Assembling heat exchangers: tightness of connections 

Why 90% of leaks in heat exchangers occur at the assembly stage

In our practice of servicing industrial systems, we have encountered harsh statistics: more than 85% of cases of leakage of plate and shell-and-tube heat exchangers are associated not with metal defects or factory defects in seals, but with errors made during installation and final assembly of units. Heat exchanger assembly: Sealing of connections is a critical process where the cost of error is measured not only by the cost of replacing gaskets, but also by production line downtime, coolant loss and personnel safety risks. Many engineers mistakenly rely solely on bolt torque, ignoring the condition of the mating surfaces and the temperature history of the sealing materials. We have seen projects where perfectly designed hydraulic units began to leak within 48 hours of startup because the installer used an impact wrench instead of a torque wrench.

This article was written by engineers who personally assembled components in workshops from St. Petersburg to Novosibirsk. There are no theoretical calculations from textbooks here - only proven quality control methods, material specifications and action algorithms that allow you to achieve zero leakage even in systems with pressures up to 2.5 MPa. Whether you are preparing to launch a new facility or performing routine maintenance, this data will save you weeks of stress and significant budgets.

Critical surface preparation requirements before installing seals

The tightness of any flange connection begins long before you pick up the wrench. The condition of the mating surface (mirror) of the plate or flange is the foundation of reliability. In our practice, there was a case at a chemical plant in Tatarstan, where a new heat exchanger began to produce micro-leakages in an aggressive environment immediately after hydraulic tests. The reason turned out to be trivial: during transportation, small metal shavings fell on the mirror of the plate, which were not noticed during a visual inspection. When tightened, this particle was pressed into the rubber gasket, creating a channel for leakage.

Requirements for surface roughness are strictly regulated by the GOST R 53637-2009 standard and international TEMA standards. For plate heat exchangers with soft seals (EPDM, NBR), the optimal roughness should be in the range Ra 3.2–6.3 µm. A surface that is too smooth (Ra < 1.6) is dangerous because the gasket can slip due to thermal expansion, breaking the seal. A surface that is too rough acts like a file, cutting through the seal material when compressed.

Before starting assembly, be sure to troubleshoot the slabs. Use the “paint” method or special indicator pastes to identify scratches, pits and corrosion pits. Any scratch greater than 0.1 mm deep, running perpendicular to the flow direction or seal edge, requires either grinding or replacement of the plate. Do not try to mask defects with sealants - in high-temperature environments they burn out, and the problem returns with a vengeance.

Pay special attention to removing old adhesive residues if adhesive fastening of gaskets is used. Residue from the vulcanized adhesive creates uneven surfaces that prevent the new gasket from laying flat. We recommend using special solvents approved by the seal manufacturer and plastic scrapers to avoid damaging the base metal. After cleaning, the surface must be degreased with alcohol or acetone and completely dried.

Action:Before ordering new gaskets, request a quality data sheet from the supplier indicating the Shore A hardness and ensure that it falls within the range of 60-65 units for standard operating conditions.

Lubricant selection: the hidden success factor

Ignoring seal lubrication is one of the most common mistakes newbies make. During installation, dry rubber creates high friction against the metal. When you begin to tighten the plate pack, the dry gasket may curl, move, or tear. We use only specialized silicone lubricants that are compatible with the gasket material. No grease, lithol or motor oil - they can cause the rubber to swell or degrade over time.

Apply a thin, even layer of lubricant to both sides of the gasket and to the mating surface of the slab. Excess lubricant is just as harmful as too little: it can be squeezed out into the coolant flow and contaminate the system, especially in food production where strict HACCP standards apply. In one of our projects at a dairy plant, the use of an uncertified lubricant led to the appearance of an off-taste in the product, which cost the client a shipment of goods.

Algorithm for correct tightening of bolted connections: step-by-step instructions

Assembling heat exchangers: the tightness of the connections directly depends on the sequence and tightening force of the fasteners. Chaotic tightening “crosswise” without controlling the force leads to distortion of the pressure plate. This creates a situation where on one side the gasket is compressed to the limit (risk of destruction), and on the other there is a gap (risk of leakage). Below is a proven algorithm that we use on all objects.

