Ratings from banks typically don't have an time horizon beyond a year. In the following video, Motley Fool analyst Taylor Muckerman dissects changes for three midstream companies. For him, the two upgrades should hold for longer than a year given the market prospects for natural gas liquids. ONEOK Partners (NYSE:OKS) is even a company that he has been following for quite some time. Why might this company and a peer have been upgraded while a somewhat similar midstream company lost a spot on the ratings ladder? Tune in below for our take.