How to Select Bolts for ANSI Flanges: A Complete Guide

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How to Select Bolts for ANSI Flanges: A Complete Guide

15/04/2026

🔷 Overview of ANSI flange bolts

In industrial piping systems, flanges are connected using:

Bolts (or stud bolts)
Nuts
Gaskets

👉 Among these, bolts play a critical role in:

Providing clamping force
Ensuring sealing between flanges
Maintaining connection stability under pressure and temperature

⚙️ Key factors when selecting flange bolts

1. Material standards (ASTM)

👉 The most important factor

ASTM A193 B7: alloy steel, high strength (most commonly used)
ASTM A193 B8 / B8M: stainless steel 304 / 316, corrosion-resistant

✔️ Choose based on the working environment

2. Flange pressure class (ANSI)

Class 150, 300, 600, 900, 1500, 2500

👉 Higher class requires:

Larger bolt diameter
Higher strength
More bolts

3. Bolt size

Includes:

Diameter
Length

👉 Must comply with standards such as:

ASME B16.5 (flanges)
ASME B18.2.1 (bolts)

4. Bolt types

✔️ Stud bolts

👉 Most commonly used type

Used with two nuts
Provides more uniform tightening force

✔️ Hex bolts

Used for small systems or low-pressure applications

🔧 How to select bolts by application

👉 High-pressure oil & gas systems

→ Stud bolt ASTM A193 B7 + nut A194 2H

👉 Corrosive environments (chemical plants)

→ Stainless steel stud bolts B8/B8M

👉 High-temperature applications

→ B7 or B16 (heat-resistant)

📊 Example of bolt selection by flange

Flange	Class	Bolt size
2”	150	5/8”
2”	300	3/4”
4”	600	1”

👉 (Actual dimensions should follow ASME B16.5 tables)

⚠️ Common mistakes

Selecting wrong material → bolt failure or corrosion
Incorrect bolt length → insufficient clamping force
Using regular bolts instead of stud bolts → poor sealing
Improper tightening torque

🔥 Quick selection tips

👉 ANSI systems → follow ASME B16.5 tables
👉 High pressure → choose B7 + 2H
👉 Chemical environments → choose B8/B8M stainless steel
👉 Always prioritize stud bolts

🏁 Conclusion

Bolts for ANSI flanges must be selected based on:

Material standards
Dimensions
Pressure class

👉 Proper selection helps:

Ensure gasket sealing performance
Improve system safety
Prevent leakage and failures

📞 Contact Information

Phuc Minh Engineering Co., Ltd (PM-E) specializes in supplying bolts, nuts, flanges, gaskets, and piping components that meet international standards.

🌐 Website: pm-e.vn
📧 Email: info@pm-e.vn
📱 Hotline: +84 907 450 506 – +84 902 720 814 – +84 979 737 351

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