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Heat Exchangers2026-06-1510 min read

Tube Vibration and Baffle Spacing in Shell-and-Tube Heat Exchangers

Tube vibration is a leading cause of bundle failure in refinery and chemical exchangers. Baffle spacing, shell-side velocity, and tube span limits must be checked at design stage — not after tubes start leaking.

tube vibrationbaffle spacingTEMA unsupported spanshell side velocityheat exchanger failure

When shell-side fluid flows across a tube bundle, vortex shedding creates alternating forces on the tubes. If the shedding frequency approaches the tube's natural frequency, resonance occurs — tubes strike baffles, wear at support points, and eventually fail by fatigue. Acoustic resonance in the shell-side gas space is a second failure mode, particularly in large-diameter shells with low-density vapours.

TEMA Limits on Unsupported Tube Span

TEMA specifies maximum unsupported tube lengths based on tube OD and material. For Class R exchangers, the limits are the most conservative. Exceeding these spans — whether by widening baffle spacing to reduce pressure drop or by omitting baffles in inlet zones — directly increases vibration risk.

Tube OD (mm)Max Unsupported Span — Class R (mm)Max Unsupported Span — Class C (mm)
19.05 (3/4 in)584711
25.4 (1 in)711889
31.75 (1-1/4 in)8891016
38.1 (1-1/2 in)10161143

Shell-Side Velocity Guidelines

High shell-side velocity improves heat transfer but increases vibration risk. Practical design targets:

  • Liquid service: 0.3–1.5 m/s at the minimum flow cross-section (between tubes at the baffle cut).
  • Vapour/gas service: keep ρv² below 744 (kg/m³)(m/s)² at the inlet nozzle to avoid impingement plate requirement; stay below acoustic resonance thresholds in large shells.
  • Two-phase inlet: impingement plate is mandatory when ρv² exceeds TEMA threshold — do not omit to save pressure drop.
  • Part-load operation: check vibration at turndown. Reduced flow lowers velocity but can shift resonance into the operating range.

Design Measures to Prevent Vibration Failure

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Replacing failed tubes without addressing baffle spacing or velocity is a temporary fix. The replacement bundle will fail again unless the root cause is corrected in the redesign.

  • Use rod baffles or no-tubes-in-window (NTIW) designs for high-velocity gas service — eliminates baffle cut-induced vibration.
  • Add intermediate tube supports (mid-span supports) when thermal design requires wide baffle spacing.
  • Specify double-segmental or triple-segmental baffles to reduce cross-flow velocity while maintaining heat transfer.
  • Request vendor vibration analysis (HTRI or proprietary software) for exchangers above 24-inch shell diameter or with vapour shell-side service.

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