As a steel pipe product with a special structure, internal threaded steel pipe has an irreplaceable and important position in industrial heat exchange, petrochemical equipment, air conditioning systems and energy engineering. Its inner wall is made into a spiral or corrugated thread structure through mechanical processing or forming process. This design greatly increases the effective contact area of the inner wall of the pipe, and has significant advantages in enhancing heat transfer, disturbing fluid, improving mass transfer and improving system efficiency. With the development of industrial technology, the performance requirements for internal threaded steel pipes are increasing, and the selection of its specification parameters has become more and more critical. Understanding and mastering its detailed specifications is of great significance to ensure stable, safe and efficient operation of equipment.
What is internal threaded steel pipe
Internal threaded steel pipe refers to a spiral or other form of threaded structure processed on the inner wall of the steel pipe. With the help of these microstructures, the fluid flow state inside the pipe is changed, thereby improving the heat exchange efficiency or enhancing the overall performance of the system. Most of these steel pipes use
seamless steel pipes as the base, and the inner wall is threaded by CNC turning, roll forming or hot extrusion. Compared with ordinary light tubes, internally threaded steel pipes have higher requirements for material pressure resistance, corrosion resistance and dimensional stability due to their complex structure and precise manufacturing process. They are widely used in heat exchangers, condensers, boilers, air conditioning equipment, petrochemical pipelines and other systems. In terms of energy saving and consumption reduction and improving heat transfer efficiency, internally threaded steel pipes have become one of the preferred high-efficiency pipes in modern industrial engineering.
Common specifications and parameters of internally threaded steel pipes
The specifications and parameters of internally threaded steel pipes cover multiple aspects such as outer diameter, wall thickness, internal thread form, pitch, length and material grade. Each parameter is not only related to the mechanical strength and fluid conveying performance of the pipeline, but also directly affects its adaptability and economy in specific applications. Usually the outer diameter ranges from 15mm to 200mm, and the wall thickness ranges from 1.5mm to 10mm. The specific selection needs to be comprehensively considered based on working conditions, use pressure, heat transfer requirements and on-site installation space. In addition, the form of the internal thread (such as rectangle, trapezoid, wave, etc.) and the pitch design will significantly affect the fluid disturbance intensity and boundary layer destruction effect, thereby changing the heat transfer capacity and pressure drop characteristics of the pipeline. For high-efficiency heat exchanger systems, a reasonably matched thread structure design can often double the heat transfer rate per unit area without increasing the volume of the equipment.
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Outer Diameter
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15 mm – 200 mm
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Depends on application (HVAC, power plant, petrochemical, etc.)
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Wall Thickness
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1.5 mm – 10 mm
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Thicker walls for high pressure and thermal loads
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Thread Shape
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Rectangular / Trapezoidal / Sawtooth
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Affects flow resistance and heat transfer efficiency
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Thread Pitch
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2 mm – 10 mm
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Smaller pitch = more threads, better heat exchange
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Standard Length
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6 meters (custom up to 12 m)
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Can be cut or customized as needed for project layout
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Material Grades
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20G, SA210C, T11, T12, 15CrMoG, 12Cr1MoVG
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Selected based on temperature, pressure, corrosion resistance
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Manufacturing Standard
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ASTM A213 / GB 5310 / ASME SA210
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Varies by region and project specification
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Advantages of the application of internal threaded steel pipes in heat exchange systems
In heat exchange systems, when the fluid flows through the inner wall of an ordinary light pipe, its heat transfer efficiency is often limited due to the presence of a boundary layer. The internal thread structure changes the movement trajectory of the fluid, breaks the original laminar state, promotes forced convection, and causes the fluid to produce turbulence and vortex effects in the pipe, thereby significantly enhancing heat transfer. This structure can not only increase the temperature difference gradient between the fluid and the pipe wall, but also effectively prolong the residence time of the fluid in the pipe, further improving the heat transfer efficiency. Especially under heat exchange conditions with low temperature difference and high heat load, the use of internal threaded steel pipes can effectively reduce the required heat exchange area, reduce the volume of equipment, and reduce system costs. Therefore, it is widely used in condensers, evaporators, absorbers and waste heat recovery devices, and has become an important part of industrial energy-saving projects.
Material and manufacturing standards
Internal thread seamless steel pipes are typically produced from high-grade boiler and pressure vessel steels to ensure mechanical strength, corrosion resistance, and high-temperature performance. Some commonly used materials include:
SA210C – A carbon-manganese steel used in superheaters and economizers
20G – A widely used boiler steel in China, known for good machinability and weldability
15CrMoG – Chromium-molybdenum alloy steel with excellent thermal strength
12Cr1MoVG – Suitable for high-temperature and high-pressure service
T1, T2, T12 – ASTM A213 grades for heat exchanger tubes with elevated temperature capabilities
These materials are selected based on operating pressure, temperature, medium, and design life requirements. High-temperature steel grades offer oxidation resistance and maintain structural stability even after prolonged use.
Practical applications in different fields
In air conditioning and refrigeration systems, internally threaded steel pipes are widely used in refrigerant transportation and condenser heat exchange units. Through their spiral structure, they enhance the heat exchange efficiency during the condensation process, reduce energy consumption, and improve the economy and comfort of system operation. In the chemical industry, its pressure and corrosion resistance make it an ideal choice for the transportation of acid-base fluids, corrosive gases and high-temperature process fluids. In boilers and pressure vessels, internally threaded steel pipes can increase the heat exchange rate between high-temperature flue gas and boiler water, thereby improving thermal energy utilization and reducing emissions. In energy engineering, such as nuclear power plants and cogeneration systems, internally threaded steel pipes are widely used in high-efficiency heat exchange devices in primary and secondary circuits due to their excellent thermal performance and structural reliability, showing extremely high engineering value and technical advantages.
Selection recommendations and precautions
When purchasing internally threaded steel pipes, factors such as pipe diameter, wall thickness, internal thread shape and material should be comprehensively considered according to the temperature, pressure, fluid medium type and heat transfer requirements of the actual application environment. For example, in high-pressure boiler systems, alloy steel materials with high strength and good heat resistance should be preferred, and the pitch and thread depth should be reasonably controlled to avoid excessive pressure drop due to excessive disturbance. In chemical systems with high corrosion resistance requirements, stainless steel materials should be used, and attention should be paid to the compatibility of the thread structure and the medium to prevent equipment failure due to crevice corrosion or stress corrosion. In addition, it is necessary to ensure that the internal thread processing accuracy and the overall pipe size tolerance meet the standard requirements to avoid affecting the system sealing and connection performance due to error accumulation.
Baowi Steel has many years of experience in manufacturing internal threaded seamless pipes. If you need to know more about product customization parameters, material recommendations or industry application cases, please contact us for technical support.
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