Hi,

I'm trying to check the axial stress due to thermal expansion in a straight jacketed pipe with 2 spiders at the ends.

First Model:

Core: 2": Stainless steel, length 6000 mm, T = -25°C. Node 20 to 40 with anchor in 20 and +Z node 40
Jacket: 3": Carbon steel, length 6000 mm, T = +50°C, Node 1020 to 1040 with anchors on 1020 Cnode 20 and 1040 Cnode 40.

Axial Stress abtained 115.7 Mpa at node 40.

Second Model:

Core: 2": Stainless steel, length 1000 mm, T = -25°C. Node 20 to 40 with anchor in 20 and +Z node 40
Jacket: 3": Carbon steel, length 1000 mm, T = +50°C, Node 1020 to 1040 with anchors on 1020 Cnode 20 and on 1040 Cnode 40.

Axial Stress abtained 115.7 Mpa at node 40.

How we can obtains the same stress whene the lenght are differents. Logically, the stress have to be higher in first model because the thermal expansion is higher due to the length .

You can check the image attached.

Regardless of element length, for the same structural properties (E and I) and same thermal conditions, equal axial stresses will be imposed.

Generally, each unit length of combined jacket and core pipe has a given expansion and a given axial spring rate which absorbs that expansion.