ASTM A193 Grade B7 Alloy Steel Stud Bolts | Continuous Thread, 1/4″ to 4″

Product Introduction
Continuous-thread stud bolts manufactured from AISI 4140/4142 chromium-molybdenum alloy steel (1Cr-0.2Mo), oil-quenched and tempered at a minimum of 593 °C (1,100 °F). Fully threaded end to end to ASME B18.31.2. Threads conform to ASME B1.1 Class 2A in UNC, UNF, or 8UN series. Standard supply includes two ASTM A194 Grade 2H heavy hex nuts. Diameters 1/4″ through 4″, with common flange-bolting sizes from 1/2″ to 2-1/2″. Grade B7 is the default alloy steel stud material across ASME pressure classes 150 through 2500 for flanged joints, pressure vessels, heat exchangers, and valve bonnet bolting in refining, petrochemical, and power generation.

Material & Mechanical Properties
Chromium-molybdenum alloy steel, oil-quenched and tempered at a minimum of 593 °C.

• Diameters up to 2-1/2″: minimum tensile strength 125 ksi (862 MPa); minimum yield strength 105 ksi (724 MPa); minimum elongation 16%; minimum reduction of area 50%; hardness 235–331 HB (maximum 35 HRC).

• Diameters over 2-1/2″ to 4″: minimum tensile strength 115 ksi (793 MPa); minimum yield strength 95 ksi (655 MPa), reflecting reduced through-thickness quenching response in heavier sections.

Maximum continuous service temperature is 450 °C (840 °F). Above this limit, yield strength degrades rapidly due to tempering effects and ASTM A193 B16 (Cr-Mo-V) must be specified. Minimum service temperature without impact testing is –29 °C (–20 °F); below this, ASTM A320 L7 is required. Mechanical values are certified by heat lot; Mill Test Reports are available.

Geometry & Thread
The stud is dimensioned by thread size and overall length, measured end to end including chamfers. Threads are Class 2A external fit per ASME B1.1: UNC coarse for 1″ and smaller (1/2″-13, 5/8″-11, 3/4″-10, 7/8″-9, 1″-8); 8UN series for 1-1/8″ and larger to maintain consistent thread engagement across large-diameter flange bolting. The continuous-thread geometry allows adjustment across the full stud length, accommodating flange thickness and gasket compression variations. Stud lengths for ASME B16.5 flanges are tabulated in the B16.5 stud bolt chart as a function of flange rating, nominal pipe size, and gasket thickness.

Marking & Certification
Each stud 3/8″ and larger is permanently marked with the “B7” grade symbol and the manufacturer’s identification mark. Heat codes on the stud ends link each fastener to its Mill Test Report for full melt and heat-treatment traceability. Grade B7 studs are paired with ASTM A194 Grade 2H heavy hex nuts, quenched and tempered to 248–352 HB (24–35 HRC) with a 175 ksi proof load stress through 4″. EN 10204 Type 3.1 inspection certificates are available, stating chemical composition, heat-treatment condition (austenitizing temperature, tempering temperature, quenching medium), and mechanical test results.

Application Suitability
Flanged joints, pressure vessels, heat exchangers, and valve bonnet bolting in ASME pressure classes 150 through 2500. The continuous-thread design provides adjustable grip across the full stud length, suiting variable flange stack-ups. For sour service per NACE MR0175/ISO 15156, Grade B7M (maximum 22 HRC, 100% hardness tested) is the specified alternative. For service above 450 °C or below –29 °C, B16 or L7 grades should be selected.