•Results of DNS of transient flow in a pipe are compared with those in a channel.•The transient pipe flow is a laminar–turbulent bypass transition even the initial flow is turbulent.•Correlation between transition Re and free stream turbulence is the same in pipe and channel.•Responses in channel and pipe are the same near the wall but somewhat different in the core. Direct numerical simulation (DNS) is conducted to study the transient flow in a pipe following a near-step increase of flow rate from an initial turbulent flow. The results are compared with those of the transient flow in a channel reported in He and Seddighi (2013). It is shown that the flow again exhibits a laminar–turbulent transition, similar to that in a channel. The behaviours of the flow in a pipe and a channel are the same in the near-wall region, but there are significant differences in the centre of the flow. The correlation between the critical Reynolds number and free stream turbulence previously established for a channel flow has been shown to be applicable to the pipe flow. The responses of turbulent viscosity, vorticity Reynolds number, and budget terms are analysed. Some significant differences have been found to exist between the developments of the vorticity Reynolds number in the pipe and channel flows.