Environment Sensitive Cracking Research Articles

Environmental Degradation of Marine Aluminum Alloys - Past, Present and Future

Aluminum alloy usage in maritime environments has fluctuated over the past 125 years with localized corrosion or environment sensitive cracking during service repeatedly preventing their full commercial exploitation, despite a series of innovations. Following a historical overview, discussion will focus on aluminum-magnesium alloys, highlighting current corrosion-related issues (e.g., intergranular corrosion, environment sensitive cracking) and potential opportunities to eliminate these problems in future commercial alloys.

Transgranular environment-induced cracking of 7050 aluminium alloy under cyclic loading conditions at low frequencies

The environment sensitive cracking behaviour of alloy 7050 plate in different tempers was studied under cyclic loading conditions using short transverse oriented notched tension specimens immersed in substitute ocean water. The cyclic loading tests were carried out at displacement rates in the range from 2 × 10 −6 to 2 × 10 −4 mm s −1 applying a sawtooth wave form. The maximum load corresponded to an initial stress of 600 MPa, except for alloy 7050-T7651 being loaded up to 500 MPa. Number of cycles to failure decreased with decreasing displacement rate. A linear relationship was found between log values of the number of cycles to failure and the loading frequency. Fractographic examinations of failed specimens revealed brittle transgranular fracture with crack arrest markings on flat facets. The sensitivity to transgranular environment-induced cracking proposed to be associated with hydrogen embrittlement did not depend on heat treatment conditions.

Corrosion Properties of HNS

In this overview passivation mechanisms of high nitrogen steels (HNS) are decribed first and then the various corrosion properties related to general corrosion, pitting corrosion, crevice corrosion, intergranular corrosion (sensitization), stress corrosion cracking and hydrogen embrittlement are summarized based on the present knowledge. The effects of nitrogen on pitting corrosion of stainless steels have been studied most systematically and a number of different mechanisms have been proposed for the effect of nitrogen on pitting and crevice corrosion related to observed synergistic interactions with Mo in the alloy. There is a fairly consistent agreement that N additions improve the pitting corrosion resistance of austenitic and duplex stainless steels by increasing the pitting potential or temperature in aqueous chloride solutions or by decreasing the weight loss in standard FeCl 3 test. There is much less results on the effects of nitrogen alloying on active dissolution or general corrosion, and almost no systematic studies on the effects of N content on environment sensitive cracking of these steels.

A joint action mechanism of anodic dissolution and hydrogen entrance during environment cracking

Environment sensitive cracking refers, mainly, to stress corrosion cracking (SCC) and corrosion fatigue (CF) in aqueous solutions. Presently, the research devoted to environment sensitive cracking primarily focuses on SCC. Compared to SCC, the research of CF is relatively rare. There are some similarities between SCC and CF crackings; although, they are two different kinds of environment sensitive cracking. It is suggested that static stress is a special function of cyclic stress, or cyclic stress is a special function of static stress; therefore, the mechanisms of SCC and CF can be substituted in many cases. There are some limitations to explain crack growth in aqueous solutions using previous SCC or CF mechanism. For example, hydrogen embrittlement (HE) is widely accepted as the principle cause of SCC or CF in high strength steels. Anodic dissolution (AD) is another process believed to propagate cracks by stress assisted corrosion in low strength steels, but a problem arises for the researchers because of their inability to explain the mechanisms of crack growth for high strength steels. Fracture theory of surface film is a successful explanation of crack growth in filmed systems; however, it is not supported in an acidified solution. Although many researchers have triedmore » to propose universal mechanisms of environmental cracking, they have not procured a unified theory. In this paper the authors propose a joint action mechanism of anodic dissolution and hydrogen entrance during environment sensitive cracking based on the electrode reactions at the crack tip, and they also propose a remedy for the weakness of previous mechanisms.« less

Long-Term Predictions Relating to Environment Sensitive Cracking.

ABSTRACTConsideration is given to the environmental requirements of environment sensitive cracking (ESC) of ferritic steels, involving hydrogen-induced or dissolution-related mechanisms of cracking. Pitting, with associated local pH changes, may result in hydrogeninduced cracking of simple ferritic steels, as has been observed with high pressure gas pipelines in contact with ground waters, and may constitute a greater potential failure mechanism for waste containers than dissolution-related cracking with its requirement of relatively concentrated solutions. However, the stochastic nature of pit initiation, together with the distributions of crack nucleation and growth rates, suggest that a probabilistic, as opposed to a purely deterministic, approach will need to be applied to life prediction estimates for waste containers.

