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CrMo B7 Double End Stud
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Name: Putian CrMo B7 Double End Stud
Standard: ASTM
Material: A193 B7
Size: 3/4 inch
Lenght: 100 mm
Surface: Black/ PTFE/ Zinc
Standard: ASTM
Material: A193 B7
Size: 3/4 inch
Lenght: 100 mm
Surface: Black/ PTFE/ Zinc
Quantity
CrMo B7 Double End Stud strictly conforms to ASTM A193 B7, is made of Cr-Mo alloy steel with tensile strength up to 125 ksi, and resists high temperature and high pressure. The 3/4-inch diameter × 100 mm double-ended design offers flexible assembly; optional black, PTFE or galvanized finishes meet various anti-corrosion needs, making it a cost-effective choice for petrochemical, valve and pressure-vessel bolting.
What is A193 B7 stud material?
1. Basic definition
ASTM A193 Grade B7 is the representative U.S. grade for high-temperature/high-pressure alloy-steel bolts/studs and the most common material for CrMo B7 Double End Stud on the market. Based on AISI 4140/4142 Cr-Mo steel, it is quenched and tempered at ≥593 °C, giving room-temperature tensile strength ≥860 MPa (125 ksi), yield ≥720 MPa (105 ksi) and hardness 21-35 HRC, and it can be used continuously from –29 °C to +427 °C. Thanks to this balanced performance, CrMo B7 Double End Stud is the default high-temperature bolting solution for refineries, power plants and pressure-vessel manufacturers worldwide.
ASTM A193 Grade B7 is the representative U.S. grade for high-temperature/high-pressure alloy-steel bolts/studs and the most common material for CrMo B7 Double End Stud on the market. Based on AISI 4140/4142 Cr-Mo steel, it is quenched and tempered at ≥593 °C, giving room-temperature tensile strength ≥860 MPa (125 ksi), yield ≥720 MPa (105 ksi) and hardness 21-35 HRC, and it can be used continuously from –29 °C to +427 °C. Thanks to this balanced performance, CrMo B7 Double End Stud is the default high-temperature bolting solution for refineries, power plants and pressure-vessel manufacturers worldwide.
2. Chemistry and heat treatment
C 0.37-0.49 | Cr 0.75-1.20 | Mo 0.15-0.25 | Mn 0.65-1.10
Quenching & tempering produces a tempered-sorbite microstructure that ensures high strength and toughness; every lot is tensile-, hardness- and chemically tested, but impact testing is not required by the standard. Although the Mo content in CrMo B7 Double End Stud is only 0.25 %, it is sufficient to suppress grain-boundary softening at high temperature, so the stud retains more than 75 % of its room-temperature strength at 427 °C.
C 0.37-0.49 | Cr 0.75-1.20 | Mo 0.15-0.25 | Mn 0.65-1.10
Quenching & tempering produces a tempered-sorbite microstructure that ensures high strength and toughness; every lot is tensile-, hardness- and chemically tested, but impact testing is not required by the standard. Although the Mo content in CrMo B7 Double End Stud is only 0.25 %, it is sufficient to suppress grain-boundary softening at high temperature, so the stud retains more than 75 % of its room-temperature strength at 427 °C.
