Why Stud Bolts Are Used in Flanged Connections

Stud bolts are the standard fastener for pipe flanges, especially in refinery, petrochemical, power, and offshore service. The main reasons:

Even, accurate load transfer

A studs is threaded along its full length and tightened with a nut at each end. Torque is applied through the nut, so the stud sees almost pure tension. A hex head bolt, by contrast, picks up friction under the head and can bend slightly, which gives less consistent preload.

Better gasket seating

Flange sealing depends on uniform, predictable clamping force. Studs with nuts on both sides spread that force evenly around the bolt circle, which is critical for spiral-wound, ring-type joint (RTJ), and other high integrity gaskets.

Suited to high pressure and temperature

Studs are available in alloy grades such as ASTM A193 B7, B16, and B8, paired with A194 2H nuts. They handle thermal cycling, creep, and heavy loads well, and the full-length thread engagement gives strong grip.

Easy installation and removal

Studs can be inserted from either side of the flange, and flanges can be aligned and separated without turning a bolt head against a restricted space. Nuts are replaced easily if threads are damaged, so you don't have to scrap the whole fastener.

Fits large diameters and long lengths

Heavy flanges need long, thick fasteners. Studs are easier to manufacture and handle in these sizes than equivalent bolts.

Hydraulic tensioning and bolt up flexibility

Both ends are exposed, so hydraulic tensioners and stud-tensioning tools can be fitted, allowing simultaneous, controlled tightening of multiple studs.

Corrosion and maintenance advantages

Coatings can be applied along the full length, and a corroded nut is cheaper to replace than a full bolt. Studs also resist seizing in the field better when proper lubricant is used.

Standardized and interchangeable

Dimensions and materials follow codes such as ASME B16.5, B16.47, and ASME B1.1 for threads, which makes selection, procurement, and inspection straightforward.