Suppose you table is
MyXMLData
and the column name is
XmlDataColumn
SELECT [XmlDataColumn].query('.//InstalledDate').value('.','VARCHAR(MAX)')
FROM [MyXMLData]
With regarding your comments, please check following query
SELECT [XmlDataColumn].value('(//ID)[1]', 'VARCHAR(MAX)') AS ID, [XmlDataColumn].value('(//PartNo)[1]', 'VARCHAR(MAX)') AS PartNo
FROM [MyXMLData]
WHERE [XmlDataColumn].value('(//parent::node()/InstalledDate)[1]', 'VARCHAR(MAX)') ='2013-01-15T00:00:00+05:30'