ASTM A193 specifies alloy and stainless steel bolt materials and their components for pressure equipment operating under high-temperature, high-pressure conditions or other special applications. This standard covers multiple bolt grades, such as ferritic steel and austenitic stainless steel, with common grades including B5, B6, B7, B8, and B8M. These different bolt grades exhibit variations in chemical composition, mechanical properties, and heat treatment requirements to meet the demands of diverse operating conditions.

ASTM A193 Material Details

ASTM A193 Bolts Grades Details

Grade B7

ASTM A193 B7 bolts and studs are manufactured from chromium-molybdenum steel and undergo quenching and tempering (heat treatment) to achieve the required mechanical properties (strength). Grade B7 is the most commonly used A193 bolt grade in the construction industry. B7 studs and short-head bolts are readily available on the market. B7 bolts are frequently used in pipeline flange connections. They typically feature hot-dip galvanizing, zinc plating, Xylan coating, PTFE coating, or other corrosion-resistant finishes. B7 bolts demonstrate outstanding performance in applications such as boiler pressure vessel connections in the power industry and high-pressure reactor connections in the chemical industry. Their high strength enables them to withstand immense pressure, while their excellent toughness ensures resistance to fracture under temperature fluctuations or in vibrating environments.

Chemical Composition

Mechanical Property

Grade B7M

ASTM A193 Grade B7M bolts and studs share the same chemical composition as Grade B7 (quenched and tempered medium-carbon alloy steel), but feature lower strength requirements and mandate 100% hardness testing for all fasteners within the same production lot. B7M bolts possess resistance to chloride, sulfide, and hydrogen-induced stress corrosion cracking (SCC), making them suitable for use in sour gas environments.

Grade B8

B8 grade bolts are manufactured from AISI 304 stainless steel and undergo solution treatment. These bolts offer excellent corrosion resistance and are widely used in industries with stringent corrosion requirements, such as food processing, pharmaceuticals, and marine engineering. In food and beverage production equipment, B8 bolts prevent product contamination from corrosion while ensuring structural integrity.

Chemical Composition

Mechanical Property

Grade B8M

B8M grade bolts are manufactured from AISI 316 stainless steel and undergo the same solution treatment. Compared to B8 bolts, B8M offers superior corrosion resistance due to the addition of molybdenum, demonstrating exceptional performance against pitting and crevice corrosion. In highly corrosive environments such as chemical processing and seawater desalination, B8M bolts serve as an ideal fastening solution, ensuring long-term stable operation of equipment under harsh conditions.

Chemical Composition

Mechanical Property

Grade B16

ASTM A193 Grade B16 bolts and studs are manufactured from chromium-molybdenum-vanadium alloy steel. While the strength requirements for A193 Grade B16 bolts and studs are similar to Grade B7, the addition of vanadium and a higher tempering temperature enable these fasteners to maintain their microstructure and strength at higher ambient temperatures than Grade B7. Unlike the stainless steel grades in the A193 specification, Grade B16 does not possess corrosion resistance unless coated.

Chemical Composition

Mechanical Property

Grade B5  

B5 grade bolts are manufactured from 4-6% chromium ferritic steel. This material provides the bolts with favorable high-temperature performance and moderate corrosion resistance, making them suitable for environments with specific temperature requirements and moderate corrosion risks.

Chemical Composition

Mechanical Property

Grade B6

B6 grade bolts are made from 13% chromium ferritic steel. With appropriate heat treatment, they exhibit good strength and resistance to high-temperature oxidation. They are commonly used in high-temperature applications such as valves and pipe connections. In the high-temperature piping systems of petroleum refineries, B6 bolts reliably connect pipe components, ensuring no loosening or failure occurs during the transportation of oil products under high temperature and pressure conditions.

Mechanical Property

How to choose the right ASTM A193 bolt?

Selecting the right ASTM A193 bolts requires considering several key factors:

Operating Temperature: Select the appropriate grade based on the maximum and minimum temperatures of the application. For example, B16 is preferred for high-temperature applications, while B7 is sufficient for ambient conditions.

Operating Pressure: The bolt’s strength grade (such as B7 and B16) directly affects its load-bearing capacity.

Corrosive Environment: If corrosive media, such as acidic or saltwater environments, are present, a stainless steel grade (such as B8 or B8M) must be selected.

Coating and Surface Treatment: To improve corrosion resistance, bolts can be hot-dip galvanized or PTFE-coated. Choosing the right coating can extend the bolt’s service life.

ASTM A193 Standard

This specification” covers alloy and stainless steel bolting for pressure vessels, valves, flanges, and fittings for high temperature or high pressure service, or other special purpose applications. See Specification A962/A962M for the definition of bolting. Bars and wire shall be hot-wrought and may be further processed by center less grinding or by cold drawing. Austenitic stainless steel may be carbide solution treated or carbide solution treated and strain-hardened.When strain hardened austenitic steel is ordered, the purchaser should take special care to ensure that Appendix X1 is thoroughly under-stood.

High Temperature Tests

Tests to determine high temperature properties shall be made in accordance with Test Methods E21, E139, and E292, and Practices E150 andE151.

Charpy Impact Tests

Charpy impact tests based on the requirements of specification A320/A320M, shall be made as agreed between the manufacturer and the purchaser. When testing temperatures are as low as those specified in specification A320/A320M, bolting should be ordered to that specification in preference to this specification

100 % Hardness Testing of Grade B7M

Each Grade B7M bolt or stud shall be tested for hardness by indentation method and shall meet the requirements specified in tables

 Length Tolerances for Bolts

Applications

Petrochemical Industry — High-pressure pipelines, heat exchangers, reactors

Energy and Power Generation — Boilers, steam pipelines, turbines

Shipbuilding and Offshore Engineering — Corrosion-resistant equipment, offshore platforms

Valves and Flange Connections — High-temperature, high-pressure sealing systems

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