1. Scope and purpose
This manual covers critical maintenance procedures for plate and shell and tube heat exchangers used in industrial environments. It is designed to provide optimal thermal efficiency, prevent leaks, and extend equipment life. The procedures include cleaning the heat exchange surfaces from dirt, replacing the gaskets and checking the overall thermal performance.
Regular maintenance of heat exchangers is mandatory for maintaining the stability of technological processes, reducing energy consumption and preventing unplanned production stops. This guide should be used during scheduled maintenance when a decrease in thermal efficiency, an increase in pressure drop or external/internal leaks is detected.
2. Precautions
WARNING: Before starting any maintenance work on the heat exchanger, it is necessary to completely de-energize and isolate the equipment. Apply the blocking/marking procedure (LOTO) in accordance with the company's internal standards and the requirements of DSTU EN 10398:2020 "Machine safety. General design principles. Risk assessment and risk reduction."
WARNING: Always use personal protective equipment (PPE), including safety glasses (DSTU EN 166), chemically resistant gloves (DSTU EN 374), protective clothing and, if necessary, respiratory protection (DSTU EN 149) and protective footwear (DSTU EN ISO 20345).
WARNING: Working with chemical reagents (acids, alkalis) requires special care. Consult the Chemical Safety Data Sheets (MSDS/SDS) and follow all handling, storage and disposal recommendations.
WARNING: Hot surfaces, high pressure and residual energy are potential sources of injury. Make sure the heat exchanger has cooled down to a safe temperature (<40°C) and is completely depressurized to atmospheric before opening it.
3. Necessary tools and materials
| The name of the tool/material |
Specification |
Quantity |
| Wrench/socket set | metric, from 13 mm to 36 mm | 1 set |
| Torque wrench | Range: 50–300 Nm, accuracy ±4% | 1 pc. |
| Manometer | Range: 0-10 bar, accuracy class 1.0 | 2 pcs. |
| Digital contact thermometer | Range: -50°C to +250°C, accuracy ±0.5°C | 2 pcs. |
| A set of brushes for cleaning pipes | According to the diameter of the pipes (eg, 15-25 mm) | 1 set |
| High pressure device | Pressure up to 150 bar, consumption 10-15 l/min | 1 pc. |
| Pump for chemical circulation | Productivity 20-50 l/min, resistant to aggressive environments | 1 pc. |
| Means for removing gaskets | Spatulas are plastic, brass | 1 set |
| New sealing gaskets | According to OEM specification (material, size) | Required quantity |
| Lubricant for bolts | Anti-scratch, e.g. copper paste | 1 tube |
| Means for chemical cleaning | Acidic/alkaline solutions, corrosion inhibitors (depending on contamination) | 5-20 l (depends on the volume) |
| Buckets, containers for waste collection | Resistant to chemicals | A few |
| Industrial rag, absorbent | | Sufficient quantity |
| A set of socket wrenches for internal bolts | Depends on the design of the heat exchanger | 1 set |
| Measuring ruler/caliper | To check clearances and dimensions | 1 pc. |
| Plug flange | For sealing pipelines during testing | 2 pcs. |
4. Inspection before service (checklist)
| Item |
Verification |
Acceptance/rejection criteria |
Notes |
| 1. Visual inspection | Inspect the heat exchanger for external leaks, insulation damage, corrosion of flanges and fasteners. | Absence of visible leaks, mechanical damage, significant corrosion. | Record any deviations. |
| 2. Process data | Record the current values of inlet/outlet temperatures and pressures of both circuits (before shutdown). | Deviation from normal operating parameters (±5% from design). | Important for comparison after service. |
| 3. Pressure drop | Check the pressure drop on both circuits of the heat exchanger. | Pressure drop within design values. An increase of 15% or more indicates pollution. | A high drop indicates heavy pollution. |
| 4. Documentation | Check the availability of drawings, diagrams, heat exchanger passport and previous service reports. | Complete and up-to-date documentation. | Necessary to determine the type of gaskets, tightening moments. |
| 5. Provision of LOTO | Ensure that the LOTO is fully completed and confirmed. | All energy sources are isolated, testing for lack of energy has been carried out. | Security critical. |
| 6. Drainage and ventilation | Make sure the heat exchanger is fully drained and ventilated. | There is no liquid/gas inside, the pressure is equal to atmospheric. | Possible residual fluid or pressure. |
| 7. Temperature | Check the temperature of the external surfaces of the heat exchanger. | The temperature is below 40°C. | Hot equipment can cause burns. |
5. Step-by-step procedure
5.1. Isolation and preparation
- Isolation of the heat exchanger: Close all inlet and outlet valves on both circuits of the heat exchanger. Apply LOTO to all valves and pump supplies connected to the heat exchanger. Ensure LOTO is performed according to company security procedures.
