Temperature difference

[tpolleri]

Hello,


I am dealing with thermal expansion for a 32'' Steel pipe that will transport water. Parts of the pipe will be buried and some other exposed. I am very unsure on what to use as dT when calculaten the stress created by thermal expansion. Is is the largest difference in ambient temperature for the area, or the difference between operating temperature and ambient temperature? May something completely different I am not sure. BTW I am trying to calculate linear expansion not radial. Please help!

Sorry for the bad english

 

[BigInch]

You should use the difference between tie-in temperature and maximum temperature, or tie-in temperature and minimum pipe temperature. Max - tie-in will give you the highest axial compressive stress (usually the worst case, because of the combined stress result of "adding" compression with hoop tension stress). Tie-in - Minimum Temperature will give you the maximum axial tension stress.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[tpolleri]

Thank you very much for your answer. I can't find the definition of tie-in temperature online would you please elaborate on that?

 

[BigInch]

It's the ambient temperature at the time when you weld the strings together. Once welded in at that temperature there will be no thermal stress, so it is the "reference temperature" for all thermal stresses developing thereafter.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[spipeliner]

Tpolleri,

You need to use the difference between the the pipe temperature at the time of installation (normally 10 or 15 deg.C) and the warmest or coldest pipe operating temperature.

The idea is to calculate the maximum thermal expansion/contraction of the pipe after installation. Hence, dT= (pipe temp. at the time of installation)-(warmest or coldest metal temp.)

 

[tpolleri]

Thanks everyone for their answers I really appreciate all the help.