DEVELOPMENT OF A DUAL-WALL TUBE FOR A COAL-GASIFICATION POWER-PLANT THROUGH A HOT ISOSTATIC PRESSING HOT EXTRUSION PROCESS

Research was done to develop a candidate syngas cooler tube for installation in coal gasification plants. Laboratory tests were conducted to develop alloy compositions with resistance to high temperature corrosion and down-time corrosion in simulated environments of coal gasification plants. 25Cr-30Ni-2Mo-2.5Si-1.5A1-Fe was the best composition, which showed excellent resistance to both types of corrosion. However, since ductility was substantially degraded during high temperature ageing, the developed alloy cannot be utilized for stress components. Therefore, the commercial product form for the developed alloy was a dual-wall tube. The dual-wall tube billet was manufactured by hot isostatic pressing compaction of the developed alloy powder with a hollow billet of type 347H steel. Hot extrusion was employed for the tube-forming process. Welding and bending tests were performed to evaluate the fabricability of the material.