A purge dam assembly for confining a volume within an assembly of pipes with electropolished inner surfaces, the assembly of pipes including a distal pipe and a proximal pipe together arranged for butt welding at a seam, the purge dam assembly comprising: a distal disk, a distal bootie, a proximal disk, a proximal bootie and a cross-member, the distal disk being covered at its periphery with the distal bootie comprising a gasketing material, the distal disk being sized such that the distal bootie contacts but does not completely seal against an inner surface of the distal pipe permitting a purging flow of purge gas from the volume and past the distal disk when the purge disk assembly is inserted into the assembly of tubes or pipes; the proximal disk being covered at its periphery with the proximal bootie comprising the gasketing material, the proximal disk defining a purge gas portal for admitting of a purging flow of purge gas into the volume, the proximal disk further being sized such that the proximal bootie contacts but does not completely seal against an inner surface of the proximal pipe permitting a purging flow of purge gas from the volume and past the proximal disk; and the cross-member having a proximal and a distal end, the proximal end being affixed to the proximal disk and the distal end being affixed to the distal disk in a manner to preserve the spatial separation between the proximal disk and distal disk and to maintain the proximal and distal disks in coaxial alignment, characterised in that the gasketing material for both the distal bootie and the proximal bootie is a synthetic textile of 100% continuous-filament polyester, the filament being sufficiently soft to contact the electropolished surface without significantly scratching that surface. a distal disk, a distal bootie, a proximal disk, a proximal bootie and a cross-member, the distal disk being covered at its periphery with the distal bootie comprising a gasketing material, the distal disk being sized such that the distal bootie contacts but does not completely seal against an inner surface of the distal pipe permitting a purging flow of purge gas from the volume and past the distal disk when the purge disk assembly is inserted into the assembly of tubes or pipes; the proximal disk being covered at its periphery with the proximal bootie comprising the gasketing material, the proximal disk defining a purge gas portal for admitting of a purging flow of purge gas into the volume, the proximal disk further being sized such that the proximal bootie contacts but does not completely seal against an inner surface of the proximal pipe permitting a purging flow of purge gas from the volume and past the proximal disk; and the cross-member having a proximal and a distal end, the proximal end being affixed to the proximal disk and the distal end being affixed to the distal disk in a manner to preserve the spatial separation between the proximal disk and distal disk and to maintain the proximal and distal disks in coaxial alignment, characterised in that the gasketing material for both the distal bootie and the proximal bootie is a synthetic textile of 100% continuous-filament polyester, the filament being sufficiently soft to contact the electropolished surface without significantly scratching that surface.