In addition to the general pipe stresses (the pressure stress and the moment stress) as described in the previous sections, there are certain local pipe wall stresses produced by:
(1) restraint of the pipe radial thermal and internal pressure expansion of pipethrough- structural-steel type of anchors.
(2) the transfer of load from the supporting surface to the pipe surface over a contact length along the axis of the pipe.
(3) attachments welded to pipe (e.g., lugs and trunnions).
(1) restraint of the pipe radial thermal and internal pressure expansion of pipethrough- structural-steel type of anchors.
(2) the transfer of load from the supporting surface to the pipe surface over a contact length along the axis of the pipe.
(3) attachments welded to pipe (e.g., lugs and trunnions).
Local Stresses and Code Requirements ⬇️
The local stresses SL, SL1, SL2, SL3 can be expressed as follows:
SL = local stress due to deadweight, psi
SL1 = local stress due to deadweight, seismic inertia, and other dynamic loads, psi
SL2 = local stress due to thermal expansion and seismic anchor movement, psi
SL3 = local stress due to concurrently acting loads, psi
The local stresses SL, SL1, SL2, SL3 can be expressed as follows:
SL = local stress due to deadweight, psi
SL1 = local stress due to deadweight, seismic inertia, and other dynamic loads, psi
SL2 = local stress due to thermal expansion and seismic anchor movement, psi
SL3 = local stress due to concurrently acting loads, psi
Strictly speaking, the present piping codes give no specific limits for local stresses. As an industry practice, the calculated local stress is added to the general pipe stress and then compared with the pipe stress allowables specified by the applicable code. As an example, the total (general plus local) pipe stresses for ASME Class 2 and 3 piping shall satisfy the following equations ⬇️
Local Stresses⏬
1. Design loading
2. Service loadings
3. Sustained and thermal expansion loading
4. Local stress limit loading
1. Design loading
2. Service loadings
3. Sustained and thermal expansion loading
4. Local stress limit loading
Local Stress Due to Restraint of Pipe Radial Expansion⬇️
The membrane and flexural stresses can be calculated as follows⏬
In the case of the local stress produced by restraint to the pipe radial expansion SL = SL1 = 0, For fillet weld, i = 2.1 should be used. In addition, the stress check on limit loading is required. Here, SL3 = SL2.
Local Stress Due to Contact⬇️
The membrane and flexural stresses can be calculated as follows:
The membrane and flexural stresses can be calculated as follows: