ASTM A333 Gr6 steel is a C-Mn carbon steel widely used for fluid transportation in the petrochemical industry and in low-temperature, high-cold regions. The market demand in North America and Europe exceeds 20,000 tons annually. This article discusses the production of ASTM A333 Gr6 seamless steel pipes for low-temperature applications.
Composition Design of ASTM A333 Gr6 Steel
Basic Principles of Alloying
ASTM A333 Grade 6 steel is classified as C-Mn carbon steel. The composition requirements for this grade are outlined in the ASTM A333 standard, which specifies the chemical composition (mass fraction) of ASTM A333 Grade 6 steel.
| Standard | C | Si | Mn | P | S | Cu | Cr | Ni | Mo | V | AI |
| ASTM A333 | ≤0.30 | ≥0.10 | 0.29～1.06 | ≤0.025 | ≤0.025 | / | / | / | / | / | / |
| Control Range | ≤0.12 | 0.17~0.35 | 1.00~1.30 | ≤0.02 | ≤0.010 | ≤0.020 | ≤0.025 | ≤0.025 | ≤0.15 | ≤0.08 | ≤0.05 |
- The ASTM A333 standard states that for each reduction of 0.01% carbon below the specified maximum carbon content, the manganese content may be increased by 0.05%, but the manganese content shall not exceed 1.35%.
- As ≤ 0.030%, Sn ≤ 0.020%, As + Sn + Pb + Sb + Bi ≤ 0.050%.
Role of Elements in Steel and Control Ranges
Carbon: Carbon has a significant impact on steel’s performance. As the carbon content increases, the strength of steel at room temperature improves, but plasticity and toughness decrease, especially affecting low-temperature toughness. High carbon content can also adversely affect welding performance. The ASTM A333 standard specifies C ≤ 0.30%. Practically, higher levels negatively affect plasticity and toughness. To ensure strength while minimizing carbon equivalent, our company controls the carbon content to no more than 0.12%.
Manganese: Manganese can dissolve in ferrite and form cementite-type carbides, lowering the critical transformation temperature and refining the pearlite structure, thus enhancing strength. To ensure the strength of ASTM A333 Gr6 pipes while appropriately lowering carbon content, manganese content should be increased. Therefore, we control manganese content to be above 1.00% to 1.30% for optimal toughness.
Silicon: Silicon mainly acts as a deoxidizer and reducer during steelmaking. It enhances oxidation resistance but also promotes graphitization, so its content should not be too high, controlled between 0.17% and 0.35%.
Aluminum: Aluminum has a strong affinity for nitrogen and oxygen in steel and is primarily used for deoxidizing and nitrogen control during steelmaking. When aluminum content is below 0.05%, it refines the intrinsic grain size of steel, raises the grain coarsening temperature, inhibits aging in low-carbon steel, improves impact toughness, lowers the brittleness transition temperature, and enhances toughness at low temperatures.
Sulfur and Phosphorus: These elements are harmful to steel performance and should be minimized.
Other Elements: Elements like chromium, nickel, copper, molybdenum, and vanadium are considered impurities; excessive amounts can increase the carbon equivalent of steel, thus requiring strict control.
Five Harmful Elements: Arsenic, tin, lead, antimony, and bismuth collectively reduce steel performance and must be strictly controlled. Considering the above factors, our company controls the chemical composition of ASTM A333 Gr6 steel as per Table 1.
Normalization Process for Steel Pipes
The ASTM A333 standard stipulates that Gr6 steel pipes must be delivered in a normalized condition. After normalization, the mechanical properties of the steel pipes should meet the requirements specified in Table.
| Mechanical Properties Requirements of Steel Pipes | ||||
| Property | Tensile StrengthRm/MPa | Yield StrengthRa/MPa | Elongation A50mm/% | Akv(-45℃)/J |
| Requirements | ≥415 | ≥240 | ≥30① | ≥18② |
| Note: ① For longitudinal strip specimens with a thickness of less than 8 mm, the minimum allowable elongation rate is related to the actual thickness of the specimen: A50mm=1.87t+15.00 | ||||
| where: A 50mm— allowable minimum elongation rate, %; t — actual thickness of the specimen, mm. | ||||
| ②The table shows that the required impact energy for the 10mm x 10mm x 55mm specimen is Akv. For the specimens measuring 10mm x 7.5mm x 55mm, 10mm x 5mm x 55mm, and 10mm x 2.5mm x 55mm, the minimum impact energies are 14 J, 9 J, and 5 J, respectively. | ||||
The normalized test was conducted using a nitrogen-protected heat treatment furnace for steel pipes with specifications of Φ60.3 mm × 5.54 mm, subjected to a temperature of 915°C for 15 minutes. After normalizing, samples were taken to test the mechanical properties of the steel pipes according to standard requirements, and the microstructure was observed. The mechanical properties after normalizing are shown in the table.
