Scope

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

B8

B8M

B8

B8M

Alloy steel, AISI 4140/4142 quenched and tempered

Class 1 Stainless steel, AISI 304, carbide solution treated.

Class 1 Stainless steel, AISI 316, carbide solution treated.

Class 2 Stainless steel, AISI 304, carbide solution treated, strain hardened

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

B7

Up to 2-1/2

125

105

16

50

2-5/8 – 4

115

95

16

50

4-1/8 – 7

100

75

18

50

B8 Class 1

All

75

30

30

50

B8M Class 1

All

75

30

30

50

B8 Class 2

Up to 3/4

125

100

12

35

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

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

0.37 – 0.49%

0.08% max

0.08% max

Manganese

0.65 – 1.10%

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

0.75 – 1.20%

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