Butt Weld

Butt weld (also called groove weld) is a weld between two pieces of metal in the same plane — joining edges directly. Distinguished from fillet welds (between perpendicular surfaces). Butt welds are used where full strength of the base metal must be developed — connecting plates end-to-end, joining plate-girder web sections, splicing structural columns. Per IS 816:1969 + IS 9595:1996 + IS 800:2007 Cl. 10.7, butt welds are categorised by joint preparation: V-groove (single side bevel), U-groove (deeper bevel for thick plates), square (no bevel for thin plates), double-V (welded from both sides for full penetration).

For thick plates (>10 mm), V-groove or U-groove preparation is needed for full penetration. Single-V welds from one side may have incomplete penetration on the back; back-gouging and capping is required for full strength. Double-V (welded from both sides with back-gouging between) achieves 100% penetration. Square butt welds (no bevel) are used for thin plates (<6 mm) and partial-penetration applications. Design per IS 800:2007 Cl. 10.7: butt weld design strength = 0.7 × leg size × length × fy × γm⁻¹ for full-penetration; reduced for partial-penetration. Inspection: (1) Visual — full bead coverage, no undercut, smooth contour. (2) Radiographic — required for tension butt welds in important structures (IS 822). (3) Ultrasonic — for thick plates, full-penetration verification. (4) Magnetic particle — for ferromagnetic materials.