Tube sheet flaring: technology and quality control (Guide 2026) 

Key parameters and standards of flaring in 2026

The main thing in 30 seconds:

• Fit accuracy:The gap between the pipe and the tube sheet should not exceed 0.4 mm to ensure tightness without excessive stress.
• Hardness control:The hardness of the pipe material must be at least 30 HB lower than the hardness of the tube sheet to prevent plastic deformation of the holes.
• Compliance:In 2026, compliance with TR CU 010/2011 and ASME Section VIII Div is critical. 1 for admission of equipment to operation in the Russian Federation and the EAEU.

Flaring of tubes into a tube sheet remains one of the most critical components in the assembly of shell-and-tube heat exchangers, condensers and evaporators. Errors at this stage lead to mixing of media, stress corrosion and production shutdowns. With increasing environmental and safety regulations in the oil and gas industry, pipe-to-grid technology has evolved from a simple mechanical seal to a highly precision engineered process requiring strict control of every parameter.

Modern approach totube sheet flaringimplies not just mechanical expansion of the pipe, but the creation of a monolithic unit capable of withstanding cyclic thermal loads. Engineers are increasingly faced with the dilemma of choosing between pure flaring, flaring welding and the use of composite materials. Understanding the physics of the process and metallurgical aspects of the interaction of materials allows you to avoid typical design and installation errors.

For purchasing engineers and technicians, the key factor is not only the price of the component, but also the proven reliability of the supplier. Companies such asWuxi Kaisheng Electric Power and Petrochemical Equipment Co.,Ltd, integrate flaring quality control directly into the production cycle using automated pipe expansion systems, which minimizes the human factor and ensures the stability of the joint geometry even in large-scale production.

Physics of the process and choice of connection method

The flaring process is based on plastic deformation of the pipe wall as it expands inside the tube sheet hole. In this case, residual contact pressures arise, which ensure the tightness of the connection and the transfer of loads. However, blindly following standards without taking into account the rheology of materials often leads to dire consequences.

Mechanical vs Hydraulic flaring

Traditional mechanical flaring using roller tools is still widely used, but has significant disadvantages: uneven force along the length of the contact and the risk of microcracks on the inner surface of the pipe due to friction. In response to these challenges, the industry is actively switching to hydraulic (explosive or hydraulic pulse) flaring.

The hydraulic method ensures uniform radial pressure along the entire length of the contact between the pipe and the grid. This is especially critical for high-pressure heat exchangers, where temperature differences can reach 200–300°C. The uniform distribution of stresses prevents the phenomenon of “creep” of the connection, which is often observed with the mechanical method after several months of operation.

Important:When choosing a method, it is necessary to take into account the ratio of the thickness of the pipe wall and the tube sheet jumpers. If the thickness of the web is less than 1.2 times the diameter of the hole, mechanical flaring can lead to warping of the grid itself.

Combined method: Flaring + Welding

In aggressive environments typical for petrochemicals (sour oils, acid gases), flaring alone is not enough. ASME and GOST standards recommend a combined connection: flaring ensures heat transfer and fixation, and subsequent welding of the pipe ends guarantees absolute tightness.

However, here lies a common mistake: performing welding before the dimensions are completely stabilized after flaring. The metal of the pipe after deformation is in a stressed state. If a technological pause is not maintained or annealing is not carried out, additional thermal stresses will arise during welding, leading to intergranular corrosion in the heat-affected zone.

On production linesWuxi Kaisheng Electricity Petrochemical Equipment Co., Ltd.this process is automated: after the flaring stage, ultrasonic control of the fit is carried out, and only then robotic welding complexes perform welding. This approach, proven by ASME U certification, eliminates the risk of human error when manually checking the gap before welding.

Quality criteria and defect control

Flaring quality control is not a one-time procedure, but a multi-stage process. In 2026, non-destructive testing (NDT) requirements have become even more stringent with the introduction of equipment digital twins, which require accurate input data about the state of each connection.

Geometric control and clearances

Primary inspection begins with preparing the holes in the tube sheet. The surface roughness of the hole should be within the range of Ra 3.2–6.3 µm. A surface that is too smooth impairs adhesion; a surface that is too rough creates channels for micro-leakage.

The key parameter is the initial gap between the outer diameter of the pipe and the inner diameter of the hole. The optimal gap is 0.2–0.4 mm. Exceeding this value requires an increase in the degree of flaring, which leads to thinning of the pipe wall and a decrease in its service life. Insufficient clearance makes a good fit impossible.

Defects detected during operation

One of the most insidious problems is “reverse leakage,” which does not appear immediately, but after 6–12 months of operation. It occurs due to stress relaxation in the pipe material. In our practice, we recorded a case at an enterprise in Eastern Europe, where after a year of operation there was a pressure loss of 15% in the cooling circuit due to an incorrect choice of the degree of flaring for AISI 321 stainless steel pipes. The pipes had a high tendency to harden, and the standard flaring mode did not provide the necessary residual pressure.

