US 7,396,597 B2 · Ni-Cr-Fe alloy and Ni-Cr-Fe alloy pipe having resistance to carburization and coking

Abstract

A stainless steel pipe includes a base metal containing 20-35 mass % of Cr, and a Cr-depleted zone is formed in the surface region of the pipe. The Cr concentration in the Cr-depleted zone is at least 10%, and the thickness of the Cr-depleted zone is at most 20 micrometers. A Cr-based oxide scale layer having a Cr content of at least 50% and a thickness of 0.1-15 micrometers may be provided on the outer side of the Cr-depleted zone. An Si-based oxide scale layer with an Si content of at least 50% may be provided between the Cr-based oxide scale layer and the Cr-depleted zone. The pipe is particularly suitable for use in petroleum refineries or petrochemical plants, such as for use as a pipe of a cracking furnace of an ethylene plant.

Claims12

Dependent claims

A Ni—Cr—Fe alloy for use in a carburizing gas atmosphere comprising a base metal having a chemical composition comprising in mass %, C:

0.01-0.6%, Si:
0.1-5%, Mn:
0.1-10%, P:
at most 0.08%, S:
at most 0.05%, Cr:
22-55%, Ni:
23-70%, N:
0.001-0.25%, O:
oxygen:
at most 0.02%, and a remainder of Fe and impurities, the base metal having in its surface region a Cr-depleted zone with a Cr concentration of at least 10 mass % but less than a concentration of Cr in the base metal, and a thickness of at most 20 micrometers, said surface of the base metal formed by removing an oxide scale generated by heating of the base metal.

7 more elements

Dependencies are inferred from the claim text.

Ni-Cr-Fe alloy and Ni-Cr-Fe alloy pipe having resistance to carburization and coking

Life of this patent

Ni-Cr-Fe alloy and Ni-Cr-Fe alloy pipe having resistance to carburization and coking

Life of this patent

Abstract

Claims12