ASTM A333 Grade 6 is the standard carbon steel pipe for low-temperature service, usable down to about -45 degrees Celsius. It is a nickel-free, aluminium or silicon killed, fine-grain carbon-manganese steel with a minimum yield strength of 240 MPa and a minimum tensile strength of 415 MPa, and Charpy V-notch impact testing at -45 degrees Celsius is a mandatory requirement of the grade rather than an optional extra.
Download ASTM A333 Grade 6 Pipe data sheet (PDF) One-page summary of the supply range, chemistry, mechanical properties and inspection documents on this page. The standard is the governing document.
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Size range and specification
- Outside diameter 1/2 inch – 36 inch (12.7 – 914 mm)
- Wall thickness SCH 10 – SCH XXS, or by wall thickness
- Length SRL 5.8 m, DRL 11.8 m, or fixed length
- Ends Plain end, beveled end, threaded and coupled
- Surface treatment Black varnish, bare, rust preventive oil, 3PE or FBE on request
- Manufacturing process Seamless, ERW, or welded
- Heat treatment Normalized, fine grain
- Delivery standard ASTM A333 / ASME SA333, dimensions to ASME B36.10M
- Delivery condition Normalized; impact tested at the specified temperature
How this grade is supplied
- Inspection Inspected by the producing mill’s own inspection department, which is independent of production, against the delivery standard above. Third-party inspection — SGS, BV or TUV, or an inspector you send yourself — can be arranged at the mill or before shipment; give us the dates and the scope at the order stage.
- Certificate A mill test certificate to EN 10204 3.1 showing the heat number, the chemical composition and the mechanical results is standard on every order. EN 10204 3.2, countersigned by the inspector you nominate, is available on request.
- Documents with the goods The mill test certificate and the packing list travel with the shipment, and the heat number is traceable from cast through to the finished product.
- Packing Sea-worthy export packing: bundled by size with end protection, corrosion protection on request, stencilled with the size, grade and heat number.
- MOQ One bundle or one truckload; mixed sizes within a bundle accepted.
- Lead time Counted from order confirmation, not from the enquiry. Stock sizes 5–10 days; mill run or non-stock 3–5 weeks. The delivery window is fixed on the quotation.
- How we supply Sourced through partner mills; the producing mill is named on the quotation.
ASTM A333 Grade 6 chemical composition (%)
| Element | Requirement | Element | Requirement |
|---|---|---|---|
| Carbon, C | 0.30 max | Silicon, Si | 0.10 min |
| Manganese, Mn | 0.29 – 1.06 | Nickel, Ni | not required |
| Phosphorus, P | 0.025 max | Chromium, Cr | no requirement |
| Sulphur, S | 0.025 max | Molybdenum, Mo | no requirement |
Grade 6 is deliberately a nickel-free grade: its low-temperature toughness comes from a fine grain size, from killing the steel with aluminium or silicon, and from normalizing, not from alloying with nickel. Phosphorus and sulphur are each held to 0.025 maximum because both elements attack impact toughness at low temperature, and those two limits are why this grade is ordered with impact testing rather than on strength alone. Secondary sources also quote residual limits for chromium, copper, molybdenum and vanadium for this grade; the limits shown above are the ones that decide whether the grade can meet its impact requirement.
Source: chemical composition requirements of ASTM A333 / ASME SA333, Table 1. The standard is the governing document.
ASTM A333 Grade 6 mechanical properties
| Grade | Tensile strength | Yield strength | Elongation | Impact test |
|---|---|---|---|---|
| A333 Grade 6 | 415 MPa min (60,000 psi) | 240 MPa min (35,000 psi) | 30% min | Charpy V-notch at -45 degrees C: 18 J average of three, 14 J single minimum |
The impact requirement is the reason the grade exists. Three Charpy V-notch specimens are taken in the longitudinal direction and the average must reach 18 J, with no single specimen below 14 J; where the wall thickness does not allow a full-size 10 x 10 mm specimen, sub-size specimens are used with proportionally reduced acceptance values. The elongation figure is the tabulated minimum for the standard specimen and varies with specimen size and wall thickness, so it should be read together with the test report rather than on its own.
