Patriot Bolt machines ASTM A320 Grade L7 stud bolts for flanges that operate below the range where ordinary alloy steel stays tough. L7 uses the same quenched and tempered chrome-moly steel as B7, with a required Charpy V-notch impact test at −150 °F on each lot.
We make L7 studs to your purchase order or drawing and supply impact-tested A194 Grade 7 nuts. Every order ships with mill test reports and impact test results traceable to the heat.
A320 L7 Stud Bolts at a Glance
- Specification
- ASTM A320 / ASME SA320 Grade L7
- Material
- AISI 4140 / 4142 chrome-moly steel, quenched and tempered
- Strength
- 125 ksi min tensile, 105 ksi min yield (2-1/2 in and under)
- Impact test
- Charpy V-notch at −150 °F, 20 ft-lb average
- Matching nut
- A194 Grade 7 (7L) heavy hex
- Configurations
- Fully threaded, double-end and tap-end
Why Engineers Specify A320 L7 Stud Bolts
Steel that is tough at room temperature can turn brittle in deep cold. A320 adds impact testing so the stud is proven ductile at the low end of the design range.
- Impact tested. Each lot is Charpy tested at −150 °F, with a 20 ft-lb average and 15 ft-lb single-specimen minimum on full-size specimens.
- B7 strength. 125 ksi minimum tensile and 105 ksi minimum yield, the same as B7 in sizes up to 2-1/2 in.
- Matched nuts. A320 requires nuts to be impact tested too. A194 Grade 7 nuts tested this way are marked 7L.
For larger diameters, A320 L43 keeps the same strength up to 4 in.
A320 L7 Stud Bolt Specifications
A320 lists L7 in sizes up to 2-1/2 in.
| Diameter | Tensile, min | Yield (0.2%), min | Elongation, min | Reduction of area, min | Charpy test |
|---|---|---|---|---|---|
| 2-1/2 in and under | 125 ksi | 105 ksi | 16% | 50% | −150 °F, 20 ft-lb avg / 15 ft-lb single |
Studs 1/2 in and under are exempt from impact testing unless your order calls for it.
A320 L7 Chemical Composition
| Element | Weight % |
|---|---|
| Carbon | 0.38–0.48 |
| Manganese | 0.75–1.00 |
| Phosphorus | 0.035 max |
| Sulfur | 0.040 max |
| Silicon | 0.15–0.35 |
| Chromium | 0.80–1.10 |
| Molybdenum | 0.15–0.25 |
Limits per the current edition of the specification. The mill test report for your heat is the controlling document.
Stud Configurations
- Fully threaded studs, threaded end to end, for flange bolting where grip length varies.
- Double-end studs, threaded on both ends with an unthreaded center.
- Tap-end studs, with one end made to thread into a tapped hole.
Applications and Industries
- LNG and cryogenic: Liquefaction, storage and regasification flanges. See Oil & Gas.
- Petrochemical: Ethylene, propylene and ammonia refrigeration systems. See Petrochemical & Refining.
- Cold climates: Outdoor plant and pipeline flanges with a low minimum design temperature.
Certification and Traceability
Patriot Bolt is ISO 9001:2015 certified. Each L7 order includes mill test reports traceable to the heat, along with a certificate of conformance to the specification on your purchase order.
Studs are marked with the grade symbol and our identification, as the specification requires.
L7 certifications include the Charpy impact results for the lot.
Compare L7 with other bolting grades in our Fastener Materials Matrix.
A320 L7 Stud Bolts FAQ
What is the difference between L7 and B7?
They use the same steel, heat treatment and strength. L7 adds a mandatory Charpy impact test at −150 °F, so it is proven tough at low temperature.
Can L7 studs be dual certified to B7?
L7 that meets both specifications can be certified to A193 B7 and A320 L7. Ask for dual certification when you order.
Which nut goes with L7?
ASTM A194 Grade 7 nuts impact tested per A320 and marked 7L.
What if I need L7 above 2-1/2 in?
A320 L43 is made from 4340 steel, which hardens more deeply and keeps 125 ksi minimum tensile up to 4 in.
Request a Quote
Send us the stud configuration, diameter, length, thread, specification and quantity, or upload your drawing. Our team will confirm the material and lead time. Call (281) 581-0176 or request a quote.
Also in L7: A320 L7 fasteners hub · A194 Grade 7 heavy hex nuts · L43 stud bolts · All stud bolts