Shell-and-tube heat exchanger — Failure Modes & Failure Rate

Static heat-transfer device with one fluid in tubes and another in the shell. Failure rate dominated by tube leaks — internal cross-contamination, gradual fouling-driven thinning, or vibration-induced fatigue. Long expected life but the consequence of failure can be major (cross-contamination of process streams, loss of containment).

λ typical

5.0×10-6 / h

Range

1.0×10-6 – 2.0×10-5

Source

EIReDA

Failure modes

Tube leak (cross-contamination)

Root causes: Tube-side or shell-side corrosion thinning the tube wall; chloride stress-corrosion cracking in stainless tubes; tube-to-tubesheet joint failure; flow-induced vibration fatigue at the U-bends or unsupported spans.
Detection: Cross-contamination detected by analysis of the lower-pressure side (e.g. hydrocarbon in cooling water; conductivity rise in steam condensate); shell-side level rise; pressure imbalance.
Mitigation: Material selection per the corrosion environment (duplex stainless, Inconel for severe service); tube vibration analysis per TEMA; eddy-current testing at scheduled inspection intervals; partial re-tubing program. See <a href="/templates/oil_gas_hydrocarbon_release">hydrocarbon-release template</a> for cooling-water cross-contamination scenarios.

Tube plugging (fouling)

Root causes: Scaling from hard water; bio-fouling in seawater service; coke / asphaltene deposition in heavy-hydrocarbon service; particulate deposition with low velocity.
Detection: Fouling-factor trend (UA degrades over time); pressure-drop rise across the tube bundle; thermal-performance shortfall against design.
Mitigation: On-line cleaning systems (Taprogge ball cleaning for water service); chemical-treatment program; periodic mechanical cleaning during turnaround; design with sufficient fouling-resistance margin.

Gasket / flange leak

Root causes: Gasket compression set after thermal cycling; differential thermal expansion between tubesheet and shell; bolt-stud relaxation; gasket-material chemical attack.
Detection: External leak visible at the flange face; gas-detection alarm in hydrocarbon service.
Mitigation: Spiral-wound or kammprofile gaskets for thermal-cycling service; controlled bolt tightening per ASME PCC-1; periodic torque check after first thermal cycle.

Shell-side erosion / corrosion

Root causes: Shell-side velocity exceeding the corrosion-allowance design basis; impingement at the inlet nozzle; sustained vibration.
Detection: Ultrasonic thickness measurement during turnaround; visual inspection at the inlet zone.
Mitigation: Impingement plate at the shell-side inlet; velocity check at design and re-rate stages; periodic UT thickness survey.

Typical applications

Process heating / cooling (refinery, chemicals, power); steam condensers; lube-oil coolers on rotating machinery; gas-gas exchangers in cryogenic service; reboilers and condensers on distillation columns.

How to model in a fault tree

For loss-of-containment / cross-contamination FTAs, the heat exchanger is usually modelled with separate basic events for tube leak (the dominant cross-contamination contributor) and shell breach (lower-rate but higher-consequence). For SIS-protected services where the heat exchanger is between the process and a hazardous downstream system (e.g. ammonia chiller leaking into water side), λ_DU on the tube-leak mode dominates the IPL credit calculation. Periodic eddy-current inspection — a form of revealed-fault testing — directly reduces effective λ_DU.