Desuperheater Cracking
Desuperheater Cracking
(OP)
I am currently experiencing cracking in several desuperheaters, and cannot work out why, as they have been ok in the past. The only condition that I can see that does not meet the the data sheet requirements is the spray water pressure, which is 1 -2 Bar high. Is this likely to cause problems in the desuperheater?
Thanks for any help.
Thanks for any help.





RE: Desuperheater Cracking
Where are the location(s) of cracking? Have you performed a visual inspection of the desuperheater nozzle and liner?
RE: Desuperheater Cracking
RE: Desuperheater Cracking
RE: Desuperheater Cracking
Another trick is to de-tune the temperature control loop. If the water control valve is cycling open-close many times per startup , and each quench- warmup sequence counts as a fatigue cycle, the best way to extend the fatigue life is to reduce the frequency of the open-close cycles of the valve.
Yet another means of extdending the life of the spray nozzles is to replace the older injection-quil style simple spray nozzles with tangentially mounted , spring loaded , wide turndown spray nozzles. The old- fashioned injection quil style nozzles , with stainless bodies, would develop thte initial crack in the body of the nozzle due to thermal stress. Traces of Chlorides in the spray condensate would attack this initila crack and the crackmay spread due to chloride stress sensitization. Final failure is caused by hi cycle fatigue , due to fluid elastic vibrations of the quil- its profile in the main flow path will excite such vibrations.
RE: Desuperheater Cracking
Designs that avoid this failure mode include:
a) do not use stainless steel - use an inlcolnel or P91 liner
b) seal weld the inlet section of the liner to steam pipe ass'y. If then is makes the ass'y too rigid for thermal stress reasons, then one can evaluate the use of thermal stress reliefs cut into the liner body.
c) the best design is one that kinetlically defoms the liner to the exact ID of the steam pipe- so called " detna-formed" incolnel liners.
RE: Desuperheater Cracking
RE: Desuperheater Cracking