A New Alloy for Ethylene Pyrolysis Furnaces

The application of nickel alloys in the petrochemical sector has become increasingly important as the safety, reliability, energy efficiency, life extension of existing equipment and improved material performance drive the trend for more cost effective use of material. Probably the most important base chemical in the petrochemical sector is ethylene. Wrought INCOLOY 803 has a long service history of use in pyrolysis tubing for ethylene production though alloys which allow higher operating temperatures and longer life are needed to meet the industries demands for high efficiency plant. The focus of the material development efforts was to improve service performance by enhancing carburisation resistance and improving creep and rupture properties. INCOLOY 890 is the latest alloy for elevated temperature service which has been designed to give superior performance as radiant section tubing.

Carburisation is considered the most damaging mechanism in ethylene service because of the high metal temperatures 1832-2102 °F (1000-1150 °C) and the high carbon potential associated with the hydrocarbon feedstock. Carburisation is serious as it affects the tube life by reducing ductility making the tube more susceptible to stress damage caused by thermal cycling. High levels of chromium and silicon in INCOLOY 890 are used to enhance the protective oxide scale to provide excellent oxidation and carburisation resistance whilst also reducing catalytic coke formation.

The benefits of increased high temperature creep strength allow the tubes to operate at higher temperatures to either improve ethylene yield and productivity or to increase the run time between de-coking cycles. INCOLOY 890 shows improved strength levels for 100,000 hr stress rupture life when compared to INCOLOY 803 and HK40, due to higher alloying of solid solution strengthening elements.

This paper will show how Special Metals alloys and advanced alloy processing techniques have been developed to support the rapid change in process technology and show the outstanding service history of both INCOLOY 803 and 890 in ethylene production.