Need to encrypt column which has partitions using TDE

Hello Experts,

We are using oracle database version 11.2.0.4 in our solution and facing an issue while using column wise encryption using TDE. We are referring below link for TDE-

https://docs.oracle.com/cd/E11882_01/network.112/e40393/asotrans.htm#CHDHAHAB

We are trying to alter an existing column which has partition based on range with below query -

SQL> alter table FILESTORAGE modify("BFILEDATA" encrypt using 'AES256' 'NOMAC' NO SALT);

But not able to alter the same. The query keeps on loading and gets hanged after some time. We tried the same alter query on other test env, which doesnt have column partition and alter works there as expected.