How to build a Crystal Report by using a Session?

using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using CrystalDecisions.Web;
using System.Web.UI.WebControls.WebParts;
using CrystalDecisions.CrystalReports.Engine;
using CrystalDecisions.Shared;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using System.Xml.Linq;
using System.Web.SessionState;


namespace SACSCOCLogin1._1
{
    public partial class ReportFormA : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                string SelectFormula = "{COCINST.inst_id} > 10000 "
                + "AND Mid({COCINST.LongName}, 1, 1) = \"A\"";
            }

            CrystalReportViewer1.Visible = true;
            ReportDocument crystalReport = new ReportDocument();
            crystalReport.Load(Server.MapPath("~/Reports/ReportA.rpt"));
            CrystalReportViewer1.ReportSource = crystalReport;
            CrystalReportViewer1.SelectionFormula = "{COCINST.inst_id} = '" + Session["inst_id"].ToString() + "'";
            //CrystalReportViewer1.SelectionFormula = "{FIN2013.inst_id} = '" + Session["inst_id"].ToString() + "'";
        }

        protected override void OnPreRender(EventArgs e)
        {
            Session["inst_id"] = "inst_id";
            CrystalReportViewer1.Visible = true;
            ReportDocument crystalReport = new ReportDocument();
            crystalReport.Load(Server.MapPath("~/Reports/ReportA.rpt"));
            crystalReport.SetDatabaseLogon
            ("Admin", "master22", @"SQL", "Hot");
            CrystalReportViewer1.ReportSource = crystalReport;
            CrystalReportViewer1.SelectionFormula = "{COCINST.inst_id} = '" + Session["inst_id"].ToString() + "'";
            //CrystalReportViewer1.SelectionFormula = "{FIN2013.inst_id} = '" + Session["inst_id"].ToString() + "'";
        }
        
    }
}