Stress corrosion cracking environments

A.J. Forty and P. Humble, Surface Films and Stress-Corrosion Cracking, Environment-Sensitive Mechanical Behavior, A.R.C. Westwood andN.S. Stoloff, Ed., Gordon and Breach, New York,... 

E.A. Charles, R.N. Parkins, Generation of stress corrosion cracking environments at pipeline surfaces. Corrosion 51 (1995) 518-527. 

This is a chromium-nickel-molybdenum alloy, with its composition shown in Table 8.4. It has excellent resistance to chloride pitting and stress corrosion cracking environments. It finds use in the chemical processing and utility industries. 

Table 6.4 Some Stress Corrosion Cracking Environments for Metais...

Table 4.7 shows stress corrosion cracking environments. 

Staehle, R. W., Understanding Situation-Dependent Strength A Fundamental Objective, in Assessing the History of Stress Corrosion Cracking. Environment-Induced Cracking of Metals, Houston, Tfex., NACE International, 1989, pp. 561-612. 

C.-Y. Yu 2007. Analyses of stress corrosion cracking environments of petrochemical equipment. Corrosion and Protection 28 (1), 23-28. 

A process involving combined corrosion and straining of the metal due to residual or applied stresses. The occurrence of stress corrosion cracking is highly specific only particular metal/environment systems will crack. 

Stress corrosion cracking, prevalent where boiling occurs, concentrates corrosion products and impurity chemicals, namely in the deep tubesheet crevices on the hot side of the steam generator and under deposits above the tubesheet. The cracking growth rates increase rapidly at both high and low pH. Either of these environments can exist depending on the type of chemical species present. 

Corrosion control requires a change in either the metal or the environment. The first approach, changing the metal, is expensive. Also, highly alloyed materials, which are resistant to general corrosion, are more prone to failure by localized corrosion mechanisms such as stress corrosion cracking. 

Virtuallv evety alloy system has its specific environment conditions which will prodiice stress-corrosion cracking, and the time of exposure required to produce failure will vary from minutes to years. Typical examples include cracking of cold-formed brass in ammonia environments, cracking of austenitic stainless steels in the presence of chlorides, cracking of Monel in hydrofluosihcic acid, and caustic embrittlement cracking of steel in caustic solutions. 

In addition to the form of attack described above, sensitized welds are prone to pitting, stress-corrosion cracking in certain environments (see Chap. 9), and crevice corrosion (see Chap. 2). 

In concert with the stress environment (stress corrosion cracking, corrosion fatigue)... 

If, after fabrication, heat treatment is not possible, materials and fabrication methods must have optimum corrosion resistance in their as-fabricated form. Materials that are susceptible to stress corrosion cracking should not be employed in environments conducive to failure. Stress relieving alone does not always provide a reliable solution. 

Eliminate unfavorable environments. The presence of oxygen and other oxidizers is a critical factor in stress corrosion cracking. For example, the cracking of austenitic stainless steel in chloride solutions can be reduced or completely eliminated if oxygen is removed. 

The corrosive environments which cause SCC in any material are fairly specific, and the more common combinations are listed in Table 53.2. In the case of chloride stress corrosion cracking of the 530 series austenitic stainless steels it is generally considered that the risk is... 

Steel is the most common constructional material, and is used wherever corrosion rates are acceptable and product contamination by iron pick-up is not important. For processes at low or high pH, where iron pick-up must be avoided or where corrosive species such as dissolved gases are present, stainless steels are often employed. Stainless steels suffer various forms of corrosion, as described in Section 53.5.2. As the corrosivity of the environment increases, the more alloyed grades of stainless steel can be selected. At temperatures in excess of 60°C, in the presence of chloride ions, stress corrosion cracking presents the most serious threat to austenitic stainless steels. Duplex stainless steels, ferritic stainless steels and nickel alloys are very resistant to this form of attack. For more corrosive environments, titanium and ultimately nickel-molybdenum alloys are used. 

The presence of stress raisers, including sharp comers and imperfect welds, produces locally high stress levels. These should be avoided where possible or taken into account when designing the materials for use in environments in which they are susceptible to stress corrosion cracking or corrosion fatigue. 

Certain environments containing nitrate, cyanide, carbonate, amines, ammonia or strong caustic, due to the risk of stress corrosion cracking. Temperature is an important factor in assessment of each cracking environment ... 

Hardness, including surface hardness, especially for materials for sour service or environments in which stress corrosion cracking is expected. It is also important where erosion corrosion is likely ... 

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