Diffusion method for coating high temperature nickel chromium al

Details Diffusion method for coating high temperature nickel chromium al Diffusion method for coating high temperature nickel chromium al

1999-02-22

2000-10-31

Sheehan, John

Metal treatment

Process of modifying or maintaining internal physical...

Processes of coating utilizing a reactive composition which...

148285, 148519, 427239, 4272557, 427328, C23C 880

Patent

active

061396494

ABSTRACT:
The inner surface of a high temperature nickel chromium alloy product such as ethylene furnace tubes is cleaned with high temperature hydrogen to prepare the surface for the deposition, diffusion and modification of metals. A first layer of chromium or chromium and silicon is deposited and diffusion heat treated or covered by the second layer of aluminum, magnesium, silicon and manganese and third layer of rare earth metals such as yttrium and zirconium. Each layer or the combination of layers is diffusion heat treated at sufficient time and temperature to cause a diffusion depth ranging from 50 microns to 150 microns with a maximum of 250 microns. The surface is then heated to convert the immediate surface to a spinel and further pretreated with argon and nitrogen to stabilize the surface oxides. The surface of the final coating can be polished to minimize sites for carbon buildup. When ethylene is produced using furnace tubes which are coated in this manner less coking occurs.

REFERENCES:
patent: 3365327 (1968-01-01), Puyear
patent: 4004047 (1977-01-01), Grisik
patent: 4904501 (1990-02-01), Davis
patent: 5135777 (1992-08-01), Davis et al.
Reprint from Oil & Gas Journal, "Aluminized ethylene furnace tubes extend operating life," Reprinted from the Aug. 31, 1987 edition of Oil & Gas Journal, Copyright 1987 by PennWell Publishing Company.
"A Study Of The Results Of 31/2 Years of Exposure Of Alonized Tubes In An Ethylene Pyprolysis Furnace," Nov., 1984.

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