Carbon Steel Stud Bolt — Factory Direct Supplier | Huaxia-Steel
Carbon steel stud bolts are fully threaded fasteners used with two hex nuts to create bolted connections in flanged joints, pressure vessels, heat exchangers, valves, and structural assemblies. Unlike standard hex bolts, stud bolts have no head — they are threaded along their full length or have a reduced-diameter unthreaded section in the center — providing uniform clamping force and simplified assembly in applications where both sides of the joint are accessible.
Huaxia-Steel supplies carbon steel stud bolts manufactured to ASME B18.31.2, ASTM A193, and ASTM A307 specifications, with UNC, UNF, 8UN, and metric thread forms. Available in diameters from M6 (1/4″) to M100 (4″) and lengths from 40mm to 2000mm, our stud bolts are produced from certified carbon and alloy steel bar stock with complete material traceability.
Product Overview
Stud bolts are manufactured in two primary configurations:
- Fully threaded stud bolt (Type 1 / continuous thread): Threaded from end to end over the entire length. Used where the joint thickness may vary, as nuts can be positioned anywhere along the stud. Common in general industrial bolting and non-critical flanged connections.
- Tap-end stud bolt (Type 2 / double-end): Has unequal thread lengths — a shorter tap end threaded into a tapped hole, and a longer nut end for the mating nut. The center section may be unthreaded. Used on pump casings, valve bodies, and engine blocks where one component has a tapped hole.
- Double-end stud bolt (Type 3): Equal thread lengths at both ends with an unthreaded center section. The most common type for pipe flanges and pressure vessel bolting per ASME B16.5. The unthreaded center provides a precise grip length and reduces stress concentration.
Specifications and Dimensions
ASME B16.5 Flange Stud Bolts (Typical)
| Flange Size (NPS) | Bolt Diameter | Number of Bolts | Stud Length (mm) — 150# | Stud Length (mm) — 300# |
|---|---|---|---|---|
| 1/2″ (DN15) | 1/2″ UNC | 4 | 55 | 65 |
| 1″ (DN25) | 1/2″ UNC | 4 | 65 | 70 |
| 2″ (DN50) | 5/8″ UNC | 4 | 80 | 90 |
| 3″ (DN80) | 5/8″ UNC | 4 | 90 | 100 |
| 4″ (DN100) | 5/8″ UNC | 8 | 90 | 110 |
| 6″ (DN150) | 3/4″ UNC | 8 | 100 | 120 |
| 8″ (DN200) | 3/4″ UNC | 8 | 110 | 140 |
| 10″ (DN250) | 7/8″ UNC | 12 | 115 | 150 |
| 12″ (DN300) | 7/8″ UNC | 12 | 130 | 170 |
| 16″ (DN400) | 1″ 8UN | 16 | 150 | 200 |
| 20″ (DN500) | 1-1/8″ 8UN | 20 | 170 | 230 |
| 24″ (DN600) | 1-1/4″ 8UN | 20 | 190 | 260 |
Stud lengths include allowance for two heavy hex nuts per ASME B18.2.2. For higher pressure classes (600#, 900#, 1500#, 2500#), consult dimensional tables.
Thread Specifications
| Thread Standard | Diameters | Typical Application |
|---|---|---|
| UNC (Unified Coarse) | 1/4″ to 4″ | General industrial, structural bolting |
| UNF (Unified Fine) | 1/4″ to 1-1/2″ | High-vibration applications, fine adjustment |
| 8UN (8 Threads per Inch) | 1″ and above | Pipe flanges, pressure vessels (ASME B16.5 standard) |
| Metric ISO (M) | M6 to M100 | European and Asian equipment, EN flanges |
Material Grades and Mechanical Properties
| Grade | Standard | Yield (MPa, min) | Tensile (MPa, min) | Max Service Temp |
|---|---|---|---|---|
| ASTM A307 Gr B | A307 | — | 415-690 | 200°C |
| ASTM A193 Gr B7 | A193 | 725 | 860 | 450°C |
| ASTM A193 Gr B7M | A193 | 550 | 690 | 450°C |
| ASTM A193 Gr B16 | A193 | 725 | 860 | 525°C |
| ASTM A320 Gr L7 | A320 | 725 | 860 | -50°C to 350°C |
| ASTM A320 Gr L7M | A320 | 550 | 690 | -75°C to 350°C |
| ISO 898-1 Class 8.8 | ISO 898-1 | 640 | 800 | 300°C |
| ISO 898-1 Class 10.9 | ISO 898-1 | 940 | 1040 | 300°C |
A193 B7 is the most commonly specified grade for carbon steel stud bolts in pressure piping and flange connections. It is a chromium-molybdenum alloy steel (similar to AISI 4140/4142) quenched and tempered to achieve high strength at elevated temperatures. A320 L7 is the low-temperature equivalent of B7, suitable for service down to -50°C (or -75°C for L7M).
For less critical applications, A307 Gr B provides a cost-effective option with lower strength requirements (no specified minimum yield, tensile 415-690 MPa). Class 8.8 (ISO) is widely used in non-petrochemical applications and general machinery.
Manufacturing Process
- Raw material verification: Incoming bar stock is verified against mill certificates — chemical composition per ASTM A751, mechanical properties per ASTM A370.
- Cutting: Bars cut to length on automated saws with controlled length tolerance (+/- 0.5mm for standard lengths).
- Thread rolling: Threads are cold-rolled (not cut) for sizes up to M36 (1-1/2″). Thread rolling produces superior fatigue resistance compared to cut threads because the grain flow follows the thread profile. Above M36, threads are machined by single-point threading or thread milling.
