Hi,

I'd like to ask regarding pipe bending situation where there is also a inner pressure applied.

I have a DN1000 pipe with wall thickness of 11mm. It has a inner pressure of 2,5MPa and the bending moment(using distributed load) affecting at the end of the pipe is 878,8kNm. The inside pressure will cause a tensile force of 1943kN and that is placed on the end of the pipe.

The constraints are so that x-axis is symmetrically constrained, while the top and bottom are constrained in Z-radius and the points on the both sides are constrained in Y-radius.

When there is a bending moment, the stresses should be equal on top and bottom(tension and compression) sides, right? After adding the pressure the tension side(top) should have higher stresses due to the tensile force!?

The results should have a stresses where the top of the pipe(tension side) has higher stresses and the bottom(compression side) has lower stresses. However, this does not happen, instead I get equal stresses on both sides.

If I test it without the tensile force modelled, the stresses differ on the top and bottom, but the compression side has higher stress??

What am I doing wrong in this simulation set up? How am I supposed to model both bending and pressure on the same occasion?

It's not clear to me how your synthetic boundary conditions and load are set up.

So I set up the problem literally on a long section of pipe. A one meter section in the middle is refined. The remote ends are fixed to plates, one fixed the other loaded. Half symmetry is used.

The same result is obtained. A quick review of literature, and experience trying to route pressurized hoses and pipes, suggests that this is expected. Three dimensional objects do not hew to one dimensional beam theory, which requires that planar sections remain planar and ratios between dimensions hold near constant.

Setup,

With pressure only,

Bending only,

Simultaneous bending and pressure,