Is cymbalta (duloxetine) as strong as tramadol for pain relief ?

It's not so much: a matter of strength. They work differently and are used for different types of pain. Tramadol is usually prescribed for acute or temporary pain and can be taken as needed. Sometimes this is not the case, but that's generally the idea. Cymbalta is prescribed when pain is long term or chronic, and needs to be taken daily. If it's not taken as prescribed it will be much less effective.