TEMA DEU/CEU Heat Exchanger - Connection Challenges & Analysis

[MchA]

Hello Everyone,

I am currently designing a TEMA type DEU (or CEU) Heat Exchanger and am encountering some challenges, particularly regarding the simulation of the shell-to-tubesheet connection.

Below are the key design conditions for the heat exchanger:

• Design Code: ASME VIII-1 Ed. 2023
• Design Pressure SS / TS: 85.5 barg + FV / 125 barg + FV
• Design Temperature SS / TS: 190 °C / 390 °C

Materials:

• Shell Course: ASME SA-516 Gr.70 + WO SA-240 321
• Shell Girth Flanges: ASME SA-765 Gr.2 + WO SS 347
• Channel + Tubesheet:
  • Option 1: ASME SA-765 Gr.2 + WO 347
  • Option 2: ASME SA-182 F321
• Exchanger Tubes: SAF 625 (Strength expanded and strength welded)

I have the following concerns and questions, and I would greatly appreciate your insights and, if possible, any direct experience you might have:

• Tubesheet Bolts: The original drawing specifies 2 3/8" bolts, a size not typically found in the TEMA standard. Is this size characteristic for such applications, despite not being under the TEMA standard?
• Shell Girth Flange to Tubesheet Connection (DEU Type): The connection uses captive bolts within the tubesheet. However, for a DEU type, the channel typically does not feature an extended tubesheet configuration where the channel's outer diameter is smaller than the tubesheet's. Could this pose a simulation challenge? I'm finding it difficult to accurately model the tubesheet and the interface between its outer portion and the shell girth flange. Do you have any experience with this kind of TEMA Type? Does this configuration meet the DEU type definition?
• CEU Type Design (Extended Tubesheet): If I consider a TEMA CEU type design, I can have an an extended tubesheet (configuration e, ASME VIII-2), but typically with through-bolts (not captive). The code provides calculations only for the extended portion. I suspect this simulation might not be fully realistic. Perhaps it would be more accurate to treat the extended portion of the tubesheet as an "integral flange" (even if this is a somewhat forced interpretation). Do you have experience with this type of heat exchanger? Would through-bolts be preferable to captive bolts in this scenario? How might I best consider this kind of connection and interaction in the analysis?
• Temperature Difference & Material Compatibility: I am significantly concerned about the large temperature difference between the shell side (190 °C) and the tube side (390 °C). Furthermore, in the second channel configuration (with SA-182 F321 Integral as tubesheet/channel material), there is also a notable difference in materials between major components (e.g., carbon steel shell vs. stainless steel channel/tubesheet/tubes). How do these factors impact thermal stresses and potential issues like differential expansion? What design considerations or mitigation strategies should be prioritized here?
• Nozzle Self-Reinforcement: In several high-pressure designs (like this one), nozzles are made with butt-welded self-reinforcement. Is this a mandatory requirement or merely a common practice driven by experience and conservative design principles? Do you have any advice on this?
• Diaphragm Gasket: Is there any way to avoid the use of a diaphragm gasket in this specific design, and if so, what are the potential implications or alternative solutions?
• Design Improvement: Lastly, are there any ways to improve this heat exchanger design, perhaps in terms of efficiency or cost, given the current specifications?

Thank you in advance for your attention and for any suggestions or shared experiences.

 

[EdStainless]

I stopped reading after the materials list, thermal expansion is a big deal.
From RT to 390C, let's assume an 8m long unit. the expansion would be:
Shell - 39mm
overlay - 56mm
Tubes - 46mm
As for construction I would recommend against using captive bolts is corrosive service.

 

[Trestala]

Try considering NEU type heat exchanger since you're using corrosion resistant alloy in the tubes and weld overlay on the base metal anyway. That would address a lot of your design issues. Do you need mechanical cleaning for the shell side?

With that pressure as well, it would be difficult designing that captive bolts or girth flange. The bolting would also experience additional loading from the weight of the channel. You might need to add a saddle on the channel.

 

[georgeverghese]

Hazop should have indicated that design T should be same on both sides. Design T should also state the range in temperatures from min design to max design for each side. Ask the plant operator what are the design cases for temp on both sides for diff thermal expansion consideration. Am not familiar with TEMA D head, have yet to see this being used in design or in a plant.

A materials selection engineer ought to chip in on possible galvanic corrosion concerns between tubes and tubesheet.