1. Instrument preparation and calibration.Use only working torque wrenches with a current calibration certificate. Hydraulic tensioners are preferable for large devices with a diameter of more than 1 meter. Make sure the stud threads are clean and lubricated with graphite or copper grease to prevent galling. Never use impact wrenches for final tightening - they do not provide torque control.
2. Pre-assembly of the package.Install all plates and spacers into the frame. Use your hands to tighten all the nuts until the washers touch the plate. At this stage it is important to check that the plate pack is level with the guide rods. It will be almost impossible to correct the distortion of the package at this stage later without complete disassembly.
3. First tightening pass (30% force).Tighten the nuts evenly, moving from the center to the edges or using the diagonal pattern indicated in the product data sheet. The goal of this step is to simply pick out all the gaps and fit the bag tightly. The force should be approximately 30% of the nominal tightening torque specified by the manufacturer. Check the package size (“Dimension A”) - it should decrease evenly on all sides.
4. Second tightening pass (60% force).Repeat the tightening pattern, increasing the torque to 60%. At this stage, carefully monitor the behavior of the gaskets. If you see that the rubber is beginning to be squeezed out unevenly, stop and check that the seal is installed correctly in the groove. A common mistake is getting the edge of the gasket under the adjacent plate.
5. Final pass (100% effort) and control.Tighten to 100% of the rated torque. Be sure to perform a control pass 15–20 minutes after the first full tightening, as primary creep of the gasket material and relaxation of the metal occurs. Measure the final size of the package and compare it with the data from the device’s service book. A deviation of more than 2 mm requires clarification of the reasons.

Attention:Never exceed the maximum tightening torque specified by the manufacturer. An attempt to “tighten it harder to make sure it doesn’t leak” leads to irreversible deformation of the plates and rupture of the gaskets. We have recorded cases where overstretched plates broke at the first water hammer.

Specifics of working with adhesive and non-adhesive systems

Modern heat exchangers are divided into two types according to the method of fastening the gaskets: glued and clip-on. Errors in the assembly of these systems are radically different. In adhesive systems, the main danger is insufficient drying time for the adhesive before assembling the bag. If you start tightening the device too early, the gasket will move in the grooves under the influence of friction forces. We recommend a minimum of 24 hours at +20°C after gluing before assembly.

In adhesive-free systems, the risk of displacement is lower, but the risk of damage to the fixing clips (locks) is higher due to careless installation. Plastic locks are fragile in the cold. If you are assembling the heat exchanger outdoors in winter, allow the gaskets to warm to room temperature for several hours. Cold rubber loses its elasticity, and when you try to snap the lock, the latch can break off, making the gasket unusable.

Seal materials and their effect on sealing in different environments

The choice of gasket material determines not only the chemical resistance, but also the mechanical behavior of the assembly during assembly. Different polymers have different modulus of elasticity and coefficient of linear expansion. Incorrect selection of material leads to the fact that even with perfect tightening, the connection will leak when the temperature changes.

EPDM (Ethylene Propylene Rubber):The most popular material for water systems and heating. It holds temperatures well up to 150–160°C. However, EPDM is strictly incompatible with mineral oils and fats. In our practice, there was a case when the heat exchanger of the heating system was connected to a circuit with coolant oil due to operator error. EPDM gaskets swelled and turned into a jelly-like mass in 3 days, losing their seal completely. Always check chemical compatibility before starting.

NBR (Nitrile rubber):Standard for oils and petroleum products. The operating temperature range is usually limited to +110…+120°C. The main feature of NBR is that it is less elastic in the cold. When assembling winter objects using NBR gaskets, special attention to the tightening force is required: in the cold they become “oaky” and require more force for crimping, but when heated they can lose contact density due to shrinkage.

Viton/FKM (Fluororubber):Premium material for aggressive chemical environments and high temperatures (up to 200°C). It is expensive, but indispensable in the chemical industry. Viton has a high compression ratio and low permanent deformation. However, it is very sensitive to the quality of the metal surface. The slightest scratch on a plate is more critical for Viton than for soft rubber.

Graphite gaskets:Used in extreme conditions. They are inelastic and require perfectly flat surfaces and very high tightening force. When assembling graphite seals, the problem of material “squeezing out” often occurs if there are no restrictor rings. We recommend using multi-layer graphite gaskets with metal perforations to increase mechanical strength.

Action:Ask your supplier for a Chemical Resistance Chart specific to your gasket brand, as properties may vary between manufacturers (Alfa Laval, GEA, Sondex, SWEP).

Quality control and methods for detecting hidden defects

How can you understand that the assembly of heat exchangers: the tightness of the connections is made qualitatively, even before pressure is applied? A visual inspection is not enough. We are implementing a multi-level control system at all critical facilities.

