Fasteners used in industry construction and manufacturing are required not just to hold the parts together but also provide predictable performance and performance in harsh conditions. ASTM International (previously known as the American Society For Testing and Materials) publishes standards that are highly popular and which define the chemical composition, mechanical and dimensional properties of bolts, nuts and other fasteners. They have to know these standards when utilizing high strength bolts and nuts. Selecting the right ASTM bolts, ASTM fasteners and ASTM nuts directly affects the safety and reliability of structures.
ASTM A325 Bolts
The ASTM A325 is one of the most commonly specified structural bolts that discuss the heavy-hex structural bolts employed in steel-to-steel connections. These bolts are high tensile and are normally employed with heavy hex nut and hardened washers to form a tight clamp that cannot vibrate and shear. ASTM A325 structural bolts find considerable application in bridge girders, steel structures and connections in buildings in the construction industry. A325 bolts have the required strength to withstand high-load applications because of the medium-carbon or alloy steel that they are made out of and the heat-treated steel.
ASTM A325 bolts are under the larger standard ASTM F3125 that unites A325 and A490 structural bolt standards. They can be found in Type 1 (carbon/boron steel) and Type 3 (weathering steel) in order to be more resistant to corrosion. Engineers also have to choose the appropriate size of thread length in specifying A325 bolts. Nuts of heavy-hex grade corresponding to the grade of bolt are necessary to give the full strength of the joint.
Alloy and Stainless Steel Bolts
ASTM A193 Grades B7 and B16
ASTM A193 includes alloy and stainless steel bolts, which are supposed to be used in the high-temperature and/or high-pressure service. The workhorse in this standard is Grade B7 which is a chromium-molybdenum alloy steel. B7 fasteners are heat-treated to attain a tensile strength of 125 ksi ([?]860 MPa), yield strength of 105 ksi and hardness to 35 HRC. These qualities enable B7 bolts to accommodate the extreme pressure and the changes in temperature. They find application in a large number in petrochemical plants, power generation equipment and structural connections. In sour-gas conditions, Grade B7M offers the same strength and low hardness to minimize hydrogen embrittlement.
Another alloy steel outlined in ASTM A193 is grade B16. Although B7 bolts are intended to service a maximum temperature of around 800 degF (427 degC), B16 bolts contain vanadium to provide enhanced creep resistance and frequently are found in high-temperature boilers and turbines. The A193 B16 bolts are used in the oil and gas drilling with Hastelloy C276 nuts to avoid corrosion.
Grades B8 (A193 B8 bolts) and B8M (A193 B8 M bolts) of Stainless Steel
In ASTM A193 B8 Bolts made of austenitic stainless steel are defined as grade B8 and B8M. B8 fasteners are composed of Type 304 stainless steel (18-8 composition) and they have a general industrial corrosion resistance. A193 B8 M bolts are made of Type 316 stainless steel, which is molybdenum alloyed to be more resistant to chlorides and acids, which is best suited in the marine and chemical-processing plant. The two grades come in Class 1 (solution-annealed) and Class 2 (strain hardened) condition to fulfill varying strength needs.
ASTM A320 L7 and A453 Grade 660
Where service at low temperature is essential, the ASTM A320 provides specifications of bolting materials that retain ductility at low temperature. Grade L7 bolts normally accompanied by A194 Grade 7 nuts, retain their mechanical like qualities down to [?]50 degF ([?]46 degC). They are used in the cryogenic piping, LNG plants and constructions in cold climate.
ASTM A453 Grade 660 bolts are used in high temperature conditions where high temperature is required like in power plants and turbine assemblies. This iron-nickel-chromium alloy is high strength to temperatures in and around 1000 degF (540 degC) and is commonly used to bolster flanges of steam turbine or exhaust tools.
ASTM F593 Bolt
ASTM F593 establishes the standards of stainless-steel bolts, studs and threaded rods to be employed in general corrosion resistant service. F593 Bolts are designed to be used in normal structural and mechanical applications, unlike A193 which is designed to address pressure and temperature limits, where corrosion resistance in the atmosphere is of primary concern. Its fasteners are made of various grades of stainless steel, such as 304, 316, 321, 347, and 410 and are grouped into Group 1 to Group 6, according to chemical composition.
Carbon Steel Bolts – ASTM A307
Carbon steel bolts are cost effective when they are not required to have high strength. ASTM A307 includes carbon steel bolts and studs between 1/ 4 inches and 4 inches. One of the most common general-purpose specifications of bolts is A307. The standard contains three grades:
- Grade A bolts can be applied in general use including headed bolts, bent bolt and threaded rod where no high degree of special strength will be needed.
- Grade B bolts (in most cases heavy-hex bolts or studs) are designed to be used in flanged joints in piping systems.
- Grade C has been replaced by ASTM F1554 Grade 36 but is still supplied for anchor-bolt applications.
