capacity.

If you have liquid slugs, changes of the liquid's momentum at bends must be resisted by axial tension of the pipe, in the direction from which the slug arrived and a certain amount of shear, perpendicular to the direction at which the slug leaves. Axial tensile forces are removed from the pipe at the first 100% anchor, or are distributed amongst all partially anchoring (< 100% anchor)supports ccording to each supports stiffness to resist the pipe's axial loads, according to the relative portion of the total stiffness of the group of supports taken as a structure, if there are several supports. If the pipe is simply laying on a support (beam or sleeper)and if the momentum forces are larger than frictional forces, the pipe moves, and only frictional loads are imparted to the supports. If buried pipe, then soil cohesive forces and circumferential friction tend to remove the axial loads an inch of pipe length at a time.

Catchers. Change in pressure (surge variation) * x-sectional pipe area * direction components of the pipe geometry entering and/or leaving any node pretty well sums it up. AT the slug catcher, most of the mass does not leave. AT a slug catcher, Liquid mass x change of liquid velocity between entering and stagnation point. if there are no hold down clamps at vertical supports or stops in the axial direction, the pipe lifts off or slides. If there are stops, sometimes the pipe snakes, if the axial load is > buckling load of the pipe "column".

Force * TIME = IMPULSE = mass * change in velocity... almost getting like rocket science now.



BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[GregLamberson]

Thanks for the input.

I've been skipping around on the various forums of late just to see what's out there, maybe in some of the more remote forums (remopte from a pipelining perspective) and last night I had to chuckle as I was going through some of them looking at the more interesting post titles, and while Meteng gets around too - you are everywhere.

I appreciate your prolific posts and spot on advice.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[BigInch]

There's a website in Holland that has quite alot about fluid force and pipe interaction analysis. I'll try to dig it up, or get you a copy of whatever it was I ripped from there. Least I think I ripped them off for something or other.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[marcoh]

Thanks for the replies.

The pipe in question is DN500 steel pipe with victaulic couplings and used for chilled water so pipe will contract when the water is cooled.

 

[BigInch]

Followup, sorry it took so long.

Fluid-Structure interaction website is,

http://www.win.tue.nl/fsi/

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com