Stress Corrosion Tests Research Articles

Stress Corrosion Cracking in Fibreglass Composite Structures - A Case Study

One failure mechanism experienced by fibreglass composite structures is stress corrosion cracking, which occurs in structures under load in a corrosive environment. Over time, stress corrosion cracking attacks the glass fibres, which weakens the structure and can lead to premature failure. Stress corrosion cracking failure is characterized by flat fracture surfaces perpendicular to the fibres at both the macroscopic and microscopic levels. Prevention of stress corrosion cracking includes proper selection of fibre and resin, and use of a protective layer between the glass fibres and the environment. Fibreglass structures that have failed due to stress corrosion cracking include chemical tanks, sewer pipe and pressure vessels. This paper describes the phenomenon of stress corrosion cracking in fibreglass composite structures. It also presents, as a case study, the investigation of the failure of a fibreglass overwrapped compressed air cylinder, used in a self-contained breathing apparatus. The failure was attributed to stress corrosion cracking following exposure to a highly acidic cleaning fluid. The cause of the failure was determined based on the results of fractography, chemical analysis, and stress corrosion tests performed on samples of the accident cylinder.

Stress Corrosion Cracking in Fibreglass Composite Structures - A Case Study

One failure mechanism experienced by fibreglass composite structures is stress corrosion cracking, which occurs in structures under load in a corrosive environment. Over time, stress corrosion cracking attacks the glass fibres, which weakens the structure and can lead to premature failure. Stress corrosion cracking failure is characterized by flat fracture surfaces perpendicular to the fibres at both the macroscopic and microscopic levels. Prevention of stress corrosion cracking includes proper selection of fibre and resin, and use of a protective layer between the glass fibres and the environment. Fibreglass structures that have failed due to stress corrosion cracking include chemical tanks, sewer pipe and pressure vessels. This paper describes the phenomenon of stress corrosion cracking in fibreglass composite structures. It also presents, as a case study, the investigation of the failure of a fibreglass overwrapped compressed air cylinder, used in a self-contained breathing apparatus. The failure was attributed to stress corrosion cracking following exposure to a highly acidic cleaning fluid. The cause of the failure was determined based on the results of fractography, chemical analysis, and stress corrosion tests performed on samples of the accident cylinder.

Hot salt stress corrosion resistance of Ti 6246 alloy

Hot salt stress corrosion tests have been performed on Ti 6246 smooth test samples, under simulated gas turbine working conditions. The test procedure has been optimised to be representative of these working conditions. The sample lifetime is measured and a mean crack velocity is determined. A model based on surface self diffusion of the aggressive species has been developed to describe the cracking. The influence of the temperature on the model parameters is discussed.

Stress Corrosion Testing of a Superplastically Deformed Aluminum-Lithium Alloy

Abstract An investigation was conducted to study the stress corrosion cracking (SCC) tendency of a superplastically deformed aluminum-lithium-based alloy (AA X2094 [UNS A92094]) that had been received in a thermomechanically processed form suitable for dynamic recrystallization. Tensile specimens made from sheets of this material were superplastically deformed at a constant true strain rate of 2 × 10−4/s and a temperature of ∼ 500°C. Specimens then were subjected to stress corrosion testing using the slow strain rate tensile testing (SSRT) technique at a constant initial strain rate of 2 × 10−6/s. Effects of different superplastic deformation variables and stress corrosion testing conditions on the stress-strain relationship of the test specimens were studied.

Material factors influencing notch tip strain rate

AbstractWhen precracked or notched specimens are used in slow strain rate stress corrosion testing, it is the local strain rate at the crack or notch tip and not the global strain rate or externally applied testing displacement rate that governs the process. This paper presents computational results from an elastic-plastic finite element analysis of notched specimens, demonstrating that the relationship between local and global strain rates depends not only on the specimen geometry but also on the stress-strain curve of the material and on the load applied on the specimen (the latter two factors controlling the plastic strain distribution in the overall geometry, particularly in the vicinity of the notch tip), which implies that local strain rate changes with time, even for a constant global strain rate externally applied, as in the case of slow strain rate tests. It is shown that the evolution (or variation with time) of the notch tip strain rate depends on the spreading of the plastic zone and thus on t...