The tensile strength of A307 bolts is relatively low, ranging between 60 ksi and 60-100 ksi, and Grade A and Grade B respectively. This renders them fit in non-critical structural connections, assembly of machinery and agricultural equipment. Being cost-effective and available, they are an option to consider because of their affordability and accessibility to the contractor and OEMs in situations where high-performance alloys are not needed.
Heavy Hex and Specialty Nuts
The choice of nut is as significant to make as that of bolt. The grade and material of the bolt should be compatible with the nuts to ensure that the joint gains the full strength and it does not become loose. ASTM has a number of specifications on nuts such as A194 and A563.
ASTM A194: High-Pressure, High-temperature Nuts
ASTM A194 covers carbon, alloy and stainless steel heavy-hex nuts intended for high-pressure or high-temperature service. Important characteristics are high tensile strength, resistance to temperatures, resistance to corrosion (of stainless grades) and heat treatment in order to obtain the desired mechanical properties. The most common grades are:
- Grade 2H-: Carbon steel, quenched and tempered; in combination with ASTM A193 B7 bolts, is used in high-pressure, high-temperature applications.
- Grade 7: Quenched and tempered alloy steel, can be used in low temperatures up to 50 degF.
- Grade 8 and 8M: Austenitic stainless steel (Type 304 and Type 316). Grade 8 has the normal corrosion resistance whereas Grade 8M has superior resistance in marine and chemical processing conditions. In corrosive conditions these grades are usually combined with stainless steel bolts.
- Grade B6: Martensitic stainless steel( Type 410) to be used in high strength and moderate corrosion resistance applications.
ASTM A563: General‑Purpose Structural Nuts
ASTM A563 is a nut made of carbon and alloy steel that is used in general structural and mechanical applications. There is a variety of applications of A563 nuts, which are applied to bolts, studs, and other external threaded components. They are of various grades like A, C, DH and DH3 with variations in their strength. As an example, Grade DH nuts are medium-carbon steel and heat treated; they should not be used with Grade A490 of the ASTM F3125 structural bolts and other high-strength bolts. A563 nuts normally get coated (zinc, galvanized or weathering steel) to adhere to the environment. In choosing the nuts to be used in structural connections, the engineers are to indicate the grade and style of the nuts, thread series and coating to be used to be compatible.
Matching Nuts to Bolts
The integrity of a bolted joint can be damaged by the use of an incorrect nut. The heavy-hex nuts are larger and thicker than the normal hex nuts, which gives them stronger thread engagement and redistribution of the load on a large surface. ASTM A325 structural bolts are normally complemented by ASTM A563 Grade DH or ASTM A194 Grade 2H nuts, depending on whether the assembly will be weathering steel or high-temperature. Since ASTM A193 B7 or B16 bolts are used, ASTM A194 Grade 2H nuts are used, and the stainless steel bolts (B8/B8M) are used with ASTM A194 Grade 8M Nuts or ASTM F594 nuts. Gauge a relevant ASTM standard and a fastener supplier during the choice of bolt-nut combinations.
Importance of ASTM Standards
ASTM standards are not simple textual descriptions of materials but they outline mechanical, chemical and dimensional specifications such that fasteners manufactured by various manufacturers can be used interchangeably. ASTM standards give a standard of quality and safety that manufacturers can use to produce goods that meet or exceed the set standards. The standards provide uniformity and dependability within industries besides improving safety in the form of rigorous tests and performance requirements. The process of development includes identification of the needs of industry, establishment of expert committees, research and review of the same by the people, and finally publication of consensus based specifications.
Explore Our ASTM Product Range
Jade Alloys offers a wide variety of bolts, fasteners and nuts certified by ASTM. Our inventory includes:
- Structural Bolts (A325/F3125): Steel-to-steel bolts which are high-strength bolt types (high-strength heavy-hex, Type 1 and Type 3).
- Alloy and Stainless Steel Bolts (A193/A320): Grades B7, B16, B8, B8M, L7, etc., which are used in high pressure or high temperature or in low pressure or low temperature.
- Specialty Bolts (F593, A453 Grade 660): Alloys of nickel-chromium and stainless steel used in extreme temperatures and corrosive conditions.
- Carbon Steel Bolts (A307): Low cost general-purpose bolts and studs where non-critical connections are to be made.
- Heavy Hex and Specialty Nuts (A194/ A563): A wide range of carbon, alloy and stainless steel nuts with Grades 2H, 7, 8, 8M and A563 DH to be used with our bolts.
Our team can help you identify the right ASTM bolts, ASTM fasteners and ASTM nuts for your project, ensuring full compliance with international standards.
The Bottom Line
Manufacturers and engineers are using ASTM standards to achieve the well-defined performance standards of strength, temperature resistance and durability of bolts and nuts. Be it your project requires high strength A325 structural bolts, heat defiant A193 B7/B16 studs, resistant to corrosion stainless steel fasteners or low cost A307 carbon steel bolts, Jade Alloys can provide the certified products that you require. We have certified bolts and nuts that are of ASTM which serve as a reminder that we value quality, safety, and reliability.
Contact us today to discuss your requirements and experience why we are a trusted global high-strength ASTM fasteners supplier.
