ASTM A193 Grade B7 bolts and fasteners are globally utilized for the operations demanding high temperature throughout various industries. These fasteners are popular for their superior strength, longevity and resistance against corrosion. It is necessary to know their standards, applications, properties for guaranteeing excellent performance in complex industrial operations.

Our comprehensive guide will demonstrate to you the important parameters of ASTM A193 Grade B7 bolts and fasteners with their grades, production process, uses and norms for choosing the ideal grade of ASTM fasteners and bolts.

What is ASTM A193?

ASTM A193 standard made by the American Society for Testing and Materials, it defines the requirements for alloy and stainless steel fasteners developed for elevated temperature, high pressure and other structural applications. It involves a large variety of externally threaded fasteners like screws, studs and bolts that are generally utilised in valves, flanges, fittings and high pressure vessels in the sectors like power generation, petrochemicals and oil & gas.

Detailed Overview of ASTM A193 Grades

Grade B7 is a specification that includes alloy steel fasteners that can offer high strength in the most demanding service conditions. B7 is one of the most widely specified grades of fasteners under the A193 specification because it has great mechanical properties and is reliable for high pressure and high temperature applications. A193 B7 Bolts are used in some of the most harsh industrial applications, such as oil and gas, petrochemical plants, power generation plants and other industries where long-lasting fasteners are required.

Grade B8 are stainless steel fasteners that are designed for corrosive and high-temperature environments. Although they are included in the A193 specification, B8 fasteners are distinguished by being made from stainless steel, providing superior corrosion resistance, an important factor when selecting a bolt type, especially when durability in harsh environments is also a factor.

Grade B8M consists of stainless steel fasteners constructed from Type 316 stainless steel, characterized by their high strength and excellent corrosion resistance levels. This grade is often used in chloride-rich and marine environments that require protection against aggressive environments. The alloying elements in Type 316 stainless steel, which includes chromium, nickel and molybdenum, provide increased pitting, crevice, and corrosion resistance. Therefore, B8M bolts are widely reliable for a variety of challenging applications.

Grade B16 designates bolting manufactured from chromium-vanadium alloy steel, with reliable properties produced for elevated-temperature applications. This grade is primarily employed in high-temperature pressure vessels and power generation and other critical applications where strength and heat resistance is needed.

Grade B8T means fasteners which are manufactured from Type 321 stainless steel. Type 321 stainless steel has high strength, and stability for elevated-temperature applications. This grade is ideal for applications with carbide precipitation resistance, offering reliable service at high temperatures over a long period of time.

Features and of ASTM A193 Grade B7 Bolting:

Material Composition: ASTM A193 Grade B7 bolts are constructed from chromium-molybdenum alloy steel (AISI 4140). This alloy offers both high strength and excellent wear resistance.

Tensile Strength: These bolts have a minimum tensile strength of 125 ksi (860 MPa), which greatly exceeds the performance of regular mild or low carbon steel fasteners.

Yield Strength: Grade B7 bolts have a minimum yield strength of 105ksi (720mpa), which allows them to withstand substantial stresses and maintain their shape without permanent deformation.

Hardness: The bolts have exceptionally good hardness and deformation resistance under heavy loads, typically within the 35 – 40 HRC range on the Rockwell C scale.

Thread Type: They are usually produced with either Unified National Coarse (UNC) or Unified National Fine (UNF) thread types, depending on application requirements.

Manufacturing Process of ASTM A193 Grade B7

The production of ASTM A193 Grade B7 bolts and fasteners involves several steps:

Material Selection: High-quality chromium-molybdenum steel is selected based on ASTM specifications.
Heating: The steel is heated to a high temperature to facilitate shaping and forming.
Forging: The heated material is forged into the desired bolt shape.
Heat Treatment: The bolts undergo quenching and tempering to enhance mechanical properties.
Threading: Threads are machined or rolled onto the bolts.
Surface Treatment: The bolts may be coated with zinc, black oxide, or other protective finishes.
Testing and Inspection: Each batch is tested for tensile strength, hardness, chemical composition and dimensional accuracy to meet ASTM standards.

Applications of ASTM A193 Grade B7 Bolts

ASTM A193 Grade B7 bolts are utilized across a range of industries that have high performance and reliability expectations:

Petrochemical and Refinery Operations: Check valves, piping and heat exchangers used in high-temperature and high-pressure applications.

Power Generation: Fastening applications in boiler piping, steam turbines, and advanced technology central to nuclear power generation.

Construction and Structural Engineering: Structural connections and applications to support a load in bridges, tall buildings and heavy structural frames.

Oil and Gas: Drilling applications, offshore platforms, and pressure vessels operated in arduous service conditions.

Automotive and Heavy Equipment: Highly loaded applications in high-performance engines or equipment requiring precision strength and durability for arduous service conditions.

Differences Between ASTM A193 Grade B7 and Other Bolt Grades

Although ASTM A193 Grade B7 is a common grade, there are several additional related grades developed for specific service conditions:

ASTM A193 Grade B7M: A modified version of B7 providing lower hardness and yield strength, suitable for sour gas service or other applications where resistance to hydrogen embrittlement is required.

ASTM A320 Grade L7: A grade with very similar composition and properties to B7, developed for reliable performance at low-temperatures.

ASTM A194 Grade 2H Nuts: These nuts are generally used with B7 bolts to produce a high-strength bolted assembly for pressure vessels and structural applications.

Maintenance of ASTM A193 Grade B7 bolts

In order to ensure reliability and a long service life for ASTM A193 Grade B7 bolts, the following best practices are advised:

Selecting Size and Grade: Confirm that the size and grade of bolts you select is satisfactory for the mechanical and environmental requirements of the application.
Using Compatible Nuts and Washers: Use B7 bolts with ASTM A194 Grade 2H nuts for optimum tightness and strength.
Inspecting Bolts Regularly: To minimize the risk of bolt failure, inspect bolts periodically for signs of wear, corrosion, and fatigue.
Torque Properly: Never over or under-torque a bolt. Ensure that torquing is to the recommended specifications.
Use the Correct Environment: Use coatings or materials that are intended for harsh environments, such as high humidity, chemicals, or marine conditions.

Conclusion

At Jade Alloys, we believe that an understanding of the chemical makeup and mechanical attributes of B7 fasteners is paramount to their application specific needs. This understanding helps ensure the engineer and procurement team select the correct solution for the demanding projects. Whether in heavy industrial machinery or critical infrastructure, our ASTM A193 Grade B7 bolts deliver consistent reliability, safety and durability.

Bolts and fasteners which conform to ASTM A193 Grade B7 are important when operating in environments with high pressure and high temperature, where strength and reliability are important. These products are durable, tough and flexible, so they are found in many industries – primarily in oil & gas, construction and power generation.