Effet d'un grenaillage de précontrainte sur la résistance à la corrosion sous contrainte de l'alliage de titane Ti 6246

Hot salt stress corrosion tests performed on a specific test bench have revealed a suceptibility of the tested material to hot salt stress corrosion cracking. This alloy may have to face the applied stress corrosion conditions in service when it is used to realise gas turbine compressors. It is, therefore, necessary to apply a surface treatement to this material that protects it from the corrosion effect. The benefical effect of shot peening is evaluated in this paper. We see that this surface treatment provides a protective effect that remains efficient up to 500 °C.

Esis technical committee 10 “environmentally assisted cracking”

We present a brief sketch of the history of creation of the Technical Committee 10 on “Environmentally Assisted Cracking” at the ESIS and outline its principal tasks. They are based on the application of the approaches of fracture mechanics to the investigation of the processes of corrosion cracking and corrosion fatigue. Since 1990, the TC 10 has organized six meetings with 154 participants from 15 countries. Recent years are marked by a significant increase in the number of participants from the countries of Eastern and Central Europe. As an achievement of the TC 10, one can also mention the appearance of a series of methodical works, in particular, by R. J. H. Wanhill “Fracture Control Guidelines for Stress Corrosion Cracking of High Strength Alloys” and by G. Gabetta and I. Cole “Fracture Control Guidelines for Environmentally-Assisted Cracking of Low-Alloy Steels.” In addition, the TC 10 developed the first draft of “Recommendations for Stress Corrosion Testing Using Precracked Specimens” (ESIS Document P4-92D). In future, the attention of the TC 10 will also be given to the development of procedures for the evaluation of lifetime, investigation of the mechanisms of corrosion cracking and corrosion fatigue, and simulation of these processes.

Hardness and stress-corrosion of rubber dam clamps

Rubber dam clamps fracture infrequently during use. There are no American National Standards Institute or International Standards Organization standards for their manufacture. The purpose of this study was to measure the hardness of the clamps and test their resistance to a stress-corrosion test. Upper molar, lower molar, and premolar clamps were obtained from two manufacturers (A, B). The Rockwell C hardness at four sites on the bow of each clamp was then determined. Fresh clamps were placed on blocks corresponding to the average buccal-lingual dimension of the tooth on which they would be used. These blocks were then submerged in room temperature 5.25% sodium hypochlorite for 20 min and then allowed to air dry for 30 min. This was repeated 10 times. Rockwell C hardness values ranged from C30 to 38, with the clamps of manufacturer B being significantly harder. None of the clamps from manufacturer B cracked or corroded. When a third batch received from manufacturer A was tested in the same manner, none of the clamps fractured or corroded either.

Stress corrosion monitoring of 7000 series aluminium alloy welded specimens using acoustic emission

AbstractAcoustic emission (AE) was continually monitored during stress corrosion tests on weldable aluminium alloys (7000 series) supplied by the Defence Research Agency of the UK Ministry of Defence to progress the investigation and understanding of stress corrosion in differently treated aluminium alloys. The welded structures were exposed under known stress conditions to two corrosive environments (marine and humid). The monitored AE activity enabled the crack initiation and propagation associated with stress corrosion cracking to be detected. The different nature of the two environmental conditions to which all of the aluminium alloy specimens were exposed under load greatly influenced the stress corrosion cracking propensity of the alloys. The humid environment was found to be more aggressive than the marine environment, resulting in more rapid crack initiation and failure within the alloys tested. It was concluded that differences in alloy composition and surface treatment had a profound effect on t...

Local strain rate at crack tip: implications in stress corrosion cracking

Local strain rate at a crack tip of a cracked cylindrical specimen was calculated as a function of the global strain rate externally applied to the specimen ends. The results demonstrate that local strain rate increased with time (as the load increased and the plastic zone spread), even when the global strain rate remained constant, as in the case of an externally applied constant displacement rate. In axisymmetric specimens, the crack tip strain rate increased quasilinearly as straining proceeded, whereas in the plane strain specimens the relationship between local and global strain rate was almost constant when a certain strain level was reached. The application of these results to stress corrosion testing is discussed.

