I'm assuming you have defined this column as clob .. and not as
xmltype.
Try this for example:

ORA92> desc txml
Name
Null? Type
-----------------------------------------------------------------
-------- --------------------------------------------
A
NUMBER
B
CLOB

ORA92> select * from txml;

A B
----------
--------------------------------------------------------------------------------
1 <tag1>
<tag2>str1a</tag2>
<tag2>str2a</tag2></tag1>

2 <tag1>
<tag2>str1</tag2>
<tag2>str2</tag2>
<tag2>str3</tag2>
<tag2>str4</tag2>
</tag1>


ORA92> col val format a10
ORA92> l
1 select a, extract(value(t1),'/tag2/text()').getStringVal() val
2* from txml t, TABLE( xmlsequence (extract (xmltype(t.b),
'/tag1/tag2' ) ) ) t1
ORA92> /

A VAL
---------- ----------
1 str1a
1 str2a
2 str1
2 str2
2 str3
2 str4

6 rows selected.


Anurag