scope:

Description of Driving Event:

During detensioning operations of a holddown post, while pressure of approximately 8K to 10K lbs was being applied, a loud "bang" was heard. Pressure on the tensioner fell to zero. It was later determined that the loud "bang" was the result of thread failure between the puller bar socket and the SRB holddown stud. With only 8 threads engaged, the shear stresses increased to 96,000 psi, as compared to 98,000 psi shear strength of the stud. Examination of the holddown stud revealed that 8 threads sheared on a 135 degree circumferential segment of the holddown stud.