Grade B8M stud refers to a stainless steel stud bolt made in accordance with the ASTM A193 or ASTM A320 specification, specifically using Type 316 austenitic stainless steel.
Both ASTM A193 and ASTM A320 standard specified the grade B8M stud bolt.and they share the same chemical compostion.Are they the exactly the same grade?what is the main difference between those 2 grades?You can find below comparion chart for A193 B8M and A320 B8M.
ASTM A193 vs A320 B8M Comparison Chart
| Feature | ASTM A193 B8M | ASTM A320 B8M |
|---|---|---|
| Application | High-temperature / pressure service (e.g., piping, valves, vessels) | Low-temperature service (cryogenic, cold climate) |
| Material | Type 316 SS (Austenitic) | Type 316 SS (Austenitic) |
| Service Temperature Range | Up to elevated temps (~1000°F / 538°C) | Designed for low temps (down to -150°F / -101°C) |
| Heat Treatment | Carbide solution treated for class1 | Carbide solution treated for class 1 |
| Charpy Impact Test | Not required | Required for certain sizes/grades at -150°F |
| Marking | B8M CL1/CL2 | B8M (Class 1 or 2) |
| Typical Use | Refineries, power plants, boilers | LNG, cryogenic tanks, arctic pipelines |
| Standards Referenced | ASTM A193 | ASTM A320, ASME SA320 |
From above chart,we can see,the main difference are their service temperature and testing requirements.
The Served Temperature Difference
ASTM A193 Standard ,It is the Specification for Alloy-Steel and Stainless Steel Bolting Materials for High-Temperature Service
ASTM A320 is a standard that covers alloy steel and stainless steel bolting materials specifically designed for low-temperature service.
Testing Difference
According to ASTM A193,Charpy Impact Testing is not required unless agreed between manufacturer and purchaser,but it is specifed the testing in SUPPLEMENTARY REQUIREMENTS.
Charpy Impact Tests S2.1 Charpy impact tests based on the requirements of Specification A320/A320M, Sections 6 and 7, shall be made as agreed between the manufacturer and the purchaser. When testing temperatures are as low as those specified in Specification A320/A320M, bolting should be ordered to that specification in preference to this specification
ASTM A320 Impact testing requirement
Impact tests are required for the grades shown in Table 3. Class 1, 1A, and 2 austenitic steels for temperatures above -325 °F [-200 °C];
