ASTM A320 L7 Bolts

ASTM A320 Grade L7 Bolt Specification

Property	Details
Standard	ASTM A320 / ASME SA320
Grade	L7 (4140 Chromium-Molybdenum Alloy Steel)
Dimensions	ASME B18.2.1 (Hex Bolts), ASME B18.3 (Socket Head), ASME B16.5 (Stud Bolts)
Thread Configuration	ASME B1.1 2A/3A Inch Unified Threads; ASME B1.13M 6h Metric Coarse Threads
Size Range	1/4″ to 4″ (6mm to 100mm) | Custom sizes available
Length Range	3mm to 3000mm (as per requirement)
Certification	Dual certified as per ASTM & ASME codes
Additional Standards	NACE MR0103 / MR0175 / ISO 15156 Compliance
Melt Origin	India, Japan, South Korea, South America, East Europe
Additional Certifications	PED 97/23/EC Certified, Merkblatt AD 2000 W2 Certified
Mandatory Requirements	Free from Mercury & Radioactive Contamination
Heat Treatment	Quenched and Tempered (Q+T)
Equivalent Grade	AISI 4140, DIN 1.7225 (42CrMo4), BS EN 4140
Compatible Nuts	ASTM A194 Grade 4, Grade 7, Grade 7M

ASTM A320 L7 Equivalent Grades – International Standards

Understanding cross-standard equivalents is critical for global procurement. The following table shows the international equivalent standards for ASTM A320 Grade L7:

ASTM	AISI/SAE	UNS	DIN / EN	BS	ISO
A320 Grade L7	4140	G41400	42CrMo4 / 1.7225	BS4140	ISO 4014

ASTM A320 Grade L7 Chemical Composition (%)

The chemical composition of Grade L7 (AISI 4140 alloy steel) as per ASTM A320 specification is shown below. The chromium and molybdenum content provides the high hardenability and low-temperature toughness characteristic of this grade:

Element	C	Mn	Si	P max	S max	Cr	Mo	Ni
Content %	0.38–0.48	0.75–1.00	0.15–0.35	0.035	0.040	0.80–1.10	0.15–0.25	–

Note: The Cr-Mo combination in Grade L7 provides excellent hardenability, high fatigue resistance, and superior toughness at subzero temperatures compared to carbon steel fasteners.

ASTM A320 Grade L7 Mechanical Properties

ASTM A320 Grade L7 bolts are classified into four tensile classes (A, B, C, D). Tensile Classes A, B, and C are the most commonly specified for standard
low-temperature service:

Tensile Class	Tensile Str. min (ksi)	Tensile Str. min (MPa)	Yield Str. 0.2% (ksi)	Yield Str. 0.2% (MPa)	Elongation in 4D min %	Reduction of Area min %
A, B and C	130	895	85	585	15	18
D	130	895	105	725	15	18

ASTM A320 Grade L7 Hardness Requirements

Tensile Class	Brinell Hardness (HBW)	Rockwell Hardness min (HRC)	Rockwell Hardness max (HRC)
A, B and C	248 – 341	24 HRC	27 HRC
D	248 – 321	24 HRC	35 HRC

ASTM A320 Grade L7 Stress Rupture Requirements

Tensile Class	Test Temperature °F [°C]	Stress min (ksi)	Stress min (MPa)	Time to Rupture min (h)	Elongation min %
A, B and C	1200 [650]	56	385	100	5
D	1200 [650]	40	275	100	5

ASTM A320 L7 vs L7M – Key Differences Explained

One of the most frequently asked questions from procurement engineers is: what is the difference between ASTM A320 Grade L7 and Grade L7M? (See also: ASTM A193 vs A320 – High Temperature vs Cryogenic Bolting) Both grades are used in low-temperature bolting, but they differ in material, dimensional scope and impact testing requirements:

