A320-L7 vs A193 B7: What’s the difference and when to use each?

In industrial bolting applications, ASTM A320 Grade L7 and ASTM A193 Grade B7 are two of the most commonly specified materials for stud bolts. While they share similarities in mechanical strength and alloy composition, these two grades are designed for different service environments. Understanding their differences is critical for engineers, procurement teams, and maintenance professionals working in oil & gas, power generation, petrochemical, and cryogenic systems.

This article explores the key differences between A320 L7 vs A193 B7, helping you select the right material for your bolted joint applications.

1.Overview of ASTM A193 B7 and ASTM A320 L7

Property	ASTM A193 Grade B7	ASTM A320 Grade L7
Material Type	Chromium-Molybdenum Alloy Steel	Chromium-Molybdenum Alloy Steel
Heat Treatment	Quenched & Tempered	Quenched & Tempered
Service	High-temperature/General service	Low-temperature/Cryogenic service
Typical Use	Refinery, petrochemical piping	LNG, cryogenic vessels, cold storage
Standards	ASTM A193	ASTM A320
Impact Testing	Not required unless specified	Mandatory impact testing at -101°C

2.Temperature Service Range

The most significant difference between A193 B7 and A320 L7 lies in the temperature service they are designed for:

A193 Grade B7: Intended for high-temperature and general-purpose bolting in pressure vessels, valves, and flanges. Suitable for environments above -29°C (–20°F).

A320 Grade L7: Specifically engineered for low-temperature applications, with mandatory Charpy impact testing at -101°C (–150°F). It is widely used in cryogenic service, such as LNG facilities and low-temp storage tanks.

3.Mechanical Properties Comparison

Both grades offer similar tensile strength, but A320 L7 is impact-tested to ensure ductility and toughness under sub-zero conditions.

Property	A193 B7	A320 L7
Tensile Strength (MPa)	≥ 860	≥ 860
Yield Strength (MPa)	≥ 720	≥ 720
Hardness (HB)	197 – 235	197 – 235
Impact Requirement	Optional	Required (-101°C test)

4.Application Examples

When to use A193 B7:

• Power plants piping systems
• High-pressure steam lines
• Heat exchangers
• Chemical reactors

When to use A320 L7:

• Cryogenic vessels and equipment
• LNG processing plants
• Cold storage flanges
• Low-temperature pressure vessels

5.Certification & Inspection Requirements

A320 L7 requires stricter quality control and documentation due to its use in critical cryogenic applications:

A320 L7 bolts must come with impact test reports, usually to EN 10204 3.1 or 3.2 standards.

Common supplementary requirements include NACE MR0175, MESC SPE 81/002, or ISO 10474-3.1B for oil & gas services.

6.Can A193 B7 and A320 L7 Be Interchanged?

Not recommended.
Even though their chemistry and strength may appear similar, the absence of impact testing in A193 B7 makes it unsafe for low-temperature environments. Substituting B7 for L7 in cryogenic service can lead to brittle fracture failures.

However, in non-cryogenic environments, L7 may sometimes be used in place of B7 if superior toughness is required, subject to engineering approval.

7.Conclusion: Choose Based on Service Temperature

When selecting between A320 L7 vs A193 B7 stud bolts, the decision primarily depends on the minimum design temperature of the application:

For general and high-temp service: Choose A193 B7

For cryogenic and low-temp service: Choose A320 L7

Understanding these differences ensures safe, compliant, and cost-effective bolted joint design.

Looking for certified A320 L7 or A193 B7 fasteners?

Haihao Group supplies a full range of stud bolts, nuts, and flanges complying with ASTM, ASME, and MESC standards, with complete 3.1 certifications. Contact us today for customized low- and high-temperature bolting solutions.