Stud Bolt and Nuts
A193 B7 Stud Bolt is a bolt with threads on both ends that designed to be screwed into a fixed part at one end, and to receive a nut on the other end. In Petroleum or Chemical industry, they are prominently used for flange connection, so stud bolt used with two nuts on either side is the most common combination which replaces bolt and nut assembly.
As we know that Stud Bolts have many categories, the type for flange connection is called flange stud bolts, which has fully thread with chambered ends. The theoretical length is measured the thread. Continuous threaded stud bolt is very similar to it, except no chambered ends.
Stud Bolt Materials
The most common materials for stud bolts (for flanges) are ASTM A193 (grade B7, B8, B8M, B8T), ASTM A453 (grade 660), ASTM A320 (grade L7, L7M), and ASTM A182 (duplex and super duplex bolting). For aggressive fluids and environments, stud bolts can be coated with Xylan/PTFE, Zinc and other materials.
ASTM A193 Stud Bolts: Chemical Composition
| Physical Element |
ASTM A193 grade B7 (AISI 4140) |
ASTM A193 grade B8 (AISI 304) |
ASTM A193 grade B8M (AISI 316) |
| Carbon |
0.38 - 0.48% |
0.08% max |
0.08% max |
| Manganese |
0.75 - 1.00% |
2.00% max |
2.00% max |
| Phosphorus, max |
0.035% |
0.045% |
0.045% |
| Sulfur, max |
0.040% |
0.030% |
0.030% |
| Silicon |
0.15 - 0.35% |
1.00% max |
1.00% max |
| Chromium |
0.80 - 1.10% |
18.0 - 20.0% |
16.0 - 18.0% |
| Nickel |
absent |
8.0 - 11.0% |
10.0 - 14.0% |
| Molybdenum |
0.15 - 0.25% |
absent |
2.00 - 3.00% |
ASTM A193 Stud Bolts: Mechanical Properties
| ASTM A193 |
Size |
Min Tensile Strength (KSI) |
Min Yield Strength (KSI) |
Min Elongation (%) |
RA % min |
Max HBW |
Max HRC |
| ASTM A193 grade B7 |
Up to 2-1/2 |
125 |
105 |
16 |
50 |
321 |
35 |
| 2-5/8 - 4 |
115 |
95 |
16 |
50 |
| 4-1/8 - 7 |
100 |
75 |
18 |
50 |
| ASTM A193 grade B8 Class 1 |
All |
75 |
30 |
30 |
50 |
223 |
35 |
| ASTM A193 grade B8M Class 1 |
All |
75 |
30 |
30 |
50 |
223 |
96 |
| ASTM A193 grade B8 Class 2 |
Up to 3/4 |
125 |
100 |
12 |
35 |
321 |
35 |
| 7/8 - 1 |
115 |
80 |
15 |
35 |
| 1-1/8 - 1-1/4 |
105 |
65 |
20 |
35 |
| 1-3/8 - 1-1/2 |
100 |
50 |
28 |
45 |
| ASTM A193 grade B8M Class 2 |
Up to 3/4 |
110 |
95 |
15 |
45 |
321 |
35 |
| 7/8 - 1 |
100 |
80 |
20 |
45 |
| 1-1/8 - 1-1/4 |
95 |
65 |
25 |
45 |
| 1-3/8 - 1-1/2 |
90 |
50 |
30 |
45 |
The material chosen for the threaded stud and the hex nuts should be compatible. Materials for bolting sets shall be selected based on the process's working temperatures, as shown in the table below:
| |
TEMPERATURE °C ( °F ) |
| STUD BOLTS MATERIALS |
MIN. |
MAX. |
| CARBON STEEL |
-29 (-20) |
300 (572) |
| A193 B7, L7 |
-73 (-100) |
400 (752) |
| A193 B6 |
0 (32) |
500 (932) |
| A193 B8 |
-200 (-325) |
575 (1067) |
| A193 B16 |
0 (32) |
520 (968) |
| A193 B17B |
-29 (-20) |
650 (1202) |
| A913 Inconel 718 |
0 (32) |
750 (1382) |
| A453 Gr. 660 |
-29 (20) |
538 (1000) |
ASTM A453 Stud Bolts for High-Temp. Service
ASTM A320 Stud Bolts for Low-Temp. Service
Stud Bolts' Coating
Stud bolts can be coated to increase the resistance to corrosion. The most common types of coatings for stud bolts are listed below:
- Electro zinc plating
- Electro cadmium plating
- Hot dip galvanizing
- PTFE Coating
- Phosphate coating
- Electroless nickel plating
- Zinc-nickel coating
- Aluminum coating
- Silver coating
- Zinc/Nickel by electrodeposition
- Xylan coating
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