TABLE OF CONTENTS The attachment and positioning of hardware, coverbands, and tie wires, is often achieved by brazing and welding. If these techniques are used, it is imperative to closely control the heating and cooling rates, and the deposition. Not doing so can result in failure and extended outages. The heat fusion processes are defined in "quality" terms as special processes (see chapter 11). This is because at completion, they cannot always be fully tested. Therefore, the quality of the joint is judged by control of the process that has been specified and calibrated with considerable care.
There are various requirements for achieving acceptable braze jointing on a coverband or tie wire, and irrespective of the procedure or braze materials used, it is essential to follow certain basic requirements, which are common to all procedures:
The surfaces to be joined must be clean. The surfaces must be prepared and made free of any oxide surface scale. It is also necessary to remove any grease, oil, and dirt and to cover the surface in such a manner that the formation of oxides is prevented during the brazing process. An oxide scale would prevent the formation of a strong joint, and the oxidization would be accelerated by the application of the higher temperatures
The braze metal must "wet" the surfaces so it can flow under capillary action.
There are various methods of cleaning and oxide scale removal. The most common in...
