A modular two-part welding and processing platform is described. A cart section is capable of rotating around objects such as pipes and cylinders, or of linear travel along plates or the like. This cart section reversibly couples to a processing section supplied for instance with welding apparatus, painting apparatus, cleaning means, analysis means or the like. By means of this two-part device, work pieces can be cleaned, welded, and inspected quickly and accurately. Special marks may be provided on the work piece which in conjunction with sensors and motoring means on the cart, allow for precise positioning of the process head with respect to the work.