Weldability and Corrosion Resistance Evaluation of Branch Joint With Branch Outlet Fittings on Process Piping With Heavy Wall Made of CRA Clad Material

Abstract Where sizes of run pipe and branch are largely different, branch outlet fittings set on run pipes are usually selected to compose branch joints. CRA (corrosion resistant alloy) solid piping materials are often selected when process fluids are corrosive, e.g., produced water of oil and gas crude. To optimize cost of process plant construction, CRA clad or weld overlay on CS (carbon steel) / low alloy steel parent metal (hereafter CRA clad material) may be applied to process piping. However, manufacturing process of piping materials constrains the minimum diameter of CRA clad piping materials such as NPS 6 (DN 150), therefore, CRA solid materials are used to lesser diameters than the minimum. CRA clad materials also constrain the minimum size of fabricated branch design because branch holes on CRA clad piping material must also be protected by CRA weld overlay. And accessibility of welding torch/arc and visibility of molten pool during weld overlay work on small bore holes must be considered in terms of weldability and weld overlay quality. To make up for these shortcomings, other production method for holes on CRA clad run piping materials, such as insert sleeve made of CRA materials welded with groove joint on the holes, were introduced. Mockup coupons of the sleeve design branch and conventional CRA weld overlay design were prepared with branch outlet fitting, and weldability and corrosion resistance were studied by the comparison using both mockup coupons. This paper discusses and evaluates the weldability, corrosion resistance and materials selection of both branch designs and potentials that can eliminate the piping design constraints with their comparison.