Property	ASTM A320 Grade L7	ASTM A320 Grade L7M
Base Material	AISI 4140 (Cr-Mo Alloy Steel)	AISI 4140 (Cr-Mo Alloy Steel)
Heat Treatment	Quenched and Tempered	Quenched and Tempered at higher temp.
Yield Strength (Class A–C)	85 ksi (585 MPa) min	75 ksi (515 MPa) min
Tensile Strength	130 ksi (895 MPa) min	100 ksi (690 MPa) min
Hardness (BHN)	248 – 341	235 – 321
Min. Temp. Rating	-150°F (-101°C)	-150°F (-101°C)
Impact Test Temp.	-150°F (-101°C)	-150°F (-101°C)
Charpy Impact Value	15 ft-lb min	15 ft-lb min
Primary Differentiation	Higher strength, general low-temp service	Slightly softer; better for H2S/sour service per NACE MR0175
NACE MR0175 Compliance	Not inherently compliant	Compliant (for sour service)
Common Applications	Pressure vessels, LNG, cryogenic piping	Sour gas, offshore, NACE environments

Procurement Tip: Specify Grade L7M when the service environment involves H2S (hydrogen sulfide/sour service) and NACE MR0175/ISO 15156 compliance is required. For standard cryogenic and low-temperature service without sour gas exposure, Grade L7 is the preferred choice.</em >

Dimensions of ASTM A320 L7 Hex Bolts (ASME B18.2.1)

The following dimensional table covers nominal sizes from 1/4 inch to 3 inches. All dimensions are in inches unless otherwise stated:

Nominal Size (in)	Body Dia. (in)	Width Across Flats F	Head Height H	W. Across Corners G (Max/Min)	Thread Length LT (≤6in / >6in)
1/4	0.25	7/16	11/64	0.505/0.484	0.75/1.00
5/16	0.3125	1/2	7/32	0.577/0.552	0.875/1.125
3/8	0.375	9/16	1/4	0.650/0.620	1.00/1.25
7/16	0.4375	5/8	19/64	0.722/0.687	1.125/1.375
1/2	0.500	3/4	11/32	0.866/0.826	1.25/1.50
5/8	0.625	15/16	27/64	1.083/1.033	1.50/1.75
3/4	0.750	1-1/8	1/2	1.299/1.240	1.75/2.00
7/8	0.875	1-5/16	37/64	1.516/1.447	2.00/2.25
1	1.000	1-1/2	43/64	1.732/1.653	2.25/2.50
1-1/4	1.250	1-7/8	27/32	2.165/2.066	2.75/3.00
1-1/2	1.500	2-1/4	1	2.598/2.480	3.25/3.50
1-3/4	1.750	2-5/8	1-5/32	3.031/2.893	3.75/4.00
2	2.000	3	1-11/32	3.464/3.306	4.25/4.50
2-1/2	2.500	3-3/4	1-21/32	4.330/4.133	5.25/5.50
3	3.000	4-1/2	2	5.196/4.959	6.25/6.50

A320 Grade L7 Heavy Hex Bolt Size Chart (Metric)

Diameter	Diameter (mm)	Diameter (inch)	Nut Size (mm)
M10	10	0.3937	17
M12	12	0.4724	19
M14	14	0.5512	22
M16	16	0.6299	24
M18	18	0.7087	27
M20	20	0.7874	30
M22	22	0.8661	32
M24	24	0.9449	36
M27	27	1.0630	41
M30	30	1.1811	46
M33	33	1.2992	50
M36	36	1.4173	55
M39	39	1.5354	60
M42	42	1.6535	65
M45	45	1.7717	70
M48	48	1.8898	75
M52	52	2.0472	80
M56	56	2.2047	85
M60	60	2.3622	90
M64	64	2.5197	95

ASTM A320 Grade L7 Bolts Torque Chart

Proper torque is essential for achieving the correct bolt preload and preventing gasket failure in flanged connections. The following torque values apply to Grade L7 bolts with lubricated nuts (molybdenum disulfide or similar):

Torque Values – Imperial (FT-LBS)

