Dear members,

We are reviewing a Stress Analysis of 10" Sch. STD - Product line, 5D Bend, A106 Gr.B pipe material, Design Temp of 100 Deg. C and design pressure of 20 kg/sq. cm. Our sub-contractor provided a trunnion / dummy support for the 5D bend in three locations of the vertical run and one location of horizontal run.

In stress analysis, they located a Trunnion/dummy support at the mid node of the 5D bend. But in real practice, the center line of the Trunnion/dummy support will be located inline with the center line of the vertical pipe. The offset distance between the mid node and the end node of the bend will be more.

Is this kind stress analysis for locating Trunnion/dummy support is acceptable. Please clarify.

I have seen a standard Trunnion/dummy support drawing for 3D bend but not for 5D bend.

Is there is a standard practice to provide a Trunnion/dummy support for 5D bend.

Dear Mr.Richard,

Can u please reply, is it a good practice to provide a trunnion support for a 5D bend.

My query is, our subcontractor located the trunnion support at the 5D bend mid node in Caesar-II. What i suspect is in real practice, the location of trunnion support will be in line with the centerline of the vertical pipe. But in caesar, if the support is located at the mid of bend node, the offset distance between the centerline of vertical pipe and mid node of bend will be more. There will be more variation in the result when compared with the real practice of trunnion support to the Caesar modeled trunnion support.

I also want to inform that in our case the load at the trunnion support is critical.

Please clarify.

I can't answer this question, it depends on your company standard, the application, and the fabrication techniques.

If I were you I would ask the subcontractor how they passed the concept, and the supporting calculation if I have a concern first. The answer might be satisfactory.

Making the elbow radius from 5D (might be for the process reason) to 3D will change the stresses, however it will not be as much as you expect in case the trunnion is under the horizontal elbow. But it may be effective under the vertical elbow, and location of vertical trunnion will additionally change the piping behavior in addition to the elbow stresses.

If you can not get anything from your subcontractor or their answer is not satisfactory you may need to involve in FEA, the simple solution is to use FE-Pipe or NozzlePro or FE-BEND. Visit www.PAULIN.COM web site, I guess you will find them easily. For the vertical pipe application FE-BEND might be the solution for you.

Hope it helps.

Ibrahim Demir