Source: tensile requirements of ASTM A333 / ASME SA333, Table 1. The standard is the governing document.
Impact energy by specimen size
The Grade 6 impact requirement is written for a full-size Charpy specimen, but thin wall means the specimen has to be smaller, and the acceptance energy is reduced with it:
| Specimen size | Minimum average absorbed energy (3 specimens) |
|---|---|
| 10 x 10 mm (full size) | 18 J |
| Sub-size (10 x 7.5 mm or 10 x 5 mm) | Reduced; read from the current ASTM A333/A333M table |
The specimen size must appear on the mill certificate, because an 18 J result on a full-size specimen is not the same as an 18 J result on a sub-size specimen.
What Is ASTM A333 Grade 6 Pipe?
ASTM A333 Grade 6 is a seamless or welded carbon steel pipe for low-temperature service, defined by a minimum yield strength of 240 MPa (35,000 psi) and a minimum tensile strength of 415 MPa (60,000 psi). It sits in the same strength band as an ordinary carbon pipe, but it is ordered for a different reason: it has to stay tough when it is cold. The grade is a carbon-manganese steel with no nickel addition, made to a fine grain size and normalized, and the specification requires Charpy V-notch impact testing at -45 degrees Celsius on the material supplied.
Why Impact Testing Defines the Grade
Strength alone does not decide whether a pipe survives low temperature. A carbon steel that is perfectly strong at room temperature can fail in a brittle mode at low temperature if its toughness has fallen away, and toughness is measured by an impact test rather than by a tensile test. That is why A333 Grade 6 is not simply an A106 pipe with a cold-weather label: the chemistry is tightened on phosphorus and sulphur, the steel is killed and grain-refined, and every heat is impact tested at -45 degrees Celsius with an 18 J average acceptance requirement. The impact test is what a buyer is paying for, and it belongs on the enquiry and on the mill certificate.
The test temperature is not the service limit
-45 degrees Celsius is the impact-test temperature Grade 6 must pass; it is not a promise that the pipe is suitable at exactly -45 degrees Celsius under every condition. The actual minimum design metal temperature is set by the design code, using wall thickness, stress, service fluid and other factors.
In practice this means: do not read “-45 degrees Celsius” as “safe to -45”. Confirm the design minimum temperature from the piping specification, then check that the impact test temperature, specimen size and acceptance energy match it before ordering.
Where A333 Grade 6 Pipe Is Used
Grade 6 is used wherever a carbon steel line has to operate cold: low-temperature process piping in refineries, gas plants and chemical plants, refrigeration and cold-storage circuits, piping exposed to low ambient temperatures in cold climates, and cold-box and air-separation piping whose design temperature stays above about -45 degrees Celsius. Where the design temperature goes below that – into LNG and cryogenic service – the carbon grades are no longer qualified and a nickel-bearing grade such as A333 Grade 3 or Grade 8 is required instead.
A333 Grade 6 versus A106 Grade B and A333 Grade 3
A106 Grade B and A333 Grade 6 have the same minimum yield and tensile strength, and the same nominal dimensions, so the difference between them is not strength but service temperature. A106 Grade B is the ordinary high-temperature carbon pipe and does not carry a low-temperature impact requirement; A333 Grade 6 does, which is why it is specified when the design temperature drops below the point where A106 is considered qualified. A333 Grade 3 is the next step down in temperature: it contains 3.5 percent nickel and is impact tested colder than Grade 6. Moving from Grade 6 to Grade 3 buys a lower service temperature at the cost of a nickel-bearing, more expensive steel, so it is ordered only when the design temperature requires it.
Sizes, Delivery Condition and Certification
A333 Grade 6 is supplied as seamless, ERW or welded pipe from small diameters up to about 36 inch outside diameter, with plain, beveled or threaded ends. Dimensions follow ASME B36.10M where a standard wall is ordered. The material is supplied normalized and fine grain, and every length is impact tested, so the mill certificate carries both the tensile results and the Charpy results together with the test temperature. Because the impact result is the point of the order, the certificate should be checked for the test temperature and the specimen size, not only for the strength values.
