Carbon Steel Stud Bolt with Nut for Flange - A Key Component for Secure Connections

Carbon steel stud bolts with nuts are the standard fasteners used to clamp pipe flanges, valves, and pressure vessels together. When paired with the right gasket and tightened to specification, they hold a flanged joint leak-tight under pressure, temperature, and vibration. For a matched sealing set, see our flange gaskets and flange products.

What a Carbon Steel Stud Bolt Assembly Is

A stud bolt is a headed double-end stud: full-length unified or metric thread, no head, driven through the flange bolt holes with two heavy hex nuts. The assembly carries the clamping load; the nuts convert torque into axial tension. Carbon steel grades dominate because they deliver high strength at low cost for the bulk of flange services.

Common Carbon Steel Grades

• ASTM A193 B7 — quenched and tempered alloy steel, the workhorse for ASME B16.5 flanges up to about 450 deg C.
• ASTM A194 2H — heavy hex nut grade matched to B7; also used with B7M for sour service.
• ASTM A307 — low-strength carbon steel for low-pressure, non-critical joints.
• ASTM A325 / F1554 — structural carbon steel bolts for skids and supports rather than pressure flanges.

Selecting Bolt to Flange Class

Why Secure Connections Matter

A flanged joint fails from loss of bolt tension, not from low initial torque. Vibration, thermal cycling, gasket creep, and relaxation all bleed preload over time. The nuts must stay put: 2H nuts with a hardened washer face and a sound tightening procedure keep the joint sealed through start-up and load swings.

What Poor Bolting Causes

• Leaks of product, steam, or gas — the most common and most visible failure.
• Gasket blow-out when preload drops below the seated load.
• Corrosion under the nut face and thread galling during assembly.
• Unsafe joint separation under pressure or thermal growth.

Applications

Carbon steel stud bolt assemblies are used across oil and gas, petrochemical, power, and water service wherever ASME B16.5 or B16.47 flanges are specified. They suit most ambient-to-medium temperature lines; for cryogenic or high-temperature duty, step up to low-alloy or stainless grades rather than pushing carbon steel past its limit.

Where They Fit in the Joint

The studs do not seal — they clamp. Sealing comes from the gasket compressed between the flange faces, while the studs and flange hold the faces together. Treat the bolt, nut, washer, and gasket as one system, not four separate buys.

Assembly and Tightening

Use a calibrated torque wrench or tensioner, a proven bolting pattern (star or criss-cross), and lubricate the threads and nut face to a known friction factor. Tighten in at least two passes to the target torque, and re-check after the system reaches operating temperature. Do not over-tighten: too much preload stretches the stud and crushes the gasket.

Frequently Asked Questions

Can I reuse carbon steel stud bolts?

Only after inspection. Check for thread damage, stretch, corrosion, and correct length; replace any doubtful stud. Nuts should be replaced more often than studs.

B7 or B7M for sour service?

B7M is the lower-hardness version required by NACE MR0175/ISO 15156 for H2S environments. Specify B7M with A194 2HM nuts when the line is sour.

How do I stop the nuts loosening?

Use 2H heavy hex nuts, a hardened washer, proper lubrication, and the correct torque. For vibration-heavy lines add a mechanical lock method approved by the joint standard.