The effect of retrogression and reaging on the resistance to stress corrosion of an 8090 type aluminium alloy

The influence of retrogression and reaging (RR) treatment on the resistance to stress—corrosion cracking of a commercial Al Li 8090 alloy was investigated. The retrogression was performed for various times at temperatures in the range 200–260°C. The reaging treatment was carried out at 170°C. Stress corrosion tests were performed using C-ring specimens and by alternate immersion. Changes in the microstructure of the material near the grain boundaries were studied by transmission electron microscopy. It was shown that RR treatment substantially improved the resistance to SCC of the alloy. As with 7000 type Al alloys, the RR treatment brings about the dissipation of dislocations; the greater the extent of dissipation of dislocations, the greater the resistance to SCC. Another factor which, possibly, affects the sensitivity to stress—corrosion in this alloy is the presence of the δ′ precipitates near the grain boundaries. The best results on SCC resistance were obtained for retrogression performed for 30 min at 260°C followed by reaging. For such treatment a zone completely free of δ′ precipitates was developed near the grain boundaries.

Influence of Stress and pH on Susceptibility of Copper-Containing Type 304 Stainless Steels to Stress Corrosion Cracking in Sulfuric Acid

Abstract Stress corrosion tests on type 304 (UNS S30400) stainless steels (SS) with 0.3 wt% or 1.3 wt% Cu addition were conducted in hot sulfuric acid (H2SO4)-sodium hydroxide (NaOH) solutions under constant loads. Cracking susceptibility, corrosion morphology, average crack growth rate (CGR), and average uniform corrosion rate were examined as functions of pH, sulfate ion (SO42−) concentration, and applied stress. The steel with 0.3 wt% Cu exhibited stress corrosion cracking (SCC) from pH 0.3 to 2.4, in which range the CGR was greater than the corrosion rate. The steel with 1.3 wt% Cu exhibited pit-like attack, crevice corrosion, pit-like attack with cracking, or cracking, depending upon pH (−0.3 to 0.3) and stress level (150 MPa to 325 MPa).

Study of stress corrosion behaviour of laser welded superduplex stainless steels

Summary Superduplex (i.e. with PRE [pitting resistance equivalent] number over 40) SAF 2507 stainless steel (25Cr‐7Ni‐4Mo‐0.3N) rolled sheets, with a thickness of 3 mm, were used for this research. The sheets were laser welded (5 kW, 2.3 m/min) and corrosion tested in H2SO4 solutions with various chloride concentrations; stress corrosion tests (slow strain rate, 1 × 10‐6 sec‐1) were also conducted in the same solutions. The results obtained showed excellent chemical and mechanical behaviour in the welded joints. In the stress corrosion tests, only the solution with greater chloride concentration caused fracture in the weld bead, while under all other test conditions fracture occurred in the base metal, well away from the bead. These results were correlated with the information gathered from microstructural analysis, carried out by optical and electron microscopy. It has been verified that the laser welding process can also be effective with superduplex stainless steels, to achieve chemically and mechanica...

Fractal characteristics of stress corrosion cracking in SNCM 439 steel having different prior-austenite grain sizes

An approach by fractal geometry was examined for the SCC problem on a NiCrMo steel. Stress corrosion tests were conducted in 3.5% NaCI solution by using SNCM439 steel specimens. These specimens had different prior-austenite grain sizes due to variations in heat treatment. After summarizing the results of analysis, we explain the profiles of stress corrosion cracks having fractal characteristics. The relevant fractal dimension D was about 1.05 for the region where the intergranular cracking was predominant, while D was about 1.10 for the region having mixed fracture of intergranular and transgranular cracking. The fractal analysis concluded that the crack growth rate da dt depends on the grain size d, but not stress intensity factor K. The investigations of crack growth phenomena were seen to be an important factor to explain the mechanism.

New and powerful method for the evaluation of multiparameter corrosion tests

A new method for the evaluation of corrosion and stress corrosion tests performed with cementitious materials has been developed. The method is based essentially on a transformation of the strength-time data obtained usually from corrosion experiments. Results of the application of the method to the evaluation of stress corrosion data from cement mortars in aqueous ammonium salt solutions are discussed.