Metallography of environment sensitive fracture

Environment sensitive cracks initiate at structurally related sites—grain, twin or interphase boundaries, slip steps or persistent slip bands. That is so even if cracks are initiated from nonstructually dependent pits and whether the mechanism of cracking is essentially dissolution controlled or due to the localized embrittlement of the metal. The subsequent growth of such cracks often, but not invariably, shows the same structural dependence as the initiation stage. The metallography of intergranular, transgranular, and mixed-mode cracking is considered in the context of various metal/environment combinations, together with its implications for some aspects of the mechansims of environment sensitive cracking. Finally, attention is drawn to the importance of the coalescence of environment sensitive cracks, manifest at the microscopic as well as the macroscopic level, in relation to crack growth kinetics and the prediction of the remaining safe life of components.

Cyclic loading effects in the environment sensitive cracking of α-brass

Cyclic loading tests have been carried out on an α-brass exposed to sodium nitrite or soluble arsenic salt solutions to test the hypothesis that environment sensitive crack growth in such systems should be dependent upon the frequency of cyclic loading if the mechanism of crack growth involves film-induced cleavage. No significant effect was observed for changes over a few orders of magnitude of the frequency of load cycling. The results show that continuing micro-plastic deformation is necessary for the initiation and growth of environment sensitive cracks in these systems.

Effects of MnS Inclusion Dissolution on Environmentally Assisted Cracking in Low-Alloy and Carbon Steels

Abstract In fatigue both monotonic and cyclic plastic zones are formed ahead of the crack tip, inside which the strain history can be studied on the basis of stable hysteresis loops and structure anticipated in the crack-tip process zone and in the area of the maximum tensile stress (MTS) ahead of the crack tip. With these materials, slow strain rate tests (SSRT) were performed both in bulk pressurized water reactor (PWR) environments and in the simulated crack tip environments (MnS-contaminated PWR water). Environment-sensitive cracking occurred in the simulated crack tip environment at low corrosion potentials, −550 to −700 mV (vs a standard hydrogen reference electrode [SHE]), and in pure PWR water after anodic polarization to 0.0 mVSHE.

Environment sensitive cracking in pressure boundary materials of light water reactors

A review of the various forms of environment sensitive cracking in pressure boundary materials of light water reactors is presented. The available methods and the most promising future possibilities of preventive maintenance to counteract the environmental degradation are evaluated. Environment sensitive cracking is considered from the metallurgical, mechanical and environmental points of view. The main emphasis is on intergranular stress corrosion cracking of austenitic stainless steels and high strength Ni-base alloys as well as on corrosion fatigue of low alloy and stainless steels. Additionally, some general ideas on how to predict, reduce, monitor or eliminate environment sensitive cracking in service are presented.

Cavallaro Medal Lecture 1985: Inhibitors and environment sensitive fracture

AbstractAlthough there are some well known instances of inhibitors being used to control environment sensitive fracture, the application of this approach to prevention of such failure is less frequent than might be expected. This may be partly a result of some substances, identified by ad hoc tests, not having proved effective inhibitors, and there is a consequent need for a better understanding of how inhibitors operate. The problem is considered from the viewpoint of inhibiting crack tip dissolution controlled growth and hydrogen related cracking, where the requirements of inhibitors are markedly different. Consideration is given to the possibility of stopping growing cracks by the use of inhibitors and some of the dangers in applying experience from inhibiting general corrosion to the control of environment sensitive cracking are indicated.

