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, plain finish 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. Plain 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 plain 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.
Does this also apply to A193 B7 Stud bolts?
@Jeffrey- The guidelines we referenced in this FAQ were specific to structural bolts, and were published by the AISC, which handles structural steel. We are not aware of any similarly published guidelines for A193 B7 bolts.
Anthony,
I have similar situation except I did not use TC bolts, but plain hex heads. I used 1 inch A490 and they were torqued to 475 for some temporary hold points. Can I reuse?
@Nate- Per the AISC/RCSC guidelines, A490 bolts should not ever be re-used. However, if your project engineer has reviewed the variables and is willing to sign off on it, that would be up to them.
Anthony:
I am currently working on a project in the Middle East and the structural steel is being fastened using tension control bolts (splined tip at the end of the bolt). The application uses both TC490 and ASTM F3125 bolts. The installer set the bolts to the designed torque when the splined tip sheared off. However, recently the need arose to loosen some of the hardware. The installer would like to reuse the bolts. My understanding is that once the splined tip on TC bolts is broken off that bolt has been tensioned to its plastic region and must not be reused. I would appreciate your thoughts on the matter. Thanks.
@Adrian- The AISC/RCSC says that A490 bolts do not have sufficient ductility to undergo more than one pretension and shall not ever be reused. Additionally, because these are TC bolts (I assume button head), and the spline has already snapped off, that adds a layer of difficulty due to the fact that you will have a hard time holding the head still when re-tightening. I’d say that the safe bet is to scrap them and procure new bolts.
We have some ASTM A193 Grade B8M stud bolts, diameter 1.1/4″ L=200mm, and applied a tightness as 650 N.m, that represent 10% more than specified (590 N.m). Can we reuse this studs?
@Andre- We are not aware of any published guidelines that reference the reuse of stainless studs, so we’d have to leave that decision up to the project engineer. If the studs have been elongated or deformed, they for sure should not be reused, but in the absence of visible damage, it is a judgement call.
Mr.Dane,
Can We perform Bolt torque (100%) more than once at construction for 4″ gate valve installation?
@Ishad- Once a bolt is torqued to 100%, it should not be reused unless the engineer make an allowance for it. Galvanized A325s and plain A490 bolts should never be reused, plain A325 bolts can be reused at the discretion of the project engineer.