Session State variables aren't working

Question

I am using sessionID to keep track of items requested....but its not working the way i had expected. I thought after it times out a different sessionID would be assigned. 

//Get Current SessionID
string sessionID = this.Session.SessionID; 

Problem. 

In IE and Firefox, my sessionIDs keep changing after pressing F5. So pressing 3x you get 3 different sessionIDs. 

sessionID: 3vm1kpxwgg2f5sxbdrrblrrr
sessionID: ekt5b2vzlsewglblzenalsql
sessionID: el23cjjtltk3tvct4ajptjnm

In Chrome browser, it is persisting the sessionID...meaning the stays the same.
sessionID: xwauqxwxqtcmbxmzj1c4vwke
sessionID: xwauqxwxqtcmbxmzj1c4vwke
sessionID: xwauqxwxqtcmbxmzj1c4vwke

Even if I close the browser or logout the sessionID is still the same.  

--- WEB.config ---- 
<system.web>
    <sessionState  cookieless="false"  regenerateExpiredSessionId="true"   timeout="30" />
</system.web>
can you help?