TWI Industrial Member Report Summary 661/1998
L S Smith and M F Gittos
Experience has shown that arc welds in titanium and its alloys typically exhibit thin strips of blue interference film parallel to the weld-line, either side of the fusion zone. These features can cause difficulty in meeting conventional colour acceptance criteria, even though the fused zone may be silver. They have been called 'tramlines' or 'rail tracks' and develop within the shielded area, largely irrespective of the integrity of the shielding. The 'tramlines' either side of keyhole plasma welds are far broader than observed typically for TIG welds, presenting a better opportunity to study their formation and character. Furthermore, conventional gas shielding methods have been shown in previous work by TWI to be inadequate for protecting the inside of pipe welds welded using the keyhole plasma process (i). Whilst this difficulty was overcome using complex shielding arrangements, it is important to understand the source of such obvious contamination.