Diffusion coated ethylene furnace tubes
AssigneeAlon, Inc.
InventorsKim A. Wynns, George T. Bayer
Life of this patent
Estimating the term…
Abstract
The inner surface of ethylene furnace tubes is diffusion coated with a sufficient amount of chromium or chromium and silicon to form a first coating having a thickness of at least two mils. This coating is then cleaned, neutralized, and grit blasted. Then a second coating of a sufficient amount of aluminum or aluminum and silicon is diffused onto the first coating to form a total coating thickness of at least five mils. The surface of the second coating is cleaned and polished to remove the nickel and iron-rich overlay which is present as a result of the coating process and to provide a smooth uniform surface. When ethelyene is produced using furnace tubes which are coated in this manner less coking occurs.
Claims20
A method of coating a surface of ethylene furnace tubes formed from a metal alloy containing nickel, chrome and iron comprising:
- a. diffusing a sufficient amount of chromium onto the surface to form a first coating having a thickness of at least two mils;
- b. cleaning the first coating;
- c. roughening the first coating;
- d. diffusing a sufficient amount of aluminum onto the first coating to form a second coating of aluminum having a thickness of at least two mils and a nickel and iron-rich overlay;
- and
- e. polishing the second coating to remove the nickel and iron-rich overlay.
An improved tube for ethylene furnaces comprised of a tubular member formed from an alloy containing nickel, chromium and iron and a coating on an inner surface of the tubular member, the coating formed by the steps of:
- a. diffusing a sufficient amount of chromium onto the inner surface to form a first coating having a thickness of at least two mils;
- b. cleaning the first coating;
- c. roughening the first coating;
- d. diffusing a sufficient amount of aluminum onto the first coating to form a second coating of aluminum having a thickness of at least two mils and a nickel and iron-rich overlay;
- and
- e. polishing the second coating to remove the nickel and iron-rich overlay.
An improved ethylene furnace of the type comprised of a plurality of tubes formed from an alloy containing nickel, chromium and iron, and in which feed stock is passed and heated wherein the improvement comprises a coating on an inner surface of at least one of the tubes, the coating formed by the steps of:
- a. diffusing a sufficient amount of chromium onto the inner surface to form a first coating having a thickness of at least two mils;
- b. cleaning the first coating;
- c. roughening the first coating;
- d. diffusing a sufficient amount of aluminum onto the first coating to form a second coating of aluminum having a thickness of at least two mils and a nickel and iron-rich overlay;
- and
- e. polishing the second coating to remove the nickel and iron-rich overlay.
Dependencies are inferred from the claim text.