Metallurgical Failure Analysis of MH-1A Reactor Core Hold-Down Bolts.

摘要

The Naval Research Laboratory (NRL), at the request of the U.S. Army Engineer Power Group (USAENPG), has performed a failure analysis on two MH-1A reactor core hold-down bolts that broke in service. Adherence to fabrication specifications, post-service properties and possible causes of bolt failure were investigated. The bolt material was verified as 17-4PH precipitation hardening stainless steel. Measured bolt dimensions also were in accordance with fabrication drawing specifications. Bolt failure occurred in the region of a locking pin hole which reduced the bolt net section by 47 percent. The failure analysis indicates that the probable cause of failure was net section overloading resulting from a lateral bending force on the bolt. The analysis indicates that net section overloading could also have resulted from combined tensile stresses (bolt preloading plus differential thermal expansion). Recommendations are made for improved bolting. (Author)