Search Results for UNS N08825

Plate perforation occurred in the cylindrical section and walls of the inlet foot (2.38 mm thick Incoloy 825 plate welded using INCO welding rod 135) of an inert gas fire prevention system in an oil tanker. Cross-sectional microprobe analysis showed the corrosion product to contain sulfur, mainly from the flue gas, and calcium and chlorine, mainly from the sea water. The gray corrosion product was interspersed with rust and a black carbonaceous deposit. Corrosion pitting and poor weld penetration, with carbide precipitation and heavy etching at grain boundaries, indicated sensitization and susceptibility to aqueous intergranular corrosion. Chemical analysis showed the predominant acid radical to be sulfate (6.20% in the carbonaceous deposit and 0.60% in the corrosion product), suggesting that oxidation of SO2 in the flue gas caused the corrosion. Moisture condensation, the carbon acting as a cathode, and alloy susceptibility to intergranular corrosion contributed to the corrosion.

A pressure vessel failed causing an external fire on a nine-story coke gasifier in a refinery power plant. An investigation revealed that the failure began as cracking in the gasifier internals, which led to bulging and stress rupture of the vessel shell, and the escape of hot syngas, setting off the fire. The failure mechanisms include stress relaxation cracking of a large diameter Incoloy 825 tube, stress rupture of a 4.65 in. thick chromium steel shell wall, and the oxidation of chromium steel exposed to hot syngas. The gasifier process and operating conditions that contributed to the high-temperature degradation were also analyzed and are discussed.

This article addresses the forms of corrosion that contribute directly to the failure of metal parts or that render them susceptible to failure by some other mechanism. It describes the mechanisms of corrosive attack for specific forms of corrosion such as galvanic corrosion, uniform corrosion, pitting and crevice corrosion, intergranular corrosion, and velocity-affected corrosion. The article contains a table that lists combinations of alloys and environments subjected to selective leaching and the elements removed by leaching.

Corrosion is the electrochemical reaction of a material and its environment. This article addresses those forms of corrosion that contribute directly to the failure of metal parts or that render them susceptible to failure by some other mechanism. Various forms of corrosion covered are galvanic corrosion, uniform corrosion, pitting, crevice corrosion, intergranular corrosion, selective leaching, and velocity-affected corrosion. In particular, mechanisms of corrosive attack for specific forms of corrosion, as well as evaluation and factors contributing to these forms, are described. These reviews of corrosion forms and mechanisms are intended to assist the reader in developing an understanding of the underlying principles of corrosion; acquiring such an understanding is the first step in recognizing and analyzing corrosion-related failures and in formulating preventive measures.