ASTM A333 Grade 6 Carbon Steel Pipes
Dec 04, 2025
What Is A333 Grade 6 Pipe
A333 Gr.6 low-temperature pipe is a seamless steel pipe for low-temperature service conforming to the ASTM A333/ASME SA333 standard. It is primarily used in petrochemical equipment (such as reactors, heat exchangers, and separators), natural gas processing, and cryogenic equipment manufacturing. Grade 6 is a nickel-free silicon-killed carbon-manganese steel whose fine-grain structure and normalized condition provide the notch toughness required at design temperatures down to about minus 45 deg C. It is the most widely used A333 grade because it achieves low-temperature toughness without the cost of nickel-alloyed grades.
Chemical Composition
| Element | Grade 1 | Grade 3 | Grade 6 |
|---|---|---|---|
| Carbon, max | 0.30 | 0.19 | 0.30 |
| Manganese | 0.40-1.06 | 0.31-0.64 | 0.29-1.06 |
| Phosphorus, max | 0.025 | 0.025 | 0.025 |
| Sulfur, max | 0.025 | 0.025 | 0.025 |
| Silicon | - | 0.18-0.37 | 0.10 min |
| Nickel | - | 3.18-3.82 | - |
Note that Grade 6 contains no nickel requirement; the nickel-bearing grade in this family is Grade 3 (3.5 percent nickel).
Heat Treatment and Mechanical Properties
The delivery condition requires normalization heat treatment at about 900-930 deg C, which refines the grain structure and establishes the low-temperature toughness. Minimum tensile strength is 415 MPa, minimum yield strength is 240 MPa, and elongation requirements follow the ASTM A333 tables (for example 30 percent minimum in 2-inch longitudinal strip tests for walls of 8 mm and over). Charpy V-notch impact testing is required at the specified low temperature, commonly at about minus 45 deg C for Grade 6 service.
Common Sizes and Production Routes
Common specifications include an outer diameter of 21.3-762 mm and a wall thickness of 2.0-140 mm, produced via hot-rolled, cold-drawn, or hot-expanded processes. The pipe is supplied in single random, double random, or fixed lengths as required.
A333 Gr.6 vs A106 Gr.B
| Parameter | ASTM A333 Gr.6 | ASTM A106 Gr.B |
|---|---|---|
| Standard scope | Low-temperature piping to about -45 deg C | Carbon steel pipe for service to about 425 deg C |
| Key metallurgy | Fine-grain normalized C-Mn steel, nickel-free | Hot-finished C-Mn steel, no impact requirement |
| Temperature range | About -45 deg C to +50 deg C (design basis) | About -29 deg C to +425 deg C |
| Mechanical focus | Charpy impact at -45 deg C | Tensile and hydrostatic testing |
| Mandatory testing | Cryogenic Charpy impact test | Tensile, flattening, hydrostatic |
| Typical use | LNG secondary piping, ammonia plants, cold boxes | Steam lines, boiler feed, general O&G piping |
Applications
Typical applications include valve connecting pipes in secondary cryogenic sections of LNG facilities, ammonia synthesis towers and ethylene cold boxes in chemical processing, and natural gas processing and distribution piping. For service below about minus 45 deg C, nickel grades such as A333 Grade 8 (9 percent nickel) or austenitic stainless steel are normally required.
Frequently Asked Questions
Q: What is A333 Grade 6 pipe? A: A nickel-free fine-grain carbon steel pipe per ASTM A333 for low-temperature service down to about minus 45 deg C.
Q: What is the tensile strength of Grade 6? A: 415 MPa minimum, with 240 MPa minimum yield strength.
Q: What heat treatment is required? A: Normalization at about 900-930 deg C.
Q: What is the difference between Grade 6 and Grade 3? A: Grade 3 contains 3.5 percent nickel for improved low-temperature toughness; Grade 6 is nickel-free and achieves toughness by fine grain and normalization.
Q: Where is Grade 6 used? A: LNG secondary piping, ammonia plants, ethylene cold boxes, and natural gas processing.
Q: What testing is mandatory? A: Charpy V-notch impact testing at the specified low temperature, plus tensile and dimensional tests.
Need ASTM A333 Grade 6 pipe with impact-test certificates? Send your size, wall, and quantity for a quotation.
