Katsumi Masamura

Polarization Behavior of High-Alloy OCTG in CO2 Environment as Affected by Chlorides and Sulfides

Abstract Pitting corrosion resistance of 13% Cr steel, duplex stainless steel, and high Ni austenitic stainless alloys for Oil Country Tubular Goods (OCTG) has been examined by electrochemical meas...

Critical Contents of Nickel and Chromium Required for SCC Resistance of High Alloy Oil Country Tubular Goods

Abstract Based on the laboratory SCC test results of 10 to 37% Cr, 25 to 45% Ni, 3% Mo, bal. Fe alloys, it is shown that the beneficial effect of increased Ni content on SCC resistance is retained only when the Cr content is appropriate. Good SCC resistance is obtained when the stability of austenite is above a critical value; therefore, the content of ferrite formers, e.g., Cr and Mo, should not exceed a certain limit determined by the content of austenite formers, e.g., Ni. The critical stability of austenite depends on the annealing temperature, a higher temperature requiring a higher stability of austenite.

ENVIRONMENTAL EFFECTS ON CORROSION BEHAVIOR OF STAINLESS STEEL IN A SIMULATED REFUSE INCINERATOR CONDITION

Effects of salt chemistry on corrosion behavior of type 304 SS in a simulated environment are discussed to establish a corrosion test condition for selecting super heater tube material. In NaCl-KCl-Na2SO4-K2SO4 system, amount of chlorides does not affect corrosion rate of type 304 SS at 450 and 500°. Main factor affecting corrosion of type 304 SS in synthetic ash is melting point and volume of fused salt. Below the melting point of an ash, corrosion rate of stainless steel increases with temperature. However, above melting point, corrosion rate is leveling off and independent from temperature, because melt covers the surface of test piece resulting limited gas supply. When chlorides with low melting point (ZnCl2 and PbCl2) were added into salt, corrosion rate increased. However, corrosion rate was independent from temperature above melting point of salt. Addition of Al2O3 that promotes corrosion above melting point of salt, keeps the supply of environment gas to the metal surface.

Statistical characteristics of pit depth observed on inner surface of carbon steel pipes.

Statistical characteristics of pitting corrosion observed under tubacular on carbon steel used for fresh water pipes are discussed. Thirty three cases were analysed using the statistical method. The Gausian distribution was applied for the distribution of pit depth in carbon steel. The mean and standard deviation of pit depth had no dependence on duration of use in practice. The standard deviation of pit depth rather than the mean is a good indicator for the estimation of potential occurrence of penetration. The index, m+3σ, is a good indicator for the occurrence of perforation. The standard deviation and mean of pit depth showed good correlation. It is difficult to estimate the life time of pipes using statistical analysis of pit depth because the law of pit growth is unclear.