- Draining: Open the drain valves at the bottom points of the heat exchanger to completely drain the liquid from both circuits. To speed up drainage, open the ventilation holes at the upper points. Collect used liquids in appropriate containers for further disposal.
- Check for lack of pressure: Using a pressure gauge, make sure that the pressure in both circuits is equal to atmospheric (0 bar).
- Cooling: Make sure the heat exchanger temperature is below 40°C. If necessary, use natural cooling or supply coolant to speed up the process.
5.2. Disassembling the heat exchanger and removing the gaskets
- Removal of insulation (if present): Carefully remove the outer insulation from the flange connections to gain access to the fasteners.
- Unscrewing the fastening bolts: With the help of a wrench or socket heads, in a criss-cross sequence, loosen the fastening bolts of the cover flanges (for shell-and-tube) or tension bolts (for plate ones). Avoid rapid and uneven unscrewing to prevent deformation of flanges or plates.
- Removing the covers/plates: Carefully remove the covers (for shell and tube) or spread the plates (for plate). Use lifting mechanisms if the items are heavy.
- Removing old gaskets: Using plastic or brass spatulas (so as not to damage the sealing surfaces), carefully remove old gaskets from flanges, tube grids or plate grooves. It is strictly forbidden to use metal brushes or sharp objects that can leave scratches on the sealing surfaces.
- Cleaning of sealing surfaces: Thoroughly clean all sealing surfaces of gasket residues, corrosion and dirt. Use a soft cloth and, if necessary, special cleaners compatible with the materials.
5.3. Cleaning of heat exchange surfaces
5.3.1. For shell and tube heat exchangers (pipe cleaning)
- Mechanical cleaning (with brushes): Choose brushes corresponding to the inner diameter of the pipes. Using a flexible shaft or a special air tool, pass the brushes through each pipe. It is advisable to use a low-pressure water supply simultaneously with a brush to wash off dirt. Repeat the procedure several times until the deposits are completely removed.
- Chemical cleaning (if necessary): If mechanical cleaning is not sufficient (for example, to remove solid deposits or scale), use chemical cleaning.
- Solution preparation: Dilute the chemical cleaner (eg, citric acid solution 5-10% or special detergent) according to the manufacturer's instructions. Add corrosion inhibitor. Always add acid to water, not the other way around.
- Circulation: Connect the chemical circulation pump to the tube space of the heat exchanger. Circulate the solution for 2-8 hours (depending on the degree of contamination and concentration of the solution) at a temperature of 40-60°C. Monitor the pH of the solution.
- Neutralization and washing: After cleaning, drain the chemical solution. Flush the pipe space with plenty of clean water to a neutral pH. Neutralize wash water before disposal.
- Visual control: After cleaning, check the cleanliness of the inner surface of the pipes using an endoscope or visually. The surface of the pipes must be clean, without visible deposits.
5.3.2. For plate heat exchangers (plate cleaning)
- Disassembling the plate pack: Loosen the tension bolts until they are completely loosened. Depending on the design, move the movable plate apart, or completely remove the plates from the frame.
- Mechanical cleaning: Clean each plate with a soft brush and water under light pressure. To remove dense deposits, use special cleaners compatible with the material of the plates and gaskets. It is strictly forbidden to use metal brushes, abrasives or sharp tools that can damage the surface of the plates or sealing grooves.
- Chemical cleaning (if necessary): Immerse the plates in a bath of chemical solution (similar to shell and tube) or circulate the solution through the assembled heat exchanger (if permitted by the manufacturer and design).
- Washing and drying: Thoroughly rinse each plate with clean water and dry.