ChemInform Abstract: Environment‐Sensitive Cracking Problems in Nuclear Installations Containing High Temperature Water

Chemischer InformationsdienstVolume 16, Issue 52 Physical Inorganic Chemistry ChemInform Abstract: Environment-Sensitive Cracking Problems in Nuclear Installations Containing High Temperature Water - -, - -Search for more papers by this author - -, - -Search for more papers by this author First published: December 31, 1985 https://doi.org/10.1002/chin.198552018Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume16, Issue52December 31, 1985 RelatedInformation

Significance of pits, crevices, and cracks in environment-sensitive crack growth

Results are presented which show that for environment-sensitive cracking the changes in environment composition or potential that may occur in pits, crevices, or cracks are probably as important as the stress concentration associated with such discontinuities. However, with some solutions, especially those in which the solvated metal is very slightly soluble and the pH is effectively buffered, the changes of composition and potential in discontinuities will probably be small and less important than the stress concentration. When the stress concentration is appreciable, it is the attendant plastic strain, and even more so the rate of its manifestation, that is important, because of the time dependence of the associated corrosion-related reactions in environment-assisted crack growth.MST/65

Meeting on environment sensitive cracking problems in nuclear installations containing high temperature water

Meeting on environment sensitive cracking problems in nuclear installations containing high temperature water

Environment sensitive cracking of a nickelaluminium bronze under monotonic and cyclic loading conditions

It has been demonstrated that a cast nickelaluminium bronze is susceptible to environment sensitive cracking in natural seawater over a restricted range of potentials in the vicinity of the free corrosion potential. The cracking shows structural sensitivity, being particularly likely to initiate and follow the interfaces of α− κ 1 regions, and is also strain rate sensitive. In monotonic strain rate tests the threshold stress for cracking decreases from the UTS at a strain rate of about 10 −8 s −1 to about 60% of the 0.2% proof stress at a strain rate of about 10 −6 s −1. Cyclic loading at various relatively low frequencies (below 10 Hz) also promotes cracking only above a threshold of about 60% of the 0.2% proof stress. There is some evidence that dwell times interposed between periods of changing stress raise the thresholds somewhat towards the 0.2% proof stress. Crack velocities above the thresholds are in the range 10 −7 to 10 −6 mm s −1, depending upon stressing conditions, although higher crack velocities obtain as stresses rise at faster strain rates to approach conditions for mechanical separation. The effects of strain rate and the observed crack velocities are consistent with a crack growth mechanism that is essentially dissolution controlled.

Environment sensitive cracking of pre-stressing steels

Slow strain rate stress corrosion tests on notched or pre-cracked specimens of pre-stressing steel immersed in Ca(OH) 2 solutions, to which HCl was added where the pH needed to be reduced, have shown that enhanced cracking results at potentials below about − 900 mV, irrespective of pH, and that there is a further regime of environment sensitive fracture at higher potentials, with an intermediate region in which cracking is absent or less severe than at other potentials. The lower potential regime of cracking appears to be related to the ingress of hydrogen into the steel, whereas that at higher potentials occurs when the pitting potential is exceeded and appears to be dissolution-related.

Influence of metallurgical variables on environment-sensitive cracking of austenitic alloys

The influence of metallurgical variables on the environment-sensitive cracking of austenitic Fe—er—Ni alloys, in particular austenitic stainless steels, has been examined. It has been demonstrated that the cracking susceptibility is sensitive to such metallurgical variables as composition, grain size, microstructure, thermal treatment, and radiation damage. Environment sensitive cracking has been classified as selective dissolution of an active path (deformation structures, Cr-depleted zone, and segregations) and hydrogen-induced cracking. The common metallurgical factors involved in stress-corrosion cracking and hydrogen embrittlement of these alloys are identified. Finally, possible aspects of the role and mechanism of hydrogen-induced cracking in environment-sensitive cracking are discussed.

Variation of Potential in Stress Corrosion Cracks

A model due to Doig & Flewitt (‘Mechanisms of Environment Sensitive Cracking of Materials’. 1977.p.113 (London: The Metals Society))for the variation of potential in a stress corrosion crack is examined using more general boundary conditions, which include the electrochemical reactions at the crack tip. Analytic solutions have been obtained for situations where the potential drop is small. Under most conditions of potentiostatic control the potential drop down a crack will be small unless the crack is very long. or unless there is a very large currentflowingfrom the crack tip. Under free corrosion conditions the anodic reactions at the crack tip have to be balanced by cathodic reactions on the surface of the specimen in addition to the cathodic reactions on the sides of the crack.

Influence of metallurgical variables on environment-sensitive cracking of austenitic alloys

Influence of metallurgical variables on environment-sensitive cracking of austenitic alloys