ASTM A333 Grade 6 Low Temperature Steel Pipe

ASTM A333 - Standard Specification for Seamless Pipe and Welded Steel Pipe for Low-Temperature Service and Other Applications with Required Notch Toughness.

ASTM A333 is a piping material standard designed for low temperature environments. It is suitable for manufacturing low temperature pressure vessels and low temperature heat exchanger piping systems. This standard was developed by the American Society for Testing and Materials (ASTM) and mainly includes seamless steel pipes and welded steel pipes. It is widely used in various equipment and systems in low temperature environments.

This specification covers thick wall seamless and welded carbon steel and alloy steel pipes for low temperature use. The pipes should be manufactured by seamless or welding processes, and no filler metal is added during the welding process. Some product specifications may not be covered by this standard due to the adverse effect of excessive wall thickness on low temperature impact performance. The standard includes multiple ferritic steel grades.

Materials and specifications:

ASTM A333 includes multiple grades, which can be divided into Grade 1, Grade 3, Grade 4, Grade 6, Grade 7, Grade 8, Grade 9, Grade 10, Grade 11 according to the material. 

Among them, A333 Gr.6 and Gr.3 are the most commonly used.

Outer diameter (OD): 1/2" (21.3mm) ~ 36" (914.4mm)
Wall thickness (WT): SCH 10S ~ XXS (2.11 ~ 60mm)

Product application:
Applicable to seamless steel pipes for low-temperature pressure vessel pipelines and low-temperature heat exchanger pipelines at -45℃～-195℃.
Mainly used for transporting low-temperature media such as liquefied natural gas (LNG), liquid nitrogen, and liquid oxygen.
Commonly used in petrochemical, natural gas processing, refrigeration systems and other fields.

Main grades and applicable temperatures:

ASTM A333 includes multiple grades, each with different chemical composition and applicable temperature:

Grade	Applicable temperature limit	Typical material	Key features
Gr.1	-45℃	Low carbon steel	Basic low temperature pipe
Gr.3	-100℃	3.5Ni steel	Nickel alloy enhances low temperature toughness
Gr.6	-45℃	Low carbon steel	Low carbon steel Similar to Gr.1, but contains aluminum
Gr.7	-100℃	2.25Ni steel	Ultra-low temperature application
Gr.8	-195℃	Austenitic stainless steel, 9Ni	Extremely low temperature environment
Gr.9	-75℃	2.5Ni	Contains nickel, good welding performance
Gr10	-60℃	10MnDG	Nickel-free, high manganese steel
Gr.11	-196℃	36Ni	Extremely low temperature (below -196℃)

Note: Gr.6 and Gr.3 are most commonly used, Gr.7/Gr.8 are used for ultra-low temperature (such as LNG storage tanks)

Nickel-free steel (Gr.1, Gr.6, Gr.10): low cost, suitable for -45℃ ~ -60℃ environment.
Nickel-containing steel (Gr.3, Gr.7, Gr.8, Gr.9, Gr.11): suitable for lower temperatures (-75℃ ~ -196℃), but the cost is higher

Performance characteristics:
‌1. Low temperature toughness‌: ASTM A333 steel pipe has been specially treated and has excellent low temperature toughness, and can maintain excellent mechanical properties and impact toughness in low temperature environments from -45℃ to -195℃‌.
‌2. High strength‌: These steel pipes have high tensile strength and yield strength and can withstand greater pressure and load‌.
‌3. Good weldability‌: ASTM A333 steel pipes have good weldability and can be connected by various welding methods, such as arc welding, resistance welding, etc. ‌.
‌4. Corrosion resistance‌: It has good corrosion resistance in low temperature environments and can resist the erosion of various corrosive media‌.

Chemical Requirements of ASTM A333:

		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
Phosphorous, 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

Tensile Requirements of ASTM A333:

The material shall conform to the requirements as proscribed:

		Grade 1		Grade 3		Grade 6
		psi	MPa	psi	MPa	psi	MPa
Tensile Strength, min		55,000	380	65,000	450	60,000	415
Yield Strength, min		30,000	205	35,000	240	35,000	240
		Longitudinal	Transverse	Longitudinal	Transverse	Longitudinal	Transverse
Basic minimum elongation for walls 5/16 in. [8 mm] and over in thickness, strip tests, and for all small sizes tested in full section		35	35	30	20	30	16.5
When the standard round 2-in. or 50-mm gage length or proportionally smaller size test specimen with the gage length equal to 4D (4 times the diameter) is used		28	20	22	14	22	12
For strip tests, a deduction for each 1/32in. [0.8 mm] decrease in wall thickness below 5/16 in. [8 mm] from the basic minimum elongation of the following percentage		1.75	1.25	1.50	1.00	1.50	1.00

