ASTM A333 Grade 6 Seamless Pipe for Low-Temperature Service
Dec 04, 2025
What Is A333 Grade 6 Pipe
A333 Gr.6 (ASTM A333 Grade 6) is a seamless steel pipe widely used in low-temperature environments, with its core advantage lying in cryogenic toughness and resistance to embrittlement. Contrary to some marketing descriptions, Grade 6 is a nickel-free silicon-killed carbon-manganese steel; its low-temperature toughness comes from a fine-grain normalized structure and strict compositional control, not from nickel additions. The nickel-bearing grades in the A333 family are Grade 3 (3.5 percent nickel) and Grade 8 (9 percent nickel). Grade 6 maintains superior toughness (Charpy impact energy of 18 J average for full-size specimens at about minus 45 deg C) and strength, making it a cost-effective solution for low-temperature piping systems.
Chemical Composition
| Element | Composition (%) |
|---|---|
| Carbon (C) | 0.30 max |
| Manganese (Mn) | 0.29-1.06 |
| Phosphorus (P) | 0.025 max |
| Sulfur (S) | 0.025 max |
| Silicon (Si) | 0.10-0.50 |
Mechanical Properties
| Property | Value |
|---|---|
| Tensile strength | 415 MPa (min) |
| Yield strength | 240 MPa (min) |
| Elongation | 30 percent (min, reference) |
| Impact energy | 18 J average at minus 45 deg C (full-size specimen) |
Impact Requirements
Charpy V-notch impact testing is mandatory. For a full-size 10 by 10 mm specimen, the minimum average value of a set of three specimens is 13 ft-lbf (18 J) at minus 50 deg F (minus 45 deg C), with a minimum of 10 ft-lbf (14 J) for one specimen only of a set. Smaller specimens use proportionally reduced values. The service limit of Grade 6 is related to its ductile-to-brittle transition temperature, commonly referenced around minus 70 deg C; applications below that require materials such as 9 percent nickel steel or austenitic stainless steel.
Application Scenarios
Oil and gas industry: low-temperature sections of LNG plants and gas processing facilities, and oil and gas equipment in arctic regions.
Chemical industry: piping for cryogenic reactors and heat exchangers, and structural supports in cold service plants.
Other fields: structural applications in cold climates (bridges and towers) and refrigeration systems of the minus 50 deg C class. Note that for LNG transfer at about minus 162 deg C, the piping material itself must be a lower-temperature grade such as 9 percent nickel steel or austenitic stainless steel; Grade 6 is limited to the minus 45 deg C class.
Design and Fabrication Notes
During design and construction, special consideration must be given to welding procedures and cryogenic fabrication measures to ensure operational safety and reliability. Preheat may be required for thicker sections, and the welding procedure specification must be qualified for the low-temperature service class.
Frequently Asked Questions
Q: What is A333 Gr.6 pipe? A: A nickel-free fine-grain carbon steel pipe per ASTM A333 for low-temperature service to about minus 45 deg C.
Q: Does Grade 6 contain nickel? A> No. Grade 6 has no nickel requirement; Grades 3 and 8 are the nickel-bearing grades.
Q: What is the impact test requirement? A> 18 J average (13 ft-lbf) for full-size specimens at minus 45 deg C, per the A333 tables.
Q: Can Gr.6 be used for LNG at minus 162 deg C? A> No. LNG piping requires 9 percent nickel steel or austenitic stainless steel at that temperature.
Q: What is the tensile strength? A> 415 MPa minimum, with 240 MPa minimum yield strength.
Q: What heat treatment is applied? A> Normalization to refine the grain and establish low-temperature toughness.
Need A333 Grade 6 pipe with impact certificates for your low-temperature project? Contact us with your size and specification.
