Hydrogen-assisted stress

HSCC - Hydrogen- assisted stress-corrosion cracking. 

The load is apphed as a rising step load or step-modified slow strain rate testing protocol under displacement control that measures the threshold load for the onset of hydrogen assisted stress cracking by a drop in load that can be used as a quantitative, accelerated (S24 h) test method. Equivalence between the displacement control test method is assumed to occur when the threshold load in the accelerated test is >75 % of the notched ftBcture strength of the square bar in bending. 

Hydrogen embrittlement, 428 Hydrogen production increase (catalyst poisoning), 164-165 Hydrogen sulfide, 90,106,111—112, 116, 133, 144, 173, 421-422 Hydrogen-assisted stress corrosion cracking, 90... 

To a lesser extent, the above warning applies to all amine systems. The presence of carboxylic acids produced from heat-stable salts, overloaded amine, and cyanides accelerates the process of hydrogen-assisted stress-corrosion cracking. 

Often massive corrosion failures occur suddenly, without the warning of any small leaks. Lines part at welds, vessels burst apart as a result of hydrogen-assisted stress corrosion cracking, and thin elbows peel back like the top of a soup can. Process plants are dangerous places, mainly because of corrosion hence the importance of monitoring corrosion. It is the responsibility of the imit chemical or process engineers to monitor corrosion on their units. 

Figure 46.2 Hydrogen-assisted stress corrosion crack causes vessel to fail.

Of course, the cracked weld was not a result of corrosion that day, or that week, or that month. The crack was a result of hydrogen activity and pressure accumulation inside the vessel wall for the past decade. It was a result of 10 years of proton penetration of the vessel wall. However, the final effect appeared suddenly. That s the nature of hydrogen-assisted stress corrosion cracking. 

To proceed with simulations of stress-assisted diffusion with rather modest computational facilities available, it turned out to be indeed necessary to reduce the FEM-problem size. Among two possible approaches, i.e., coarsening of the mesh of the modelled "full-scale" specimen or shrinking the domain of diffusion simulation focusing on the locations of prospective hydrogen assisted fracture initiation near the notch, the second one seems to be preferable. The relevant data about stress fields may be transferred to this domain from the full scale mechanical analyses, performing their interpolation for the finite element mesh for diffusion, if convenient. 

The numerical approach presented in this paper allows one to calculate the distribution of hydrogen in stressed solids with limited expenditure of computer resources. Its generalization for the case of stress and strain assisted diffusion is straightforward. 

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