Managing Air Cooler Tube Corrosion: Repair and Replacement Strategies

Air coolers are essential in refinery and petrochemical operations, where they facilitate efficient heat transfer by cooling process fluids with air. Over time, however, their tubes can suffer from corrosion and other forms of damage, potentially compromising performance. Understanding how to address these issues through repair or replacement is crucial for maintaining operational efficiency and safety.

Corrosion in Air Cooler Tubes

Corrosion in air cooler tubes can arise from various factors, including environmental conditions, chemical exposure, and operational stresses. Common forms of tube corrosion include:

• General Corrosion: Uniform thinning of the tube walls, often due to prolonged exposure to corrosive substances.
• Localized Corrosion: Includes pitting and crevice corrosion, which can lead to small but significant damage points.
• Stress Corrosion Cracking: Occurs when a combination of tensile stress and a corrosive environment leads to crack formation.

Inspection and Testing

Effective management begins with thorough inspection and testing of the air cooler tubes to determine the extent of corrosion and damage:

• Visual Inspection: Regular visual checks can identify obvious signs of corrosion or damage. However, this method may not detect all issues, especially those hidden within the tube bundle.
• Leak Testing: To detect leaks, the exchanger can be tested on either the shell side or tube side before dismantling. Leaks may be observed at drain points such as disconnected nozzles or open bleeders.
• Advanced Detection Methods: Technologies such as eddy current testing (ET), remote field ET, magnetic flux leakage, laser scanning, and ultrasonic testing (UT) can provide detailed assessments of tube condition. These methods help identify corrosion, pitting, cracking, and other defects.

Repair Strategies

When corrosion is detected, several repair methods can be employed depending on the severity of the damage and operational considerations:

1. Tubeside Repair by Plugging

Plugging involves sealing damaged tubes to prevent leaks. Key considerations include:

• Piercing: Tubes should be pierced at both ends for vertical tubes and at the top and bottom for horizontal tubes to allow venting and drainage. This prevents plug blowout and verifies the integrity of the plug.
• Types of Plugs:

1. Friction Fit Tapered Plugs: Suitable for lower pressure and temperature conditions. These plugs are not recommended for high-pressure services or when the tube cannot be pierced.
2. Mechanical Plugs: Designed for high-pressure and high-temperature environments. These are installed using pneumatic or hydraulic systems and are suitable for severe conditions.

• Documentation: Maintain a map recording the number and location of plugged tubes. A sudden increase in tube failures may indicate the need for a more comprehensive repair or replacement.

2. Tubeside Repair by Sleeving

Sleeving involves inserting a new tube liner into the existing tube. This method is useful for localized damage:

• Installation Methods: Techniques include ball forcing, welding, roller expansion, explosive bonding, and hydraulic expansion. Care should be taken to avoid tube bulging, which can complicate future repairs.
• Documentation: Similar to plugging, a map should track the number and location of sleeved tubes. Significant increases in failures may suggest the need for a tube bundle replacement.

3. Tubeside Repair by Ferrule Installation

Ferrules are inserted into the tube to provide a seal and support:

• Installation: Ferrules can be installed by flanging, expanding, or welding. Ensure that the ferrule fits uniformly inside the tube to avoid complications.

4. Tubeside Repair by Pulling Tubes

Pulling and plugging tubes may be an option when other methods are not viable:

• Considerations: This method may cause damage to internal components like baffles. Consultation with a heat transfer specialist might be necessary.

Replacement Strategies

If corrosion or damage is extensive, tube replacement may be necessary:

• Replacing Individual Tubes: This may involve repairing or refurbishing the tubesheet in addition to replacing the affected tubes.
• Replacing the Entire Tube Bundle: In cases where multiple tubes are damaged, replacing the entire bundle might be the most effective solution.

Below video illustrate example tube repair by Sleeving process