Controlling Chloride Stress Corrosion Cracking
The main options for preventing or controlling Chloride Stress Corrosion Cracking CLSCC are management of chloride levels,
temperature, and pH. Inhibitors can also be effective where the process allows it. As noted
above, electrode potential has a major effect on CLSCC susceptibility and while positive
potentials increase cracking, lowering the potential can prevent cracking by cathodic protection. Wrapping with aluminium foil or coating with thermally sprayed aluminium are
established techniques for preventing external CLSCC when the pipework or vessels are
insulated. Austenitic stainless steel heat exchanger tubes are also thought to be
cathodically protected from pitting and CLSCC when used with carbon steel tube plates and
shells.
When components are designed, the susceptibility of CLSCC can be reduced by choosing more
resistant alloys and by lowering the stress. Alloys with greater resistance to CLSCC include
ferritic and duplex (austenitic-ferritic) stainless steel, and alloys containing >42% nickel.
Resistance to CLSCC is usually assessed by ranking alloys on their performance in accelerated
tests using conditions that promote cracking.
The three most common tests, in order of
increasing severity, are boiling acidified sodium chloride, evaporation of sodium chloride using
droplets or a wick on a heated surface, and boiling magnesium chloride. Even high alloy grades
of austenitic and duplex stainless steel containing >22% chromium and >5% molybdenum can
crack in less than 24 hours when tested in boiling magnesium chloride. It should be
recognised, however, that while duplex grades and highly alloyed grades are more resistant than
the common austenitic types, they might not be immune to CLSCC under severe conditions, e.g.
where chloride solutions evaporate.
Stress in components can be lowered by down rating working pressures, but where pipe work
and vessels are fabricated by welding, there is likely to be residual stress (with a magnitude
approximately equal to the parent metal proof stress) from welding. Residual stress may also
arise from cold working during manufacture. A stress relief heat-treatment can lower residual
stress but its application is often limited by concerns over distortion, surface finish and
sensitisation.
Related References:
1. austenitic stainless steel
2. Stress Corrosion Cracking SCC
3. Chloride Stress Corrosion Cracking (CLSCC)
4. Stress Corrosin Cracking SCC of Duplex Stainless Steel
5. Chloride Stress Corrosion Cracking in Austenitic Stainless Steel
6. Recommendations for Assessing Susceptibility to CLSCC
7. Main Findings on CLSCC in the Reactors
8. Literature Review to Chloride Stress Corrosion Cracking
9. CLSCC Chloride Stress Corrosion Cracking Mechanism
10. Factors Affecting CLSCC Chloride Stress Corrosion Cracking
11. Controlling Chloride Stress Corrosion Cracking
12. Structural Integrity Assessment
13. Non-Destructive Examination NDE
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