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Technical Library > STUD BOLTS > INTRODUCTION TO STUD BOLTS > Stud Bolts and Nuts for Flanges
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STUD BOLTS AND NUTS


Stud bolts and nuts are fasteners used in the petrochemical industry to mate flanges. A stud bolt set consists of a threaded rod and two heavy hexagonal nuts. In this article, we define stud bolts, give an overview of the most common ASTM materials, illustrate the torque and flanges’ bolting charts per ASME B16.5.


 

STUD BOLTS AND NUTS

A stud bolt (otherwise called, “bolting set”) consists of one fully threaded steel rod and 2 hexagonal heavy nuts (each with 6 sides). Stud bolts are widely used for flanged connections in pipeline works (oil & gas, power generation, construction, shipbuilding). The number, the length, the diameter of the stud bolts needed for a flanged joint depends on the flange type, nominal size, and pressure rating.

 

flanged connection

Other types of stud bolts are “double ends” (threaded both ends only), “tap ends” (for threaded holes) and “step-down” (ends have different diameters).

Stud bolts are available in a wide size range (diameters and lengths combinations), both in imperial and metric sizes and in a variety of materials from carbon steel to alloy, stainless and nickel alloys. To increase the resistance to corrosion or aggressive conditions, stud bolts can also be coated with special materials (zinc, xylan, Xylar, Cadmium, etc).

The material chosen for the threaded stud and the associated nuts should be compatible. Materials for bolting sets shall be selected based on the process working temperatures, as shown in the table below:

MATERIAL TEMPERATURE °C ( °F )
MIN. MAX.
CARBON STEEL -29 (-20) 300 (572)
B7, L7 -73 (-100) 400 (752)
B6 0 (32) 500 (932)
B8 -200 (-325) 575 (1067)
B16 0 (32) 520 (968)
B17B -29 (-20) 650 (1202)
INC 718 0 (32) 750 (1382)
660 -29 (20) 538 (1000)

 

THE THREADED STUD

threaded rod of stud bolts

The threaded rod is the steel element that is inserted into the holes of the flanges and tightened with appropriate hex heavy nuts at both ends.

For piping applications, the length of the stud is measured starting from the first thread excluding the chamfers and depends on the type of flanged connection to be executed (flange size, diameter, rating). Standard lengths are shown in the bolting chart reported below.

The steel rod is threaded according to the specifications set by ASME B1.1. The most used thread is the symmetrical thread pitch type with a “V-profile” (a 60-degree angle), as it is easier for the manufacturer to inspect compared to the non-symmetrical types. Thread series relate to the diameter and pitch combinations, measured by the number of threads per inch (“TPI”) applied to a single diameter.

bolt thread pitch .       v pitch 60 degrees

The standard thread pitches are:

  • Coarse thread series (UNC/UNRC): this is the most common type which is used for most screws, bolts, and nuts. Coarse threads are used for threads in low strength materials such as iron, mild steel, copper and softer alloy, aluminum, etc. The coarse thread is also more tolerant of adverse conditions and it facilitates quick assembly
  • Fine thread series (UNF/UNRF) is widely used for precision duties and when a higher tensile strength is required (vs. the coarse thread series)
  • 8-Thread series (8UN) is the elective threading method for several ASTM standards including A193 B7, A193 B8/B8M, and A320. This series is widely used for diameters from one inch upwards

What is the difference between screws, bolts, and studs?

bolt, screw and stud: differences

HEX HEAVY NUTS FOR STUD BOLTS

Hexagonal nuts for stud bolts

A nut is a fastener with a threaded hole. Steel nuts are screwed on a mating bolt to fasten two parts together.

The stud and the nut are kept together due to the friction existing between their respective threads, by a slight stretching of the bolt, and the compression of the two joined parts. The first types of nuts had a squared head. Nowadays, squared head nuts have been fully replaced by hexagonal head nuts, which have six sides instead of four and are the easiest and most effective types to fasten.

Nuts for petrochemical applications are tightened to a specific torque by means of torque wrenches. The mechanical strength of the nut material shall be compatible with the strength of the mated bolt.

 


FLANGE BOLTING TORQUE CHARTS

Charts are for reference only and assume properly lubricated ASTM A193 B7 stud bolts with ASTM A194 2H.