| Property | Tensile StrengthRm/MPa | Yield StrengthRa/MPa | Elongation A50mm/% | Akv(-45℃)/J |
| Requirements | ≥415 | ≥240 | ≥30 | ≥18 |
| Test results | 465 | 340 | 33 | 92，88，97 |
The mechanical properties of the steel pipes after normalizing fully meet the standard requirements, particularly with very high low-temperature impact energy, which is advantageous for the safety of the steel pipes. Microscopic observation results indicate that the microstructure consists of a “ferrite + pearlite” structure, with a grain size of 10. A high grain size level is beneficial for enhancing the low-temperature toughness of the steel pipes.
Production Process Flow and Key Control Points
1.Pipe Blank Production Process Flow
- Hot-pressed block iron + high-quality pig iron, scrap steel → Electric furnace → Secondary refining → Vacuum degassing → Continuous casting → Cutting of cast blanks to specified length → Inspection of cast blanks
- Product specifications range: Φ120–150 mm round pipe blanks
- Key process control points:
Use high-quality scrap steel and pig iron combined with sponge iron to control the residual content of harmful elements. Steelmaking employs ultra-high power electric arc furnace melting, with eccentric bottom tapping to ensure slag separation and slag-free tapping. The entire process of ladle refining includes blowing argon for stirring. The molten steel undergoes vacuum degassing and treatment with Si-Ca wire. Continuous casting is used, and during the pouring process, a long nozzle and argon protection technology are implemented to isolate the molten steel from air and prevent secondary oxidation.
2. Steel Pipe Production Process Flow
There has three production lines for ASTM A333 Gr6 steel pipes, specifically the Φ108 mm line, Φ89 mm line, and Φ50 mm line. The process flows are as follows:
(1) Φ108 mm Line Process Flow
- Pipe blank heating → Two-roll conical perforation → Three-roll pipe rolling → Rod removal → Reheating → High-pressure water descaling → Micro-tension reduction → Straightening → Manual inspection → Normalizing → Eddy current testing → Re-inspection → Marking → Weighing → Storage
- Product specifications range: Φ45–127 mm × 7–27 mm
- Key process control points:
Ensure the surface quality of rolls and molds is good to minimize damage to the pipe surface. The pressure of high-pressure water descaling should be greater than 10 MPa, and all nozzles should be functioning properly to reduce pipe surface pitting.
(2) Φ89 mm Line Process Flow
- Pipe blank heating → Conical perforation → Semi-floating mandrel continuous rolling → Rod removal → Head cutting → Reheating → Tension reduction → Saw cutting → Normalizing → Straightening → Eddy current and magnetic flux leakage testing + ultrasonic diameter and thickness measurement → Manual inspection → Cutting to specified length → Re-inspection → Marking → Weighing → Storage
- Product specifications range: Φ25–127 mm × 2.5–16 mm
- Key process control points:
Ensure the surface quality of rolls and molds is good to minimize damage to the pipe surface. The pressure of high-pressure water descaling should be greater than 15 MPa, and all nozzles should be functioning properly to reduce pipe surface pitting.
(3) Φ50 mm Line Process Flow
- Product specifications range: Φ16–76 mm × 2–8 mm.
- Key process control points:
Strictly control the pickling temperature and time of the steel pipes to prevent excessive pickling from causing deformation and non-conformance. The final normalizing temperature should be controlled between 900–930°C to ensure the mechanical properties of the steel pipes are compliant.
Why SSM is Your Trusted Supplier of ASTM A333 Pipe ?
With years of experience, SSM’s professional team provides expert guidance while maintaining competitive pricing and ensuring timely delivery to reduce project delays.
We focus on building long-term relationships and provides personalized service, along with comprehensive technical support and customization options to meet specific project needs.
SSM’s strong reputation in the industry makes it the preferred choice for carbon steel pipe solutions.
FAQ
Commonly used in oil and gas, chemical processing, and power generation industries where low temperatures are involved.
It has excellent toughness and low-temperature impact resistance, typically with a minimum yield strength of 240 MPa (35,000 psi).
While it is designed for low temperatures, it can be used in high-pressure applications, provided it meets the specific engineering requirements.
Welding should be performed using low-hydrogen processes, and preheating may be necessary to prevent cracking.
More information about ASTM A333 Pipe:
