Dear expert,
We have done pipe stress analysis for natural gas pigging line (aboveground piping with sleeper supports) around 2Km with 3D expansion loop considering design code ASME B31.3 and also the construction/hydro test of the line has been completed for 712.5 psig. Further to that the two times soft pigging was done successfully. Here the 3rd time normal pig is launched and after few minutes found that some portion of the line is fall down from the sleeper supports, line vibration was observed and most of the supports are damaged near the loop portion.

Kindly advice any additional force need to be considered for pigging operation. Also what may be the cause of failure?

Regards,
Venkat.A

You can ask if there are transient forces such as surge/waterhammer (possible source is fast closing valves or pump trip etc.).

Cheers!!

Consider adding external forces (m*a, i.e., the mass of the pig times the accelerator or decelerator) at the loop bends in the CAESAR model.

Bryan
Hexagon CADWorx & Analysis Solutions

Just a suggestion related to Bryan post.
Even the pig has constant speed (and consequently zero acceleration in the direction of velocity), in a circular motion through a curve will be a centrifugal/ centripetal acceleration (due to change of the direction of vector velocity, not necessary to the change in value).
For such case, the "lateral" acceleration may be constant for the pig but is a moving vector for the bend, so is dynamic in nature for your system. You can try with this approach when apply acceleration.
Note that in fact the problem is far complicated due to fluid mechanics involved and how the differential pressure is consolidated through pig motion (and consequently may be an acceleration also in velocity direction, more familiar -because is similar to the "regular" acceleration of a car, as example- but hard to guess it in your case).
Again in my opinion, somehow the problem is similar to a single slug traveling through bends.