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ABOUT FLANGES   Revised: 09/29/2014

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API Bolt Torque Calculators

This Web Site Tool offers two calculators to determine torque to properly tighten API flange bolts to specified tightness, using various lubricants.

Calculator to provide the torque necessary to achieve a % of bolt yield.


Calculator to provide the torque necessary to achieve psi tension in the bolt.

For ASTM A193 B7 and ASTM A320 L7 bolting, API recognizes both % of bolt yield strength, and psi stress in bolts, as measures of flange clamping force necessary to provide a secure connection. As a result of API recognizing two methods of expression of clamping force, but also de-facto recognizing only torque as a means of achieving this clamping force, this website tool will offer two calculators. The first provides a torque value to achieve a % of bolt yield strength, and the second provides a torque value to achieve a tension in the bolt measured in psi.

Keep in mind that torque provides a method of measurement that may vary a great deal depending on conditions and the lubrication of bolts, nuts, and the surface the nuts bear against. Everything should be clean, smooth and well lubricated.

API recognizes two methods of bolt and nut lubrication: bolts and nuts with bare metal or plated, lubricated with thread compound tested in accordance with API RP 5A3 / ISO 13678, or bolts and nuts coated with Fluoropolymer material.

If you have chosen one of these lubrication methods, you can have some confidence in choosing the friction factors API has recognized for them. If you have chosen another lubricant, you must obtain that manufacturer's friction factor and use it to obtain meaningful torque values.

Calculator to provide the torque necessary to achieve a % of bolt yield strength tension in the bolt.

Calculator to provide the torque necessary to achieve psi tension in  the bolt.

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Information above, and in other parts of this Web Site, may help persons who really seek to know. If you have a question, and you think WOODCO USA may have the capacity to answer it, please use our Contact Us link and give us a chance to help.

WOODCO USA provides Web Site Tools for identification, estimating, and reference only. Do not use this information for manufacturing or inspection. Users of these tools should not use them as a substitute for professional engineering advice.  Anyone making use of the information presented does so at his own risk and assumes any and all liability resulting from such use.



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