Connect to database using sys users:
Execute the following query.
Sql>Select * from dba_profiles
Here PASSWORD_LIFE_TIME field is responsible for expiring of password after 180 days.
Execute following command to disable this feature:
Sql> alter profile default limit password_life_time unlimited;
Now crosscheck for disabling of this feature.
Sql > select * from dba_profiles;
The value in PASSWORD_LIFE_TIME has changed to unlimited. Now password will never expire.