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Primary bending stress or secondary stress

Primary bending stress or secondary stress

Primary bending stress or secondary stress

I am analysing a manifold/header which is connected to 74 tubes (in two rows) using linear static FEA. The ends of tubes are welded to a rectangular tubesheet. One end of the header is connected to piping. Due to moments from piping, the first joint of tube to tubesheet next to the piping has a high stress. The stress is over the cross section of the tube - one side is in tension, the other side is in compression. My question is which stress limit should I use to assess this stress, Primary bending stress or Primary+Secondary stress?

For a typical branch on a pressure vessel, the stress in the nozzle neck due to a moment should be classified as primary bending stress. However, in my current job, if a tube joint is yielded, the loads will be carried by the surrounding tube joints (self-equilibrating). In this case, can we treat this stress as secondary stress?

RE: Primary bending stress or secondary stress

sounds more like a piping question than FEA ... maybe post in the piping forum ?

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RE: Primary bending stress or secondary stress

Go with the conservative choice unless you can demonstrate (usually using non-linear methods) that the non-conservative choice is appropriate.

RE: Primary bending stress or secondary stress

You say that the high stress is due to moments from piping, so I can't see how this relates to the tube joints yielding. You should better describe you geonetry (sketch) and the loading conditions.

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