3. Comparison with other common grades
| Grade | Base steel/heat treatment | Tensile strength | Temperature range | Features & typical applications |
| A193 B7 (CrMo B7 Double End Stud) | 4140 Q & T | 860 MPa | –29 °C–427 °C | High strength, medium corrosion resistance; universal high-temperature bolting for refineries, power plants, pressure vessels |
| A193 B7M | 4140 Q & T + stress relief | 690 MPa | –29 °C–343 °C | Hardness ≤22 HRC, resistant to H₂S stress-corrosion cracking; used in sour wellheads and chemical plants |
| A193 B16 | Cr-Mo-V Q & T | 860 MPa | –29 °C–538 °C | Vanadium added for better relaxation resistance; used for ultra-high-pressure steam and gas-turbine casing bolts |
| A320 L7 | 4140 Q & T + low-temp temper | 860 MPa | –101 °C–343 °C | Charpy impact tested at –101 °C, high low-temperature toughness; for LNG, air-separation and cold boxes |
| A193 B8-2 | 304 strain-hardened | 690 MPa | –196 °C–+800 °C | Stainless, mildly corrosion-resistant, but strength drops rapidly with temperature; used in nuclear and food industries |
| 8.8 carbon steel | 1045 Q & T | 830 MPa | –40 °C–+200 °C | Low cost for ambient building steelwork; creeps at high temperature and is not allowed in pressure vessels |
4. Performance advantages
- High-temperature retention: at 427 °C CrMo B7 Double End Stud keeps ≥75 % of its room-temperature strength, whereas 8.8 carbon steel has already fallen to ~50 % at 400 °C, so the same flange can use 1-2 fewer bolts, saving space and weight.
- Fatigue resistance: the Mo in the 4140 matrix segregates intragranularly and retards vacancy diffusion, giving a fatigue limit 30 % higher than that of 45# steel; ideal for CrMo B7 Double End Stud in reciprocating compressors and high-speed pumps.
- Cost-effectiveness: B7 material is mass-produced worldwide, costing only 10-15 % more than 8.8 grade while providing 1.3× preload and 2× high-temperature life, giving petrochemical plants the lowest life-cycle cost.
- High-temperature retention: at 427 °C CrMo B7 Double End Stud keeps ≥75 % of its room-temperature strength, whereas 8.8 carbon steel has already fallen to ~50 % at 400 °C, so the same flange can use 1-2 fewer bolts, saving space and weight.
- Fatigue resistance: the Mo in the 4140 matrix segregates intragranularly and retards vacancy diffusion, giving a fatigue limit 30 % higher than that of 45# steel; ideal for CrMo B7 Double End Stud in reciprocating compressors and high-speed pumps.
- Cost-effectiveness: B7 material is mass-produced worldwide, costing only 10-15 % more than 8.8 grade while providing 1.3× preload and 2× high-temperature life, giving petrochemical plants the lowest life-cycle cost.
5. Usage notes
1) Welding: with 0.4 % C it is crack-sensitive; field welding is basically not recommended. If unavoidable, preheat to 200 °C and post-weld stress-relieve at 650 °C.
2) Corrosion protection: the 1 % Cr gives better atmospheric corrosion resistance than carbon steel, but in coastal or strong-acid environments choose zinc, PTFE or B8M stainless; if CrMo B7 Double End Stud strength must be kept, use a duplex system of hot-dip galvanizing plus epoxy coating.
1) Welding: with 0.4 % C it is crack-sensitive; field welding is basically not recommended. If unavoidable, preheat to 200 °C and post-weld stress-relieve at 650 °C.
2) Corrosion protection: the 1 % Cr gives better atmospheric corrosion resistance than carbon steel, but in coastal or strong-acid environments choose zinc, PTFE or B8M stainless; if CrMo B7 Double End Stud strength must be kept, use a duplex system of hot-dip galvanizing plus epoxy coating.
3) Hardware pairing: per ASME B16.5, CrMo B7 Double End Stud should be used with A194 Gr.2H heavy hex nuts and F436 hardened washers to develop 100 % strength.
Conclusion
CrMo B7 Double End Stud is currently the most economical and mature medium-strength alloy-steel solution for high-temperature/high-pressure flange joints; when temperature exceeds 427 °C or when H₂S or low-temperature impact requirements exist, upgrade to B16, B7M or L7 materials.
CrMo B7 Double End Stud is currently the most economical and mature medium-strength alloy-steel solution for high-temperature/high-pressure flange joints; when temperature exceeds 427 °C or when H₂S or low-temperature impact requirements exist, upgrade to B16, B7M or L7 materials.
