A stud bolt is a mechanical fastener with an external thread. A stud bolt connection is typically created by two nuts and the stud. Washers and extra nuts may be used occasionally. Stud bolts are commonly utilized in high-pressure pipework and pipeline flange connectors. This article will tell us about the different types, standards, materials, selection, and sizes of stud bolts.
What is a Stud Bolt?
A stud bolt is a type of mechanical fastener with visible threads but no head. The external thread is either the entire length of the stud or partly threaded from each end. It requires at least two nuts, one on each side, for installation. Stud bolts come in a variety of sizes, types, and thread styles.
What are the types of Stud Bolts?
Different types of stud bolts are available, depending on the threading pattern and design, as shown below:
- Fully threaded stud bolt – also called as continuous threaded stud bolt with a fixed thread length
- Tap ends stud bolt – with uneven threads on both ends and a non-threaded center.
- Double-end stud bolts – with threaded ends of equal length and a non-threaded center.
- Flange Stud Bolts – a fully threaded stud bolt with a chamfered end, specifically designed for flanged connections.
- Double-end stud bolt with reduced shank – the non-threaded center component has a smaller diameter than the actual diameter.
Stud bolts are classified into three groups based on their material strength:
- High Strength stud bolt
- Intermediate-strength stud bolt
- Low strength stud bolt
Stud Bolt Threads different Types
Depending on the application, stud bolts utilize a range of screw thread profiles. The following are some of the most popular thread profiles:
- ISO metric thread
- ACME thread
- UNC thread
- UNF thread
- UN thread
- WHITWORTH thread
Stud Bolts Coating Materials
To avoid galvanic corrosion, the material of the nut and washer must be suitable for the stud-bolt material. To improve corrosion resistance, stud bolts are sometimes coated. The following are examples of common coating materials:
- Electro zinc plating
- Electro cadmium plating
- Hot dip galvanizing
- PTFE Coating
- Phosphate coating
- Electro less nickel plating
- Zinc-nickel coating
- Aluminum coating
- Silver coating
- Zinc/Nickel by electrode position
- Dacromet
- Geomet
- XYLAN 1070
- XYLAN 1024
- Xylar 1
Xylan and Xylar coatings for stud bolts have multiple advantages:
- Less friction than uncoated bolts (CoF as low as 0.02).
- Even at high pressures, improved bolts have good corrosion resistance.
- High corrosion and chemical resistance in adverse conditions.
- Increased resistance to harsh weather (such as extreme sunlight and chemical exposure from saltwater)
- Greater temperature operating range (from -420° to +550°F, or -250° to 285°C).
- Color codes for easier identification
- Pliability: Xylan coatings bend freely and often, but do not break.
- Machinability: The stud bolts can be coated with several Xylan coatings.
- Excellent adherence to bolting materials
Stud bolt length (OAL/FTF)
The length of the stud can be measured either as overall length (i.e., “OAL”) or as “first useable thread to first useable thread” (i.e., “FTF”).
The FTF length is the standard stud length measurement for piping applications, and it is obtained by subtracting a quarter of an inch from the OAL length.
Flanges of various diameters and ratings necessitate studs of various lengths and diameters.
Stud Bolt Size/Dimension
The size and dimensions of the stud bolt are determined by the regulatory standards ASME B16.5 and ASME B16.47, which specify the bolt diameter and number of bolts required based on the pressure class, flange type, and pipe size.
In general, as the pressure class and NPS increase, so does the bolt area. The bolt area is determined by two parameters: the bolt diameter and the number of bolts. As a result, any of the two or both parameters can be adjusted to increase the bolt area.
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