Heat exchangers are critical equipment in chemical, petrochemical, fertilizer, pharmaceutical, oil and gas, and power-generation industries. They are used for heating, cooling, condensation, evaporation, heat recovery, and process temperature control.

Among all heat exchanger components, tubes are particularly vulnerable to failure because they are continuously exposed to pressure, temperature, corrosive fluids, velocity effects, vibration, and mechanical stresses.

A single tube failure can result in process contamination, loss of production, environmental emissions, equipment damage, or an unplanned shutdown. Therefore, heat exchanger tube failure analysis is an important part of reliability engineering and preventive maintenance.

This article explains the major causes of tube failure, failure-analysis methods, common failure patterns, and practical prevention strategies.

Why Do Heat Exchanger Tubes Fail?

Heat exchanger tubes can fail because of several interacting mechanisms rather than one single cause.

The most common causes include:

• Corrosion
• Erosion
• Pitting
• Stress corrosion cracking
• Corrosion fatigue
• Vibration-induced damage
• Fouling and under-deposit corrosion
• Thermal fatigue
• Tube-wall thinning
• Mechanical damage
• Improper material selection
• Manufacturing defects
• Excessive pressure or temperature
• Poor water chemistry
• Improper cleaning

Understanding the actual failure mechanism is essential before deciding on corrective action.

Simply plugging a failed tube may restore short-term operation but does not necessarily eliminate the underlying problem.

Common Types of Heat Exchanger Tube Failure

1. General Corrosion

General corrosion causes relatively uniform reduction in tube-wall thickness.

It can occur when the tube material is incompatible with the process fluid.

Factors affecting corrosion include:

• pH
• Temperature
• Chloride concentration
• Dissolved oxygen
• Acid concentration
• Flow velocity
• Contaminants
• Material composition

Carbon-steel tubes, stainless-steel tubes, copper alloys, and nickel alloys each have different corrosion resistance.

Prevention

Material selection should be based on actual process chemistry rather than temperature alone.

Process-fluid analysis should include relevant parameters such as pH, chlorides, dissolved gases, solids, and corrosive contaminants.

2. Pitting Corrosion

Pitting is a localized corrosion mechanism that produces small but deep cavities in the tube wall.

It can be particularly dangerous because the overall tube may appear healthy while localized penetration progresses rapidly.

Chloride-containing environments can be especially challenging for susceptible materials.

Typical Characteristics

• Small localized pits
• Deep penetration
• Leakage with limited overall wall loss
• Frequently observed near deposits or stagnant areas

Prevention

Control water chemistry, minimize stagnant zones, select suitable materials, and maintain appropriate operating conditions.

For stainless-steel equipment, chloride control can be particularly important.

3. Erosion-Corrosion

High fluid velocity can mechanically remove protective surface films and accelerate corrosion.

This mechanism is known as erosion-corrosion.

It is commonly associated with:

• High velocity
• Turbulent flow
• Suspended solids
• Gas-liquid flow
• Improper inlet distribution
• Sharp changes in flow direction

Tube entrances, bends, and regions near impingement plates can be vulnerable.

Prevention

Maintain appropriate design velocity and improve flow distribution where required.

If solids are present, filtration or separation upstream may reduce the problem.

4. Tube Vibration Failure

Tube vibration is a major mechanical failure mechanism in shell-and-tube heat exchangers.

Flow passing across tubes can generate forces that cause vibration.

If the vibration frequency interacts with the natural frequency of the tube, significant damage can occur.

Possible consequences include:

• Tube-to-baffle wear
• Fretting
• Fatigue cracking
• Tube rupture
• Baffle damage

Causes

• Excessive shell-side velocity
• Poor tube support
• Improper baffle spacing
• Two-phase flow
• Flow-induced vibration
• Acoustic excitation

Vibration-related damage should be investigated carefully because simply replacing the failed tube may not solve the problem.

5. Fretting and Tube-to-Baffle Wear

Small repeated movements between tubes and supporting baffles can cause localized wear.

The damaged area may initially appear as a small groove or polished region.

Continued operation can reduce wall thickness until leakage occurs.

Prevention

Engineering solutions may include:

• Improved tube support
• Correct baffle spacing
• Appropriate tube-to-baffle clearances
• Reduced vibration
• Improved flow distribution

6. Stress Corrosion Cracking

Stress corrosion cracking occurs when a susceptible material is exposed simultaneously to a specific corrosive environment and tensile stress.

The cracking process can be difficult to detect visually because cracks may be narrow and deep.

Potential contributing factors include:

• Chlorides
• Temperature
• Residual stress
• Fabrication stresses
• Material susceptibility

Inspection methods such as dye penetrant testing, eddy-current testing, and metallurgical examination may be required depending on the material and failure mechanism.

7. Thermal Fatigue

Repeated temperature changes can produce cyclic thermal stresses in tubes.

Examples include:

• Frequent startup and shutdown
• Rapid temperature changes
• Steam hammer
• Intermittent operation
• Uneven temperature distribution

Repeated cycles can eventually initiate fatigue cracks.

Prevention

Avoid unnecessary thermal cycling and control startup and shutdown rates according to equipment design requirements.

8. Tube Rupture Due to Overpressure

Heat exchanger tubes are designed for specific pressure and temperature limits.

A tube can fail if actual pressure exceeds its allowable design condition or if corrosion has significantly reduced wall thickness.

Pressure-related failure may be caused by:

• Blocked outlet
• Closed valve
• Control-system malfunction
• Thermal expansion of trapped liquid
• Incorrect operating procedure
• Relief-system failure

Proper pressure protection and operating procedures are essential.

