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Heat
Exchanger Technology
Expanding thicker tube sheets in heat exchangers: a practical guide for operators
Heat exchangers are critical components in nuclear, petrochemical, and energy production, often operating under high pressure and corrosive environments. These demanding conditions frequently necessitate the use of thicker tube sheets to ensure longevity and structural integrity.
While thicker tube sheets offer enhanced durability, they present unique challenges during the tube expansion process. This article provides a practical guide for operators and end-users on effectively expanding tubes into thicker tube sheets.
By Erica Dzomba, Product Marketing Specialist, Elliott Tool Technologies
Understanding the challenges of thicker tube sheets Tube sheet thickness is determined by several factors, including pressure requirements, thermal expansion considerations, corrosion allowance, and the necessary tube support. Industry standards like TEMA, API, and ASME provide specific guidelines for determining appropriate thicknesses. However, thicker tube sheets introduce complexities in the expansion process:
• Increased torque requirements: Expanding a thicker tube sheet requires long reach tooling, leading to significantly higher torque being applied. This increased torque can damage tooling through galling, pitting, or heat damage.
• Uneven expansion: The stepped expansion process used with thicker tube sheets can result in uneven expansion if not performed carefully. Missed areas can create ridges or“ catch points” in the tube, which become potential failure points during operation.
• Work hardening: Overlapping expansion areas or multiple operations in the same location can lead to work hardening of the tube material. This can cause elongation and embrittlement, reducing the tube’ s lifespan.
• Increased time and labor: Expanding thicker tube sheets can require 2 – 4Xs the labor compared to thinner sheets. This is due to the step rolling process, the increased number of tools needed, higher costs, and more extensive setup time for each expansion step.
The expansion process: a step-by-step guide 1. Choosing the right expander Selecting the appropriate expander is crucial for successful tube expansion. Consider the following:
• Tube and tube sheet material compatibility: If the tube and tube sheet materials have similar yield strengths, a multi-roll tool is generally recommended. For high-yield tube materials( e. g., super duplex stainless steel), a short-roll tool is often preferred due to the lower torque applied to the tool.
• Double radius rolls: Using double radius rolls can minimize the formation of ridges during expansion, simplifying the overlap between expansion steps.
Figure 1. SA350 LF2 Tube Sheet, Thickness 8.75” × 66” diameter. Image provided by SHECO- Southern Heat Exchanger.
2. Step rolling technique Step rolling is essential for achieving uniform expansion in thicker tube sheets. Follow these steps:
• Expander setup: Begin with a long-reach expander. Set the tool so that the roll ends approximately 1 / 8” before the back face of the tube sheet. For the next step, use another long-reach tool and set it to overlap the previous expansion by about 1 / 4”. Continue this process until you reach the operator side of the tube sheet.
30 Heat Exchanger World June 2025 www. heat-exchanger-world. com