1. Packet size control (Dimension Check).This is the simplest and most reliable method. Each manufacturer indicates in the instruction manual the minimum and maximum size of the assembled plate package (size “A”). If after tightening your size is outside these limits, it means either there are too many/too few spacers, or they are installed incorrectly, or the plates are deformed. The measurement is carried out with a caliper at four points around the perimeter. A spread of values ​​of more than 1 mm indicates a skew.

2. Hydraulic tests with water.Before putting into operation the device must be pressure tested. The test pressure is usually 1.25–1.5 times the working pressure, but does not exceed the maximum design pressure of the housing. It is important to test slowly, increasing the pressure in steps to allow air to escape and the gaskets to adjust. A sudden surge in pressure can knock out a poorly installed gasket.

3. Thermal imaging control.An innovative method that we actively use. When supplying hot coolant and a cold countergent, the faulty connection will have a different temperature from the working area. A thermal imager allows you to see micro-leakages that have not yet appeared in the form of water droplets, but are already disturbing the thermal balance. This is especially effective for identifying internal flows between channels.

4. Ultrasonic flaw detection.Allows you to detect delaminations in composite gaskets or cracks in plates that are invisible to the eye. This method requires a skilled operator and expensive equipment, but is indispensable for critical components in the nuclear or oil and gas industry.

One of our clients, the owner of a pulp and paper mill, saved millions of rubles thanks to thermal imaging control. When accepting the new station, we discovered an abnormal heating zone on the heat exchanger body. It turned out that during assembly one of the plates was installed upside down (the 90/180 degree rotation angle was broken), which created a short-circuited channel. Without a thermal imager, this error would have surfaced only after a month of operation, when problems with the technological regime of pulp cooking would have begun.

Typical installation errors and their consequences

Analysis of complaints over the past 5 years allowed us to make a rating of the most common mistakes that installation teams make. Knowing these “rake” will help you avoid repeating the failures of others.

• Using expired gaskets.Rubber ages even in storage. The shelf life is usually 3–5 years depending on the material. An old gasket loses its elasticity, cracks when compressed and does not regain its shape. Always check the production date on the packaging or labeling of the gasket itself. We have seen cases where “new” gaskets from 10-year-old stocks fell apart in our hands during installation.
• Tightening by eye or with a pneumatic tool without torque limit.The human sense of effort is extremely subjective. One installer will tighten with a torque of 50 Nm, the other - 80 Nm. The result is uneven crimping. Using impact wrenches without an adapter-limiter is guaranteed to result in overtightening and damage to the stud threads.
• Ignoring temperature compensation.The heat exchanger operates in heating and cooling cycles. Metal and rubber expand differently. If you do not take this factor into account during cold assembly (for example, do not make an additional tightening after the first heating cycle), then when you reach the operating mode, the connection will weaken. In the instructions of many manufacturers there is a point “Hot Tightening”, which is often ignored.
• Foreign objects entering the channels.Scraps of gloves, rags, welding scale, forgotten inside the channels during assembly, can cause local overheating and burnout of the plate. Before closing the end cap, be sure to illuminate the channels with a flashlight.

Important:Never use used gaskets. Even if they look intact, they have already suffered a compression set and will not be able to seal a second time. The savings on gaskets are negligible compared to the risk of an accident.

Specifics of assembly in the Far North and aggressive environments

Working in Russia requires taking into account harsh climatic conditions. Assembling heat exchangers outdoors at temperatures of -20°C and below requires special protocols. Rubber at such temperatures turns into a glassy state. An attempt to install standard gaskets in the cold is doomed to failure.

Если работа неизбежна, необходимо организовать теплый контур (тепляк) вокруг места монтажа и прогреть аппарат и прокладки до плюсовой температуры минимум за 12 часов до начала работ. В качестве альтернативы используйте специальные морозостойкие модификации материалов (например, EPDM с особыми добавками), но даже они имеют предел. Мы сталкивались с ситуациями, когда при пуске системы зимой прокладки, смонтированные летом, давали течь из-за того, что не успели адаптироваться к резкому охлаждению. В таких случаях помогает предварительный прогрев системы циркуляционным насосом на малых оборотах перед выходом на полную мощность.

Для агрессивных сред (кислоты, щелочи) критически важна чистота рук монтажников. Жировые пятна от пальцев на поверхности графитовой или фторопластовой прокладки могут стать очагом коррозии или местом нарушения адгезии. Работы должны проводиться в чистых нитриловых перчатках.

Frequently Asked Questions

Как часто нужно проводить подтяжку болтов теплообменника?

Первичная подтяжка обязательна через 24 часа после ввода в эксплуатацию или после первого полного цикла нагрева-остывания. Далее периодичность зависит от условий работы. Для стабильных систем без вибраций достаточно проверки раз в год во время планового ТО. Если система работает в режиме частых термоциклов или подвержена вибрациям, проверку момента затяжки следует проводить ежеквартально. Всегда сверяйтесь с регламентом производителя вашего оборудования.

Можно ли использовать анаэробный герметик на фланцах теплообменника?

Нет, это категорически запрещено для разборных пластинчатых теплообменников. Герметики предназначены для неразборных соединений. Использование герметика сделает последующую разборку аппарата для чистки или замены пластин невозможной без повреждения деталей. Герметичность должна обеспечиваться исключительно механическим сжатием эластичной прокладки. Исключение составляют некоторые виды сварных теплообменников, но там технология иная.

Что делать, если прокладка постоянно выдавливается при затяжке?

Это признак одной из трех проблем: 1) Превышен момент затяжки (слишком сильное сжатие). 2) Прокладка не подходит по толщине или типу для данной модели пластин. 3) Привалочная поверхность имеет дефекты (неровности), из-за которых прокладка не ложится в паз, а выталкивается наружу. Также проверьте, не перепутаны ли типы пластин (A и B) в пакете — неправильная комбинация меняет геометрию сжатия.

Какой инструмент лучше всего подходит для затяжки?

Для небольших аппаратов (до 100 пластин) достаточно качественного динамометрического ключа с головкой соответствующего размера. Для средних и крупных агрегатов настоятельно рекомендуется использовать гидравлические синхронизированные натяжители. Они обеспечивают одновременное и равномерное усилие на все шпильки, исключая перекос плиты. Ручная затяжка больших аппаратов несколькими рабочими “по команде” часто приводит к рассинхронизации усилий.

Заключение и рекомендации по выбору поставщика услуг

Сборка теплообменников: герметичность соединений — это не просто механическая операция, а сложный технологический процесс, требующий высокой квалификации, специального инструмента и понимания физики материалов. Ошибки на этом этапе стоят дорого. Надежность вашей энергосистемы зависит от того, насколько точно соблюдены технологии монтажа.

Мы рекомендуем не экономить на услугах профессиональных монтажных бригад, имеющих допуски СРО и опыт работы с конкретными брендами оборудования. Самостоятельная сборка без надлежащей подготовки часто приводит к ложной экономии. Помните, что качественная прокладка и правильная затяжка — это инвестиция в бесперебойную работу вашего предприятия на годы вперед.

Однако долговечность оборудования закладывается еще на этапе производства. Именно поэтому компании, такие какWuxi Kaisheng Electric Power and Petrochemical Equipment Co., Ltd., уделяют особое внимание не только проектированию, но и контролю качества каждого компонента. Специализируясь на разработке и производстве высоконапорных теплообменников (включая титановые кожухотрубные модели и аппараты стандарта ASME), компания обеспечивает соответствие продукции строжайшим международным нормам PED и ASME. Использование передовых материалов — от морской латуни C46400 и сплавов Cu-Ni до никелевых сплавов N06625 и нержавеющей стали 316 — гарантирует исключительную коррозионную стойкость и теплоэффективность даже в самых агрессивных средах нефтепереработки, химической промышленности и опреснения воды.

Выбирая оборудование от надежного производителя, вы получаете не просто набор металлических пластин и труб, а инженерное решение, где каждая трубная решетка и каждый пучок гофрированных труб изготовлены с учетом реальных условий эксплуатации. Это значительно снижает риски, связанные с заводскими дефектами, позволяя сосредоточиться на грамотном монтаже. Компания «Уси Кайшэн» предоставляет индивидуальные решения и стабильное оборудование заказчикам по всему миру, становясь надежным партнером в создании энергоэффективных систем.

Если вы столкнулись с проблемами герметичности, нуждаетесь в подборе оригинальных запчастей или ищете подрядчика для профессионального монтажа и обслуживания теплообменного оборудования, наша команда готова помочь. Мы поставляем сертифицированные уплотнения для всех ведущих мировых брендов и оказываем услуги шеф-монтажа с гарантией результата.

Каталог запчастей для теплообменников | Услуги сервиса и обслуживания

Свяжитесь с нами сегодня для консультации и расчета стоимости работ. Наши эксперты помогут продлить срок службы вашего оборудования и исключить риски аварийных остановок.