Finite Element Analysis of Split Type Header in Air Cooled Heat Exchanger

Split type header is a part of tube bundle of an Air-cooled heat exchanger, used in refinery and oil & gas production. Typically, header can be considered as a pressure vessel subjected to uniform internal pressure. Hence the header and nozzle in various design and operating conditions needs to be checked and verified for soundness of participating components. Top plate due to uniform internal pressure in the nozzle & header plate can produce high-localized stress and deformation. If the components are not designed for these conditions, safety of the equipment is at stake. Hence check for the stress and displacement of the header during operating condition is carried out using finite element analysis software and observed that header nozzle is free from collapse and serviceability failure. I. Introduction (1) Heat exchangers are systems that transfer heat between fluid mediums. The fluids or gases in a heat exchanger can be mixed or the energy transference can go through a conductive wall that keeps them separate. Air-cooled heat exchangers typically have rectangular bundles containing several rows of tubes. The hot fluid enters at the top of the bundle through nozzle pipe. While air is blown by fans vertically upwards across the tube bank, i.e. counter current flow. Structural integrity of the header box can be checked by using (12) Appendix 13 of ASME Sec VIII Div I and other parts of the exchanger header box with the respective clauses of ASME code. For installing the nozzle on the header box opening is made on it, this opening of the vessel must be reinforced with an equal amount of metal which has been cut out for the opening. The reinforcement may be an integral part of the vessel and nozzle or may be an additional reinforcing pad. In addition the compensation must account for the bending strength as well as the membrane strength. The reinforcement calculations for nozzle openings according to UG-39 are required in addition to bending & membrane strength. However, the calculation of "Area required", according to UG-39, requires that the "required thickness"(tr) be substituted for in the formula, and it has not been calculated, since the method used in Appendix 13 is by assuming a thickness and calculating stresses then comparing with allowable stresses and yield stress. This means that "required thickness" (tr) cannot be directly calculated. Accordingly, the required area "A" cannot be directly calculated however in this case nozzle opening is larger than ½ of the header opening hence is beyond the scope of UG-39 of ASME Sec VIII Div-I and therefore the calculation has to done by finite element method.