The ASTM A193 specification comprises various grades, each defined by its own distinct chemical composition, mechanical strength, and testing protocols. While this site provides a helpful overview of how these grades compare, you should consult the official ASTM International documentation for the definitive technical standards and requirements.
The ASTM A193 specification comprises various grades, each defined by its own distinct chemical composition, mechanical strength, and testing protocols. While this site provides a helpful overview of how these grades compare, you should consult the official ASTM International documentation for the definitive technical standards and requirements.
Grade B7
ASTM A193 Grade B7 fasteners are high-strength, heat-treated bolts and studs crafted from chromium-molybdenum steel. As the most widely used grade in construction and pipe flange applications, B7 hardware is readily available in both headed and threaded varieties. While typically sold in a plain finish, they are frequently treated with coatings like zinc, hot-dip galvanizing, Xylan, or PTFE to prevent corrosion. However, users should be aware that these coatings can limit the fastener’s high-temperature performance compared to uncoated versions.
Grade B8
ASTM A193 Grade B8 (Class 1) fasteners are produced from AISI 304 stainless steel, the industry standard for austenitic fasteners. To ensure peak corrosion resistance, these parts undergo carbide solution treatment (solution annealing), which involves heating the material and water-quenching it. For higher strength and better galling resistance, Class 2 (B8SH) fasteners are further strain-hardened after annealing; these are identified by an underlined grade symbol.
Grade B8M
While ASTM A193 Grade B8M Class 1 fasteners share similarities with Grade B8, they are crafted from AISI 316 stainless steel rather than AISI 304. The inclusion of molybdenum in Type 316 provides enhanced corrosion resistance. In terms of processing, Class 1 requires carbide solution treatment, whereas Class 2 involves an extra strain hardening step to boost strength and prevent galling. Class 2 items are identified by an underlined “B8MSH” mark.
Grade B7M
While sharing the same chemical composition as Grade B7 (quenched and tempered medium-carbon alloy steel), ASTM A193 Grade B7M fasteners have lower strength thresholds and must undergo 100% hardness testing per production lot. Their resistance to chloride, sulfide, and hydrogen stress corrosion cracking (SCC) makes them a standard choice for sour gas environments.
Grade B16
ASTM A193 Grade B16 bolts and threaded studs are crafted from a chromium-molybdenum-vanadium alloy. While they share similar strength specifications with Grade B7, the addition of vanadium and a higher tempering process allows B16 fasteners to maintain their structural integrity and strength at much higher temperatures. Consequently, they are a staple in the power and petrochemical sectors for use in boilers and turbines. It is important to note that Grade B16 lacks inherent corrosion resistance and requires a coating if exposure is a concern.
Grade B5
ASTM A193 Grade B5 fasteners, including bolts and threaded studs, are fabricated from quenched and tempered AISI 501 stainless steel. This heat treatment ensures enhanced durability for high-temperature flange applications within severely corrosive settings.
Grade B6
ASTM A193 Grade B6 fasteners, including bolts and threaded rods, are fabricated from quenched and tempered AISI 410 stainless steel to enhance mechanical strength. Their stainless steel composition makes them ideal for high-temperature applications within highly corrosive environments.
Less common A193 grade variations B6X, B8A, B8C, B8CA, B8MA, B8M2, B8M3, B8P, B8PA, B8N, B8NA, B8MN, B8MNA, B8MLCuN, B8MLCuNA, B8r, B8RA, B8S, B8SA, B8LN, B8LNA, B8MLN, B8MLNA, B8CLN, B8CLNA, B8T, and B8TA are excluded from this overview. If you need information regarding these specific types, Contact us.