Scope of ASTM A333
ASTM A333 is the standard specification for seamless and welded steel pipe intended for low-temperature service. It defines several grades with increasing nickel content, which extend the usable temperature range from moderate cold service to deep cryogenic temperatures. The specification is widely used for carbon and alloy steel piping in LNG, petrochemical, and cold-climate applications, and it is paired with impact testing requirements that verify the toughness of the steel at the design temperature.
Chemical Composition of Common Grades
| Element | Grade 1 | Grade 3 | Grade 6 | Grade 8 |
|---|---|---|---|---|
| Carbon, C, maximum | 0.30% | 0.19% | 0.30% | 0.13% |
| Manganese, Mn | 0.40% to 1.06% | 0.31% to 0.64% | 0.29% to 1.06% | 0.90% maximum |
| Nickel, Ni | Not specified | 3.18% to 3.82% | Not specified | 8.40% to 9.60% |
| Phosphorus, P, maximum | 0.025% | 0.025% | 0.025% | 0.025% |
| Sulfur, S, maximum | 0.025% | 0.025% | 0.025% | 0.025% |
Mechanical Properties
| Grade | Minimum Tensile Strength | Minimum Yield Strength |
|---|---|---|
| Grade 1 | 55 ksi, equal to 380 MPa | 30 ksi, equal to 205 MPa |
| Grade 3 | 65 ksi, equal to 450 MPa | 35 ksi, equal to 240 MPa |
| Grade 6 | 60 ksi, equal to 415 MPa | 35 ksi, equal to 240 MPa |
| Grade 8 | 100 ksi, equal to 690 MPa | 75 ksi, equal to 515 MPa |
Seamless and Welded Product Forms
A333 pipe is supplied in seamless form, produced from billets by hot rolling or cold drawing, and in welded form, produced by electric resistance welding or submerged arc welding depending on the diameter. Seamless pipe is preferred for the highest pressures and the smallest diameters, while welded pipe is economical for large-diameter low-temperature lines. Both forms are heat treated and impact tested to the same requirements.
Available Sizes
| Product Form | Typical Size Range |
|---|---|
| Seamless pipe | 6 mm to 900 mm outside diameter, 1 mm to 50 mm wall |
| Welded pipe | 20 mm to 3600 mm outside diameter, 1.6 mm to 65 mm wall |
| Length | 3 m to 12 m, with custom lengths |
| Surface | Bright, polished, or black |
Heat Treatment
A333 pipe is delivered in the normalized condition as standard, and quenching and tempering is permitted where the standard allows it. Normalizing produces a fine-grained ferrite-pearlite structure with the toughness required at low temperature. The heat treatment is verified on the certificate, and the Charpy impact values are reported at the specified test temperature.
Typical Applications
A333 pipe is used in LNG liquefaction and regasification plants, ethylene and propylene plants, liquid nitrogen and liquid oxygen systems, and refrigerated storage tanks and transport systems. Cold-climate pipelines and any process lines with a low minimum design metal temperature also specify the grade. Grade 6 covers the common range, while Grades 3 and 8 serve the deep cryogenic range.
FAQ
What is the most common A333 grade?
Grade 6 is the most common grade. It is a carbon-manganese steel qualified for service down to about minus 45 degrees Celsius and covers the majority of low-temperature piping applications.
Why does A333 require impact testing?
Impact testing verifies that the steel remains ductile at the design temperature. Carbon steels can become brittle at low temperature, and the Charpy test provides the data needed to prove the pipe is safe for the intended service.
What is the difference between A333 Grade 3 and Grade 6?
Grade 3 contains 3.5 percent nickel and is qualified for service down to about minus 101 degrees Celsius, while Grade 6 is a plain carbon-manganese steel limited to about minus 45 degrees Celsius.
Can A333 pipe be supplied galvanized?
Galvanizing is not normally applied to A333 pipe because the coating process is not part of the standard and low-temperature toughness of the coating system is not verified. Corrosion protection is provided by paint or other systems per project specification.
Is A333 pipe weldable?
Yes. Qualified welding procedures and low-temperature consumables are used, and post-weld heat treatment is applied when the design code requires it for the wall thickness and service temperature.
What certificates are provided?
Mill test certificates document the chemical composition, tensile properties, heat treatment, and Charpy impact test results at the specified temperature, which are essential for low-temperature piping documentation.