TORQUE CHARTS FOR ASME B16.5 CLASS 150

Flange
Size
B16.5 Class 150 RF/ Ring Gaskets B16.5 Class 150 FF/ Full Face Gaskets
Torque / Round (ft-lbs) Bolt Tighten Sequence* Torque / Round (ft-lbs) Bolt Tighten Sequence*
1st 2nd Final Dwg*/No. Bolt Size 1st 2nd Final Dwg*/No. Bolt Size
1/2″ 10 20 30 4-bolt 1/2″ 20 40 60 4-bolt 1/2″
3/4″ 13 27 40 4-bolt 1/2″ 20 40 60 4-bolt 1/2″
1″ 15 30 50 4-bolt 1/2″ 20 40 60 4-bolt 1/2″
1-1/4″ 20 40 60 4-bolt 1/2″ 20 40 60 4-bolt 1/2″
1-1/2″ 20 40 60 4-bolt 1/2″ 20 40 60 4-bolt 1/2″
2″ 40 80 120 4-bolt 5/8″ 40 80 120 4-bolt 5/8″
2-1/2″ 40 80 120 4-bolt 5/8″ 40 80 120 4-bolt 5/8″
3″ 40 80 120 4-bolt 5/8″ 40 80 120 4-bolt 5/8″
3-1/2″ 40 80 120 8-bolt 5/8″ 40 80 120 8-bolt 5/8″
4″ 40 80 120 8-bolt 5/8″ 40 80 120 8-bolt 5/8″
5″ 60 120 200 8-bolt 3/4″ 60 120 200 8-bolt 3/4″
6″ 60 120 200 8-bolt 3/4″ 60 120 200 8-bolt 3/4″
8″ 60 120 200 8-bolt 3/4″ 60 120 200 8-bolt 3/4″
10″ 95 190 320 12-bolt 7/8″ 95 190 320 12-bolt 7/8″
12″ 95 190 320 12-bolt 7/8″ 95 190 320 12-bolt 7/8″
14″ 147 294 490 12-bolt 1″ 147 294 490 12-bolt 1″
16″ 147 294 490 16-bolt 1″ 147 294 490 16-bolt 1″
18″ 213 426 710 16-bolt 1-1/8″ 213 426 710 16-bolt 1-1/8″
20″ 213 426 710 20-bolt 1-1/8″ 213 426 710 20-bolt 1-1/8″
24″ 300 600 1,000 20-bolt 1-1/4″ 300 600 1,000 20-bolt 1-1/4″

TORQUE CHARTS FOR ASME B16.5 CLASS 300

Flange Size B16.5 Class 300 RF/ Ring Gaskets
Torque / Round (ft-lbs) Bolt Tighten Sequence*
1st 2nd Final Dwg/No. Bolt Size
1/2″ 10 20 30 4-bolt 1/2″
3/4″ 15 30 50 4-bolt 5/8″
1″ 21 42 70 4-bolt 5/8″
1-1/4″ 30 60 100 4-bolt 5/8″
1-1/2″ 45 90 150 4-bolt 3/4″
2″ 33 66 110 8-bolt 5/8″
2-1/2″ 42 84 140 8-bolt 3/4″
3″ 60 120 200 8-bolt 3/4″
3-1/2″ 60 120 200 8-bolt 3/4″
4″ 60 120 200 8-bolt 3/4″
5″ 60 120 200 8-bolt 3/4″
6″ 60 120 200 12-bolt 3/4″
8″ 95 190 320 12-bolt 7/8″
10″ 147 294 490 16-bolt 1″
12″ 213 426 710 16-bolt 1-1/8″
14″ 195 390 650 20-bolt 1-1/8″
16″ 273 546 910 20-bolt 1-1/4″
18″ 300 600 1,000 24-bolt 1-1/4″
20″ 300 600 1,000 24-bolt 1-1/4″
24″ 465 930 1,550 24-bolt 1-1/2″


FLANGE BOLTING CHART

stud bolts for flanges

The number of bolts required by a flanged connection, as well as the length and the diameter of the bolts, depends on the flange diameter and class (the higher the class, the greater the number of holes), as shown in the following ASME tables (ASME B16.5):

BOLTS FOR CLASS 150 ASME B 16.5 RF AND RTJ FLANGES

NPS BOLTS DIAMETER in. LENGHT RF LENGHT
RTJ
BOLTS NUMBER
1/2 1/2 55 4
3/4 1/2 65 .. 4
1 1/2 65 75 4
1.1/4 1/2 70 85 4
1.1/2 1/2 70 85 4
2 5/8 85 95 4
2.1/2 5/8 90 100 4
3 5/8 90 100 4
3.1/2 5/8 90 100 8
4 5/8 90 100 8

NPS BOLTS DIAMETER in. LENGHT RF LENGHT
RTJ
BOLTS NUMBER
5 3/4 95 110 8
6 3/4 100 115 8
8 3/4 110 120 8
10 7/8 115 125 12
12 7/8 120 135 12
14 1 135 145 12
16 1 135 145 16
18 1.1/8 145 160 16
20 1.1/8 160 170 20
24 1.1/4 170 185 20

BOLTS FOR CLASS 300 ASME B 16.5 RF AND RTJ FLANGES

NPS BOLTS DIAMETER in. LENGHT
RF
LENGHT
RTJ
BOLTS NUMBER
1/2 1/2 65 75 4
3/4 5/8 75 90 4
1 5/8 75 90 4
1.1/4 5/8 85 95 4
1.1/2 3/4 90 100 4
2 5/8 90 100 8
2.1/2 3/4 100 115 8
3 3/4 110 120 8
3.1/2 3/4 110 125 8
4 3/4 115 125 8
NPS BOLTS DIAMETER in. LENGHT
RF
LENGHT
RTJ
BOLTS NUMBER
5 3/4 120 135 8
6 3/4 120 140 12
8 7/8 140 150 12
10 1 160 170 16
12 1.1/8 170 185 16
14 1.1/8 180 190 20
16 1.1/4 190 205 20
18 1.1/4 195 210 24
20 1.1/4 205 220 24
24 1.1/2 230 255 24

