Stress Analysis: High Temperature Line Fails Under Wind/Seismic Loading
Stress Analysis: High Temperature Line Fails Under Wind/Seismic Loading
(OP)
Hello,
I'm currently doing stress analysis in Caesar II on an existing 8" SS line with a design temperature of 1400F. The client would like to know if the line is overstressed and potentially replace it if so. Since this is an existing line, the analysis uses all of the existing springs and snubbers in their current locations.
After making changes, the line is no longer overstressed in Sustained or Expansion cases, but all the Occasional load cases are overstressed. The occasional load cases involve the Sustained Loads (Weight + Pressure) + Wind/Seismic. If guides and directional anchors are added to the pipe, it will fail in expansion and not be able to grow (displacements are +5"). But without them, in a shutdown state, the pipe is susceptible to overstress during high wind or seismic activity.
What are some ways to resolve an issue like this? Any help would be appreciated.
Thanks,
Dmitriy
I'm currently doing stress analysis in Caesar II on an existing 8" SS line with a design temperature of 1400F. The client would like to know if the line is overstressed and potentially replace it if so. Since this is an existing line, the analysis uses all of the existing springs and snubbers in their current locations.
After making changes, the line is no longer overstressed in Sustained or Expansion cases, but all the Occasional load cases are overstressed. The occasional load cases involve the Sustained Loads (Weight + Pressure) + Wind/Seismic. If guides and directional anchors are added to the pipe, it will fail in expansion and not be able to grow (displacements are +5"). But without them, in a shutdown state, the pipe is susceptible to overstress during high wind or seismic activity.
What are some ways to resolve an issue like this? Any help would be appreciated.
Thanks,
Dmitriy





RE: Stress Analysis: High Temperature Line Fails Under Wind/Seismic Loading
"Whom the gods would destroy, they first make mad "
RE: Stress Analysis: High Temperature Line Fails Under Wind/Seismic Loading
hydraulicMECHANICAL snubbers"With that pipe surface temperature, and the huge growth, you will be much happier with mechanical snubbers, and the maintenance folks will be much, much happier. Hydraulic snubbers require a lot of scheduled maintenance. Mechanical ones need a lot less frequent and less messy maintenance. And they can be run a lot hotter than hydraulic ones.
http://en.wikipedia.org/wiki/Mechanical_snubber
RE: Stress Analysis: High Temperature Line Fails Under Wind/Seismic Loading
Dave, Caesar II automatically applies higher allowable stress for occasional load cases. I verified this in the model after reading your comment. Thank you.
The line already has snubbers in place. But from my understanding of snubbers (limited as I've only recently been introduced to and used them in design), they activate during an earthquake for example but are supposed to allow for thermal expansion and regular operating conditions. This means in the C2 model, I have placed displacements on them for those points at the operating conditions, and therefore they become rigid when the occasional loads displaceme the pipe PAST those operating displacements.
However, I am now realizing that snubbers become rigid for vibrations and impulse forces but are supposed to allow for gradual deflection. Would it be accurate then to design with Sustained Case displacements on the snubbers instead of expansion? And if I did so, I assume that my loads and reactions in the Operating + Occasional load cases would be innacurate because the snubbers would be activating much sooner (ie: become rigid at 1" displacement instead of 5").
Thanks again for the replies and help,
Dmitriy
RE: Stress Analysis: High Temperature Line Fails Under Wind/Seismic Loading
Have a look at B31E for seismic!!!!
RE: Stress Analysis: High Temperature Line Fails Under Wind/Seismic Loading
Don't remember who makes it or what it is called; it solved a severe slug shock problem on a coker line in a refinery. Worked beautifully.
RE: Stress Analysis: High Temperature Line Fails Under Wind/Seismic Loading