Modeling of Shell and Tube Heat Exchanger in Caesar II for Stress Analysis

Shell and Tube heat exchangers are frequently used in Oil & Gas, Power plant, Refinery, 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.
  • Sheel side inlet and outlet design temperature.
  • Channel or tube side inlet and outlet design parameters.

Modeling of the Heat exchanger without expansion bellow

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

Schematic of Shell & Tube Heat Exchanger without bellow
Fig. 1: Schematic of Shell & Tube Heat Exchanger without bellow
Region Node No OD & Thickness Process Parameters Temperature Material Length Remark
Fixed Saddle (A) 10000 to 10020 Shell Shell ( Tis + Tos ) /2           Shell Shell OD/2 i.e Length A Fixed Anchor at node 10000
Part of Shell in between Fixed and Sliding saddle (B) 10020 to 10070 Shell Shell ( Tis + Tos ) /2           Shell Length B from equipment GA  
Sliding saddle (C) 10070 to 10090 Shell Shell ( Tis + Tos ) /2           Shell Shell OD/2 i.e Length C Hold Down + Guide at node 10090
Shell part after sliding Saddle (D) 10070-10110 Shell Shell ( Tis + Tos ) /2           Shell Length D from Equipment GA  
Channel Length (E) 10110-10120 Channel Tube ( Tit + Tot ) /2          Channel Length E  
Remaining Shell after Fixed Saddle (F) 10020-10200 Shell Shell ( Tis + Tos ) /2           Shell Length F from GA  
Channel Length (G) 10200-10210 Channel Tube ( Tit + Tot ) /2          Channel Length G  

Here

  • Tis = shell inlet temperature
  • Tos = shell outlet temperature
  • Tit =   tube inlet temperature
  • Tot =   tube outlet temperature

Modeling the Equipment Nozzle Connection

Modeling steps are shown for Nozzle N1

  • At first, model a rigid element from the 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 mechanical datasheet)
  • Then model the element 10230 to 10240 as a flange element with all mechanical and physical properties of the flange (refer mechanical datasheet).

All other nozzle modeling procedure 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 Fig. 2 and Table below that simultaneously to model the elements as shown.

Shell and Tube Heat exchanger with an expansion bellow in the shell
Fig. 2: Shell and Tube Heat exchanger with an expansion bellow in the shell
Region Node No OD & Thickness Process Parameters Temperature Material Length Remark
Fixed Saddle (A) 10000 to 10020 Shell Shell ( Tis + Tos ) /2           Shell Shell OD/2 i.e Length A Fixed Anchor at node 10000
Part of Shell in between Fixed Saddle and Channel (B) 10020 to 10200 Shell Shell ( Tis + Tos ) /2           Shell Length B from equipment GA  
Complete Shell Length (C) 10200 to 10110 Shell Tube ( Tit + Tot ) /2           Tube Length C from GA  
Shell Part in between Nozzle N4 and channel (D) 10110-10100 Shell Shell ( Tis + Tos ) /2           Shell Length D from Equipment GA  
Shell Part in between Nozzle N4 and sliding saddle (E) 10100-10070 Shell Shell ( Tis + Tos ) /2          Shell Length E from GA  
Sliding Saddle 10070-10090 Shell Shell ( Tis + Tos ) /2           Shell Shell OD/2 Hold Down and Guide at node 10090
Channel part (F) 10110-10120 Channel Tube ( Tit + Tot ) /2          Channel Length F from GA  
Channel part (G) 10200-10210 Channel Tube ( Tit + Tot ) /2          Channel Length G from GA  

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

Few companies model the Saddle/Skirt part from the bottom of the shell. In that case rigid element to be modeled from node 10000 and 10090 with saddle length as per GA. (Different saddle temperature 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.

Sample Shell and tube heat exchanger model in Caesar II
Fig. 3: Sample Shell and tube heat exchanger model in Caesar II

Few more Exchanger related resources for You..

Basics of Shell and Tube Heat Exchangers: A brief presentation
An article on Plate Heat Exchanger with Steam
A typical Check List for Reviewing of Shell & Tube Heat Exchanger Drawings
A brief presentation on Air Cooled Heat Exchangers
Basic Considerations for Equipment and Piping Layout of Air Cooled Heat Exchanger Piping
Reboiler Exchanger and System Type Selection

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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.

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