Heat Exchanger Modeling in Caesar II and Stress Analysis

Shell and Tube heat exchangers are frequently used in Oil & Gas, Power plants, Refineries, and Chemical and Petrochemical industries. As piping systems connected to such equipment are considered Critical, piping stress engineers need to model it quite frequently.  But sometimes, specifically for new stress engineers, the modeling steps seem to be very difficult. In this article, I will try to illustrate the modeling considerations in caesar II.

Two types of shell and tube heat exchangers are used in industrial applications.

1. Heat exchanger without expansion bellow and
2. Heat exchanger with an expansion bellow in the shell.

The thermal profiling considerations i.e, the temperature distribution during Caesar II modeling is different in both cases.

Inputs required for Modeling

Before modeling the equipment the following details need to be collected.

• Equipment GA drawing with all dimensions.
• Fixed and Sliding saddles.
• Shell side inlet and outlet design parameters.
• Channel or tube side inlet and outlet design parameters.

Modeling of the Heat exchanger without expansion bellow

Caesar II modeling of heat exchangers that do not have an expansion bellow is quite easy. Better engineering practice is to model the equipment as a rigid body. Refer to Fig. 1 and the Table below that simultaneously for modeling the elements as shown.

Here

• Tis = shell inlet temperature
• Tos = shell outlet temperature
• Tit =   tube inlet temperature
• Tot =   tube outlet temperature
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Modeling the Equipment Nozzle Connection

Modeling steps are shown for Nozzle N1

• At first, model a rigid element from node 10210 to 10219, other parameters will same as the region (i.e, channel region G in this case). Then put the anchor at node 10220 and connecting node 10219.
• Then model from 10220 to 10230 as the pipe element with all mechanical and physical properties of the nozzle (refer to mechanical datasheet)
• Then model the element 10230 to 10240 as a flange element with all mechanical and physical properties of the flange (refer to mechanical datasheet).

All other nozzle modeling procedures will be similar to nozzle N1 modeling.

From node 10240 onwards connected piping can be modeled.

Modeling of the Heat exchanger with an expansion bellow in the shell

Refer to Fig. 2 and Table below that simultaneously to model the elements as shown.

Nozzle is to be modeled in the same way as shown for the above Heat exchanger.

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Few companies model the Saddle/Skirt part from the bottom of the shell. In that case rigid element is to be modeled from nodes 10000 and 10090 with saddle length as per GA. (Different saddle temperatures are to be considered for these elements, However, shell material, OD, and thickness can be considered for modeling this part.). In such a situation, the fixed anchor and hold down+guide supports need to be considered at the bottom of the saddle.

A sample model is shown in Fig. 3 below.

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Anup Kumar Dey

I am a Mechanical Engineer turned into a Piping Engineer. Currently, I work in a reputed MNC as a Senior Piping Stress Engineer. I am very much passionate about blogging and always tried to do unique things. This website is my first venture into the world of blogging with the aim of connecting with other piping engineers around the world.

One thought on “Heat Exchanger Modeling in Caesar II and Stress Analysis”

1. Aiden says:

where is the bellow when modelling the heat exchanger of expansion bellow in shell?