A straight crack in pattern welded barrels is quite unusual; the failure is usually along a weld line. It could be an impending 'split' in a thin wall



This is most certainly a circumstance in which Magnetic Particle Imaging would be helpful, if not definitive
https://docs.google.com/document/d/1ZIo0y746UsSRZIgRuuxwAbZjSBHitO_EanvwLYc-kGA/edit

Texas is loaded with NDT facilities serving the aerospace and petroleum industry. If you get the barrel tested PLEASE PLEASE take full size high resolution images and send them to me as jpg attachments at revdoc2@cox.net
OR ship the barrels to me (at your expense) and I'll have them tested (at my expense)
I will of course provide an attribution unless you would rather not

https://sites.google.com/a/damascusknowledge.com/www/home