Rules for Reusing Bolts
Question: Can a bolt be reused? If so, what grades and in what scenarios?
Answer: A bolt that has already been used in a given application may or may not be reused, depending on the grade, application, and recommendation of the “Engineer of Record”. There are a tremendous number of conflicting opinions on this subject, but the only definitive published information we can find on this issue from a reputable source is in regards to ASTM A325 and A490 structural bolts.
According to the Research Council on Structural Connections, Section 2.3.3:
“Reuse: ASTM A490 bolts and galvanized ASTM A325 bolts shall not be reused. When approved by the Engineer of Record, black ASTM A325 bolts are permitted to be reused. Touching up or re-tightening bolts that may have been loosened by the installation of adjacent bolts shall not be considered to be a reuse.”
“Pretensioned installation involves the inelastic elongation of the portion of the threaded length between the nut and the thread run-out. ASTM A490 bolts and galvanized ASTM A325 bolts possess sufficient ductility to undergo one pretensioned installation, but are not consistently ductile enough to undergo a second pretensioned installation. Black ASTM A325 bolts, however, possess sufficient ductility to undergo more than one pretensioned installation as suggested in the Guide (Kulak et al., 1987). As a simple rule of thumb, a black ASTM A325 bolt is suitable for reuse if the nut can be run up the threads by hand.”
When reusing bolts, it is critical to involve an engineer since the reuse of the fastener depends on a variety of factors including bolt type, application, grade, finish, installation method, etc. If the bolts have been tensioned beyond their yield point, they enter the “plastic zone” (where they elongate and do not contract once the load is removed), which means they may be subject to premature failure. Since it is virtually impossible to determine visually if a specific fastener has entered its plastic zone when previously used, the decision to reuse a fastener will be determined by the price to replace it versus the potential cost and/or liability of that fastener failing.
Spending a few hundred dollars replacing structural bolts supporting an overhead sign structure on the freeway makes sense when evaluating the potentially devastating consequences and liability involved in reusing bolts that may ultimately fail. On the other hand, attempting to reuse a few hundred dollars worth of bolts instead of replacing those fasteners on a noncritical pump or other piece of equipment might make sense when a failure would only result in the piece of equipment not working.