How to Perform Heat Exchanger Tube Failure Analysis

A systematic investigation should begin immediately after identifying a tube leak.

Step 1: Collect Operating Data

Record the operating history before the failure.

Important information includes:

• Process temperatures
• Pressures
• Flow rates
• Pressure drop
• Fluid composition
• pH
• Chloride concentration
• Startup/shutdown history
• Cleaning history
• Previous tube failures

Historical trends can reveal changes that may not be visible during inspection.

Step 2: Identify the Failure Location

Determine where the damaged tube is located.

Ask:

• Is the failure near the tube inlet?
• Is it near a baffle?
• Is it close to the tubesheet?
• Is it concentrated in one area?
• Are multiple tubes affected?

The location often provides an important clue about the failure mechanism.

For example, localized damage near a baffle may indicate vibration or fretting, while inlet erosion may indicate excessive velocity or poor flow distribution.

Step 3: Visual Inspection

The failed tube should be carefully examined before cleaning or cutting whenever possible.

Look for:

• Pits
• Cracks
• Grooves
• Deposits
• Discoloration
• Erosion
• Bulging
• Localized thinning
• Mechanical marks

Photographs should be taken and documented.

Step 4: Non-Destructive Testing

Several NDT techniques are useful for heat exchanger tube inspection.

Eddy Current Testing

Eddy current testing is widely used for detecting defects in conductive tubes.

It can identify:

• Pitting
• Cracks
• Wall thinning
• Localized defects
• Tube support damage

Ultrasonic Testing

Ultrasonic testing can be used to measure wall thickness and identify localized thinning.

It is particularly useful for determining remaining tube-wall thickness.

Dye Penetrant Testing

Dye penetrant testing can help identify surface-breaking cracks in suitable materials.

Hydrostatic or Pressure Testing

Pressure testing may be used to identify leakage, subject to applicable engineering procedures and safety requirements.

Step 5: Metallurgical Examination

If the failure mechanism remains unclear, a metallurgical investigation can provide additional information.

The examination may include:

• Microscopic examination
• Chemical composition analysis
• Hardness testing
• Fractography
• Metallography
• SEM/EDS analysis

The objective is to determine whether the failure resulted from corrosion, fatigue, cracking, material defects, or another mechanism.

Heat Exchanger Tube Failure: Diagnostic Table

The Importance of Root Cause Analysis

A common maintenance mistake is to treat tube leakage as an isolated event.

For example:

Tube leakage → Plug tube → Restart equipment

This may solve the immediate leakage but not the root cause.

A better approach is:

Tube leakage → Inspect failure → Identify mechanism → Determine root cause → Correct process/design issue → Monitor remaining tubes

If multiple tubes fail over time, the exchanger should be considered a system-level reliability problem rather than a series of independent tube failures.

How to Prevent Heat Exchanger Tube Failures

1. Select the Correct Material

Material selection should consider:

• Temperature
• Pressure
• Process chemistry
• Chlorides
• pH
• Corrosive species
• Velocity
• Fouling tendency
• Cleaning chemicals

The cheapest material is not necessarily the lowest-cost option over the complete equipment life cycle.

2. Control Water Chemistry

For cooling-water systems, maintain appropriate control of:

• pH
• Conductivity
• Chlorides
• Hardness
• Microbiological activity
• Dissolved oxygen where relevant

Poor cooling-water management can significantly reduce tube life.

3. Monitor Pressure Drop

A gradual increase in pressure drop can indicate fouling or blockage.

A sudden change may indicate a process upset, flow-distribution problem, or mechanical issue.

4. Monitor Heat-Transfer Performance

Track:

• Heat duty
• Inlet/outlet temperatures
• Approach temperature
• Pressure drop
• Overall heat-transfer coefficient

A gradual reduction in performance can provide an early indication of fouling or tube-side problems.

5. Establish Inspection Programs

Depending on service criticality, inspection may include:

• Eddy current testing
• Ultrasonic thickness measurement
• Visual inspection
• Tube sampling
• Vibration monitoring
• Chemical analysis

Inspection intervals should be based on equipment criticality, service conditions, historical failures, and applicable inspection standards.

Practical Heat Exchanger Failure Investigation Example

Consider a shell-and-tube heat exchanger where repeated tube leakage occurs every few months.

Instead of repeatedly plugging leaking tubes, engineers should investigate:

1. Where are the tubes failing?

If failures are concentrated near baffles, vibration may be involved.

2. Is wall thickness reducing?

UT or eddy-current data can establish the corrosion/thinning rate.

3. Is the process chemistry changing?

Check pH, chloride, solids, temperature, and other relevant contaminants.

4. Has flow increased?

Higher flow can increase erosion and vibration.

5. Are deposits present?

Analyze deposits to identify scaling or under-deposit corrosion.

6. Is the material suitable?

Compare actual service conditions with material compatibility requirements.

This approach converts repeated maintenance into a structured reliability improvement program.

Conclusion

Heat exchanger tube failure analysis is essential for maintaining plant reliability and preventing repeated leakage problems. Tube failures can result from corrosion, erosion, pitting, vibration, fretting, stress corrosion cracking, thermal fatigue, overpressure, fouling, or unsuitable material selection.

The most effective investigation combines operating data, failure-location analysis, visual inspection, NDT, metallurgical examination, process chemistry, and hydraulic analysis.

The key principle is simple:

Do not only repair the failed tube—understand why the tube failed.

A well-designed tube inspection and monitoring program can identify degradation before leakage occurs, reduce unplanned shutdowns, improve heat exchanger reliability, and extend equipment service life.