FAQ
1. ¿Qué significa exactamente ASTM A193 B7 y qué resistencia ofrece?
Es el grado estándar estadounidense para pernos de aleación Cr-Mo (basado en AISI 4140/4142) para alta temperatura y presión. Ofrece resistencia a tracción ≥860 MPa (125 ksi) y límite elástico ≥720 MPa (105 ksi), tras temple y revenido a ≥593 °C.
1. ¿Qué significa exactamente ASTM A193 B7 y qué resistencia ofrece?
Es el grado estándar estadounidense para pernos de aleación Cr-Mo (basado en AISI 4140/4142) para alta temperatura y presión. Ofrece resistencia a tracción ≥860 MPa (125 ksi) y límite elástico ≥720 MPa (105 ksi), tras temple y revenido a ≥593 °C.
2. ¿Hasta qué temperatura puede trabajar el espárrago B7?
Trabaja de forma continua en el rango de –29 °C a +427 °C. A 427 °C conserva más del 75 % de su resistencia a temperatura ambiente, muy superior a un tornillo grado 8.8 que a 400 °C ya ha perdido ~50 %.
Trabaja de forma continua en el rango de –29 °C a +427 °C. A 427 °C conserva más del 75 % de su resistencia a temperatura ambiente, muy superior a un tornillo grado 8.8 que a 400 °C ya ha perdido ~50 %.
3. ¿El B7 es resistente a la corrosión por sulfhídrico (H₂S)?
El B7 estándar no es recomendado para ambientes con H₂S (sour service). Para esa condición debe usarse B7M (dureza ≤22 HRC y aliviado de tensiones), que es específicamente resistente al agrietamiento por corrosión bajo tensión por sulfuros (SCC).
El B7 estándar no es recomendado para ambientes con H₂S (sour service). Para esa condición debe usarse B7M (dureza ≤22 HRC y aliviado de tensiones), que es específicamente resistente al agrietamiento por corrosión bajo tensión por sulfuros (SCC).
4. ¿Qué tuercas y arandelas debo usar con el espárrago B7?
Según ASME B16.5, deben usarse tuercas hexagonales pesadas A194 Gr.2H y arandelas endurecidas F436 (espesor ≥1/4"). Esta combinación desarrolla el 100 % de la resistencia del espárrago.
Según ASME B16.5, deben usarse tuercas hexagonales pesadas A194 Gr.2H y arandelas endurecidas F436 (espesor ≥1/4"). Esta combinación desarrolla el 100 % de la resistencia del espárrago.
5. ¿Se puede soldar el espárrago B7 en campo?
No se recomienda debido a su alto carbono (~0,4 %), que lo hace sensible a grietas. Si es inevitable, debe precalentarse a 200 °C y realizar un revenido posterior a 650 °C. Idealmente, se evita la soldadura y se usa solo como unión roscada.
No se recomienda debido a su alto carbono (~0,4 %), que lo hace sensible a grietas. Si es inevitable, debe precalentarse a 200 °C y realizar un revenido posterior a 650 °C. Idealmente, se evita la soldadura y se usa solo como unión roscada.
6. ¿Qué acabados anticorrosión están disponibles para el B7?
Además del acabado negro, se ofrecen galvanizado, PTFE (teflón) u otros recubrimientos. En ambientes costeros o ácidos fuertes se recomienda un sistema dúplex (galvanizado + epoxi) o cambiar a acero inoxidable B8M, pero si se requiere mantener la alta resistencia del B7, se opta por el sistema dúplex.
Además del acabado negro, se ofrecen galvanizado, PTFE (teflón) u otros recubrimientos. En ambientes costeros o ácidos fuertes se recomienda un sistema dúplex (galvanizado + epoxi) o cambiar a acero inoxidable B8M, pero si se requiere mantener la alta resistencia del B7, se opta por el sistema dúplex.
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