High Pressure Seamless Pipe

What is High Pressure Seamless Pipe?

High-pressure Seamless Pipe (SMLS) is a type of pipe specifically designed to withstand extremely high pressures from internal fluids (gas or liquid). It is suitable for manufacturing high-pressure and ultra-high-pressure boilers, and for use in high-temperature and high-pressure environments such as petroleum, power, machinery, and chemical equipment. Due to its seamless manufacturing process, its overall performance is superior to welded pipes, especially exhibiting greater stability under high-pressure conditions.

High Pressure: This means the pipe must be able to safely withstand enormous internal pressure without deformation, expansion, or bursting. This places extremely high demands on the material strength, wall thickness uniformity, and overall quality of the steel pipe.

Seamless: This refers to the pipe's manufacturing process. It is produced by heating a solid steel billet at high temperatures, followed by piercing, rolling, or stretching to create a seamless pipe without any weld seams. This is the fundamental difference between it and welded pipe.

Main Applications: 

High-pressure seamless pipe is mainly used in key components of high-pressure boilers, such as superheater tubes, reheater tubes, steam pipes, and main steam pipes. It is suitable for high-temperature environments of 450℃-650℃, and some alloy pipes can maintain a creep strength of 140MPa at 650℃. Besides boilers, seamless tubes are also used in pressure-bearing applications such as oil and gas drilling, chemical equipment, and nuclear power equipment. Domestic companies have already exported ultra-supercritical boiler tubes, covering more than 60 countries along the Belt and Road Initiative.

Why Choose Seamless Steel Pipes?

1. Structural Integrity: Welds on the tube body are usually the weakest point of the pipeline, easily becoming crack initiation points under high pressure, alternating loads, and corrosive environments. Seamless tubes eliminate this weak point, possessing higher overall strength and pressure-bearing capacity.
2. Uniformity: The metal flow lines of seamless tubes are continuous, with a uniform microstructure, better able to withstand pressure from all directions.
3. Reliability: In critical applications, seamless tubes are the preferred choice due to their higher safety factor.

Manufacturing Process of High-Pressure Seamless Pipes:

High-pressure seamless tubes are mainly manufactured using hot rolling or cold drawing (rolling) processes. Hot rolling involves heating steel billets at high temperatures and then forming seamless tubes through piercing and rolling processes. This method is suitable for producing large-diameter, thick-walled pipes. Cold rolling and cold drawing processes, on the other hand, use room or low-temperature processing to achieve more precise dimensions and a smoother surface, making them suitable for small-diameter, high-precision applications.

Seamless pipe walls eliminate the weld defects that can occur in traditional welded pipes, allowing them to withstand higher internal pressures and extreme working environments. This makes them the preferred pipeline for transporting high-pressure fluids or gases in industries such as petroleum, chemical, and power generation.

Materials and Standards:

The material selection for high-pressure seamless pipes depends on the specific working pressure, temperature, and corrosiveness of the medium. Seamless pipes are typically made of carbon steel, alloy steel, or stainless steel, with different materials suitable for different working environments.

For example, carbon steel seamless pipes are less expensive and suitable for general high-pressure environments; alloy steel seamless pipes have higher strength and corrosion resistance, making them suitable for more demanding conditions; and stainless steel seamless pipes are primarily used for transporting corrosive media.

Here are some of the most common materials:

1. Carbon Steel

This is the most commonly used and economical type, suitable for medium to high pressure applications with moderately high temperatures.

ASTM A106 Gr. B: This is the most common high-pressure seamless pipe material, widely used in boilers, power plant superheaters, reheaters, and main steam pipelines. It has good strength and processing properties, suitable for steam, water, oil, and other media with operating temperatures not exceeding 425°C.
ASTM A53 Gr. B: It is used for mechanical structures and pipelines for transporting medium and low pressure fluids at normal or medium temperatures, and has a low cost.

20G (SA-106 Gr. B): This is the most commonly used boiler-specific carbon steel in China. It is mainly used for boiler tubes (water-cooled wall tubes, economizer tubes, steam pipelines) and various medium and low pressure vessels.

2. Alloy Steel

When the operating temperature or pressure increases significantly, the strength of carbon steel decreases considerably, requiring the use of alloy steel.

15CrMoG (ASTM A335 P11/P22/P91): This is a typical chromium-molybdenum steel. The addition of chromium and molybdenum significantly improves the steel's high-temperature strength, creep resistance, and oxidation resistance.

Applications: Primarily used in high-temperature and high-pressure environments, such as superheaters and reheater pipes in power plant boilers, and cracking furnace tubes in petrochemical industries. P91 steel is a new generation of high-strength steel, allowing for thinner pipe walls to withstand higher pressures.

3. Stainless Steel

Stainless steel must be used when the medium is corrosive.

304/L (ASTM A312 TP304/304L): A general-purpose austenitic stainless steel with good corrosion resistance and formability, used in high-pressure corrosive environments in the chemical, food, and pharmaceutical industries.
316/L (ASTM A312 TP316/316L): Due to the addition of molybdenum, its resistance to pitting and crevice corrosion is superior to 304, making it particularly suitable for environments containing chloride ions (such as seawater and salt spray).
321 (ASTM A312 TP321): Contains titanium, effectively preventing intergranular corrosion, and is commonly used in high-temperature ranges (approximately 800°C).

