NUBOTECK manufactures ASTM A320 Grade L7 Stud Bolts which are applied to critical bolted joints used in refineries, petrochemical plants, offshore platforms, LNG facilities, pressure vessels, valves, heat exchangers and piping systems.
Grade L7 is the most widely specified alloy steel bolting material extensively used for pressure vessels, valves, flanges, and fittings for low-temperature service. Grade L7 stud bolts provide excellent strength, toughness and reliability, making them the preferred choice throughout the oil & gas industry.
ASTM A320 standard governs the requirements specifically for Grade L7. However, the requirements given in ASTM A320 are said to be fully achieved, only when the generic/ common bolting requirements of ASTM A962 have been fully met.
Specification API 20E introduces enhanced requirements for manufacturing process control, qualification testing, traceability, metallurgical examination and documentation. These checks and controls are in addition to the regular requirements given for this grade by the ASTM standards (ASTM A320, ASTM A962)
ASTM A320 Grade L7 stud bolts are manufactured from chromium-molybdenum alloy steel which is quenched and tempered to achieve the required mechanical properties. Proper heat treatment ensures optimum strength, toughness and reliability for high-pressure service conditions.
Typical manufacturing sequence:
API-20E requirements for Hardness Testing of Bars:
In case of heat treatment using induction process, all readings for hardness must be within 3 HRC. Conversion between hardness scales shall be in conformance with ASTM E140. Test frequency shall conform to ASTM F1470-19, Table 3, sample size A
| Manufacturing Parameter | ASTM/ API-20E BSL-1 | API-20E BSL-2 | API-20E BSL-3 |
|---|---|---|---|
| Melting Practice | Basic-oxygen, Electric-furnace, Vacuum Induction Melting (VIM) | Electric-furnace, Vacuum Induction Melting (VIM) | |
| Molten steel may be vacuum treated prior to or during pouring of the ingot or strand casting. The primary melting may incorporate separate degassing or refining and may be followed by secondary melting such as electroslag remelting or vacuum remelting | |||
| The steel shall be fully killed. When steel of different grades is continuously cast identification of the resultant transition material is required. The steel producer shall remove the transition material by an established procedure that positively separates the grades | |||
| Secondary refining or ladle refining, shall be performed. When multiple heats of the same chemical composition range are sequentially strand cast, the heats shall be separated by an established procedure such that intermix material shall not be supplied (ASTM A962/A962M) | |||
| Casting | Continuous, Ingot | Continuous, Ingot | Ingot |
| Top pouring during Ingot casting not permitted unless the VIM is used | |||
| Reduction Ratio | 4.0:1 Min | 4.0:1 Min | 10.0:1 Min |
| Element | ASTM/ API-20E BSL-1 | API-20E BSL-2 | API-20E BSL-3 |
|---|---|---|---|
| Carbon | 0.38 – 0.48 | ||
| Sulfur | 0.040 Max | 0.025 Max | 0.015 Max |
| Phosphorus | 0.035 Max | 0.025 Max | 0.015 Max |
| Manganese | 0.75 – 1.00 | ||
| Silicon | 0.15 – 0.35 | ||
| Chromium | 0.80 – 1.10 | ||
| Molybdenum | 0.15 – 0.25 | ||
| Vanadium | 0.05 Max | ||
| Niobium | 0.05 Max | ||
| Boron (residual) | 0.0005 Max | 0.0005 Max |
| Property | ASTM Requirement | API-20E Requirement |
|---|---|---|
| Tensile Strength | 125 ksi (860 MPa) | |
| Yield Strength (0.2% offset) | Min 105 ksi (725 MPa) | Max 135 ksi (920 MPa) |
| Elongation (4D minimum) | 16% | |
| Reduction of Area | 50% | |
| Charpy Impact | Min 20J Avg 27J @ -101⁰C | |
| Hardness | 35 HRC Max | 34 HRC Max |
1/2" to 2-1/2"
M12 to M64
| API-20E BSL-1 | API-20E BSL-2 | API-20E BSL-3 |
|---|---|---|
| ASTM A194 7 | ASTM A194 7 | ASTM A194 7 |
Contact NUBOTECK for technical assistance, project requirements, API 20E bolting and custom manufacturing solutions.
This website is not designed to infringe our visitor's privacy.
"NUBOTECK" is our registered trademark.
© 2019 - 2026 - All rights to this website's content are reserved by NUBOTECK.