Could phosphorus increase hydrogen sulfide stress corrosion cracking?
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This post was last edited by ards3021 on 2009-12-29 at 13:47. Can phosphides increase stress corrosion cracking caused by hydrogen sulfide?
According to the theory of stress corrosion, stress corrosion occurs only in certain systems. Acidic hydrogen sulfide solutions can cause stress corrosion cracking in carbon steel and low-alloy steel, while phosphorus-containing compounds do not act as passivators in such environments, nor do they seem to accelerate corrosion within cracks. Therefore, I believe that phosphorus-containing compounds do not increase stress corrosion cracking caused by hydrogen sulfide. Personal opinion; awaits authoritative verification.
This depends on the form in which the phosphorus-containing compound exists as a medium; if the acidic compounds formed are strong enough, and the density of the surface film on certain materials is already unreliable, then the presence of phosphorus can have a promoting effect in such cases.
The main factors affecting wet hydrogen sulfide stress corrosion cracking (SSCC) are: pH value, hydrogen sulfide concentration, impurities in the steel, temperature, hardness, microstructure, strength, and tensile stress levels (applied stress or residual stress). I haven’t heard that P compounds in the environment can increase susceptibility to SCCC. However, the S and P contents in steel do affect its susceptibility to SSCC; stress corrosion cracking in a wet hydrogen sulfide environment tends to originate most frequently at impurity inclusions at the grain boundaries. For example, MnS is a typical site where stress cracking begins, and the control requirements for HIC-resistant steel also involve lower S and P contents compared to ordinary steel.
Is the poster asking about the impact of P compounds in the material, or those in the medium, on stress corrosion in a wet H2S environment? If it is the former case, it is advisable to understand the mechanism of stress corrosion cracking in wet H2S environments. Stress corrosion cracking in such environments includes hydrogen blistering (HB)/hydrogen-induced cracking (HIC)/stress-oriented hydrogen-induced cracking (SOHIC)/sulfide stress corrosion cracking (SSCC). The phosphorus content in the material affects HB and HIC; therefore, as mentioned above, in severe wet H2S stress corrosion environments, HIC steel is recommended, and HIC steel is essentially steel with low sulfur and low phosphorus content.
Yes, if not, then why would there be a need to control the levels of impurities such as P and S in steel? High-quality steel has very low levels of P and S, as their presence can lead to corrosion and stress cracking.