Hi,
I met unknowable situation at the site.
First of all, civil engineer has designed tank foundation with consideration of short-term and long-term settlement.
During the hydro-test, settlement and rebound occurred as 34mm for fully filled tank and 27mm for empty tank after hydro-test.
We tried to adjust spring hangers connected with the tank few months after the hydro-test, and we checked the indicator on spring when the tank is fully filled and lowly filled points 74mm and 41mm.
Basically, spring moves according to the tank level because the fluid of tank makes elastic settlement. Which means the differential of spring should be around the differential between settlement and rebound when its hydro-test stage. However, in this case, the differential of spring is over 20mm. That phenomenon doesn't make sense for me.
Who can explain that phenomenon? or somebody has similar experience on site?
I need your help.

Thanks.

Hi, From your above explanation it is difficult to predict anything (for me). Please elaborate, like at what distance the spring is located? what are the temp & pressure also the line size you are talking about?

We had seen simmilar cases, but for that the location of spring was not proper, the springs were located far away from tank and pipe routing is such that the expansion displacement was added to move the spring more than the difference in settlement.

Regards,
R.K.

It wouldn't be an answer for your query, but how about considering flexible joint? It will seperate tank settlement and the pipe.

The spring travel will only be the same if the force divided by spring constant is equal to the tank settlement. You would need a highly engineered spring constant to ensure this. Otherwise, the model will treat the spring as a moving pivot point.

I agree with Michael if you use single spring hanger. In case the large displacements are concern the pipe route needs to be adequate and constant load hangers should be implemented at several locations to overcome the settlement problem. Selection of locations for the constant load hangers will be important to be able reduce the number of hangers, sometimes you cannot get away from multiple hangers depending on the pipe diameter and its root/flexibility.

Seismic and wind forces will play additional role in the selection of other supports to control piping and keep the tank nozzle loading under acceptable.

These are to be done in the design stage of the tank and piping, even sometimes in the FEED study. I hope you have everything planned earlier. Later applications will be costly and problematic.

I suggest check the piping again with the stress engineer by providing the required load cases to consider the settlements and the displacements on the hangers. If necessary make the required correction now rather than later.