Bolts and Nuts for flanged connections


Types of Bolts

In Petro and chemical industry for flange connections Stud Bolts and Hex Bolts are used. The Stud Bolt is a threaded rod with 2 heavy hexagon nuts, while the Hex Bolt has a head with one nut. Nuts and head are both six sided.


Stud Bolts general

The quantity of bolts for a flange connection will be given by the number of bolt holes in a flange, diameter and length of bolts is dependent of flange type and Pressure Class of flange.

Stud Bolt length are defined in ASME B16.5 standard. The length in inches is equal to the effective thread length measured parallel to the axis, from the first to the first thread without the chamfers (points). First thread is defined as the intersection of the major diameter of the thread with the base of the point.


Measuring lengths of Stud Bolts and Hex Bolts

Notes:


Threads of Stud Bolts

Bolts threading are defined in ASME B1.1 Unified Inch Screw Threads, (UN and UNR Thread Form). The most common thread is a symmetrical form with a V-profile. The included angle is 60°. This form is widely used in the Unified thread (UN, UNC, UNF, UNRC, UNRF) form as the ISO / metric threads.
The advantage of a symmetrical threads is that they are easier to produce and inspect compared with non-symmetrical threads. These are typically used in general-purpose fasteners.
Thread series cover designations of diameter/pitch combinations that are measured by the number of threads per inch (TPI) applied to a single diameter.


Standard Thread Pitches



Hex Nuts

Hex nuts (dimensional data) are defined in ASME B18.2.2, and even as bolts the threading in ASME B1.1. Depending on a customer specification, nuts must be both sites chamfered or with on one side a washer-face.



Hex Nuts

Dimensions of above mentioned nuts, can be found on page Heavy Hex Nuts of this website.



The height of a nut for a Stud Bolt is the same as the diameter of the thread rod



Materials for Stud Bolts

Dimensions from Stud Bolts are defined in the ASME B16.5 standard. The material qualities for studs are defined in the different ASTM standards, and are indicated by Grade. Frequently used grades are A193 for thread rods and A194 for the nuts.

ASTM A193 covers alloy and stainless steel bolting material for pressure vessels, Valves, flanges, and fittings for high temperature or high pressure service, or other special purpose applications.
ASTM A194 covers a variety of carbon, alloy, and martensitic and austenitic stainless steel nuts. These nuts are intended for high-pressure or high-temperature service, or both.



Marking of Stud Bolts

Thread rods and nuts must be marked by the manufacturer with a unique identifier to identify the manufacturer or private label distributor, as appropriate. Below a number of ASTM examples.


Marking of Stud Bolts


Grades of Stud Bolts

Below a table with materials and grades for flanges, thread rods (bolts) and nuts, arranged on design temperature, flanges, thread rods and recommended nuts.


DESIGN
TEMP.
FLANGES GRADE
THREAD RODS
GRADE
NUTS
-195° to 102°C ASTM A182
Gr. F304, F304L, F316,
F316L, F321, F347
A320 Gr.B8 Class2 A194 Gr.8A
-101° to -47°C ASTM A350
Gr.LF3
A320 Gr.L7 A194 Gr.7
-46° to -30°C ASTM A350
Gr.LF2
A320 Gr.L7 A194 Gr.7
-29° to 427°C ASTM A105 A193 Gr.B7 A194 Gr.2H
428° to 537°C ASTM A182
Gr.F11, F22
A193 Gr.B16 A194 Gr.2H
538° to 648°C ASTM A182
Gr.F11, F22
A193 Gr.B8 Class1 A194 Gr.8A
649° to 815°C ASTM A182
Gr. F304H, F316H
A193 Gr.B8 Class1 A194 Gr.8A
DESIGN
TEMP.
FLG'S GRADE
THREAD RODS
GRADE
NUTS
Note: Materials in the table above are being provided for guidance purposes


YouTube Video
How a Bolt is made

YouTube Video
How it's made Nuts and Bolts

Remark(s) of the Author...

Improper Flange Connections - the Bolts are too short!

What can you do..


Improperly bolted flange



What is the proper length of a Stud Bolt..
As a rule, you can use:
The free threads of the bolt above the top of the nut is equals to 1/3 times the bolt diameter.