A Hydrocarbon process heater operating in Hydrogen service, with SS347H tube metallurgy, has a design stipulation of 2.75" cold spring to be provided between cross over tubes and radiant inlet tube. During repairs to heater coils, they were taken out by cold cutting from cross overs. After repairs, when they were welded to cross over tubes after giving a cold spring as required by drawing, the inlet tubes are pulled inwards due this tension and hanger rod for this tube is not being able to be welded in position, since it is off from the centre line of other tubes. Has any one got any idea about this cold spring and its nuances? Did any one face such problems and were mitigated? An input is highly appreciated. regards ravi.

Ravi Cold springs used for high temperature process heater coils - are normally calculated and the cold spring tension is adjusted to suit the likely spring expansion for the maximum design temperture of process heater coils (when heater coils are heated to rated design temp). One end is normally kept free to give allowance for expansion due to temperature increase either at the hanger supports connected to main "I" sections or between support plates already welded at both end but with adjustable or sliding bolt holes. If this design arrangement is available, fixing back the heater coil with new or old spring (depends on the expansion stresses the old cold springs had seen during years of operation), no major hurdle will be there or no major mis-match between spring and heater coil will be present. Hope this helps you C.V.Srinivasan Nishi Engineers Pvt Ltd India April 7, 2008 >A Hydrocarbon process heater operating in Hydrogen service, >with SS347H tube metallurgy, has a design stipulation of >2.75" cold spring to be provided between cross over tubes >and radiant inlet tube. During repairs to heater coils, they >were taken out by cold cutting from cross overs. After >repairs, when they were welded to cross over tubes after >giving a cold spring as required by drawing, the inlet tubes >are pulled inwards due this tension and hanger rod for this >tube is not being able to be welded in position, since it is >off from the centre line of other tubes. > >Has any one got any idea about this cold spring and its >nuances? Did any one face such problems and were mitigated? >An input is highly appreciated. > >regards >ravi.