SQL:Looping and Reading from XML type

i have set of records from XML type and i need to loop through the Nodes and extract data from them

    <Data xmlns:xsi="http://ift.tt/ra1lAU" xmlns:xsd="http://ift.tt/tphNwY">
  <Opxmlns="http://ift.tt/1F4yoN3">
    <ID>
      <FDSerial>00000008</FDSerial>
      <Type>1</Type>
    </ID>
    <Param>ParmString</Param>
    <OperationName>ReadData</OperationName>
  </Op>
</Data>

i already read from the record but i need to loop through the Nodes

    ;WITH XMLNAMESPACES('http://ift.tt/1F4yoN3' as ns) 
SELECT  Data.value('/Data[1]/ns:Op[1]/ns:ID[1]/ns:FDSerial[1]', 'varchar(50)')
        as Serial   
  FROM [dbo].[DB]

what i need to replace the # 1 with i in a loop