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ASTM A193

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Originally approved in 1936, this specification is heavily utilized in petroleum and chemical construction applications. The ASTM standard covers alloy steel and stainless steel bolting materials for high temperature or high-pressure service. This specification includes fasteners intended for use in pressure vessels, valves, flanges, and fittings. Although, this material is often available in national coarse (UNC) thread pitches, if being used in traditional applications, threads are specified 8 threads per inch (tpi) for diameters above one inch.

Below is a basic summary of a few of the common grades. ASTM A193 covers a number of other standard specifications not covered in this description including B5, B6, and B16.

A193 Grades

B7 Alloy steel, AISI 4140/4142 quenched and tempered
B8 Class 1 Stainless steel, AISI 304, carbide solution treated.
B8M Class 1 Stainless steel, AISI 316, carbide solution treated.
B8 Class 2 Stainless steel, AISI 304, carbide solution treated, strain hardened
B8M Class 2 Stainless steel, AISI 316, carbide solution treated, strain hardened

A193 Mechanical Properties

Grade Size Tensile ksi, min Yield, ksi, min Elong, %, min RA % min HBW Rockwell
B7 Up to 2-1/2 125 105 16 50 321 max 35 HRC max
2-5/8 - 4 115 95 16 50
4-1/8 - 7 100 75 18 50
B8 Class 1 All 75 30 30 50 223 max 96 HRB max
B8M Class 1 All 75 30 30 50 223 max 96 HRB max
B8 Class 2 Up to 3/4 125 100 12 35 321 max 35 HRC max
7/8 - 1 115 80 15 35
1-1/8 - 1-1/4 105 65 20 35
1-3/8 - 1-1/2 100 50 28 45
B8M Class 2 Up to 3/4 110 95 15 45 321 max 35 HRC max
7/8 - 1 100 80 20 45
1-1/8 - 1-1/4 95 65 25 45
1-3/8 - 1-1/2 90 50 30 45

A193 Chemical Properties

Element B7 (AISI 4140) B8 (AISI 304) B8M (AISI 316)
Carbon 0.38 - 0.48% 0.08% max 0.08% max
Manganese 0.75 - 1.00% 2.00% max 2.00% max
Phosphorus, max 0.035% 0.045% 0.045%
Sulfur, max 0.040% 0.030% 0.030%
Silicon 0.15 - 0.35% 1.00% max 1.00% max
Chromium 0.80 - 1.10% 18.0 - 20.0% 16.0 - 18.0%
Nickel 8.0 - 11.0% 10.0 - 14.0%
Molybdenum 0.15 - 0.25% 2.00 - 3.00%

A193 Recommended Hardware

Bolt Grade Nuts Washers
B7 A194 Grade 2H F436
B8 Class 1 A194 Grade 8 SS304
B8M Class 1 A194 Grade 8M SS316
B8 Class 2 A194 Grade 8 SS304
B8M Class 2 A194 Grade 8M SS316

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