What is ASTM A193? Grades of ASTM A193 Material

In the realm of industrial construction, engineering, and infrastructure, the importance of fasteners cannot be overstated. These seemingly small components are the backbone of many structures, providing the necessary strength and integrity to hold together critical components. One of the most widely used and respected standards for high-strength bolting materials is ASTM A193. In this blog post, we will delve into the details of ASTM A193, its significance, and its role in ensuring the safety and reliability of various industrial applications. Note that ASTM A193 and SA193 both refer to the same material. The term SA is the ASME designation.

What is ASTM A193?

ASTM A193 is a standard specification established by the American Society for Testing and Materials (ASTM) that defines the requirements for alloy and stainless steel bolting materials for high-temperature or high-pressure service and other special applications. This standard covers a wide range of fasteners, including bolts, screws, studs, and other externally threaded fasteners used in pressure vessels, valves, flanges, and fittings for various industries, such as petrochemical, power generation, oil and gas, and many more.

The Purpose of ASTM A193

The primary purpose of ASTM A193 is to ensure that high-strength bolting materials used in critical applications possess the necessary mechanical properties and corrosion resistance. These fasteners are often subjected to extreme conditions, such as high temperatures, pressure, and exposure to aggressive environments. As a result, the quality and reliability of the bolting materials are essential to prevent catastrophic failures and ensure the safety of personnel and assets.

Material Grades of ASTM A193

ASTM A193 is available in several material grades, each offering specific mechanical properties suitable for different application requirements. Some of the common material grades include:

ASTM A193 GR. B7

ASTM A193 Grade B7 is a specification that defines the requirements for high-strength alloy steel bolting materials. It is one of the most commonly used grades in the A193 standard due to its excellent mechanical properties and suitability for high-temperature and high-pressure applications. Grade B7 bolting is typically used in environments where elevated temperatures and challenging conditions are present, making it a popular choice in industries such as petrochemical, power generation, oil and gas, and more.

Key Features and Properties of ASTM A193 Grade B7 Bolting:

• Material Composition: ASTM A193 Grade B7 bolts are made from chromium-molybdenum alloy steel known as AISI 4140. This material composition provides excellent strength and wear resistance.
• Tensile Strength: Grade B7 bolts have a minimum tensile strength of 125 ksi (kilopounds per square inch) or 860 MPa, which is significantly higher than standard low-carbon or mild steel bolts.
• Yield Strength: The minimum yield strength of Grade B7 bolts is 105 ksi (720 MPa), ensuring the bolts can withstand high levels of stress without permanent deformation.
• Hardness: The typical hardness range for ASTM A193 Grade B7 bolts is 35 to 40 HRC (Rockwell hardness C scale), which indicates good hardness and resistance to deformation.
• Thread Type: Grade B7 bolts are typically available in unified national coarse (UNC) thread type or unified national fine (UNF) thread type.
• Applications: ASTM A193 Grade B7 bolts are commonly used in applications where high strength and temperature resistance are required. Some examples include flange connections, pressure vessels, and valves in high-temperature piping systems.

ASTM A193 GR. B8

ASTM A193 Grade B8 is a specification for stainless steel bolting materials used in high-temperature and corrosive environments. The primary difference between Grade B8 and other A193 grades is the material composition, which makes it particularly suitable for applications where resistance to corrosion is a crucial requirement.

Key Features and Properties of ASTM A193 Grade B8 Bolting:

• Material Composition: ASTM A193 Grade B8 bolts are made from Type 304 stainless steel, which contains a combination of chromium and nickel. This composition provides excellent corrosion resistance in various environments, particularly in chemical and acidic conditions.
• Tensile Strength: Grade B8 bolts have a minimum tensile strength of 75 ksi (515 MPa).
• Yield Strength: The minimum yield strength of Grade B8 bolts is 30 ksi (205 MPa).
• Hardness: The typical hardness range for ASTM A193 Grade B8 bolts is 85 HRB (Rockwell hardness B scale).
• Thread Type: Grade B8 bolts are available in unified national coarse (UNC) or unified national fine (UNF) thread type.
• Applications: ASTM A193 Grade B8 bolts are commonly used in applications where corrosion resistance is essential. These include equipment and structures in chemical processing plants, food processing facilities, pharmaceutical industries, and marine environments.