Implementation Standards:

ASTM A106: High Temperature & High Pressure Service
ASTM A335: High Temperature & High Pressure Alloy Steel Service
ASTM A53: General Pressure & Structural Service
GB/T 5310: High Pressure Boilers & Power Plants
EN 10216: Pressure Equipment & Boilers
API 5CT / API 5L: Oil & Gas Drilling & Transportation

Key Features of High-Pressure Seamless Pipes:

The core feature of high-pressure seamless pipes lies in their high-pressure resistance. Due to the absence of welds, the overall structure of the pipe is more uniform, enabling it to withstand higher internal pressures. The uniform wall thickness of seamless pipes reduces resistance during fluid transport, improving transport efficiency.

Another important feature is its temperature resistance. High-pressure seamless pipes remain stable in both high and low temperature environments, without significant deformation or strength reduction due to temperature changes. This allows them to operate reliably under extreme conditions such as high-temperature steam and low-temperature liquefied gases.

Applications of High-Pressure Seamless Steel Pipes:

High-pressure seamless steel tubes have a wide range of applications, mainly including the following:

1. Energy and Power Industry

Power Plant Boilers: This is the largest application area for high-pressure seamless steel tubes. They are used to manufacture water-cooled walls, superheaters, reheaters, and main steam pipelines for boilers. These pipelines transport high-temperature (above 600℃) and high-pressure (up to 30MPa) steam to drive turbines for power generation, requiring extremely high resistance to high-temperature creep and oxidation. Materials are mostly alloy steels such as 15CrMoG and P91/P92.

Nuclear Power: Similar to thermal power plants, the conventional island section of nuclear power plants also extensively uses high-pressure alloy steel tubes.

2. Petrochemical Industry

Oil and Gas Drilling and Production: Used for underground oil pipelines, oil well casings, and natural gas transmission pipelines, enduring the high pressure and corrosion of the formation.

Oil Refineries: In hydrocracking and hydrorefining units, pipelines between reactors and heat exchangers must withstand extremely high hydrogen partial pressures and temperatures, necessitating the use of hydrogen corrosion-resistant chromium-molybdenum steel (such as A335 P5/P9/P11).

Chemical Equipment: In high-temperature and high-pressure reaction units such as ammonia synthesis and urea production, pipelines must withstand long-term high temperatures (above 500℃) and high pressures (exceeding 20MPa). They are also frequently used to transport corrosive media such as acids, alkalis, and salts; stainless steel seamless pipes are widely used in this field.

3. Mechanical Equipment and Hydraulic Systems

Used in high-pressure fluid transmission devices such as hydraulic and pneumatic systems, pipes require high precision and high strength.

Hydraulic Supports/Cylinders: Hydraulic supports in coal mines and hydraulic cylinders in engineering machinery typically operate at very high pressures (20-40MPa), requiring smooth inner walls and strong pressure-bearing capacity. Cold-drawn precision seamless pipes are commonly used, made of A106 carbon steel or 27SiMn alloy steel.

High-Pressure Pneumatic Systems: In certain specialized factories, high-pressure seamless pipes may also be used for compressed air delivery pipelines.

4. New Energy Development

Beyond traditional industrial sectors, high-pressure seamless pipes have demonstrated significant potential in new energy development. For example, in shale gas extraction, hydraulic fracturing technology requires high-pressure pipelines to transport water-based or chemical fracturing fluids, making the high-pressure load-bearing capacity of seamless pipes crucial for operational success. Furthermore, in hydrogen storage and transportation, their seamless design avoids hydrogen embrittlement caused by hydrogen permeation, providing reliable material support for the future promotion of the hydrogen economy.

Key Considerations for Purchasing High-Pressure Seamless Pipes:

When purchasing high-pressure seamless pipes, the following key factors should be considered:

1. Material Selection: Choose an appropriate material based on the operating environment, such as carbon steel, alloy steel, or stainless steel.
2. Dimensions and Specifications: Including outer diameter, wall thickness, and length, these must meet the actual engineering requirements.
3. Pressure Rating: Ensure the pipe's pressure-bearing capacity meets system requirements to avoid safety hazards caused by excessive pressure.
4. Surface Quality: Inspect the pipe surface for smoothness, absence of cracks, rust, and other defects to ensure service life.

Maintenance and Care:
To extend the service life of high-pressure seamless pipes, regular inspection and maintenance are necessary. Key measures include:

- Regular Cleaning: Prevent scale or corrosion on the inner wall of the pipe, which can affect fluid transport efficiency.
- Inspect Surface Condition: Promptly detect and address cracks, rust, and other problems to prevent further deterioration.
- Avoid Overpressure Use: Strictly adhere to the design pressure to prevent pipe damage due to overpressure.

Market Status: 

Currently, the market demand for high-pressure seamless pipes is steadily growing, especially in the energy and chemical industries. With advancements in industrial technology, the performance requirements for pipes are continuously increasing, such as higher strength and better corrosion resistance. In the future, with the application of new materials and processes, the performance of high-pressure seamless pipes will be further improved to meet the needs of more complex operating conditions.

Conclusion: 

Due to its excellent pressure resistance and wide range of applications, high-pressure seamless pipes have become an indispensable material in industrial production, supporting the safe production and efficient operation of core industries such as energy and chemicals. Choosing the right pipe material and performing proper maintenance can ensure its long-term stable operation and provide reliable protection for various high-pressure fluid transportation systems.

Read more: Schedule 80 Steel Pipe Pressure Rating or Low, Medium and High Pressure Boiler Tube