Improvements in or relating to tubes

The structure of a butt welded metal tube is homogenized by cold reducing the wall of the tube by planetary ball swaging, and heat-treating the tube to recrystallize the structure. In an example, an 18/8 Ti stabilized stainless steel tube, produced by butt welding flat strip, is swaged to reduce the tube wall thickness by 14-32%, the tube annealed at 1050 DEG C. for 15 minutes and then oil quenched. The resulting structure includes uniform equaxial austenite grains with a distribution of ferrite. A total reduction of 55-65% followed by heating at 800 DEG -950 DEG C. for 5 hours reduces the grain size from about 30m to less than 7m . In another example, a 20% Cr, 25% Ni, Nb stabilized stainless steel tube is heat-treated in argon at 1050 DEG C. and oil quenched. In a further example, a tube of zircalloy 2, of composition 1.38% Sn, 0.084% Cr, 0.043% Ni, 0.071% Fe, balance Zr, is produced by electron beam welding, any longitudinal welds being cold reduced by 45-55% and circumferential welds by 35-40%. After heat-treatment at 820-860 DEG C. in a protective environment such as vacuum or He or Ar for 1 hour the physical properties of the tube are constant throughout. The invention is also applicable to Ni-Fe alloys, and alloys of Nb, Ti and Ta.