ASTM A193 B8M

ASTM A193 Grade B8M is a specification for high-strength stainless steel bolting materials specifically made from Type 316 stainless steel. It is a popular choice for applications requiring superior corrosion resistance, particularly in chloride-rich and marine environments. The combination of chromium, nickel, molybdenum, and other alloying elements in Type 316 stainless steel provides enhanced resistance to pitting, crevice corrosion, and general corrosion, making Grade B8M bolts suitable for a wide range of challenging conditions.

ASTM A193 B16:

ASTM A193 Grade B16 is a specification for high-temperature bolting materials made from chromium-vanadium alloy steel. It is specifically designed for applications that involve elevated temperatures, making it a suitable choice for high-temperature pressure vessels, power generation equipment, and other similar applications.

ASTM A193 B8T:

ASTM A193 Grade B8T is a specification for high-strength bolting materials made from Type 321 stainless steel. It is designed for applications that require resistance to carbide precipitation during elevated temperature service.

Selection of ASTM A193 Grades

Selecting the right grade from ASTM A193 requires careful consideration of the specific requirements and conditions of your application. Each material grade within ASTM A193 offers unique properties suitable for different environments and temperature ranges. To decide which grade to select, follow these steps:

1. Understand the Application Requirements:
   • Identify the operating conditions, including temperature, pressure, and the surrounding environment where the bolting will be used.
   • Determine the load-bearing capacity needed for the connection.
2. Consider Corrosion Resistance:
   • If the application involves exposure to corrosive substances or environments, prioritize grades with high corrosion resistance, such as B8 and B8M (stainless steel grades).
3. Evaluate Temperature Range:
   • For high-temperature applications, consider grades with enhanced temperature resistance, such as B7 and B16.
4. Analyze Strength Requirements:
   • Assess the required mechanical properties, including tensile strength and yield strength, based on the load-bearing demands of the application.
   • For high-strength applications, consider grades like B7, which offers excellent strength properties.
5. Account for Special Conditions:
   • Determine if the application requires resistance to specific factors like carbide precipitation (e.g., B8T for elevated temperatures) or hydrogen embrittlement.
6. Compare Costs:
   • Evaluate the costs associated with each material grade to ensure that the selected grade is within budget constraints while meeting the necessary requirements.
7. Long-Term Considerations:
   • Consider the maintenance and replacement requirements of the bolting in the long term, especially for critical and high-stress applications.
8. Quality Assurance and Certification:
   • Ensure that the selected grade meets the required quality assurance standards and comes with relevant certifications, such as mill test reports (MTRs).
9. Seek Supplier Guidance:
   • Consult with a reputable bolting supplier who can provide insight into the advantages and limitations of different ASTM A193 grades.

Remember that each application is unique, and the selection of the appropriate ASTM A193 grade should be based on a comprehensive evaluation of the specific demands and operating conditions. By following these steps and seeking expert advice when needed, you can make an informed decision and choose the most suitable ASTM A193 grade for your bolting needs.