Writing the impact requirement into the order
An impact requirement is not a sentence that can be added after the pipe is rolled. The test has to be planned with the heat, so the five items below are confirmed before production:
| Item | Why it is on the order | What has to be stated |
|---|---|---|
| Specification and edition | The impact requirement sits in the specification itself, and editions differ | ASTM A333/A333M, and the edition the project works to |
| Test temperature | The certificate is written against a temperature, not against “impact tested” | The test temperature you need, in degrees Celsius or Fahrenheit |
| Specimen size and orientation | The absorbed energy acceptance depends on the specimen size, and orientation changes the result | Full size or sub size specimen, and whether the specimen is longitudinal or transverse |
| Test method | The Charpy test is run to a referenced method, and the project may name a different one | The method required by the project, normally ASTM A370 |
| Verification | Witnessing cannot be arranged after the test has been run | Whether the buyer or a third party attends, and where the test is run |
What the certificate has to show
For an impact tested heat the mill test certificate is checked against the order line by line:
- The test temperature, and whether it matches the temperature on the enquiry.
- Specimen size and orientation, because a sub size specimen result is not equivalent to a full size result.
- Absorbed energy for each specimen tested, not a single average.
- The test standard, and the edition of the material specification.
- Heat number and heat treatment record, so the test result can be traced back to the pieces that were shipped.
Where a project asks for a value the specification does not require, tell us before the heat is rolled. The requirement can be added to the test programme at that point; after rolling and testing, adding it means re-testing or a new heat, and either one moves the delivery date.
Acceptance values are those of ASTM A333/A333M in the edition named on the order. Values quoted in this page’s tables are the specification requirements; they are not offered as measured results.
Typical applications
- Low-temperature process piping in refineries and gas plants
- Refrigeration and cold-storage circuits
- Piping in cold climates with a low design ambient temperature
- Cold box and air separation piping above -45 degrees C
- Low-temperature gas and liquid transfer lines
Standards covered
Frequently asked questions
At what temperature is A333 Grade 6 impact tested?
Grade 6 is impact tested at -45 degrees Celsius. Three Charpy V-notch specimens are tested and the average must be at least 18 J, with no single specimen below 14 J. Where the wall is too thin for a full-size specimen, sub-size specimens are tested with proportionally reduced acceptance values, and the specimen size appears on the test report.
What is the difference between A333 Grade 6 and A106 Grade B?
They have the same minimum yield strength (240 MPa) and tensile strength (415 MPa), and the same dimensions. The difference is the low-temperature impact requirement: A106 Grade B does not carry one, while A333 Grade 6 is impact tested at -45 degrees Celsius by specification. Where the design temperature is low, that test is the reason to specify Grade 6; where it is not, A106 Grade B is the simpler and cheaper choice.
Is A333 Grade 6 suitable below -45 degrees Celsius?
No. Grade 6 is qualified down to about -45 degrees Celsius, and below that the carbon steel grades stop being acceptable. Colder service requires a nickel-bearing grade: A333 Grade 3 contains 3.5 percent nickel and A333 Grade 8 contains 9 percent nickel, and each is impact tested at a lower temperature than Grade 6. The design temperature, not the pipe size, decides which of them is required.
Where to go next
- ASTM A333 Low Temperature Steel Pipe – pipe for low-temperature service
- ASTM A106 Grade B Pipe – the high-temperature seamless grade most often quoted
- Low Temperature Service – impact toughness and where a grade stops being qualified
- Pipe Schedule Chart – wall thickness for every schedule
- Steel Pipe Weight Calculator – work out the weight of any size and wall thickness
- Steel Pipe Standards & Grades – every grade page in this section
- Get a Quote – send the grade, size, quantity and destination port
- ASTM A106 Seamless Carbon Steel Pipe – seamless pipe for process and boiler service
- API 5L Seamless Steel Pipe – seamless line pipe to API 5L
- Butt Weld Elbow – butt weld elbows to ASME B16.9
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