A protective device for welding a seam between a pair of workpieces has a flexible metallic band extending along the seam, spaced from surfaces of the workpieces, and having longitudinal edges on which are carried respective elastomeric heat-resistant strips extending the full length of the band and engaging the surfaces of the workpieces. A flexible ceramic band is provided between the elastomeric strips on the metal band between same and the surfaces. The band has a face turned toward and spaced from the surfaces and forms with the surfaces at the seam a chamber extending along the seam.