In analysis of one Power piping system, i am geting positive displacement in range of 10~15 mm at some of the node points. Earlier 13 M span of 8 inch steam line was unsupported, in that case sag at mid of that spool was coming as "-4" mm, later on i provided +y support at mid of mentioned spool,in this case there is positive displacement coming at one of support poit(& near by nodes). What could be the possible reason, also when I am placing Spring in place of +y support, no +ve displacement is coming.
Can anyone please respond.?

We need to see the model. Open a Support Request on SmartSupport and send in your job file.