- Heat treatment: For B7, B7M, B16, L7 grades — quenching and tempering in controlled-atmosphere furnaces with time-temperature recording. Hardness testing (Brinell or Rockwell) on each heat treatment batch.
- Surface finishing: Black oxide, zinc plating (electro-galvanized), hot-dip galvanized (ASTM A153), PTFE coating (Xylan, Teflon), or cadmium plating per customer specification.
- Final inspection: Thread gauging (GO/NO-GO ring gauges), dimensional check, visual inspection, hardness verification, and marking.
Applications
- Pipe flanges (ASME B16.5 / B16.47): The largest single application — stud bolts with two heavy hex nuts for flanged joints in process piping, including refineries, chemical plants, power stations, and offshore platforms.
- Pressure vessels and heat exchangers: Body flange bolting, channel cover bolting, tube sheet bolting — typically A193 B7 or B16 studs.
- Valves: Bonnet bolting, gland bolting, body-to-bonnet connections — stud bolts provide even clamping around the sealing face.
- Pumps and compressors: Casing bolting, cylinder head studs, bearing housing studs.
- Structural steel: Moment connections, base plate connections, bridge bearings — A307 or ISO Class 8.8 studs.
- Marine and offshore: Hull penetrations, equipment foundations, mooring equipment — hot-dip galvanized or coated studs for corrosion protection.
- Power generation: Turbine casing bolting, generator frame bolting, boiler manway studs — high-temperature grades (B16, B8 Class 2).
Surface Coatings and Corrosion Protection
| Coating | Standard | Corrosion Resistance | Temperature Limit |
|---|---|---|---|
| Black oxide (self-color) | — | Minimal — indoor use only | Up to grade limit |
| Zinc electroplated | ASTM B633 | Moderate — indoor/covered outdoor | Slight reduction from ~200°C |
| Hot-dip galvanized | ASTM A153 Class C | Good — outdoor, atmospheric | ~200°C (zinc embrittlement risk) |
| PTFE / Xylan coated | Manufacturer spec | Excellent — chemical, marine | ~260°C (coating limit) |
| Cadmium plated | AMS-QQ-P-416 | Excellent — marine, aerospace | ~230°C |
| Zinc-nickel alloy | ASTM B841 | Excellent — automotive, offshore | ~300°C |
Important note on galvanized B7 stud bolts: ASTM A193 B7 is not recommended for hot-dip galvanizing due to the risk of hydrogen embrittlement during the pickling process. If galvanized high-strength studs are required, specify A193 B7M (lower hardness, 235 HRC max / 22 HRC max per NACE MR0175) or use mechanical galvanizing as an alternative coating method.
Quality Assurance and Testing
- Chemical analysis: OES on each heat; verification against ASTM A751.
- Tensile testing: Per ASTM A370 — one test per heat treatment lot (B7, B7M, L7, B16).
- Hardness testing: Brinell (HBW) or Rockwell (HRC) — 100% for B7M per ASTM A193; sample per lot for other grades.
- Charpy impact testing: For A320 L7/L7M at specified test temperature — 3 specimens per lot.
- Thread inspection: GO/NO-GO ring gauge — 100% of stud bolts (if agreed).
- Visual and dimensional: 100% inspection for surface defects, marking legibility, and key dimensions.
- Coating thickness: Per ASTM B499 (magnetic) or ASTM B568 (X-ray) for plated/coated studs.
- Optional NDT: Magnetic particle testing for surface cracks, liquid penetrant for non-magnetic coatings.
Packaging, Marking, and Shipping
- Marking: Each stud bolt end stamped with manufacturer ID, material grade (e.g., “B7”), and heat/lot number for traceability. Marking per ASME B18.31.2 requirements.
- Packaging: Stud bolts packed with matching heavy hex nuts in plywood cases or steel crates. Studs separated by size and heat number. Threads protected with VCI (volatile corrosion inhibitor) paper or light oil.
- Nuts: Supplied as matched sets — ASTM A194 Gr 2H nuts with B7 studs; A194 Gr 4 or Gr 7 nuts with B16; A194 Gr 4 or Gr 7 with L7 studs.
- Shipping: FCL container or breakbulk shipment available. Loading port: Tianjin, Shanghai, or Ningbo.
- Documentation: EN 10204 3.1 mill test certificate with chemical and mechanical test results per heat/lot; packing list; commercial invoice; certificate of origin.
Why Choose Huaxia-Steel?
- Certified production: Stud bolts manufactured in ISO 9001-certified facilities with full heat treatment capability and in-house mechanical testing laboratory.
- Complete traceability: Every batch traceable from finished stud bolt back to bar stock heat number and mill certificate.
- Matched stud + nut sets: We supply stud bolts with correctly matched nuts per ASTM A194, eliminating the risk of mismatched assemblies.
- Custom manufacturing: Special lengths, diameters, thread forms, and coatings produced to customer drawings.
- Competitive pricing: Direct factory supply for both stock and custom orders.
- Global shipping: Regular exports to Middle East (ADNOC, Aramco projects), Southeast Asia, Africa, and South America.
- Emergency supply: Rush orders for shutdown and turnaround bolting — expedited air freight available.
Send us your stud bolt specifications today. Include diameter, length, thread type, material grade, quantity, and any special requirements — we will provide a detailed quotation within 24 hours. For flange bolting sets, simply provide the flange size, pressure class, and material grade, and we will calculate the correct stud bolt dimensions.
