Which bolts require a rotational capacity test?

The rotational capacity test, sometimes referred to as a ROCAP test or RC test, serves as a quality control measure against excessively over-tapped nuts, a material with insufficient ductility, and generally assures that the assembly of elements (bolt, nut, and washer) will function together as a unit to achieve the required preloads. The test intends to evaluate the presence and efficiency of a lubricant and the compatibility of assemblies. The rotational capacity test is performed with a torque wrench and a Skidmore Wilhelm bolt tension measuring device.

Each test will require the assembly to reach a minimum rotation to sufficiently pass the rotational capacity test. The table below provides the minimum rotation required for the assembly to ensure full functionality and tension for the designated lengths of bolts.

Bolt Length
Required Rotation
Up to 4D >4D to 8D >8D to 12D
120 ksi (830 MPa) min 240° 360° 420°
150 ksi (1040 MPa) min 240° 300° 360°

When the F3125 specification was first written, a rotational capacity test was a supplementary requirement. A recent 2019 revision to the F3125 specification has shifted the rotational capacity test back to a required test for galvanized F3125 Grade A325 assemblies that include a nut and washer, to be performed by the manufacturer or responsible party. The rotational capacity test may also be requested by the purchaser to be administered on other structural grades such as A490, or other coated and plain assemblies that must be fully pre-tensioned under supplementary requirement S4.

An important exception to the rotational capacity testing requirement is that bolts more than 12 times diameters in length are exempt. Additionally, structural bolts between 8 and 12 diameters in length or bolts with extended thread lengths are extremely susceptible to rotational capacity testing failure.

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2 comments

    In the article it was never explained how the test is performed, or what is actually measured during the test, or what constitutes “failure” of the test.

    @Brian- The procedures are detailed in the F3125 standard. There are minimum tension requirements, maximum torque requirements, and the bolt must not break,. Additionally, the bolt and nut must not deform to the point that the nut will not easily thread on and off of the bolt. Essentially what you are testing is the ability of the joint to perform and required.

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