Carbon steels cracking

Dilute cyanide-water solutions at ambient temperature can exhibit a unique destructive action on stressed carbon steel. Cracks can develop in the metal in a very short time. The characteristic feature of the cracks is their transcrystalline course without formation of slip planes254. 

There is experimental evidence reported in the literature that carbon steel cracks in nitrates that form low melting compounds with iron however, it also cracks when in contact with the high melting point magnetite [64]. Other experimental evidence provided by Oriani [65] shows that the flow of the surface atoms and ions is toward the crack tip instead of the crack walls. It has also been discussed in the Hterature whether there is enough force to drive diffusion of metals and the surface vacancy formation [45]. 

Fig. 2. Typical rf signal from a 28 mm deep fatigue crack in 56 mm thick carbon steel sample...

Prompted by the success, TOFD measurements were conducted on a fatigue crack in a stainless steel compact tension specimen. Test and system parameters were optimised following the same procedure used for carbon steel specimens. A clear diffracted signal was observed with relatively good SNR and its depth as measured from the time-of-flight measurements matched exactly with the actual depth. 

Shipment nd Stora.ge, Sulfur monochloride is minimally corrosive to carbon steel and iron when dry. If it is necessary to avoid discoloration caused by iron sulfide formation or chloride stress cracking, 310 stainless steel should be used. Sulfur monochloride is shipped in tank cars, tank tmcks, and steel dmms. When wet, it behaves like hydrochloric acid and attacks steel, cast iron, aluminum, stainless steels, copper and copper alloys, and many nickel-based materials. Alloys of 62 Ni—28 Mo and 54 Ni—15 Cr—16 Mo are useful under these conditions. Under DOT HM-181 sulfur monochloride is classified as a Poison Inhalation Hazard (PIH) Zone B, as well as a Corrosive Material (DOT Hazard Class B). Shipment information is available (140). 

Materials of Construction. GeneraHy, carbon steel is satisfactory as a material of construction when handling propylene, chlorine, HCl, and chlorinated hydrocarbons at low temperatures (below 100°C) in the absence of water. Nickel-based aHoys are chiefly used in the reaction area where resistance to chlorine and HCl at elevated temperatures is required (39). Elastomer-lined equipment, usuaHy PTFE or Kynar, is typicaHy used when water and HCl or chlorine are present together, such as adsorption of HCl in water, since corrosion of most metals is excessive. Stainless steels are to be avoided in locations exposed to inorganic chlorides, as stainless steels can be subject to chloride stress-corrosion cracking. Contact with aluminum should be avoided under aH circumstances because of potential undesirable reactivity problems. 

Although hydrogen cyanide is a weak acid and is normally not corrosive, it has a corrosive effect under two special conditions (/) water solutions of hydrogen cyanide cause transcrystalline stress cracking of carbon steels under stress even at room temperature and in dilute solution and (2) water solutions of hydrogen cyanide containing sulfuric acid as a stabilizer severely corrode steel (qv) above 40°C and stainless steels above 80°C. 

Figure 11.7 shows how the mechanical properties of normalised carbon steels change with carbon content. Both the yield strength and tensile strength increase linearly with carbon content. This is what we would expect the FejC acts as a strengthening phase, and the proportion of FojC in the steel is linear in carbon concentration (Fig. 11.6a). The ductility, on the other hand, falls rapidly as the carbon content goes up (Fig. 11.7) because the a-FejC interfaces in pearlite are good at nucleating cracks.

Other examples of metallurgy decisions are red brass versus admiralty tubes with fresh water on the tubeside and suspected stress corrosion cracking conditions on the shellside, and stainless steel versus carbon steel with chlorides present. A good metallurgist should be brought in when these kinds of decisions are needed. 

Ignoring alkaline service. Just because strong alkalies do not cause severe overall corrosion in carbon steel or stainless steel, don t overlook stress coito-sion, cracking, or effects on other materials. 

The vessel is generally constructed of carbon steel that has been heat treated. Control of metal hardness is required because of the potential of sulfide-stress cracking. The iron-sponge vessel is either internally coated or clad with stainless steel. 

As the result of a heater failure, the temperature of the vessel, designed for -29°C, fell to -60°C by evaporative cooling (see Section 10.5.2) at this temperature carbon steel becomes brittle, and cracking may have started. 

Fig. 8.11 Effect of beam deflection rate of cantilever beam specimens upon stress-corrosion crack velocity of carbon steel in carbonate-bicarbonate solution...

Fig. 8.14 Effect of carbon content of very low carbon steels quenched from 920°C on cracking in a calcium nitrate-ammonium nitrate solution (after Long and Uhlig")...

---