davefitz
Mechanical
- Jan 27, 2003
- 2,927
I am sure there is an already developed a detail that accomplishes the following, but I have not found it published yet.
The issue pertains to modifying the web of the stiffening rings that are installed at intervals around an exhaust stack. The stack shell is thin wall, and the very fast startup of the gas turbine causes this shell to increase from ambient (80 F) to 600 F in 10 minutes. The external stiffening ring, however, takes much longer to heat up, and there will exist a very high thermal stress between the flange and the shell , repeated and reversed twice per startup /shutdown cycle. Fatigue cracking at the weld between the web and stack's shell can be expected after a finite number of cycles.
Hypothetically, if one could kinetically form ( aka detna formed or explosively formed) a web that has an out-of- plane flexibility "bump" in it, the thermal stress could be reduced. Alternately, cutting slots in the web with holes drilled at either end of each slot might also be expected to reduce the thermal stress. Yet, I cannot find any publised designs that have used these trick.
Can anyone advise the techinique used in high temp stacks or columsn, as perhaps in the petroleum processing business?
The issue pertains to modifying the web of the stiffening rings that are installed at intervals around an exhaust stack. The stack shell is thin wall, and the very fast startup of the gas turbine causes this shell to increase from ambient (80 F) to 600 F in 10 minutes. The external stiffening ring, however, takes much longer to heat up, and there will exist a very high thermal stress between the flange and the shell , repeated and reversed twice per startup /shutdown cycle. Fatigue cracking at the weld between the web and stack's shell can be expected after a finite number of cycles.
Hypothetically, if one could kinetically form ( aka detna formed or explosively formed) a web that has an out-of- plane flexibility "bump" in it, the thermal stress could be reduced. Alternately, cutting slots in the web with holes drilled at either end of each slot might also be expected to reduce the thermal stress. Yet, I cannot find any publised designs that have used these trick.
Can anyone advise the techinique used in high temp stacks or columsn, as perhaps in the petroleum processing business?