Shell and Tube Heat Exchanger, Excess Tube Quantity

Dude.....

There is no guideline or standard....

You, the competent specifyer and purchaser of the heat exchanger, must know what you are doing.

If a datasheet is being filled out for the particular thermal duty, the "fouling factor" is commonly made slightly larger to allow for a certain margin of surface area.

Beware that if the HX is grossly oversized there may be operational problems and issues.

Is thus your first time specifying a heat exchanger ?

For shell-and-tube heat exchangers, normally there is no spare tube. And if there is any spare thing, it should be spare area which means the exchanger has more heat transfer area than the process data required.

You might go to the exchanger mechanical datasheet or technical specification, which should have all related information.

There is some design criteria recommending an oversizing (relevant to Shell and tubes heat exchangers) of either 10% on heat surface or 10 % as design margin on flow rate.

Discuss the issue with the vendor. If the process conditions are specified, the vendor may issue a warranty for the product, in which case, nil spare tubes are needed until the end of the warranty period. However, there is no indication in the original posting as to the duty cycle of the exchanger. If it is 1 x 100% duty, then a few spares might be needed to cover breakdowns beyond the end of the warranty period. If it is 3 x 50% or 4 x 33% then the spare tubes are already installed in the idle exchanger.

Normally while designing heat exchangers, 10% tube's area is kept as ecxess which can be plugged as the need arises while exchanger is in service. Another point is spare tubes which can be replaced by pulling out defectective tube in situ, which is possible only in case tubes are straight and you have got space in front of exchanger for removal and insertion of tube.

For 2nd part there seems no standard, however in older projects normally 10% tubes (min. 4 tube) were procured along with equipments as spares.

It is the mainly regular type of heat exchanger in oil refineries and other large chemical processes, and is suited for higher-pressure applications. To be able to transfer heat well, the tube material should have good thermal conductivity. Because heat is transferred from a hot to a cold side through the tubes, there is a temperature difference through the width of the tubes.