Specifications
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
ASTM A193/A193M Grade B7 Stud Bolts – UNS G41400
The industry-standard high-strength 4140 chromium-molybdenum alloy steel stud bolt for general-purpose high-temperature and high-pressure pressure equipment bolting.
ASTM A193/A193M Grade B7 Stud Bolts are manufactured from UNS G41400, a chromium-molybdenum low alloy steel widely known as AISI 4140, and are quenched and tempered to achieve the high mechanical properties specified in ASTM A193, making Grade B7 the single most widely used stud bolt grade in pressure vessel, piping, and flange bolting applications worldwide. With minimum tensile strength of 125 ksi for diameters up to 2.5 inches and correspondingly high yield strength values, Grade B7 provides excellent load-carrying capability at temperatures up to approximately 450°C (842°F), beyond which creep and oxidation become limiting factors. ASTM A193 specifies diameter-dependent mechanical requirements that reflect the practical realities of heat treatment response in different bar sizes. Grade B7 stud bolts are used universally in oil refineries, petrochemical plants, power generation facilities, gas processing units, and virtually all industries that fabricate ASME-coded pressure vessels and piping systems, making them the default choice when stainless steel is not specifically required by the corrosion environment or low-temperature toughness specifications.
ASTM A193/A193M Grade B7 Chemical Composition - Ferritic Steels
| Grade | Description and
UNS Designation |
C | Mn | P | S | Si | Cr | Mo |
|---|---|---|---|---|---|---|---|---|
| ASTM A193 Grade B7 | Cr-MoC | 0.38-0.48D | 0.75-1.00 | 0.035 | 0.040 | 0.15-0.35 | 0.80-1.10 | 0.15-0.25 |
| Product Analysis VariationB | 0.02 | 0.04 | 0.005 | 0.005 | 0.02 | 0.05 | 0.02 |
ASTM A193/A193M Grade B7 Mechanical Requirements - Ferritic Steels (Inch)
| Grade | Diameter, in. | Minimum Tempering Temperature, °F |
Tensile Strength, min, ksi | Yield Strength, min, 0.2 % offset, ksi |
Elongation in 4D, min, % | Reduction of Area, min, %Reduction of Area, min, % | Hardness, max |
|---|---|---|---|---|---|---|---|
| ASTM A193 Grade B7 | 2 1⁄2 and under | 1100 | 125 | 105 | 16 | 50 | 321 HBW or 35 HRC |
| over 2 1⁄2 to 4 | 115 | 95 | 16 | 50 | 321 HBW or 35 HRC | ||
| over 4 to 7 | 100 | 75 | 18 | 50 | 321 HBW or 35 HRC |
ASTM A193/A193M Grade B7 Mechanical Requirements - Ferritic Steels (Metric)
| Class | Diameter,
[mm] |
Min.Tempering
Temp. °C |
Tensile Strength,
min, MPa |
Yield Strength,min,
.2% offset, MPa |
Elongation in 4D,
min, % |
Reduction of Area, min, % | Hardness,
max |
|---|---|---|---|---|---|---|---|
| ASTM A193 Grade B7 | M64 and under | 593 | 860 | 720 | 16 | 50 | 321 HBW or 35 HRC |
| over M64 to M100 | 795 | 655 | 16 | 50 | 321 HBW or 35 HRC | ||
| over M100 to M180 | 690 | 515 | 18 | 50 | 321 HBW or 35 HRC |
ASTM A193/A193M Grade B7 Bolting Components Marking - Ferritic Steels
| Grade | Grade Symbol |
|---|---|
| ASTM A193 Grade B7 | TB B7 |
In-Depth Engineering Reference
What is the maximum service temperature for ASTM A193 B7?
ASTM A193 B7 is rated for sustained service up to 427 °C (800 °F). For higher-temperature service, ASTM A193 B16 (1Cr-1Mo-¼V) is the standard substitute, rated to 593 °C (1100 °F). Below -29 °C (-20 °F), ASTM A320 Grade L7 is the cryogenic counterpart.
Is ASTM A193 B7 NACE MR0175 compliant?
Standard ASTM A193 B7 is NOT NACE MR0175 compliant — its hardness can exceed the 22 HRC (235 HBW) ceiling required for sour-service hydrogen-sulfide environments. For sour service, specify ASTM A193 B7M, which is the NACE-compliant version of B7 with a controlled-hardness tempering process.
What torque should be applied to a B7 stud bolt?
Torque depends on bolt diameter, lubricant, friction coefficient and joint design — there is no single ASTM A193 B7 torque value. Use ASME PCC-1 (Guidelines for Pressure Boundary Bolted Flange Joint Assembly) or the joint-specific torque calculator with manufacturer-supplied friction factors. As a rough proxy, dry-thread torque on ¾-10 UNC B7 is ~270–300 ft-lb, but always validate against the engineering bolted-joint analysis.
Related ASTM A193 Grades & ASME Companion Dimensions
Frequently Asked Questions
- What is ASTM A193 Grade B7?
- ASTM A193 Grade B7 is a bolting material covering AISI 4140 Cr-Mo low-alloy (UNS G41400). Used in high-temperature, high-pressure flange, pressure-vessel and heat-exchanger bolting service per ASTM A193/A193M.
- What is the UNS designation for ASTM A193 Grade B7?
- The UNS designation for ASTM A193 Grade B7 is UNS G41400. This corresponds to AISI 4140 Cr-Mo low-alloy. The UNS code is universal across ASTM, ASME (SA-193), PED 2014/68/EU and NORSOK material specifications.
- What is the service envelope for ASTM A193 Grade B7?
- B7 (AISI 4140 Cr-Mo quenched-and-tempered) is the workhorse alloy stud bolt grade for service from -29 °C (-20 °F) up to 427 °C (800 °F). Beyond 427 °C, creep-rupture limits apply; for cryogenic, ASTM A320 Grade L7 is used instead.
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