The typical chemical composition of some of the grades of ASTM A193 is provided in Table 1:

ASTM A193 Grade	Material Composition (Typical %)
B7/B7M	Carbon (C): 0.38 – 0.48
	Manganese (Mn): 0.75 – 1.10
	Phosphorus (P): 0.035 (max)
	Sulfur (S): 0.040 (max)
	Silicon (Si): 0.15 – 0.35
	Chromium (Cr): 0.8 – 1.10
	Molybdenum (Mo): 0.15 – 0.25
B8	Carbon (C): 0.08 (max)
	Manganese (Mn): 2.00 (max)
	Phosphorus (P): 0.045 (max)
	Sulfur (S): 0.030 (max)
	Silicon (Si): 1.00 (max)
	Chromium (Cr): 18.00 – 20.00
	Nickel (Ni): 8.00 – 11.00
B8M	Carbon (C): 0.08 (max)
	Manganese (Mn): 2.00 (max)
	Phosphorus (P): 0.045 (max)
	Sulfur (S): 0.030 (max)
	Silicon (Si): 1.00 (max)
	Chromium (Cr): 16.00 – 18.00
	Nickel (Ni): 10.00 – 14.00
	Molybdenum (Mo): 2.00 – 3.00
B16	Carbon (C): 0.36 – 0.47
	Manganese (Mn): 0.45 – 0.70
	Phosphorus (P): 0.035 (max)
	Sulfur (S): 0.040 (max)
	Silicon (Si): 0.15 – 0.35
	Chromium (Cr): 0.80 – 1.15
	Molybdenum (Mo): 0.5 – 0.65
	Vanadium (V): 0.25 – 0.35
B8T	Carbon (C): 0.08 (max)
	Manganese (Mn): 2.00 (max)
	Phosphorus (P): 0.045 (max)
	Sulfur (S): 0.030 (max)
	Silicon (Si): 1.00 (max)
	Chromium (Cr): 17.00 – 19.00
	Nickel (Ni): 9.00 – 12.00
	Titanium (Ti): 5x (C%) – 0.70 (max)

Mechanical Properties of ASTM A193

ASTM A193 specifies the mechanical properties that each material grade must meet. These properties include tensile strength, yield strength, elongation, hardness, and impact strength. By adhering to these specific requirements, manufacturers can ensure that the bolting materials exhibit the necessary strength and ductility to withstand demanding conditions without failure.

Below is a table outlining the mechanical properties of the ASTM A193 grades B7, B8, B8M, B16, and B8T:

ASTM A193 Grade	Tensile Strength (ksi)	Yield Strength (ksi)	Elongation (%)	Reduction of Area (%)	Hardness (HRC)
B7	125 min	105 min	16 min	50 min	35 – 43
B8	75 min	30 min	30 min	–	95 HRB
B8M	75 min	30 min	30 min	–	95 HRB
B16	125 min	105 min	18 min	50 min	35 – 43
B8T	75 min	30 min	30 min	–	95 HRB

Testing and Compliance

To ensure the quality and compliance of ASTM A193 fasteners, rigorous testing procedures are employed during manufacturing. Some of the common tests include tensile testing, hardness testing, Charpy impact testing, and grain size determination. Additionally, the fasteners must conform to specific heat treatment and chemical composition requirements.

ASTM A193 Ordering Information

Ordering ASTM A193 bolting requires providing specific information to ensure that the right type of fasteners is delivered for the intended application. When placing an order, the following information should be provided:

• Material Grade: Specify the ASTM A193 material grade required for the bolting. For example, B7, B8, B8M, B16, B8T, etc. Each grade has distinct mechanical and chemical properties suitable for different environments and temperature ranges.
• Item Description: Provide proper item description, for example, bolts, studs, bars, screws, or nuts.
• Diameter and Length: Provide the required diameter (typically expressed in inches) and length (in inches or millimeters) of the bolts or studs. The length is crucial for ensuring that the fasteners fit the intended joint or connection securely.
• Thread Type: State the thread type required for the bolting, whether it is a UNC (Unified National Coarse), UNF (Unified National Fine), or other specialized thread types.
• Quantity: Clearly specify the number of bolts or studs needed for the order. This helps the supplier to ensure that the requested quantity is available and ready for shipping.
• Finish and Coating: If a specific finish or coating is required for the bolting, such as plain finish, zinc-plated, or hot-dip galvanized, make sure to mention it in the order. Coatings can provide additional corrosion resistance, especially in harsh environments.
• Additional Requirements: If there are any additional requirements or special features needed for the bolting, such as specific markings, heat treatment, or special testing, communicate these to the supplier.
• Standards and Specifications: Apart from ASTM A193, there may be other industry standards and specifications that need to be followed for the bolting. Ensure that these are communicated to the supplier to guarantee compliance.
• Application Details: Provide information about the intended application or the environment in which the bolting will be used. This can help the supplier suggest the most suitable material grade and finish for the specific conditions.
• Quality Assurance: If certain quality assurance or testing requirements are necessary for the project, specify them in the order. These might include mill test reports (MTRs), material certifications, or additional inspection and testing procedures.
• Delivery Date and Location: Clearly state the desired delivery date and the shipping location for the bolting. This allows the supplier to plan the logistics accordingly and ensure timely delivery.

