I have a crack below the o2 bunghole on one of my test pipes. Is there any way that I can patch it instead of purchasing new ones?

 

It can be welded up by a muffler/exhaust shop. But, it may be hard to get to and may have to come off. On a rack it may be reached.
They will use an electric welder. Make sure they ground to the exhaust system or disconnect the battery. Or else you will get a fried electrical system.