Why does Portland Bolt’s torque chart not have values for stainless steel fasteners?

Portland Bolt’s Torque Chart includes approximate torque values for fastener specifications made from carbon steel and alloy steel. We have chosen to exclude torque values related to fastener specification made from stainless steel. The primary reason we have decided to omit stainless fastener specifications from our torque chart is because we are unable to locate a published friction coefficient for stainless bolts. The friction coefficient (K value) is required in determining the torque value based on the industry accepted formula:

T = (K D P)/12

T is Torque (ft-lbs), D is Nominal Diameter (inches), P is Desired Clamp Load Tension (lbs), and K is Torque Coefficient (dimensionless)

Something to consider regarding the installation of stainless fasteners is the tendency for the fasteners to experience galling. Galling, or cold welding, can occur when fasteners are subjected to a high amount of pressure causing the nut and bolt to fuse together. Due to the risk of galling, it is a very common industry practice to use a lubricant on the bolts to reduce friction. It is also somewhat common for stainless steel nuts to be coated with wax for this same reason. There are many types of lubricants and waxes used for this purpose which makes it difficult to determine a reliable and consistent friction coefficient for stainless steel fasteners.

The theoretical torque values listed on our site are intended as reference point.

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4 comments

    A few questions:
    1. What is the torque for a slip critical (Class C, 0.5) ASTM A325 bolt
    2. What is the torque for a ASTM A325 bolt (not slip critical)
    3. What is the torque for a stainless steel bolt (ASTM 193 B8 CL2)

    All A325 bolts are 5/8″ in diameter (Galv + waxed), green

    @Ed- The estimated torque needed to achieve full tension for your slip critical application is listed on our bolt torque chart. Keep in mind this is an estimate, your exact value can vary depending on your conditions. https://www.portlandbolt.com/technical/bolt-torque-chart/#bolt-torque-a325
    For a non slip critical application, if you are only tightening it to a snug tight condition, the torque needed will be in the 10-15 ft-lb range.
    For your stainless steel application, we are unable to help because we do not have any reliable friction coefficient information for stainless steel due to it’s tendency to gall under pressure.

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