Buyers frequently see two near-identical designations for the same low-temperature pipe: ASTM A333 Gr.6 and ASME SA333 Gr.6. They look like different products, but they are far more alike than they are different. Understanding the relationship saves confusion on specs, certificates and import documents.
This guide explains exactly what each designation means, where the two diverge, and how to specify low-temperature seamless pipe correctly.
Same Material, Two Publishing Bodies
ASTM A333 is the ASTM International specification for seamless steel pipe for low-temperature service. ASME SA333 is the identical material adopted into the ASME Boiler and Pressure Vessel Code. The S prefix in ASME designations simply means steel material under the ASME code. Chemistry, heat treatment and toughness for Gr.6 are the same in both.
Bottom line: ASTM A333 Gr.6 and ASME SA333 Gr.6 are the same pipe. The choice of designation follows which code your project references, ASTM for general procurement, ASME for pressure-equipment code work.
Chemistry & Properties (Identical)
| Property | Gr.6 (both A333 & SA333) |
|---|---|
| Type | Carbon-manganese, seamless |
| Yield strength | >= 240 MPa (35 ksi) |
| Tensile strength | >= 415 MPa (60 ksi) |
| Charpy @ -45C | >= 18 J avg / 13 J min |
| Heat treatment | Normalized |
When Each Designation Applies
Reference ASTM A333 Gr.6 when the purchase order or piping spec is written to ASTM
Reference ASME SA333 Gr.6 when the component falls under the ASME BPVC (e.g. pressure vessels, heat exchangers)
Many mills hold certification to both and can mark the pipe either way
Certification & Marking
A mill that is ASME-approved can issue an SA333 certificate; an ASTM-accredited mill issues A333. On a single heat of steel the underlying material is the same, only the certificate header and code reference differ. Always match the certificate to the code your project inspector expects.
Applications
Both designations cover the same service: LNG balance-of-plant, petrochemical cryogenic units, and Arctic/high-altitude lines down to about -45C. For the deepest cryogenic paths (-162C) step up to 9% nickel or 304L/316L stainless.
Sourcing Low-Temperature Pipe from China
Confirm the mill holds both ASTM and ASME approvals if you need SA333 marking
Require the -45C Charpy report on the actual heat
Confirm normalized heat treatment
Use third-party witness for cryogenic-critical orders
Baoyang Pipeline produces ASTM A333 Gr.6 and ASME SA333 Gr.6 seamless low-temperature pipe for LNG, petrochemical and cryogenic projects, with full mill test reports and export documentation.
Frequently Asked Questions
Are A333 Gr.6 and SA333 Gr.6 interchangeable?
For the material itself, yes, they are the same chemistry and properties. Use the designation your project code requires on the certificate and marking.
Which should I specify on my purchase order?
Follow the code referenced by your engineering specification. If it is an ASME pressure-equipment job, specify SA333 Gr.6; for general ASTM-based procurement, A333 Gr.6. The steel is identical.
Does SA333 cost more than A333?
Not for the material. The difference is certification and code approval, not the steel. If a mill is already ASME-approved, issuing SA333 marking is usually a documentation step, not a price change.
Can SA333 Gr.6 be used at -162C for LNG?
No. Both A333 and SA333 Gr.6 are rated to about -45C. LNG storage at -162C requires 9% nickel or austenitic stainless. Gr.6 is for the cryogenic balance-of-plant, not the tank-to-ship path.
Conclusion
ASTM A333 Gr.6 and ASME SA333 Gr.6 are the same low-temperature seamless pipe viewed through two code bodies. Specify the designation your project references, insist on the -45C Charpy report and normalized heat treatment, and verify the mill's approvals. Baoyang supplies both A333 and SA333 Gr.6 with full cryogenic documentation.
