Jingli Luo

Effects of Hydrogen on Pitting Susceptibility of Type 310 Stainless Steel

Abstract Type 310 (UNS S31000) stainless steel (SS) membranes were precharged with hydrogen at various current densities. Effects of hydrogen on pitting susceptibility were investigated by carrying...

Effect of Cathodic Potential on Hydrogen Content in a Pipeline Steel Exposed to NS4 Near-Neutral pH Soil Solution

Abstract The effect of cathodic potential on hydrogen generation and permeation behavior of a X-65 pipeline steel exposed to near-neutral pH NS4 soil environment was studied. The steel-hydrogen int...

Critical hydrogen charging conditions for martensite transformation and surface cracking in type 304 stainless steel

It is well known that the presence of hydrogen in 304 stainless steel can induce martensite transformation and surface cracking in austenitic stainless steels. The change in microstructure would affect the corrosion behavior. Martensite could be preferentially dissolved, which results in an increase in anodic dissolution and facilitates the formation of active paths for stress corrosion cracking. Hydrogen-induced martensite has some effects on pitting corrosion and is also found to be related to hydrogen embrittlement. In previous reports, almost all the results were obtained by charging the specimens at very high cathodic current densities ({ge}50mA/cm{sup 2}). The objective of this work is to investigate the critical charging conditions for hydrogen-induced martensitic transformation and surface cracking of 304 stainless steel.

Role of hydrogen in stress corrosion cracking of austenitic stainless steels

Effects of hydrogen charging on the stress corrosion cracking (SCC) behavior of 304 and 310 stainless steels under sustained load were investigated in boiling 42% MgCl2 solution. The cracking was accelerated by the incorporation of hydrogen into the steel without altering the crack growth mechanism. The fact that the active dissolution is almost unaffected by the hydrogen charging and tensile stress indicates that the phenomenon of hydrogen-promoted SCC is unlikely a result of hydrogen-facilitated active dissolution. In contrast, hydrogen significantly promotes anodic dissolution in the potential range where the active-to-passive transition occurs. The electrochemical noise detected in the SCC process implies that the crack propagation process is discontinuous and hydrogen charging can raise the frequency of film breakdown at the crack tip. These observations suggest that the hydrogen-promoted SCC may result from the hydrogen-induced passivity degradation.

Analysis of the Electrochemical Noise for Localized Corrosion of Type A516-70 Carbon Steel

Abstract Fluctuations of the corrosion potential (Ecorr) and the corrosion current were analyzed in the time domain for type A516-70 carbon steel (UNS K02700) exposed to 0.5 M sodium bicarbonate (N...

Pitting of carbon steel with banded microstructures in chloride solutions

Abstract The pitting corrosion behaviour of carbon steels with different banded microstructures has been investigated in chloride solutions using the in situ scanning reference electrode technique (SRET). The specimen surfaces were inspected with an optical microscope after SRET measurements and the variation of potential over the test surface was compared with the corrosion morphology. The regions of potential drop on the SRET maps are consistent with the sites and sizes of the observed pitting. Pitting susceptibility was found to vary with microstructure of the steel. The surface morphology showed that pits were predominantly initiated on the ferrite bands for specimens with martensite–ferrite microstructures, but preferentially on martensite for specimens with martensite–pearlite structures.

Effects of erosion on corrosion of type 430 and 316 stainless steels in aqueous environments

Abstract The effects of erosion on the corrosion of two types of stainless steel in aqueous 0·5M NaCl and 1M NaCl environments at ambient temperature have been studied using a modified rotating cylinder electrode system. Erosion by silica particles greatly increased the passive current density for both ferritic type 430 and austenitic type 316 stainless steels. It is suggested that two factors were largely responsible for the observed effects. The impact of the eroding silica particles on the specimen surface destroyed the passive film and removed corrosion products from the specimen surface; and impact with the fast moving silica particles generated numerous microplastic deformation sites on the metal surface which were activated owing to the presence of residual stress, dislocations and defects, etc., and the emission of low energy electrons.

Long Seam Welds in Gas and Liquids Pipelines and Near-Neutral pH Stress Corrosion Cracking and Corrosion Fatigue

Near-neutral pH SCC and corrosion fatigue at the toe of the longitudinal weld has been responsible for several pipeline failures in Canada. In this paper examples of such failures and other in-service toe cracks are discussed. The results of an investigation into several factors affecting near-neutral pH SCC at the toe of the longitudinal weld are discussed and summarized. Four different pipes were evaluated including both double submerged arc welded (DSAW) pipe and electrical resistance welded (ERW) pipe. The properties considered were 1) residual stresses near the toe of the weld as determined by hole drilling and slitting, 2) stress-raising characteristics of the weld shape as determined by elastic finite element analysis and 3) electrochemical properties near the toe of the weld as determined by the scanning reference electrode technique. For one line pipe we also evaluated the room-temperature creep characteristics near the weld with and without cyclic loading. The implications of these results for near-neutral pH SCC and corrosion fatigue are discussed. It is concluded that high stresses originating from the stress-multiplying effects of the weld crown contributed significantly to the failures.Copyright