Yes, there is. A193 and A320 grades B8 and B8M are assumed to be Class 1 unless otherwise specified. Class 1 fasteners are carbide solution treated, while class 2 fasteners are carbide solution treated and strain hardened. The work hardening that occurs in the manufacturing of Class 2 fasteners increases their strength. Class 2 fasteners are differentiated by the letters “SH” after the grade marking on the fastener and an underline for both A193 and A320 fasteners. The marking typically appears on the heads of bolts or the ends of threaded studs. For both A193 and A320, the marking requirement historically was only the underline, the “SH” lettering was added in approximately 2006.
| ASTM Specification | Stainless Grade |
Application | Marking Class 1 |
Marking Class 2 |
|---|---|---|---|---|
| A193 Grade B8 | Type 304 | High temperature / High pressure | B8 | B8SH |
| A320 Grade B8 | Type 304 | Low temperature | B8 | B8 |
| A193 Grade B8M | Type 316 | High temperature / High pressure | B8M | B8MSH |
| A320 Grade B8M | Type 316 | Low temperature | B8M | B8M |
Dear Sir,
I have “A-193 B8″ bolts of dia 3/4”. I understand that “A-193 B8” bolt means “A-193 B8 Class 1”.
Please confirm.
@Ijaz- that is correct. Class 2 is typically called out as A193 B8 class 2, whereas the wording “class 1” is usually omitted and just referenced as A193 B8.
B8M CL2 bolts can we confirm to Nace MR0175??
As per NACE HRC value is limited to 22. And hardness value for B8M CL2 is more than HRC 22.
@Joel- We are not familiar enough with NACE standards to know the specifics of what is permitted and what is not. There is no minimum hardness requirement for A193 B8M cl.2 bolts, so you may be able to find one that falls below 22 HRC, but you would need to check the MTRs on existing stock or contract to have the bolts manufactured in such a way that they conform to your requirement.
Hi,
We have received a B8M Class 2 Bolt Shipment from our supplier. What is the proper way to have it tested? Our supplier says that the core hardness would be less than that of surface hardness. Is that true?
@Mike- Yes, the core hardness may be lower than the surface, that is common in strain hardened stainless steels. The best way to test would be to have the tensile and yield tested per ASTM F606, as well as the mid radius hardness and see if those values conform to the A193 standard.
How is A193 B8MCL2 different to A320 B8MCL2 in terms of its application when chemistry & mech propr are same
@Jayendra- A193 is typically used in high temperature applications, whereas A320 is for low temperatures. However, the B8M cl.2 grades of these two standards are identical, they can be used interchangeably.
may I accept A193 grad. B8 Class 2 instead of class 1 for internal bolts for potable water tank?
@Mora- The class 2 version of B8 will be stronger, but slightly less ductile. You would need to have the project engineer approve any substitutions.