Heat exchangers are key components in many industrial systems, including power plants, chemical factories, oil refineries, and HVAC systems. They transfer heat between fluids to ensure processes run smoothly and energy is used optimally. However, with continuous operation, heat exchangers are prone to issues. These problems, if not detected early, can reduce efficiency, increase energy consumption, and even pose safety risks.
What is heat exchanger inspection?
Heat exchanger inspection is the process of examining and assessing the condition of heat exchangers for safe and efficient operation. It involves checking for issues such as corrosion, scaling, fouling, cracks, or leaks that can reduce performance or cause failures.
To avoid financial loss due to a damaged heat exchanger, it is important to purchase fire insurance.
Importance of heat exchanger inspections
Timely inspection of a heat exchanger is important for the following reasons:
- Regular inspection helps you identify scaling, fouling, or blockage that limits heat transfer efficiency.
- When you detect and remove deposits early, the system consumes less energy to achieve the same temperature difference.
- Inspections allow you to spot corrosion, leaks, or wall thinning at an early stage before they escalate into costly system failures.
- Inspection records create a baseline for performance comparison. It helps you track deterioration trends and schedule maintenance.
- Timely inspection saves you from emergency repairs, unplanned shutdowns, and product losses that can result from system breakdowns.
Types of heat exchangers and inspection requirements
The five most common types of heat exchangers are:
Shell tube
This heat exchanger has multiple tubes within a cylindrical shell. Both hot and cold fluids flow separately, meaning one is inside the tubes and the other is around them, for effective heat transfer. Always check corrosion under deposits and tube-sheet joint failures.
Plate heat
This heat exchanger has multiple thin, corrugated metal plates arranged to create alternating channels for hot and cold fluids. Its large surface area allows for quick heat transfer and is suitable for food, chemical, and HVAC applications. When inspecting, check for gasket wear, plate deformation, and scaling that reduce flow and performance.
Double pipe
A double pipe heat exchanger has one pipe inside another. In this, hot and cold fluids flow in opposite directions. You will mostly find them in smaller industrial operations or pilot plants. During inspection, look for scaling, internal corrosion, and weld joint integrity. During inspection, check for gasket wear, plate deformation, and scaling.
Spiral heat
A spiral heat exchanger consists of two metal plates wound into a spiral, forming separate channels for each fluid. They are ideal for handling slurries or viscous liquids common in the chemical and wastewater sectors. During inspection, focus on checking for deposit build-up, channel blockage, and weld cracks.
Air cooled
Air-cooled heat exchangers utilise ambient air as the cooling medium instead of water. They are suitable for refineries and power plants. Since vibrations from fan motors can cause tube fatigue, pay special attention to fin damage, fan imbalance, and dust accumulation that restricts airflow.
Heat exchanger inspection methods
Here are five different heat exchanger testing methods you can use for inspection:
Ultrasonic testing
In ultrasonic testing, high-frequency sound waves are employed to detect wall thickness loss or hidden defects within tubes or shells. Sound waves reflect from material boundaries, and variations in the echoes indicate possible corrosion, erosion, or cracks.
Eddy current
Eddy current testing evaluates non-ferromagnetic heat exchanger tubes, such as those made of brass, copper, or stainless steel. When the probe is inserted into the tube, it generates electromagnetic fields that change with variations in the tube wall condition.
Hydrostatic test
A hydrostatic test involves filling the heat exchanger with water and pressurising it beyond its normal operating limit to detect leaks or structural weaknesses. The pressurised condition helps identify minute cracks or faulty welds that may not appear under regular operation.
Radiographic testing
Radiographic testing uses X-rays or gamma rays to capture images of welds and joints within the heat exchanger. The radiation passes through the metal and forms a radiograph on film or digital sensors, highlighting internal flaws such as porosity, slag inclusions, or cracks.
Dye Penetrant
In this testing method, a liquid dye is applied to the clean surface of the heat exchanger. Leave it for a few minutes to allow it to seep into the tiny cracks. Remove the excess dye and apply a developer. When the dye is drawn back, it highlights defects clearly.
Addressing the most common issues
Here are the most common issues with heat exchangers and the ways to fix them:
- Fouling deposits: Perform regular chemical cleaning and use filtered fluids to minimise impurities. You can also install strainers and apply anti-fouling coatings to reduce deposit formation.
- Tube leakage: Plug the affected tube or replace it if severely damaged. Maintaining proper water chemistry and flow velocity can also help prevent further tube deterioration.
- Corrosion damage: Apply protective coatings and maintain proper chemical treatment of the circulating medium.
- Scaling formation: Scaling occurs when dissolved minerals crystallise on heat transfer surfaces due to high temperature or hardness. You can control it by softening water, reducing temperature gradients, and using descaling agents.
- Pressure drop: Clean both sides of the exchanger for uniform flow distribution. Using computational fluid analysis during design to optimise flow and avoid excessive pressure loss during operation.
- Tube vibration: Install vibration dampers and reduce flow velocity near critical frequencies to minimise mechanical wear and prevent potential tube rupture.
Considerations in Manufacturing
Inspection starts long before the unit is installed. As a manufacturer, you must:
- Use certified alloys and composites that are suited to the operating conditions.
- Ensure inspection ports and removable covers.
- Use IS-certified materials with known corrosion resistance.
- Follow ASME Section IX or IS 814 for weld quality.
Conclusion
Regular heat exchanger safety inspection is important for efficient and long-lasting operation. If you can identify corrosion, scaling, leaks, or vibration early, you can prevent costly failures while maintaining optimal performance and energy efficiency.
While inspection is important, it is also important to have property insurance in place, as it can cover the financial loss arising from damage caused by the heat exchanger.
FAQs
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What are the common signs of a failing heat exchanger?
When you notice a drop in efficiency, unusual pressure drops, leakage, vibration, or contamination between fluids, they are signs of a failing heat exchanger.
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Which testing methods are used during inspection?
To inspect a heat exchanger, you may consider ultrasonic testing, eddy current testing, dye penetrant testing, magnetic particle testing, and hydrostatic testing.
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What safety precautions should be taken before inspection?
During inspection, make sure the equipment is depressurised, cooled, and isolated from all energy sources. Your workers should wear proper personal protective equipment (PPE) and follow lockout/tagout procedures.
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What records should be maintained after inspection?
For proper tracking, maintain detailed records of inspection findings, including photos, test results, repair work, and future maintenance schedules.
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How frequently should a heat exchanger be inspected?
The inspection frequency depends on operating conditions, the type of fluid, and industry standards.