Bolt Dia (in)	30% Initial Torque (ft-lb)	70% Torque (ft-lb)	100% Final Torque (ft-lb)
1/2	16	36	52
5/8	31	73	104
3/4	55	129	184
1	107	249	356
1-1/8	127	297	424
1-1/4	179	417	596
1-1/2	246	574	821
1-9/16	168	392	560
1-3/4	240	561	801
1-7/8	298	696	994
2-1/4	529	1234	1762
2-1/2	733	1709	2442
2-3/4	986	2300	3285

Torque Values – Metric (Nm)

Bolt Dia (in)	30% Initial Torque (Nm)	70% Torque (Nm)	100% Final Torque (Nm)
9/16	31	72	102
5/8	42	99	141
3/4	75	175	249
7/8	96	225	321
1-1/8	172	403	575
1-1/4	243	565	808
1-1/2	334	778	1113
1-9/16	228	531	759
1-5/8	259	603	862
1-7/8	404	944	1348
2	496	1157	1653
2-1/4	717	1673	2389
2-3/4	1337	3118	4454
3	1748	4078	5826

Note: Torque values assume standard lubrication (moly-disulfide grease or similar). Dry torque values will be approximately 25–30% higher. Always verify with the flange or equipment manufacturer’s specifications.

A320 Grade L7 Hex Bolt Weight Chart (lbs/bolt)

Diameter (inches)	Length (inches)	Weight (lbs/bolt)
1/4″	1	0.02
1/4″	2	0.03
3/8″	1	0.04
3/8″	2	0.08
1/2″	1	0.10
1/2″	2	0.20
5/8″	2	0.40
5/8″	4	0.80
3/4″	2	0.60
3/4″	4	1.20
1″	4	2.00
1″	6	3.00

Compatible Nuts for ASTM A320 L7 Bolts – ASTM A194 Specification

Selecting the correct nut grade is critical for ensuring proper joint integrity and load-bearing capacity. ASTM A320 requires specific compatible nuts per ASTM A194. The following nut grades are qualified for use with Grade L7 bolts:

Nut Grade	Material	Min. Proof Load (ksi)	Recommended For
ASTM A194 Gr. 4	Cr-Mo Alloy Steel (4140)	144	Standard low-temperature service with L7 bolts
ASTM A194 Gr. 7	Cr-Mo Alloy Steel (4140)	175	High-pressure flanged joints, higher torque applications
ASTM A194 Gr. 7M	Cr-Mo Alloy Steel	150	Sour service / NACE MR0175 – paired with L7M bolts
ASTM A194 Gr. 2H	Carbon Steel	175	General purpose; lower cost, not ideal for low-temp

See our ASTM A194 Grade 4 Nuts and ASTM A194 Grade 7 Nuts product pages for full specification, pricing and stock availability.

Manufacturing Process of ASTM A320 Grade L7 Bolts at Jade Alloys

Jade Alloys follows a rigorous manufacturing process to ensure every batch of ASTM A320 Grade L7 bolts meets or exceeds specification requirements:

1. Raw Material Procurement: Certified 4140 Cr-Mo alloy steel bars procured from approved mills in India, Japan, South Korea, and Europe with mill test reports (MTR).
2. Chemical Analysis: Optical Emission Spectrometry (OES) testing on each heat to verify chemical composition against ASTM A320 requirements.
3. Hot/Cold Forging: Headed fasteners are produced by hot forging or cold forming based on diameter and length requirements.
4. Threading: Precision threading by thread rolling (preferred for fatigue resistance) or thread cutting per ASME B1.1 (Inch) or B1.13M (Metric).
5. Heat Treatment – Quench & Temper (Q+T): Austenitized, oil-quenched, and tempered to achieve the specified hardness and mechanical property range.
6. Mechanical Testing: Tensile, yield, elongation, and reduction of area testing on universal testing machines (UTM) per ASTM A370 test methods.
7. Impact Testing (Charpy): Low-temperature Charpy V-notch impact testing at -150°F (-101°C) to verify minimum 15 ft-lb impact energy.
8. Hardness Testing: Brinell and Rockwell hardness verification on each lot.
9. Dimensional Inspection: Thread gauging (GO/NO-GO), dimensional checks per ASME B18.2.1/B18.3.
10. Surface Finishing: Plain (black), hot-dip galvanized (HDG), zinc-plated, PTFE-coated, or phosphate & oil as specified.
11. Marking & Identification: Grade marking, heat number, manufacturer identification stamped per ASTM requirements.
12. Third-Party Inspection: Available from SGS, Bureau Veritas, TUV, Lloyds, and other approved inspection agencies.
13. Packing & Dispatch: Export-grade packaging with full documentation (MTR, CoC, test reports, packing list, CoO).

