I am trying to use PoI partclass api for getting scale but it is not working for any parthandle.

Hi,

If your goal is to change the scale of the deformed shape, then you could use the SetScale command from the poIScaleCtrl Class API. 

For instance:
set t [clock clicks]
hwi OpenStack
::post::GetActiveModelHandle mod$t
mod$t GetResultCtrlHandle res$t
res$t GetScaleCtrlHandle scale$t                 
scale$t SetInterpolationScaleMode "scale"                   
scale$t SetScale "10 10 10"

More details here:
https://help.altair.com/hwdesktop/hwd/topics/chapter_heads/poiscalectrl_class_r.htm

Also, another simpler solution could be to use the HWC language instead => just type "scale deformed value=10.000000" in the HWC console.

More details about HWC language here:
https://help.altair.com/hwdesktop/hwd/topics/reference/hwc/introduction_hwc_r.htm