Chloride stress cracking

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). 

When reviewing the materials of construction consider external corrosion concerns. Chloride stress cracking of stainless steel can be initiated by insulation capturing chlorides or insulation that contains chlorides (stainless steel should be primed). A weather barrier is needed. The principle here is to understand the potential hazards and their mechanisms. 

Chloride salts (sodium chloride, potassium chloride) tend to interfere with the formation of a protective layer over metals. Chloride salts destroy the passivity of some stainless steels and cause them to fail by rapid cracking under tensile stress at temperatures higher than about 176°F (80°C). This type of failure is called chloride stress cracking (CSC) [186,194]. 

Chloride stress cracking corrosion was also a problem when austenitic stainless steels were covered with thermal insulation. The NACE Paper also discusses the protective coatings for stainless steels and provides sandblasting and coating application guides for stainless and carbon steels. 

The quality of cooling water and steam must he considered when selecting materials of construction. The chosen materials may be resistant on the process side, but fail on tbe utility side. For example, 316 stainless steel may be applicable for vertical heat exchanger tubing that handles a weak organic acid on the process side, but it may fail from chloride stress cracking on the waterside. A duplex stainless steel may be a better choice. 

The presence of catalyst residues (e.g. from Ziegler-Natta catalyst systems) in a polymer matrix generates free acidity after the catalyst deactivation by steam stripping or solvent treatment. Antacids neutralize this acidity and prevent thereby many undesired side effects such as corrosion of processing equipment, chloride stress-cracking etc. [1]. 

The austenitic stainless steels resist hydrogen effects, but martensitic and precipitation-hardening alloys may be susceptible to both hydrogen stress cracking and chloride stress cracking. 

Only ferritic stainless steels are generally immune to both hydrogen and chloride stress cracking. 

The general corrosion resistance of type 329 stainless is slightly above that of t) e 316 stainless in most media. In addition, because the nickel content is low, it has good resistance to chloride stress cracking. 

On average, the general corrosion resistance is below that of t) e 304 stainless. However, the corrosion resistance of t) e PH 15-7 Mo alloy approaches that of type 316 stainless. The martensitic and semiaustenitic grades are resistant to chloride stress cracking. These materials are susceptible to hydrogen embrittlement. 

BRUSH ALLOY 25, a heat-treatable beryllium copper product contains 1.80 to 2.00% beryllium. BRUSH ALLOY 25 is resistant to hydrogen embrittlement, and not susceptible to either sulfide stress cracking or chloride stress cracking. Moreover, in marine and certain industrial environments this alloy outperforms stainless steel, titanium, and most copper based alloys. Beryllium copper is available in a wide range of forms, including strip, tube, rod, bar, extrusions, casting and master alloy, and forging billet. 

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