Wall Thickness		Grade 1		Grade 3		Grade 6
in.	mm	Longitudinal	Transverse	Longitudinal	Transverse	Longitudinal	Transverse
5/16 (0.312)	8	35	25	30	20	30	16
9/32 (.281)	7.2	33	24	28	19	28	15
1/4 (.250)	6.4	32	23	27	18	27	15
7/32 (.219)	5.6	30	-	26	-	26	-
3/16 (.188)	4.8	28	-	24	-	24	-
5/32 (.156)	4	26	-	22	-	22	-
1/8 (.125)	3.2	25	-	21	-	21	-
3/32 (.094)	2.4	23	-	20	-	20	-
1/16 (.063)	1.6	21	-	18	-	18	-

Key performance requirements:

Impact toughness: Must pass the Charpy V-notch impact test (-45℃ or lower temperature)
Heat treatment: Normalizing or quenching + tempering treatment is required to ensure low temperature performance
Non-destructive testing: 100% radiographic or ultrasonic testing

Typical applications:

ASTM A333 steel pipes are mainly used in the following fields:
‌Cryogenic pressure vessels‌: such as liquefied natural gas (LNG) storage tanks, liquid oxygen storage tanks, etc. ‌.
‌Cryogenic heat exchangers‌: such as heat exchangers in air separation equipment, condensers in refrigeration systems, etc. ‌. ‌Other cryogenic equipment‌: such as cryogenic transmission pipelines, cryogenic valves, etc.‌

In addition, ASTM A333 steel pipes are also widely used in petrochemical, natural gas transmission, power, aerospace and shipbuilding, such as the main structural materials for manufacturing cryogenic pressure vessel pipelines, natural gas transmission pipelines, condensers, boilers and other equipment in power equipment in the petrochemical field, and the main structural materials for hydraulic systems, fuel systems and other equipment in the aerospace field‌.

Manufacturing process:

- Steel pipes can be manufactured by two manufacturing processes, seamless or welded, but filler metal is not allowed to be added during the welding process. Both manufacturing methods require the microstructure of the steel pipe to be controlled to ensure the quality and performance of the steel pipe.

- For seamless steel pipes, they are usually produced by hot rolling, cold drawing and other processes, so that the steel pipe has high dimensional accuracy and good surface quality. Welded steel pipes are made by rolling steel plates into tubes and welding them, with high production efficiency and relatively low cost.

Surface quality requirements:

- The surface of the steel pipe should be free of obvious cracks, folds, scars, delamination and other defects. Surface flaws are considered defects if they penetrate more than 12.5% of the nominal wall thickness or infringe upon the minimum wall thickness. For steel pipes with defects, grinding to remove defects (provided that the remaining wall thickness is within the specified range), repairing according to welding repair regulations, cutting off the defective pipe section within the required length range, or directly rejecting it can be handled.

Dimensions and tolerances:

The standard clearly stipulates the dimensions of steel pipes such as outer diameter, wall thickness, length, and the corresponding tolerance range to ensure the dimensional accuracy and interchangeability of steel pipes. For example, the tolerances of outer diameter and wall thickness need to meet certain accuracy requirements to ensure that the steel pipe can be correctly connected and installed with other pipe fittings or equipment.

Mechanical performance requirements:

- Tensile properties: Steel pipes need to meet the specified tensile performance indicators such as tensile strength and yield strength. These indicators reflect the ability of steel pipes to resist deformation and damage when subjected to force.

- Impact toughness: Since it is used in low-temperature environments, impact toughness is a very important performance indicator. Steel pipes need to be impact tested under specified low-temperature conditions to ensure that they have sufficient toughness at low temperatures to prevent brittle fracture. For example, some grades of steel pipes may require impact testing at -45 or lower temperatures and have a certain minimum average notched impact value.

Test methods:

- Tensile test: Tensile test is carried out in accordance with the test methods and definitions specified in ASTM A370 to determine the tensile strength, yield strength and other mechanical properties of steel pipes.
- Impact test: The notched bar impact test method specified in ASTM E23 is used to test the impact toughness of steel pipes at low temperatures.

- Hydrostatic test: As needed, the steel pipe is subjected to a hydrostatic test to verify the tightness and strength of the steel pipe. Parameters such as the pressure and duration of the hydrostatic test need to be carried out in accordance with the provisions of the standard.
- Non-destructive testing: Manufacturers can choose to conduct non-destructive electrical testing, such as eddy current testing, ultrasonic testing, etc., to detect defects inside and on the surface of the steel pipe.

Comparison with other low-temperature pipes:

ASTM A334: Seamless pipes for low temperature, dedicated to heat exchange tubes.
ASTM A350: Forgings for low temperature, used for pipe flanges, valves, etc.
API 5L: Conventional temperature, not suitable for low temperature.

Material selection recommendations:

Above -45℃: Gr.1/Gr.6 optional
Around -100℃: Gr.3 required
-195℃ and below: Gr.7/Gr.8 required

This standard ensures that the steel pipe can maintain sufficient toughness and strength in low temperature environments through strict material control and heat treatment requirements.

Read more: ASTM A333 Seamless carbon steel pipe or ASTM A335/A335M Pipe Specification