By providing these essential details when ordering ASTM A193 bolting, you can ensure that you receive the correct and appropriate fasteners for your specific application, reducing the risk of installation issues and ensuring the safety and reliability of your project.

ASTM A193 vs ASTM A194: Differences

Below is a tabular format outlining the key differences between ASTM A193 and ASTM A194:

Aspect	ASTM A193	ASTM A194
Purpose	Standard specification for alloy and stainless steel bolting materials for high-temperature and high-pressure service and special applications.	Standard specification for carbon and alloy steel nuts for bolts used in high-pressure and high-temperature service.
Material Grade	Various material grades (e.g., B7, B8, B8M, B16) with specific mechanical and chemical properties to suit different applications.	Various material grades (e.g., 2H, 2HM, 4, 7) with different mechanical properties and chemical compositions provide appropriate strength and corrosion resistance.
Bolting Type	Covers bolts, screws, studs, and other externally threaded fasteners used in critical applications.	Focuses specifically on nuts used in conjunction with bolts to provide a secure threaded connection.
Mechanical Properties	Specifies requirements for tensile strength, yield strength, elongation, hardness, and impact strength for bolting materials.	Specifies requirements for hardness, proof load, and stress to ensure nuts offer sufficient strength and deformation characteristics.
Application Scope	Primarily used for fasteners in critical applications involving high temperatures and pressures, such as in the petrochemical, power generation, and oil and gas industries.	Primarily used for nuts in conjunction with high-strength bolting materials in high-pressure and high-temperature environments.
Common Grades	B7 (alloy steel), B8 (Type 304 stainless steel), B8M (Type 316 stainless steel), B16 (chromium-vanadium steel), B8T (Type 321 stainless steel), etc.	2H (carbon steel), 2HM (carbon steel with supplementary requirements), 4 (alloy steel), 7 (alloy steel with enhanced corrosion resistance), etc.
Coatings	Coatings are specified for bolting materials when required, such as zinc-plated or hot-dip galvanized for enhanced corrosion resistance.	No specific coatings are specified for nuts in the ASTM A194 standard. Coatings may be addressed by other relevant specifications.
Compliance	Bolting must comply with ASTM A193 requirements as well as any additional project specifications or industry codes.	Nuts must comply with ASTM A194 requirements as well as any additional project specifications or industry codes.
Usage	ASTM A193 bolting is used in conjunction with ASTM A194 nuts to create secure and reliable threaded connections in various industrial applications.	ASTM A194 nuts are used together with ASTM A193 bolting to form threaded connections that provide clamping force and maintain joint integrity.

Conclusion

ASTM A193 plays a crucial role in the industrial world by standardizing high-strength bolting materials used in critical applications. Its significance lies in ensuring the safety, integrity, and reliability of structures and equipment in various industries. By providing material grades with well-defined mechanical properties and corrosion resistance, this standard enables engineers, contractors, and manufacturers to select appropriate fasteners for specific applications. Adhering to ASTM A193 guidelines leads to enhanced performance, reduced risk of failure, and increased confidence in the structural integrity of the projects at hand.