Us protocol for colonoscopy mention to get samples from bowel tissue even there is no visual problem. is it right or not?

Not standard practic: I doubt that it is the US Protocol to biopsy normal looking mucosa unless there is a suspicion of some rare inflitrative illness (like Amyloidosis etc). If you do not have symptoms of colon origin, there would be little reason to biopsy normal looking mucosa. What are you searching for? If you can define that, we can guide you better.