Carbon steel stress corrosion cracking

Hydrochloric acid can result in pitting and stress corrosion cracking. Carbon steels can tolerate a relatively high corrosion rate during hydrochloric acid cleaning, provided an inhibitor is added, because cleaning operations are short and other damage mechanisms are not a factor. 

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. 

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. 

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. 8.21 Current density dilTerences between fast and slow sweep rate polarisation curves and stress corrosion cracking suspectiblity as a function of potential for a C-Mn steel in nitrate, hydroxide and carbonate-bicarbonate solutions...

Stress-corrosion cracking (Section 8.10) New metal/environment combinations which produce stress-corrosion cracking are continually being found. Combinations discovered in service in recent years include titanium in red fuming nitric acid carbon steel in liquid anhydrous ammonia and in... 

For carbon steels, however, a full stress-relief heat treatment (580-620°C) has proved effective against stress-corrosion cracking by nitrates, caustic solutions, anhydrous ammonia, cyanides and carbonate solutions containing arsenite. For nitrates, even a low-temperature anneal at 350°C is effective, while for carbonate solution containing arsenite the stress-relief conditions have to be closely controlled for it to be effective . 

To prompt inhibitor addition to a gas scrubbing system solution prone to cause stress-corrosion cracking of carbon steel when the potential moves towards a value at which stress-corrosion cracking is known to occur. 

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