Start-up of S&T exachanger

[KenA]

Hi - apologise if this is a dumb question or if it's been asked before but...

When starting up a shell and tube exchanger, is it possible to exceed the design temperature of the cold side if the hot side fluid is started up first on its own?

For example. Imagine an exchanger which uses steam to heat process fluid. The steam condenses on the outside of the tubes. The process fluid is say 50 to 100C and hence the tube design temperature might be 150C. The steam operates at say 200C and hence the shell side design temperature is 250C. If the steam is started first (in order to warm up the exchanger), then the outside of the tubes will be exposed to condensing steam and is there a danger of exceeding the design temperature of the tubes?

This must be a common "issue" and I can't believe that it's not accounted for but I'm struggling to find a definitive answer. Your thoughts are much appreciated!
K

 

[unclesyd]

There should be no problem as the tubes should have been designed to the maximum shell side pressure and temperature.

 

[KenA]

unclesyd,
Thanks - that's what I thought. But what I'm looking for is some documentation (e.g. TEMA standard or ASME/API etc) which states this. If you look at the standard equipment datasheet it will show tubeside and shellside design temperatures which are generally different and there is no clear statement to the effect that the tubes are designed to the max shellside P&T.
K

 

[thermmech]

KenA;

The tubeside Design Temperature is relevant for exchanger components being in contact with the tubeside fluid only.

Exchanger components that are in contact with BOTH fluids [namely: tubes and tubesheet(s)] shall have their DT equal to the higher of tubeside or shellside design tempererature.

 

[Christine74]

If the exchanger is a floating head or a "U" tube exchanger, the above comments would hold true as the tubes and tubesheets would be designed for the higher of the shell-side/tube-side design temperatures, unless stated otherwise on the Manufacturer's Data Report.

If, however, this is a fixed-tubesheet exchanger designed per TEMA, it is likely that the tubes are only designed for the mean operating metal temperature for one or more operating conditions, which may not include the case of shell-side flow only. In this case, you would have to check the manufacturer's design calculations to see which operating conditions the exchanger was designed for.

-Christine

 

[KenA]

Thanks to everyone for their interest.
Christine - I've continued to do my own investigation and I totally agree with your answer. Need to be careful for fixed tubesheets. From a Process engineers point of view, the moral of the story for me is if hot side fluid only is a credible case (eg start-up) then make sure that goes on the Process datasheet so the Thermal designers know to design for it.
K