You don't say what version of Blender you are using, but for a number of versions, Blender has included an add-on that produces several types of pipe joints: elbows, Y-joints, T-joints, C-joints, and N-joints. In versions up through 2.72, this add-on had to be explicitly activated in the add-ons tab of the User Preferences, but since 2.73, the add on has been activated by default. So you may not need to create a new set of pipes. To modify a pipe, see my answer to question 33692
Otherwise, this question appears to be a duplicate of question 27386. One aspect, though, about your image that is not referenced in either the question, or my answer, is flanges on the pipes. Upon some consideration, my personal approach to the flanges on straight pipes would be to model the cylinder, and where I wanted a flange, to locate four loop cuts around the cylinder, scaling the center two edge loops out to make the flange, and moving the other two edge loops towards the flange. Where I was using two fittings to make a joint, I would place the fittings so that there was a gap between them about the size of the flange. I'd then select the two edge loops on either side of the gap, bridge across the gap, and extrude the bridged faces out to make the flange.