 

BOLTS FOR CLASS 400 ASME B 16.5 RF AND RTJ FLANGES

NPS BOLTS DIAMETER in. LENGHT
RF
LENGHT
RTJ
BOLTS NUMBER
1/2 1/2 75 75 4
3/4 5/8 90 90 4
1 5/8 90 90 4
1.1/4 5/8 95 95 4
1.1/2 3/4 110 110 4
2 5/8 110 110 8
2.1/2 3/4 120 120 8
3 3/4 125 125 8
3.1/2 7/8 140 140 8
4 7/8 140 140 8

NPS BOLTS DIAMETER in. LENGHT
RF
LENGHT
RTJ
BOLTS NUMBER
5 7/8 145 145 8
6 7/8 150 150 12
8 1 170 170 12
10 1.1/8 190 190 16
12 1.1/4 205 205 16
14 1.1/4 210 210 20
16 1.3/8 220 220 20
18 1.3/8 230 230 24
20 1.1/2 240 250 24
24 1.3/4 265 280 24

 

ASME B 16.5 RF AND RTJ FLANGES – CLASS 600

NPS BOLTS DIAMETER in. LENGHT
RF
LENGHT
RTJ
BOLTS NUMBER NPS BOLTS DIAMETER in. LENGHT
RF
LENGHT
RTJ
BOLTS NUMBER
1/2 1/2 75 75 4 5 1 165 165 8
3/4 5/8 90 90 4 6 1 170 170 12
1 5/8 90 90 4 8 1.1/8 190 195 12
1.1/4 5/8 95 95 4 10 1.1/4 215 215 16
1.1/2 3/4 110 110 4 12 1.1/4 220 220 20
2 5/8 110 110 8 14 1.3/8 235 235 20
2.1/2 3/4 120 120 8 16 1.1/2 255 255 20
3 3/4 125 125 8 18 1.5/8 275 275 20
3.1/2 7/8 140 140 8 20 1.5/8 285 290 24
4 7/8 145 145 8 24 1.7/8 330 335 24

 

BOLTS FOR CLASS 900 ASME B 16.5 RF AND RTJ FLANGES

NPS BOLTS DIAMETER in. LENGHT
RF
LENGHT
RTJ
BOLTS NUMBER NPS BOLTS DIAMETER in. LENGHT
RF
LENGHT
RTJ
BOLTS NUMBER
1/2 3/4 110 110 4 6 1.1/8 190 195 12
3/4 3/4 115 115 4 8 1.3/8 220 220 12
1 7/8 125 125 4 10 1.3/8 235 235 16
1.1/4 7/8 125 125 4 12 1.3/8 255 255 20
1.1/2 1 140 140 4 14 1.1/2 275 280 20
2 7/8 145 145 8 16 1.5/8 285 290 20
2.1/2 1 160 160 8 18 1.7/8 325 335 20
3 7/8 145 145 8 20 2 350 360 20
4 1.1/8 170 170 8 24 2.1/2 440 455 20
5 1.1/4 190 190 8  

 

BOLTS FOR CLASS 1500 ASME B 16.5 RF AND RTJ FLANGES

NPS BOLTS DIAMETER in. LENGHT
RF
LENGHT
RTJ
BOLTS NUMBER NPS BOLTS DIAMETER in. LENGHT
RF
LENGHT
RTJ
BOLTS NUMBER
1/2 3/4 110 110 4 6 1.3/8 260 265 12
3/4 3/4 115 115 4 8 1.5/8 290 300 12
1 7/8 125 125 4 10 1.7/8 335 345 12
1.1/4 7/8 125 125 4 12 2 375 385 16
1.1/2 1 140 140 4 14 2.1/4 405 425 16
2 7/8 145 145 8 16 2.1/2 445 470 16
2.1/2 1 160 160 8 18 2.3/4 495 525 16
3 1.1/8 180 180 8 20 3 540 565 16
4 1.1/4 195 195 8 24 3.1/2 615 650 16
5 1.1/2 250 250 8  

 

BOLTS FOR CLASS 2500 ASME B 16.5 RF AND RTJ FLANGES

NPS BOLTS DIAMETER in. LENGHT
RF
LENGHT
RTJ
BOLTS NUMBER NPS BOLTS DIAMETER in. LENGHT
RF
LENGHT
RTJ
BOLTS NUMBER
1/2 3/4 120 120 4 3 1.1/4 220 230 8
3/4 3/4 125 125 4 4 1.1/2 255 260 8
1 7/8 140 140 4 5 1.3/4 300 310 8
1.1/4 1 150 150 4 6 2 345 355 8
1.1/2 1.1/8 170 170 4 8 2 380 395 12
2 1 180 180 8 10 2.1/2 490 510 12
2.1/2 1.1/8 195 205 8 12 2.3/4 540 560 1

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