Cracking intergranular

Some manufacturers have experienced die above mentioned Ni3S2 scale formation phenomenon under certain gas conditions, which led to die failure of a rotating blade. One such experience involved a fracture dial was distinctly intergranular with evidence of secondary intergranular cracks or grain separation across die fracture. Intergranular facets of die fracture were sharp and distinct with little evidence of any ductile mode. The fracture appeared to have occurred in a brittle intergranular mode. 

Embrittlement embrittlement and for improperly heat treated steel, both of which give intergranular cracks. (Intercrystalline penetration by molten metals is also considered SCC). Other steels in caustic nitrates and some chloride solutions. Brass in aqueous ammonia and sulfur dioxide. physical environments. bases of small corrosion pits, and cracks form with vicious circle of additional corrosion and further crack propagation until failure occurs. Stresses may be dynamic, static, or residual. stress relieve susceptible materials. Consider the new superaustenitic stainless steels. 

Zehr, S. W., A Study of the Intergranular Cracking of U-7-5wt.%Nb-2-5wL Zr (Mulberry) Alloy in Aqueous Chloride Solutions , Corrosion, 28, 196 (1972)... 

For normal commercial-quality mild steels in the annealed or normalised conditions in which they are almost invariably used, various workers have shown that the carbon content of the steel is the major factor determining intergranular cracking susceptibility. Figure 8.13 shows the threshold stresses for a series of commercial mild steels of different carbon contents caused to crack in boiling 4n NH4NO3. The trend of the result suggests... 

Fig. 8.34 Intergranular cracking of sensitised type 316 stainless steel tested in air-saturated water at 7S°C containing 5 ppm chloride...

Fig. 8.35 Reduction in area versus applied potential for 316 stainless steel, in 5 ppm chloride content water at 250°C. Horizontal arrows indicate RA% for tests in argon gas open-annealed, filled-sensitised. Vertical downward pointing arrows on the annealed curve indicate cracking-non-cracking boundaries. Full downward pointing arrow on the sensitised curve indicates commencement of cracking. Open upward pointing arrow on the sensitised curve indicates transition from transgranular to intergranular cracking...

S.C.C. has been examined as a function of potential in high-temperature water with chlorides present and an increased susceptibility of stainless alloys to intergranular attack was found as the potential was increased. Additional work reported that no intergranular cracking was observed in tests of short duration. 

In Section 1.1 corrosion was defined simply as the reaction of a metal with its environment, and it was emphasised that this term embraces a number of concepts of which the rate of attack per unit area of the metal surface, the extent of attack in relation to the thickness of the metal and its form (uniform, localised, intergranular, cracking, etc.) are the most significant. The rate of corrosion is obviously the most important parameter, and will determine the life of a given metal structure. Whether or not a given rate of corrosion can be tolerated will, of course, depend upon a variety of factors such as the thickness of the metal, the function and anticipated life of the metal structure and the effect of the corrosion products on the environment, etc. 

A3. K. Ishii, K. Maeda, R. Chiba, and K. Ohnishi, Intergranular Cracking of C-0.5Mo Steel in a Hydrogen Environment at Elevated Temperatures and Pressures, 1984 Proceedings, Refining Department, Volume 63, American Petroleum Institute, Washington, D.C., pp. 55-64. 

M. Ammonia plant converter exit piping intergranular cracking and internal decarburization of pipe. 

U. Hydrodesulfurization unit, C-0.5Mo steel exchanger tubesheet decarburized, fissured, and cracked under intergranularly cracked ASTM Type 304 cladding. 

A 960 516 331 2.28 26 1.5 NPS Schedule 80 nozzle was broken off a catalytic reformer outlet line during a shut down. Metallography indicated surface decarburization and intergranular cracking with bubbles. Cr content was 1.09 percent. 

B 977 525 354 2.44 14 Blistering was detected with ultrasonic examination in catalytic reformer piping. Metallography indicated surface decarburization and blistering at non-metallic inclusions, with intergranular cracks growing from the blisters. Cr content was 1.10 percent. 

Corrosion is simply the destruction or deterioration of a material because of a chemical reaction with its environment (4). Types of corrosion range from rust on an automobile to intergranular cracking of a pipe in a gas well. In addition to its economic impact, corrosion affects our health and safety, the development of new technology, the existence of ancient works of art and even, through material availability, national security ( ). 

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