Lock-exchange suspension gravity current in a tilted narrow pipe is studied experimentally at very low Reynolds numbers. We investigate the interpenetration of a heavy particle-laden fluid on top of a light pure fluid by considering the effects of the initial volume fraction of particles phi(0) and inclination angle of the pipe from vertical beta. Density mismatch between heavy and light phases is maintained low (Boussinesq limit) to allow a stable quasiparallel viscous flow. Pertaining to whether particles stay mixed in the suspension or sediment, three distinct mixing, transitionary, and sedimentary regimes are identified. Results of the classification over a wide range of particle concentration phi(0) is an element of [0.05, 0.50] and inclination angle beta is an element of [0 degrees, 88 degrees] are proposed in dimensionless phase diagrams suitable for industrial calculations. Mixing behavior emerges at sharp inclinations as flow continues steadily along the pipe. Sedimentary behavior is attributed to the decelerating flows that involve dilute or packed suspensions over nearly horizontal angles. To quantify the interpenetration rate, a scaling analysis is performed to approximate the velocity of the particle-laden front for different values of phi(0) and beta. Furthermore, the impacts of the fluid's viscosity and particle size are investigated in detail. Reducing the particle size generally weakens the sedimentary behavior of the flow. Increasing the liquid's viscosity has almost no effect on regime transition, yet it results in slower advancing speed across all tilt angles.
