The Differences between ASME And ASTM Standards for Fasteners

This is a very professional and important question. Both ASME and ASTM standards are crucial in the fastener domain, but they have fundamental differences in their objectives, scope, and focus.

Simply put, you can understand their core distinction as follows:

• ASTM: Primarily specifies "what the material is" and "how to test it". It focuses on the material itself—its chemical composition, mechanical properties, and test methods.

• ASME: Primarily specifies "how to use it to build equipment" and "what its final requirements are". It focuses on the finished part—its design, dimensions, tolerances, pressure ratings, and performance requirements in specific applications (like pressure vessels, boilers).

Below is a detailed comparison and explanation.

1. ASTM Standards - Focus on Materials

ASTM International (formerly American Society for Testing and Materials) is a global standards organization whose core mission is to develop technical standards for materials, products, systems, and services, including test methods, specifications, and guidelines.

Its Role in Fasteners:
ASTM standards are primarily used to define the grade, chemical composition, mechanical, and physical properties of the raw materials used to manufacture fasteners. They also standardize the methods for testing these properties.

Key Characteristics:

1. Material Specifications: Define the chemical composition (e.g., carbon, chromium, nickel content) and mechanical properties (e.g., tensile strength, yield strength, hardness) of the steels, stainless steels, alloy steels, or other materials used for various bolts, screws, studs, and nuts.

• ASTM A193: Specification for alloy-steel and stainless steel bolting materials for high temperature service (e.g., B7, B8 classes).

• ASTM A194: Specification for carbon and alloy steel nuts for bolts for high pressure and high temperature service (e.g., 2H, 7, 8 classes).

• ASTM A307: Specification for carbon steel bolts and studs with tensile strength of 60,000 psi.

• ASTM A320: Specification for alloy-steel bolting materials for low-temperature service (e.g., L7).

• ASTM F1554: Specification for anchor bolts (e.g., Grade 36, 55, 105).

• Common Examples:

2. Test Methods: Standardize how to test materials to ensure they meet specifications, such as tension testing (ASTM A370), hardness testing, and impact testing (e.g., Charpy V-Notch impact test).

In a nutshell: ASTM tells you what conditions the "steel" used to make this bolt must meet.

2. ASME Standards - Focus on Design and Application

ASME (American Society of Mechanical Engineers) is a professional organization focused on engineering, particularly mechanical engineering and pressure equipment. Its standards focus more on design, manufacturing, and acceptance.

Its Role in Fasteners:
ASME standards define the dimensions, tolerances, thread forms, marking, and mechanical properties of a fastener as a finished part, as well as its usage requirements in specific applications (like pressure boundary applications).

Key Characteristics:

1. Dimensions and Tolerances: Define the unified dimensions, thread forms, head shapes, etc., of standard fasteners to ensure interchangeability.

• ASME B18.2.1: Standard for square and hex bolts and screws.

• ASME B18.2.2: Standard for nuts.

• ASME B1.1: Standard for Unified Inch Screw Threads (UN/UNR thread form).

• Core Standard: ASME B18 Series, the foundational standard for mechanical fasteners.

2. Application Codes: Within the ASME Boiler and Pressure Vessel Code (BPVC), it specifies which ASTM material standards should be used for fasteners when constructing pressure vessels, piping, or boilers, adding additional manufacturing, inspection, and marking requirements.

• For example: ASME BPVC Section II (Materials) directly references ASTM A193 Gr. B7 as an acceptable bolting material. Section VIII (Pressure Vessels) then dictates under what pressure and temperature conditions B7 bolts must be used, and that their manufacture and inspection must meet ASME's additional requirements.

In a nutshell: ASME tells you what the "finished bolt" should look like and how to use it correctly in pressurized equipment.

3. Core Differences Comparison Table

4. Working Together: A Common Example

The production and use of a hex cap screw for a high-temperature pressure vessel perfectly illustrates the synergy between ASTM and ASME:

1. Material Selection (ASTM): Based on design temperature and working pressure, an engineer selects ASTM A193 Grade B7 as the bolt material. This standard defines the chemical composition (e.g., chromium, molybdenum content), minimum tensile strength (≥125 ksi), and heat treatment requirements for B7 steel.

2. Dimension & Manufacturing (ASME): The manufacturer uses ASTM A193 B7 compliant steel to machine the bolt according to the ASME B18.2.1 standard. This standard dictates all dimensions and tolerances: hex head width across flats, head thickness, shank diameter, thread length, etc. Threading is done to ASME B1.1.

3. Application Code (ASME): The ASME BPVC Section VIII mandates that this pressure vessel flange connection must use bolts conforming to ASTM A193 B7 and nuts conforming to ASTM A194 2H. Furthermore, the ASME code may require additional impact testing or more stringent inspections that go beyond the original ASTM standard requirements.

4. Marking: Finally, the head of this bolt will be laser etched with "ASTM A193 B7" to denote its material grade, and it must also satisfy ASME requirements for dimensions and marking.

Summary

• ASTM is the recipe and property list for the material.

• ASME is the design drawing and instruction manual for the part.

When selecting a fastener, you will often see both referenced: "Dimensions per ASME B18.2.1, material to meet ASTM A193 B7." This means the bolt's size and shape conform to ASME, while its intrinsic "quality" (material properties) conforms to ASTM. For critical applications, ASME codes (like BPVC) mandate compliance with both.