The best way to welding steel pipe:

First of all, cleaning the oil, paint, water, rust ect. on welded steel pipe,  then opening groove according to the wall thickness , larger open on thick wall, smaller open on thin wall (grinder), then the gap on pipe, usually the diameter of the rod or wire is 1-1.5 times, if you do a mistake and largered the groove , then smaller the gap. Tack welding at least three points, four points better in general work.

When welding should be finish in half and half, the best start point should one centimeter higher than the lowest point which is good for connection.  If the pipe wall thickness, it should be layered, at least two layers, the first layer full circle after welding can weld the second layer.