Home » Boiler Tube Failure Handbook » Cracking » Not in or near a weld » Fish-mouth rupture Fish-mouth rupture Click on images to enlarge. CommentsCaused when steam flow is blocked or severely restricted. Lack of cooling leads to tensile rupture of tube. Issue Type:Cracking » Not in or near a weldLocations:Reheater, SuperheaterBoiler Type:PowerIndustry:Electric UtilityMechanism:Short-Term OverheatDownload a PDFFish-mouth rupture