Quality Testing & Certifications for ASTM A320 L7 Bolts

Tests Performed

• Chemical Composition Analysis – OES (Optical Emission Spectrometry)
• Tensile Test – Tensile strength, yield strength, elongation, reduction of area (ASTM A370)
• Charpy V-Notch Impact Test at -150°F (-101°C) – minimum 15 ft-lb
• Hardness Test – Brinell (HBW) and Rockwell (HRC)
• Proof Load Test for Nuts (ASTM A194)
• Dimensional & Thread Gauging Inspection (GO/NO-GO gauges)
• Hydrogen Embrittlement Test (for electroplated fasteners per ASTM F1941)
• Magnetic Particle Inspection (MPI) or Dye Penetrant Inspection (DPI) – on request
• Ultrasonic Testing (UT) – on request for critical applications
• NACE MR0175 / ISO 15156 compliance verification – on request

Certifications & Documents Available

• Mill Test Report (MTR) / Material Test Certificate (MTC) – EN 10204 3.1 or 3.2
• Certificate of Conformance (CoC) / Certificate of Origin (CoO)
• Third-Party Inspection Reports (SGS, TUV, BV, Lloyds, DNV)
• PED 97/23/EC Certification
• AD 2000 Merkblatt W2 Certification
• NACE MR0103 / MR0175 Compliance Certificate
• ISO 9001:2015 Quality Management Certificate
• RoHS / REACH Compliance (Mercury & Radioactive Contamination Free)

ASTM A320 L7 Bolts for Low-Temperature and Cryogenic Service

One of the primary reasons engineers specify ASTM A320 Grade L7 over standard ASTM A193 B7 bolts is the verified low-temperature toughness. While A193 B7 and A320 L7 share the same base material (4140 Cr-Mo steel) and similar strength levels, the critical difference is that A320 L7 fasteners are impact-tested at -150°F (-101°C) and certified to absorb a minimum of 15 ft-lb (20 J) of energy without brittle fracture. This makes Grade L7 bolts essential in applications where ductile-to-brittle transition behavior of steel at low temperatures poses a safety risk. Industries and systems that rely on ASTM A320 L7 low-temperature bolting include:

• LNG (Liquefied Natural Gas) processing plants and storage terminals
• Cryogenic air separation units (ASUs) – nitrogen, oxygen and argon
  production
• Ethylene and propylene cracking furnace piping systems
• Refrigerated storage tanks and cold box equipment
• Liquefied Petroleum Gas (LPG) transport and storage facilities
• Offshore platforms operating in Arctic or sub-zero environments
• Ammonia refrigeration and cold room / food processing plants
• CO2 capture, compression and storage (CCS) systems
• Hydrogen (H2) service at low temperatures
• Pharmaceutical and chemical cold-chain process plants

Important: ASTM A320 Grade L7 impact testing is mandatory to certify low-temperature service suitability. Always request the Charpy impact test report when ordering L7 bolts for cryogenic applications.</em >

