I am doing stress analysis of DN24", Wall Thickness 38mm (2500#) topside pipeline in Caesar II. My boundary condition is from pig launcher to riser (Insulating flange) and DN18” production line from barred tee to first isolation valve.

As per client requirement following are the cases, which we have to analyze other than the normal static analysis.

CASE01- Dynamic Effect of pigging load in the pipeline. Pig weight is 20kN and pig travel speed is 3.3m/s.

CASE02-Although the above pipeline is gas pipeline but as per client requirement we have to consider dynamic effect of HIPPS valve closing scenario, HIPPS valve closing time is 24sec and the straight run is 12m from HIPPS valve to the first elbow at the upstream.

I want to perform a dynamic analysis, in particular a Time History analysis for the above two cases in Caesar II with the user defined time history waveform.

For the above case01, I am thinking to generate the spectrum (Load Vs Time). Where the time is for pig entry and exits at each 90deg 3D elbow. Which will be same for all elbows and the max. Pigging force can be calculate by the kinetic energy equation (1/2mv^2)/x. where m=20kN, v=3.3m/s and x = distance between elbows.

and in the same way for case02.

Any body can verify or give me valuable suggestion to handle the above cases.

Regards
FAP

I don't think the distance between elbows should affect your force calc, it only affects the time between force application at elbows.
For 1, how about using simple change in momentum over time, with t being the traversal time of the bend (nb. use vector addition when considering change in momentum). I guess this may work out the same if using your approach but with x being length of bend, energy term being doubled to account for change in direction, and force being multiplied by 1.41 due to angle of reaction.
For 2, I don't think you will see major loads from change in momentum. (Max rho.A.v^2) There is a joukowsky hammer effect also but within your relatively short lengths I wouldn't expect a problem. However the riser and pipeline should have been studied by others and could see larger loads due to longer unbalanced lengths.

Martin, Thank you for your suggestion.

Regarding Case01: I studied the COADE seminar notes for different cases and my feeling is that slug (short cylinder of fluid) in a gas pipeline, which is moving with a velocity is similar to pigging scenario in which short cylinder of fluid is replaced with a solid mass. And calculate the forces and impact duration using the equation as below. Is it right to say?
Pigging impact duration = (L-RΘ)/v
Pigging impact dynamic load = ρAv2 = m v2/L
Where,
L – estimated length of the pig
R – bend radius
Θ – bend angle
v – pig travelling velocity
ρ – pig density
m – mass of pig
A – inside area of pipe

Regarding Case02: Agree, but any further hints and ideas will help me to proceed for analysis.

Thanks
FAP

Hi FAP

I think what you suggest is correct for a zero bend radius and is thus conservative. But don't forget, thats the force to stop it travelling in one direction, and you simultaneously need to be applying equivalent force at 90 degrees to turn it the other way. If your pipeline can handle the load then no problems. But consider this - what sort of force do you experience when you drive around a sharp corner at 40mph compared to a gentle bend at the same speed ? Could make a difference especially with 3D or 5D bends.

Case 2 , look for literature on hydraulic transients, eg. one such paper is -
Goodling, E.C., Simplified Analysis of Steam Hammer Pipe Support Loads, ASME PVP-Vol. 149-157, 1989. Maybe your pipeline guys can provide some useful input as well.

and don't forget DLF= 2/0