The solution was the use of intermediate annealing and an increase in the degree of deformation to 4.5%, which was implemented when replacing the tube bundle by partners using technologies similar to those used inWuxi Kaisheng LLC. This case highlights the importance of individually calculating the flaring mode for a specific steel grade, rather than using average tables.

Materials Science and Compatibility

The choice of materials for the tube-grid pair determines the durability of the entire heat exchanger. In 2026, the trend is the use of bimetallic and composite solutions to optimize cost and corrosion resistance.

Galvanic corrosion problem

When joining dissimilar metals (for example, copper pipe and steel grating), there is a risk of galvanic corrosion. Flaring increases the contact area, which can speed up the process if barrier layers or insulating spacers are not provided. For such cases, it is recommended to use pipes with protective coatings or use adapter sleeves.

CompanyWuxi Kaishengactively produces composite tube sheets with copper alloy cladding based on carbon or stainless steel. This engineering solution provides a durable carbon steel base and a corrosion-resistant copper or brass contact layer directly in the flaring zone. This approach eliminates the problem of a galvanic couple at the macro level, since contact occurs between materials that are homogeneous or similar in potential.

Effect of temperature on joint density

The coefficients of linear thermal expansion (CTLE) of the pipe and grate should be as close as possible. If the pipe expands more than the grate (for example, a titanium pipe in a steel grate), the contact may loosen when heated. Conversely, if the grid expands more, it can “pinch” the pipe, causing the material to creep.

To compensate for these effects, modern designs use thermal expansion compensators or special flaring profiles (for example, with grooves), which act as spring elements, maintaining tension when temperatures change.

Logistics and delivery of ready-made solutions

For Russian industrial enterprises, not only the quality of workmanship is critical, but also the reliability of the supply chain. Sanction pressure and logistical gaps in recent years have forced buyers to reconsider the criteria for selecting suppliers of heat exchange equipment.

Geographical location of the production baseWuxi Kaisheng Electric Power and Petrochemical Equipment Co.,Ltdin an economically active area within a radius of 100 km from Shanghai provides a strategic advantage. Direct access to port terminals and airports in Shanghai (travel time to the terminal is 2 hours) allows you to quickly ship finished heat exchangers and components.

For urgent projects, air deliveries are available through eight nearby international airports. For planned deliveries, the optimal solution is rail routes to Europe and Russia, which take about 15 days. This is much faster than sea transport (45–60 days) and cheaper than air transport. This logistics flexibility allows our partners to maintain minimal inventory, working on a Just-in-Time system, which reduces frozen capital in spare parts.

In addition, the presence of TR CU (EAC) certificates and compliance with CE requirements simplifies customs clearance and commissioning of equipment in the Russian Federation and the EAEU countries. The company's products have already been successfully operated at CNPC and CNOOC facilities, and are also supplied to Italy, Iran and Indonesia, which confirms their adaptability to various international standards.

Frequently asked questions (FAQ) about flaring

What is the minimum pipe wall thickness for safe flaring?

According to ASME and GOST standards, the minimum wall thickness depends on the pipe diameter and material, but should usually not be less than 1.0–1.2 mm for pipes up to 25 mm in diameter. For thin-walled pipes (less than 1 mm), flaring is risky and is often replaced by soldering or special welding. Violation of this limit leads to longitudinal cracking of the pipe in the deformation zone.

Is it possible to re-flare a pipe after repair?

Repeated flaring is allowed, but with restrictions. The pipe material has already passed the hardening stage, and its ductility is reduced. Repeated deformation should be minimal, only to compensate for weakening of the connection. Pipe replacement is often required if the initial flaring was performed beyond the maximum degree of deformation. The decision is made based on the results of flaw detection and measurements of the residual wall thickness.

What is the advantage of expander flaring over roller flaring?

Expander (hydraulic/pneumatic) flaring provides a more uniform distribution of pressure along the circumference and length, especially in hard-to-reach areas of deep tube bundles. It causes less damage to the inner surface of the pipe, leaving it smooth, which is important for environments with a high risk of contamination or deposits. Roller flaring is cheaper, but requires highly skilled operator to avoid helical deformation.

Conclusion and recommendations for choosing a supplier

Tube sheet flaring is a technological process where savings on equipment or quality control inevitably leads to a multiple increase in operating costs. In 2026, the market requires suppliers not just to have machines, but to have an integrated engineering approach: from calculating thermal stresses to ensuring logistics reliability.

When choosing a contractor for the manufacture of heat exchange equipment, pay attention to:

• Availability of our own non-destructive testing laboratories (ultrasonic testing, capillary method).
• Certification according to ASME and TR CU, which guarantees quality recognition by supervisory authorities.
• Experience working with composite materials and bimetallic junctions.
• Transparency of logistics schemes and the ability to track cargo at all stages.

Investment in equipment from trusted manufacturers such asWuxi Kaisheng LLC, pay off by reducing the frequency of repairs and increasing the service life between repairs. A wide range of products - from H-shaped finned tubes to high-pressure ASME heat exchangers - allows you to cover the needs of your entire plant with one reliable partner.

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