Applications of ASTM A320 L7 Bolts by Industry

• Oil & Gas (Upstream/Downstream): Wellhead assemblies, subsea connectors, pipeline flanges, Christmas tree valves
• Petrochemical Plants: Reactor flanges, heat exchanger heads, column connections, low-temp process piping
• LNG & Cryogenic: LNG terminal flanges, cryogenic pipe supports, cold box bolting, storage tank connections
• Pressure Vessel Fabrication: Vessel head bolting, nozzle connections, manway covers, shell flanges
• Valve & Flange Manufacturing: Gate valves, ball valves, globe valves –bonnet and body bolting
• Offshore & Marine: Platform structure bolting, subsea pipeline connections, FPSO equipment
• Power Generation: Low-temperature steam condensers, turbine casing flanges, cooling system joints
• Wind Energy: Foundation anchor bolts, tower flange connections (wind turbine stud bolts)
• Refrigeration Systems: Compressor flanges, heat exchanger connections, industrial cold room equipment
• Chemical Plants: Low-temperature chemical reactors, distillation columns, cryogenic piping joints

ASTM A320 L7 vs ASTM A193 B7 – Which Grade Should You Specify?

Grade L7 and Grade B7 are both made from 4140 Cr-Mo alloy steel and have identical chemical compositions and similar tensile/yield strength requirements. However, the key specification difference relates to their intended service temperature and testing requirements:

Feature	ASTM A193 B7	ASTM A320 L7
Standard	ASTM A193	ASTM A320
Intended Service	High-temperature bolting	Low-temperature bolting
Temp. Range (typical)	Up to +1000°F (+538°C)	Down to -150°F (-101°C)
Impact Test Required?	No	Yes – mandatory Charpy test
Base Material	AISI 4140	AISI 4140
Tensile Strength	125 ksi (862 MPa) – varies by dia.	130 ksi (895 MPa) min
Compatible Nut	ASTM A194 Gr. 2H / 7	ASTM A194 Gr. 4 / 7
Cost	Slightly lower (no impact test)	Slightly higher (includes impact test)

Conclusion: If the service temperature is below 0°F (-18°C), ASTM A320 L7 is the correct grade. For ambient or elevated temperature service, ASTM A193 B7 is typically sufficient. When in doubt, L7 provides the additional safety margin of certified low-temperature toughness.

Surface Finish & Coating Options for ASTM A320 L7 Bolts

Coating / Finish	Description & Suitability
Plain / Black (Self-Colour)	Standard finish; no coating. Suitable for short-term use or where additional coatings are applied on-site.
Hot-Dip Galvanized (HDG)	ASTM A153 / ISO 1461. Best for outdoor, marine and atmospheric corrosion resistance. Adds ~50–80 microns zinc.
Mechanical Galvanizing	ASTM B695. Cold process; no hydrogen embrittlement risk for high-strength bolts.
Zinc Electroplating	ASTM B633. Thin, decorative zinc layer; requires post-process baking for H2 embrittlement relief.
PTFE / Xylan Coating	Non-stick, chemical-resistant coating ideal for corrosive environments and easier installation torque.
Phosphate & Oil (Parco-Lubrized)	Rust-inhibiting phosphate coat with oil. Standard for storage and short-term protection.
Dacromet / Geomet	Zinc-aluminium flake coating; excellent corrosion resistance without hydrogen embrittlement risk.
Nickel Plating	Enhanced corrosion resistance for marine and chemical service environments.

Why Choose Jade Alloys for ASTM A320 L7 Bolts?

When low-temperature service integrity is non-negotiable, ASTM A320 Grade L7 bolts are the specification of choice for engineers worldwide. Jade Alloys combines decades of alloy steel fastener expertise with modern testing infrastructure, global export capabilities, and a commitment to quality that aligns with the world’s most demanding industrial standards. From a single bolt requirement for a cryogenic research project to bulk orders for a large-scale LNG facility, Jade Alloys delivers Grade L7 fasteners with complete traceability, reliable documentation, and competitive lead times. Contact us today and receive a detailed quotation for your ASTM A320 L7 bolt requirements.

Beyond UAE, Jade Alloys exports fasteners and bolts and nuts to major markets worldwide: