Hi you need to change the default namespace when you make Xquery, here here is two solutions
DECLARE @ExportData XML
SELECT @ExportData =
'<Data xmlns="urn:semi-org:xsd.E142-1.V1005.SubstrateMap">
<BulkData>
<EachData Parts="Test1" />
<EachData Parts="Test2" />
<EachData Parts="Test3" />
</BulkData>
</Data>';
SELECT @ExportData.exist('
declare namespace ns="urn:semi-org:xsd.E142-1.V1005.SubstrateMap";
ns:*/ns:BulkData')
;WITH XMLNAMESPACES (DEFAULT N'urn:semi-org:xsd.E142-1.V1005.SubstrateMap')
SELECT @ExportData.exist('*/BulkData')