Seamless Steel Pipes for High Temperature and High Pressure

High temperature and high pressure resistant seamless steel pipes & tubes refer to seamless steel pipes that can operate safely, reliably, and stably for a long time under harsh environments of high temperature and high pressure without easily deforming or cracking.

What are "Temperature Resistance" and "Pressure Resistance"?

a. Temperature Resistance
Oxidation Resistance: The ability to resist corrosion from media such as flue gas and air at high temperatures, without the formation of severe oxide scale on the surface.
Thermal Strength: Maintaining sufficient strength and creep resistance at high temperatures.

Creep: The phenomenon of slow plastic deformation of a material over time under constant temperature and stress. This is the main cause of failure in high-temperature components.

b. Pressure Resistance
The ability to withstand the design pressure of the medium inside the pipe at the design temperature without plastic deformation or cracking.
This requires the material to have high room temperature and high temperature yield strength and tensile strength.

Main Characteristics of High Temperature and High Pressure Resistant Seamless Pipes:

1. Excellent High Temperature Resistance: Resistant to high-temperature corrosion and oxidation.
2. Good Pressure Resistance: Able to withstand extremely high pressure, ensuring safe and reliable operation.
3. High strength and good toughness: Wear-resistant, shock-resistant, tensile-resistant, and not easily deformed or cracked.
4. Good weldability: Corrosion-resistant, high weld strength, and good sealing performance.

Manufacturing Process of High-temperature and High-pressure Seamless Pipe:

High-temperature and high-pressure seamless pipe is manufactured using cold drawing or hot rolling methods, and has the following manufacturing process elements:

1. High-quality carbon steel, stainless steel, alloy steel, etc., are selected as raw materials to ensure material purity and resistance to high temperature and pressure.
2. The processing technology is selected between cold drawing and hot rolling, mainly depending on the pipe diameter, wall thickness, production quantity, etc.
3. After processing, cold drawing or heat treatment is required to ensure the mechanical properties and corrosion resistance of the pipe.
4. Process control requires meticulous attention to avoid defects such as inclusions and bubbles within the pipe, which would affect the service life and safety performance of the pipeline.

Material Selection for High-temperature and High-pressure Seamless Pipe:

1. Low-temperature/medium-temperature range (operating temperature ≤ 400°C)

At this temperature, carbon steel is the most cost-effective choice. 

ASTM A106 Gr. B: Standard choice for seamless steel pipes, used for steam and oil/gas pipelines.

ASTM A516 Gr. 60/70: Steel plates for pressure vessels, with excellent weldability.

2. Medium-High Temperature Range (Operating Temperature 400°C ~ 600°C)

This is the core temperature range for thermal power plants and petrochemical plants, where chromium-molybdenum alloy steel is the dominant material.

ASTM A335 P11, A213 T11: Commonly used in early power plants and petrochemical plants, now gradually being replaced by higher-performance steels.
ASTM A335 P22, A213 T22: Traditional mainstays, possessing good high-temperature strength and weldability, with extremely wide applications. Examples include main steam pipelines and superheaters in thermal power plants; and pipelines in hydrogenation and cracking units in petrochemical plants.
ASTM A335 P91, A213 T91: Milestone steels in modern power plants. Twice the strength of P22, allowing for thinner wall thicknesses and higher thermal efficiency. Used for main steam pipes and superheaters in supercritical units.

3. Ultra-high temperature/heat-resistant applications (operating temperature > 600°C)

When the temperature exceeds 600°C, the strength of ferritic steel decreases significantly, requiring austenitic stainless steel.

ASTM A213 TP304H/TP321H: 304H is a basic austenitic heat-resistant steel; 321H, with titanium added to stabilize carbon, has stronger resistance to intergranular corrosion and is suitable for high-temperature welded components.
ASTM A213 TP316H/TP347H: 316H, due to the presence of molybdenum, has better resistance to pitting corrosion and creep strength; 347H, stabilized with niobium, has excellent endurance strength and is used in critical parts of power plant superheaters and reheaters.

Super stainless steel/nickel-based alloys: This is the final choice when the temperature, pressure, and corrosiveness are extremely high (e.g., in aero-engines and chemical reactors), but the cost is extremely high.

In short: 

For ordinary high temperature and high pressure: A106 GR.B is sufficient.

Important high temperature and high pressure: Use chromium-molybdenum steel such as P91.
Extreme high temperature: Use stainless steel such as TP304H.

Main Application Areas:

High temperature and high pressure resistant seamless pipes are mainly used in power, petrochemical, machinery equipment, aviation, nuclear power, food and pharmaceutical fields. Specific applications are as follows:

1. Piping engineering for heat source equipment such as heat exchangers, boilers, main steam pipelines, and high-pressure feedwater pipelines.
2. Piping for hydrogenation reactors, cracking units, and high-temperature heat exchangers in oil refineries; high-temperature and high-pressure wellhead equipment in oil and gas fields.
3. Piping for precision equipment such as medical devices, spacecraft, nuclear power, and military equipment.
4. Transmission pipelines for hydraulic and pneumatic equipment.

5. Piping for production equipment in the food and pharmaceutical industries.

Key Technologies for Achieving "High Temperature and High Pressure Resistance":

The strength of ordinary carbon steel drops sharply when the temperature exceeds 400°C. Therefore, high temperature and pressure resistant seamless pipes improve performance through the following methods:

1. Special alloying design
Carbon (C): Increases strength, but too much will impair weldability and toughness.
Chromium (Cr): Core element. Improves oxidation resistance and corrosion resistance. Higher content generally results in better temperature resistance.
Molybdenum (Mo): Core element. Significantly improves high-temperature strength and creep resistance.
Vanadium (V), Niobium (Nb), Titanium (Ti): Refine grain size, improve strength and toughness.
Nickel (Ni): Improves toughness and stabilizes austenitic structure.

2. Advanced Manufacturing Process
Seamless Forming: Eliminates the potential weak point of welds, ensuring the integrity and uniformity of the pipe structure.
Strict Heat Treatment: Such as normalizing + tempering or quenching + tempering (tempering) to obtain a stable and uniform microstructure, thereby achieving optimal mechanical properties.

3. Stringent Quality Inspection
100% Non-Destructive Testing: Such as ultrasonic testing and eddy current testing to ensure no internal defects.
Strict Mechanical Property Testing: Including room temperature and high temperature yield strength, tensile strength, impact toughness, etc.
Metallographic Structure Inspection: Ensures that the microstructure meets standards.

How to Choose High-Temperature and High-Pressure Seamless Steel Pipes?

When purchasing high-temperature and high-pressure seamless steel pipes, the following aspects need to be considered:

1. Material: Choose high-quality stainless steel or alloy steel.
2. Specifications: Select the appropriate pipe diameter and wall thickness based on the pipeline's application scenario and engineering requirements.
3. Quality: Choose products from well-known brands or international manufacturers and review relevant quality certification documents.
4. Service: Choose manufacturers with comprehensive after-sales service and technical support.

Conclusion: 

High-temperature and high-pressure seamless steel pipes are high-performance seamless steel pipes produced through special alloy design and strict manufacturing processes. They can maintain structural integrity and functional reliability for a long time under extreme working conditions of high temperature and high pressure coupling, making them an indispensable key basic material for modern chemical, power, and other heavy industries. When selecting, the specific material and specifications must be determined according to the design temperature, design pressure, and media environment, following relevant international or industry standards (such as ASME, GB, etc.).

Read more: Which Material is Used for Boiler Tubes? or Seamless Pipe vs. Welded Pipe