The carbon steel heat exchanger has been replaced with stainless steel

An increased heat exchange area is required to achieve the same heat exchange efficiency, as stainless steel has a lower heat transfer efficiency than carbon steel.

Since the heat transfer performance of stainless steel is lower than that of carbon steel, if carbon steel heat exchange tubes are replaced with stainless steel ones, it is necessary to increase the heat exchange area of the stainless steel tubes (by increasing the number or length of the tubes). To determine exactly how much more heat exchange area is needed, heat exchange calculations must be carried out, and adjustments are made based on the results of those calculations. Increasing the length yields different results compared to increasing the number of roots; moreover, increasing the number of roots is likely to cause an increase in the inner diameter of the heat exchanger. The specific approach to take depends on which modification scheme you prefer, and after selecting a scheme, heat transfer calculations should be performed before modifying the existing heat exchanger.

But some people say that the thermal conductivity of the material itself has little impact on the overall heat transfer efficiency, and can even be considered negligible. Additionally, using a sufficient corrosion allowance for stainless steel allows for thinner wall thicknesses in the design. Since stainless steel does not tend to form scale, it avoids the problem of reduced heat transfer efficiency that occurs in carbon steel heat exchangers due to scaling. Therefore, switching to stainless steel does not require an increase in the heat transfer area; in fact, it can achieve better heat transfer efficiency within the same area as carbon steel – which is confusing

Firstly, the values obtained from heat transfer calculations represent those without scaling; once scaling occurs, the required heat exchange performance cannot be achieved. Secondly, heat exchange tubes are generally designed without considering a corrosion margin. In theory, when switching to stainless steel tubes, it may be necessary to thicken them, as the elastic modulus of stainless steel tubes is lower than that of carbon steel tubes; if the external pressure on carbon steel tubes is calculated properly, the stainless steel tubes might become unstable under such pressure. The allowable error in engineering can be relatively large; if the requirements are not high, and the heat exchange efficiency remains similar after making equivalent substitutions, then there is no problem. What I mean by taking the calculation results into comprehensive consideration is a thorough approach; especially for devices whose differences exceed your acceptable range, it is necessary to compensate for this by increasing the heat exchange area.

Theoretically, the lack requires an appropriate increase in the heat exchange area, but a calculation is needed to determine whether such an increase should be implemented. In your case, it’s not realistic to increase either the quantity or the length: neither the diameter nor the length of the casing can be changed easily; otherwise, it would be simpler to just replace the entire unit – why go through the hassle of replacing the tubes?-

If it is replaced, the tube sheet also needs to be treated; WOL cladding is chosen for this purpose