- Plate Inspection: Carefully inspect each plate for cracks, deformation, erosion, or other damage. Pay attention to the holes for the spacers. Damaged plates should be replaced.
5.4. Replacement of gaskets and assembly
- Installing new gaskets: Carefully install new gaskets into the grooves of the flanges, tube grids or plates. Make sure the spacers are installed evenly and without distortion. Use OEM gaskets or quality equivalents certified according to ISO 9001. Never reuse old gaskets.
- Assembling the lids/plates: Place the lids or plate pack in place. Make sure all items are oriented correctly.
- Pre-Tighten Bolts: Hand tighten all mounting bolts to light contact.
- Stage tightening of bolts with a torque wrench: Tighten the bolts in a criss-cross sequence in 3-4 stages using a torque wrench.
- Stage 1: 30% of the design torque (eg 45-60 Nm for M20 bolts).
- Stage 2: 60% of the design torque (eg 90-120 Nm for M20 bolts).
- Stage 3: 100% of design torque (eg 150-200 Nm for M20 bolts).
- Stage 4 (if needed): Test tighten to 100% after completing the third stage.
Incorrect sequence or uneven tightening may result in flange/plate deformation and leaks.
5.5. Leak testing (hydraulic/pneumatic)
- Connection to the test system: Shut off all heat exchanger outlets. Connect a hydraulic pump (for a hydro test) or a source of compressed air (for a pneumatic test) with a pressure gauge to the inlet pipe.
- Hydraulic test: Fill one circuit of the heat exchanger with water, forcing air through the top vent. Gradually increase the pressure to 1.5 times the working pressure, but not more than 10% of the test pressure specified in the equipment data sheet (for example, if the working pressure is 6 bar, the test pressure may be 9 bar). Hold the pressure for 30 minutes.
- Pneumatic test (limited): Fill the circuit with air or nitrogen at a pressure not exceeding 0.5 of the working pressure. Apply a soapy solution to the flange connections to detect leaks. Pneumatic testing is less safe than hydraulic testing and requires increased safety measures according to DSTU EN 13445-5:2020 "Vessels operating under pressure, without heating".
- Visual inspection: During the test, carefully inspect all flange connections and seals for leaks. The absence of pressure drop and visible leaks confirms the tightness.
- Depressurization: Slowly depressurize the heat exchanger and drain the water (after hydrotesting).
5.6. Thermal efficiency check (after start-up)
- Commissioning: Start the heat exchanger in working mode. Allow the system to stabilize for at least 30 minutes.
- Parameter measurements: Record the following data for both circuits:
- Inlet and outlet fluid temperatures (Tin, Tout)
- Pressure (Pin, Pout)
- Liquid consumption (Q) - if possible.
Measurements are carried out using calibrated thermometers and manometers. - Heat transfer coefficient calculation: Calculate the log mean temperature head (LMTD) and, if flow data is available, calculate the overall heat transfer coefficient (U or K). Compare the obtained value with the basic indicators of a new heat exchanger or after previous maintenance. A significant deviation (>10-15%) from the norm indicates insufficient cleaning or other problems.
- Permissible deviations: For heat exchangers in operation, a slight decrease in efficiency is allowed (usually up to 5-10% of the design). A drop of more than 15% warrants further investigation and possibly re-service.
