1. Watch the process temperature. Cracking is directly proportional to temperature and residence time.
2. Consider using wet vacuum. Injecting steam thur the vacuum furnace may help reduce cracking. This will infact increase the tube velocity.
3. Pull a deep vacuum.
4. Make sure that pr drop across the vacuum column is minimal.
5. If you have any trays in the column, consider replace with structural packing (or grid in the wash zone).