Investigation into the Vibration Characteristics and Stability of a Welded Pipe Conveying Fluid

The stability of fluid conveying welded pipe is of practical importance because the welding induced residual stresses which affected on the vibration characteristics and stability. This paper deals with the vibration and stability of straight pipe made of ASTM-214-71 mild steel, conveying turbulent steady water with different velocities and boundary conditions, the pipe was welded on its mid-span by single pass fusion arc welding with an appropriate welding parameters. A new analytical model was derived to investigate the effects of residual stresses at girth welds of a pipe on the vibration characteristics and stability. The reaction components of the residual stresses at a single pass girth weld in a pipe was used in combination with a tensioned Euler-Bernoulli beam and plug flow model to investigate the effect of welding on the vibration characteristics of a pipe. The stability is studied employing a D-decomposition method. A finite element (FE) simulation was presented to evaluate velocity and pressure distributions in a single phase fluid flow. A coupled field fluid-structure analysis was then performed by transferring fluid forces, solid displacements, and velocities across the fluid-solid interface. A prestressed modal analysis was employed to determine the vibration characteristics of a welded pipe conveying fluid. Experimental work was carried out by built a rig which was mainly composed of a different boundary conditions welded pipes conveying fluid and provided with the necessary measurement equipments to fulfill the required investigations. It has been proven theoretically and experimentally that the residual stresses due to welding reducing natural frequencies for both clamped-clamped and clamped-pinned pipe conveying fluid. Also, we proved that for small fluid velocity (sub-critical), the clamped-clamped and clamped-pinned welded pipes conveying fluid are stable. For relatively high fluid velocities (super-critical) the clamped-pinned welded pipe loses stability by divergence.