How to Prevent Thread Galling

Q: I think my bolts are galling to the heat exchanger I’m working with because now they won’t budge at all. Guessing I will have to break them to get them out. I don’t want to have this keep happening – so is there any way to prevent this from happening in the future? 
 
A: Typically galling will happen if you over tighten a bolt, which actually causes them to cold weld together. Once they have seized like this, you are correct, the only way to remove them is to cut / break the bolts or nuts. Though these suggestions won’t help this time, they may be good to keep in mind in the future to prevent galling.
 
Slow Down
One of the main causes of galling is by fastening the bolts too fast. When you do this the friction causes the heat in the threads that leads to galling. If you slow down your fastening speed, there will be less friction and less heat on the threads.
 
Check Threads Before Installation
When you have threads that are damaged – cracked or otherwise – or dirt and debri on the threads, this can also increase the likelihood of the threads galling. So don’t use a bolt with damaged threads and make sure the threads are clean before installation.
 
Use Lubricants When Possible
Although you can’t always use a lubricant – an example may be high purity applications – lubricants when possible can hugely reduce galling risk. Anti-seize lubricants like moly disulfide will drastically reduce friction.
Use Bolts for Fastener not Pulling
Bolts are used to fastener something in place. Don’t use them to pull together two elements you are fastening together. The materials must already in place. If you use the fasteners to bring together materials, it puts more stress on the bolt threads.
Remember to stop
If you feel the bolts seizing before you are completed with fastening, stop. Let the bolt rest a few minutes to reduce the heat on the threads and try again.
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