Dear all,

In analysis, i have to check liftup displacement in hot and cold sustain conditions. max temp is 65 deg and min -155 deg. if i check both max lift up and min lift-up. some modification in support and i gave a stiffness value as 0.00, and i checked. the stresses will be fail. As per client spec says 1mm. but max lift up is 4mm and min lift up is 15mm. Is it necessary to check the lift up conditions. how i solve the system in all the conditions. please some of guide me.

In this case, reroute the lines to make them stable.

Regards,

Dear dan.

rerouting is not possible....if without considered the liftup, system will be passed. shall i porceed. any justification is possible.....

Dear Shabeer,

Proceeding without lift off check is a wrong approach.
Find the nodes which are lifting and check for the displacements.Proceed further to clear the system by checking SUS stresses after removing supports which are lifting.

Check whether holddown support with guide or axial support can be provided at the lifting node. If possible then check for other nodes which are lifting leaving out holddown support.Also watchout for the holddown load carried by support.

There is a limit available for holddown load based on pipe size and it can be referred from support standard.

But the basic rule is follow the support span accurately to reduce the liftoff problems.

Regards,
SAM.

If rerouting is not possible, can try to put in a spring support where the lift-off is occurring.

Have you checked the operating stresses using Appendix P? If the operating stresses are OK, then your system is safe. Read the first few lines of B31.3 regarding Appendix P.You'll get to know the reason for doing this.

Shabeer,

Your system is having both +ve and -ve temperature. It is possible that some of the supports will be lifting up in max. Temperature case and some may be lifting in min. temperature case (especially if there is vertical leg in piping system.). Since you are checking lift up case by removing supports which are lifting, check lift up on case basis. that is check lift up for max. temperature and min. temperature separately.
If possible rearrange supporting such that there will be minimum support lift up.
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Regards,

KMF

Dear all,

Thanks for your all supports.. with help of your guidance i did. they system are in safe. once again thanks.....