Bolts and Nuts Used for Flanged Connectors

Stud bolts and hex bolts are used throughout the petroleum and chemical industries for flanged connections. The stud bolt is a threaded rod with two heavy hexagon nuts, while the hex bolt features a head with one nut. Nuts and heads are both six-sided. The amount of bolts needed for a flange connection is determined by the number of bolt holes in the flange. The diameter and length of bolts depends on the flange type and the flange’s pressure class. Stud bolt lengths are determined by ASME B16.5 standards. The length, in inches, is equal to the effective thread length measured parallel to the axis, from the first thread to the thread without chamfers (or points). The first thread is defined as the intersection of the diameter of the thread with the base of the point.

Bolt threadings adhere to ASME B1.1 standards. The most common thread is a symmetrical form with a V-profile, where the included angle is 60°. This form is used as the unified thread form in ISO/metric threads. Symmetrical threads have the advantage of being easier to produce and inspect than non-symmetrical threads. They are most commonly used in general-purpose fasteners. Hex nuts are defined by ASME B18.2.2 standards, and even as bolts with ASME B1.1. threadings. Depending on the customer’s needs, nuts can either come with both sides chamfered or with a washer face on one side.

Stud bolts are designed in a number of materials. This includes alloy and stainless steel, carbon, alloy, martensitic, and austenitic. Different materials are used for different applications. For example, stainless steel bolts are found in pressure vessels, valves, flanges, or fittings, while carbon and alloy bolts are found in high-pressure and high-temperature applications. Each thread rod and nut must be marked by the manufacturer with a unique identifier to denote the manufacturer or private label distributor. Furthermore, flanges, bolts, and nuts are marked with a grade depending on factors such as design temperature, thread rods, and more.

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