What is ASTM A193 Grade B7?
ASTM A193 Grade B7 is the most widely specified chromium-molybdenum alloy steel bolting material for high pressure and elevated temperature service. It is extensively used for pressure vessels, flanges, valves, piping systems and other critical equipment operating in demanding industrial environments. Grade B7 stud bolts provide excellent strength, toughness and reliability, making them the preferred choice throughout the oil & gas industry.
ASTM A193 standard governs the requirements specifically for Grade B7. However, the requirements given in ASTM A193 are said to be fully achieved, only when the generic/ common bolting requirements of ASTM A962 have been fully met.
Grade B7 Stud Bolts in Oil & Gas Applications
When these stud bolts are used in critical service of Oil and Gas the additional requirements of API 20E need to be applied over and above the the regular requirements given for this grade by the ASTM standards (ASTM A193, ASTM A962). Specification API 20E introduces enhanced requirements for manufacturing process control, qualification testing, traceability, metallurgical examination and documentation.
Manufacturing Process
ASTM A193 Grade B7 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
Raw Material (Steel) Manufacturing
| 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 |
Chemical Composition
| 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 |
Mechanical Properties
| 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% | |
| Hardness | 35 HRC Max | 34 HRC Max |
Available Sizes
1/2" to 2-1/2"
M12 to M64
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