Stud Bolts & Fasteners
High-Strength Bolting for Flanged Connections
Stud bolts and nuts are the tensioning elements that compress flange gaskets and maintain joint integrity. A single incorrectly specified bolt can cause a flange leak with serious safety and environmental consequences.
Stud Bolt vs. Machine Bolt
| Type | Description | Application |
|---|---|---|
| Stud Bolt (Fully Threaded) | Threaded full length. Two nuts | Standard for ASME flanges. Preferred |
| Stud Bolt (Tap End) | One end shorter thread (tap end) into blind hole | Flanged valves, pump casings |
| Continuous Thread Stud | Fully threaded rod, cut to length | Standard for flanged joints |
| Hex Head Machine Bolt | Bolt with hexagonal head, one nut | Low pressure, non-critical. Less common in oil and gas |
Applicable Standards
| Standard | Scope |
|---|---|
| ASTM A193 | Alloy and stainless steel bolting for high temperature / high pressure |
| ASTM A194 | Carbon and alloy nuts for bolts |
| ASTM A320 | Alloy and stainless steel bolting for low temperature service |
| ASME B16.5 | Flange bolt dimensions and quantities |
| ASME B16.47 | Large-diameter flange bolting |
| ASME PCC-1 | Guidelines for pressure boundary bolted flange joint assembly |
| API 6A | Wellhead and Christmas tree bolting |
Common Bolting Specifications
| Bolt Grade (ASTM A193) | Nut Grade (ASTM A194) | Temperature Range | Service |
|---|---|---|---|
| B7 | 2H | -40°C to +400°C | Standard carbon steel. Sweet service. Most common in oil and gas |
| B7M | 2HM | -40°C to +400°C | Sour service. Controlled hardness (max HRC 22 / 235 HBW) |
| B16 | 4, 7 | Up to +500°C | High temperature. Cr-Mo-Va |
| B8 Class 1 | 8 | -196°C to +600°C | Stainless 304. General corrosion. Carbide solution treated |
| B8M Class 1 | 8M | -196°C to +600°C | Stainless 316. Chlorides, offshore |
| B8 Class 2 | 8 | -196°C to +600°C | Stainless 304. Strain-hardened. Higher strength |
| B8M Class 2 | 8M | -196°C to +600°C | Stainless 316. Strain-hardened. Higher strength |
| L7 | 4, 7 | -100°C to +400°C | Low temperature carbon steel |
| L7M | 7M | -100°C to +400°C | Low temperature + sour service |
| B7M | 2HM, 7M | -40°C to +400°C | Sour service standard |
NACE MR0175 / ISO 15156 Sour Service Requirements
- B7M / 2HM: Maximum hardness HRC 22 (235 HBW). Requires controlled chemistry and heat treatment
- B7 is NOT acceptable for sour service unless qualified to lower hardness
- Stainless bolting (B8M, etc.) must be carbide solution treated and meet hardness limits
Coating Options
| Coating | Description | Application |
|---|---|---|
| Black / Plain | As-manufactured, light oil | Indoor, non-corrosive |
| Hot-Dip Galvanized (HDG) | Zinc coating per ASTM A153 | Outdoor, atmospheric corrosion resistance |
| PTFE / Xylan | Fluoropolymer coating | Sour service, chemical resistance, prevents galling |
| Zinc-Nickel Electroplating | High-performance plating | Superior corrosion resistance, no hydrogen embrittlement |
| Xylan 1070 / 1424 | PTFE-rich coating | Standard for sour service bolting (low friction, anti-galling) |
| Cadmium Plating | Traditional anti-corrosion. Phased out (environmental) | Legacy. Not for new projects |