hermal expansion on long structures like pipe rack

huangyhg

thermal expansion on long structures like pipe rack
which are the typical considerations against thermal expansion of pipe racks?
i can imagine that a pipe rack (the structure, not the pipes)would be damaged if there are no design considerations like sliding supports, separation between segments ect.
kind regards
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if exposed to the elements, in these environs, i generally limit the length of   
make sure you provide proper pipe expansion joint (accordion like). also, make sure that you restrain the pipe from bucking/getting out of plane by providing proper anchorage at the expansion joint.
good luck
the ideal thing is to miss one bay of the structure (only beams) every 45.0m. this would allow the pipe rack to expand with in that length and no aditional precautions required on any connections.
if you haven't understood my answer, please feel free to write back
regards
puthuran
i would be interested to know what other people do with longitudinal frictional forces where pipes slide metal on metal. i presume that as the temperature increases, the longitudinal force between a pipe and the support beam would increase then decrease when sliding occurs, resulting in a "saw-tooth" variation with time. i have always assumed that the maximum longitudinal forces from adjacent pipes all occur simultaneouly. is this what others do?
thanks for your information! is there any reference available (if possible @internet)?
i have seen already supports like dik mentioned.
the idea of a separation of one bay like puthuran proposed in my case (small pipes and big pipe with different span req.) would require additional foundations or  additional supports.
the expansion of pipes mentioned by lutfi is a matter for other forum (see piping and fluid mechanics engineering). the use of an expansion joint is not as simple as it seems because it adds substantial forces to the pipe rack.
the question of pxc is probably one for the piping forum. a conservative approach may do the worst case approach (all at the same time). this may also be the situation in a plant start-up.
kind regards
typically for a pipe rack:
provide a longitudinal expansion joint every 150'.
for high expansion items such as steam pipes, make piping provide expansion loops and sliding bearings and design for the anchor forces. be sure they do their calculation assuming flexible supports.
use 10% of the vertical load of the pipe as a longitudinal force. (accounts for friction and thermal expansion.) i know some of you will think this is low but i've done many massive piperacks and these numbers work.
regarding the question by pcx, in bridge design a support that is truely free to expand need only be designed for the friction force developed as the structure (pipe) slides over it.  if you have a quality roller, you may want to consider rolling friction rather than sliding friction, but if you are worried about the roller freezing up, then you are back to sliding friction.  if the support and structure are restrained, then a stiffness analysis (or other like method) is needed to predict the force.  for the pipes themselves, i recommend the "accordion like" expansion configuration where the pipe turns back and forth.  this allows the pipe to flex as the temperature changes.  other types of relief mechanisms are available, but i like the accordion types.  good luck.  -  ed
dannym,
two questions:
1. do you mean 10% of the vertical load as distributed load in the longitudinal direction?
2. what do you mean by assuming flexible supports?
thanks!
abcmex,
1. yes - 10% of the vertical (dead + live) load is used as a longitudinal force to be resisted by the beams in minor axis bending locally and at the braced bay globally. this accounts for friction of the pipes due to trermal, pressure, etc. this 10% may seem low for friction, but it is common in many chemical company standards. i've designed many piperacks using it and never had a problem.
2. when calculating the thermal loads from steam pipes etc. don't let the piping stress people assume fixed ends. the supports are beams (weak axis) and they therefore have some flexibility. this flexibility may seem small but it relieves much of the force. also, for high temperature lines have the pipers design expansion loops to relieve the loads on the steel.
keep in mind that a pipe rack typically uses smaller   
dannym
i am pleasantly suprised that you use only 10% of the vertical load as the longitudinal force. i have previously used a much larger number and this is very significant for design.
would you still use 10% if there was only 1 large pipe and the rest were small?
do you know if the value of 10% is based on site measurements or simply on the observation that pipe racks have not fallen down?
if i was to use this lower value in the future, it would be good if you (or someone else) was able to offer a reference such as a research paper or book or design code that can be quoted.