In the previous reports (2001), we presented a miniature inpipe robot called MRINSPECT (Multifunctional Robotic crawler for INpipe inSPECTion) IV which has been developed for the inspection of urban gas pipelines with a nominal 4-inch inside diameter. Its steering capability with three-dimensional differentially driven method provides the outstanding mobility for navigation and the new mechanism for steering can easily adjust itself to most of pipelines or fitting, in which other former inpipe robots can hardly travel as ever. In this paper, we present the strategy and the critical points established on using the speed modulation for the navigation in elbows and branches. The analysis for the navigation inside fittings and curved pipelines is given in detail and it is addressed how to compute the speeds of the independent wheels for the differential drive in elbows and branches.