Process for stress relieving seamless metal tubes

A process is described for stress relieving seamless metal tubes having undergone truing-up. In this process the tubes are maintained at near ambient temperature for not less than three minutes, during which time they are subjected to an internal pressure of between 0.8 Pc and Pc, Pc being the critical pressure beyond which the tube undergoes plastic deformation through its entire thickness. The elastic limit of the tube to be processed is determined by a mechanical test, the critical pressure Pc is determined by the relation Pc=R 0.2 Log r1/r0 where R 0.2 is the elastic limit, r1 the external radius and r0 the internal radius of the tube, and an internal pressure is maintained in the tube, this internal pressure being in the 0.8 Pc and Pc bracket. Water under pressure is pumped into the tube. In the case of very long curved tubes for nuclear power station steam generators, these tubes are fixed to an installation at hydrostatic pressure