Plains All American Pipeline LP (NYSE: PAA) announced two major pipeline investments on Feb. 27 amid low oil prices, which are not hurting midstream companies as much as oil and gas exploration and production companies. Houston-based Plains and Oklahoma-based Magellan Midstream Partners LP (NYSE: MMP) formed Saddlehorn Pipeline Co., a 50-50 limited liability company, to build, own and operate a 550-mile pipeline. The Saddlehorn pipeline will transport various grades of crude oil from the Denver-Julesburg…