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 |
Does recommended torque value for stud bolt ASTM A193 B8M Class 1 same with ASTM A193 B8M Class 2?
@Shyeara- Stainless steels have a tendency to gall when under pressure, so we have elected not to provide stainless torque values since they would be unreliable. That said, I would assume the torque for class 2 bolts would be higher than that of class 1, but you would need to talk to the project engineer to determine the proper amount.
I am Ramesh ,
Is it recomended B8 class 2 bolt for bolt dia more than 2 inches. Design code is B31.3.
@Ramesh – A193 B8 class 2 normally stops at 1-1/2″, although occasionally it can be found larger. As for what ASME B31.3 recommends, we are uncertain.
The reason why ASTM A-193 B8M Class 2 is most likely not available is the lack of machinery to cold draw the wire to make the blank to the strain hardened tensile requirement.
Above 1 1/2″ Diameter
@Paul- The reason is that cold drawing/strain hardening only penetrates a fraction of an inch below the surface. As the diameter of the bar increases, the center of the bar, which is not affected by the cold drawing, is left in it’s original condition. Therefore, as the bar diameter increases, it is harder and harder to get the steel to pass the elevated mechanical requirements of class 2. It is sometimes possible to find strain hardened, class 2 material larger than 1-1/2, but it is rare.
B8SH CL2
Would you recommend this bolt for low temp -20c to -190c severs
@Mike- A320 B8 cl.2 (SH) should be an appropriate call out for low temperature service down to -200C. However, since we do not have any engineers on staff, we have to stop short of making a recommendation.
I need to use a 304 SS bolt in place of an A325 HDG bolt. Would A193 B8 Class 2 be the most appropriate substitution to maintain the strength of the connection?
@David- A193 B8 Class 2 would be closer in strength to A325 than class 1, but it is not identical (it varies by diameter). Additionally, galling can often be an issue for stainless steel, especially in high tension applications, so caution should be exercised when substituting.
Hi, through visual inspection is it possible to segregate A193 B8 Cl1 from A320 B8 Cl1? The same question for A193 B8 Cl2 from A320 B8 Cl2 or A193 B8M Cl2 from A320 B8M Cl2. Our concern is that for a certain material class both A320 & A193 have got similar grade marking and to avoid any confusion at job site please advise how we can distinguish A193 & A320 (same class). Thanks for your insight and guidelines.
@Shahram- The reason that the head markings for the above grades of A193 and A320 are the same is that the bolts are 100% identical. They are made from the same steel, and to the same mechanical properties. There is no need to segregate, as all the bolts will meet the requirements of both A193 and A320.