6. Inspection after service (checklist)
| Test |
Expected result |
Actual result |
Pass/Fail |
| 1. Hermeticity | No visible leaks under working pressure. | | |
| 2. Tightening moments | All bolts are tightened to the recommended torque. | | |
| 3. Thermal efficiency | The temperature difference and the overall heat transfer coefficient are within the permissible deviations from the basic values. | | |
| 4. Pressure drop | The pressure drop through the heat exchanger is within normal limits. | | |
| 5. Cleanliness and order | The work area is cleaned, the tools are collected, the remains are disposed of. | | |
| 6. Restoration of insulation | The removed thermal insulation was restored. | | |
| 7. Absence of LOTO | All blocking/markings are removed after completion of work. | | |
7. Troubleshooting guide
| Symptom |
A possible reason |
Corrective action |
| Reduction of thermal efficiency | Pollution (fouling) of heat exchange surfaces. | Perform thorough chemical/mechanical cleaning. |
| Reduction of thermal efficiency | Mixing of environments due to internal leaks. | Check plates/tubes for cracks, replace damaged elements. |
| Reduction of thermal efficiency | Insufficient coolant/cooler consumption. | Check pumps, clogging of pipelines, valve settings. |
| External leakage (on flanges) | Damaged or improperly installed gasket. | Replace the gasket, ensure the correct sequence and torque of the bolts. |
| External leakage (on flanges) | Uneven tightening of bolts. | Retighten the bolts with a torque wrench according to the diagram. |
| External leakage (through the casing/pipes) | Corrosion, erosion or mechanical damage. | Repair or replace the damaged element/heat exchanger. |
| High pressure drop | Clogging of pipes/interplate space. | Perform intensive cleaning. |
| High pressure drop | Closed or partially closed valves. | Check the position of the valves. |
| The pressure drop is normal, but the efficiency is low | Short-circuiting of flows in multi-pass devices. | Check the correctness of assembly and sealing between sections. |
| Vibration of the heat exchanger | Incorrect fastening, lack of supports. | Check fasteners, install dampers. |
8. Recommended maintenance schedule
| Task |
Frequency |
Estimated duration |
Qualification level |
| Visual inspection (leaks, corrosion) | Daily/Weekly | 15 min | Operator/Technician |
| Pressure drop and temperature check | Weekly/Monthly | 30 min | Technician |
| Cleaning the heat exchanger (disassembly, cleaning, assembly) | Quarterly/Annually (depends on pollution) | 1-2 days | Service technician |
| Replacement of all gaskets | Every 1-3 years (or at each disassembly) | 0.5-1 day | Service technician |
| Hydraulic test | With each disassembly and assembly | 2-4 hours | Service technician |
| Checking thermal efficiency | Quarterly/After service | 1-2 hours | Engineer/Technician |
| Overhaul/replacement of pipes/plates | Every 5-10 years (depends on condition) | 3-7 days | Specialized staff |
9. Directory of spare parts
In order to ensure uninterrupted operation of heat exchangers, availability of high-quality spare parts is critically important. UNITEC-D GmbH offers a wide range of original and certified analogues for various types of heat exchangers that meet CE and UkrSEPRO standards.
| Part description |
Typical specification |
Category UNITEC |
| Pads for plates | EPDM, NBR, Viton, HNBR (depending on environment and temperature) | Sealing materials |
| Gaskets are flanged | Paronite, graphite, PTFE, spiral-wound (according to ISO 15848-1) | Sealing materials |
| Heat exchange plates | Stainless steel AISI 304/316, Titanium, Hastelloy (thickness 0.5-0.8 mm) | Elements of heat exchange |
| Tubes for shell and tube | Stainless steel AISI 304/316, Copper, Copper-nickel alloy | Elements of heat exchange |
| Fastening bolts/nuts | Stainless steel A2/A4 (ISO 3506), Galvanized steel 8.8 (ISO 898-1) | Fastening |
| Sealing rings | O-rings (NBR, Viton), according to DIN 3771 | Sealing materials |
| Manometers | Diameter 63 mm, 0-16 bar, accuracy class 1.6 (DSTU EN 837-1) | Measuring devices |
| Thermometers | Bimetallic, range -20 to +150°C, class 1 (DSTU EN 13190) | Measuring devices |
Search for the necessary spare parts in our e-catalogue: www.unitecd.com/e-catalog/
10. Links
- DSTU EN 10398:2020 "Machine safety. General design principles. Risk assessment and risk reduction".
- DSTU EN 166:2017 "Means of individual eye protection. Technical conditions".
- DSTU EN 374:2017 "Protective gloves against dangerous chemicals and microorganisms."
- DSTU EN 149:2019 "Means of individual respiratory protection. Filter half-masks for protection against particles. Requirements, testing, marking".
- DSTU EN ISO 20345:2019 "Means of personal protection. Work shoes."
- DSTU EN 13445-5:2020 "Vessels operating under pressure, without heating. Part 5. Control and testing".
- ISO 15848-1:2015 "Industrial valves - Measurement of emissions of volatile substances. Part 1: Requirements for typical tests of valves".
- ISO 9001:2015 "Quality management systems. Requirements".
- OEM documentation of the heat exchanger manufacturer.
