It has been shown that the introduction of a trailing heat sink following a welding heat source at a short distance can reduce or even eliminate the buckling deformation of welded thin plate structures. To increase the insight into the stress development during welding with a trailing heat sink, residual stress measurements were carried out by means of laboratory X-ray and synchrotron X-ray diffraction techniques. Both the laboratory X-ray and the synchrotron X-ray experiments show a difference between the residual stress distributions for the cooled and the uncooled samples. The longitudinal stresses show a reduction in the compressive stress level towards the plate edges, to a level below the critical buckling stress. The transverse stresses are drastically reduced when the active cooling is applied.