A welding apparatus for internally welding sleeves to tubes comprises a central shaft with an electrode attached thereto which are capable of being inserted in a tubular member. A plurality of remotely actuable seals are disposed on the welding apparatus and around the electrode for establishing a sealed chamber in the sleeve in which the welding may take place. The welding apparatus is capable of supplying an inert shielding gas to the sealed chamber for pressurizing the sealed chamber during the welding process and while the electrode completes a weld around the inner circumference of the sleeve. The apparatus may also be used to internally braze the sleeve to the tube.