SEM observations on stress corrosion cracking of commercially pure titanium in a topical fluoride solution

Objectives. The purpose of the present study was to determine whether commercially pure titanium is susceptible to stress corrosion cracking/hydrogen embrittlement in a topical fluoride solution used in preventive dentistry. Methods. Thin electropolished titanium test specimens were previously cold-rolled or cold-rolled and annealed before testing. For the stress corrosion tests, the U-shaped specimens of both treatment types were stressed into a radius of curvature of 30 mm. Then, the bent part was placed in the fluoride solution at 37°C for 1, 5, 10, and 20 d. The effects of the fluoride solution on cold-rolled and annealed titanium were studied using a scanning electron microscope. In addition, mechanically fractured surfaces of cold-rolled titanium specimens exposed and not exposed to the fluoride solution were examined by SEM. A qualitative evaluation of the surfaces was conducted. Results. Narrow cracks were observed in cold-rolled specimens following exposure to the fluoride solution for 5 d. The cracks were associated with branching, a characteristic of stress corrosion cracking. The cold-rolled specimen exposed to the fluoride solution exhibited a brittle fracture. In contrast, the fracture mode of the unexposed specimen was ductile in nature. Significance. Topical fluoride solutions can cause stress corrosion cracking of commercially pure titanium.

Galvanostatic, Creviced Stress Corrosion Test for Austenitic Stainless Steels in Hot Chloride Solutions

Abstract Stow strain rate (SSR) tests were carried out on creviced specimens of austenitic stainless steels (SS) using mild anodic galvanostatic polarization, which maintained the potential just above the repassivation potential (ER) for crevice corrosion regardless of variations in ER with time. Various problems were encountered, such as gradual opening of the crevice, but these mainly resulted from use of the SSR test. The galvanostatic method was simpler than painstaking determination of the limiting value of ER followed by potentiostatic testing just above this potential.

STRESS CORROSION CRACKING OF THE ALZN5MG1 ALLOY

The results of stress corrosion and corrosion tests of the AlZn5Mg1 alloy of different tempers are shown to be related to test solution composition. The most susceptible to stress corrosion cracking was the underaged alloy tested under constant load in HC1- containing solutions. The comparison of stress corrosion and corrosion tests shows that the cracking may be considered in terms of hydrogen-related crack propagation. The remarkable degradation of the underaged alloy is assumed to relate to the grain boundary microstructure.

Stress corrosion cracking of copper-nickel alloys in sulphide polluted natural seawater at moderate temperatures

A stress corrosion study on copper-nickel alloys commonly used as condenser and heat exchanger materials in marine environments has been conducted in sulphide polluted seawater. The study aimed to determine the susceptibility of 90Cu10Ni and 70Cu30Ni alloys to stress corrosion cracking (SCC) in natural seawater with and without sulphide at moderate temperatures. The stress corrosion tests were carried out in a slow strain machine. The tests were performed over a range of temperature, 25–70°C, under a constant strain rate of 1.4×10 −6 S −1 in 200–3120 ppm S −2 in seawater solutions. The concentration range was chosen in a way to simulate the pollution impact of the oil spill and oil fires in the marine environment of Kuwait. The behavior of the alloys under various conditions has been evaluated by comparing the ratio of ultimate tensile stress, elongation, and time to failure of samples tested in solution to those tested in air. In addition, confirmation of SCC and the nature of the fracture mode has been achieved by applying metallographic techniques as well as by examination of the failed samples by a scanning electron microscope (SEM).

Stress-Corrosion Cracking in Equiaxed 7075 Aluminum under Tension and Torsion Loading

The environmental response of commercially produced high-strength Al alloys, such as 7075, depends strongly on the anisotropy of the grain structure. Minimum resistance to both stresscorrosion cracking (SCC) and hydrogen embrittlement is observed in the short transverse direction of the “pancake” grain structure in commercially produced alloys. It has not been established, however, exactly how the morphology of the grain structure mediates the SCC response or the SCC mechanism. Therefore, stress-corrosion testing of a high-purity 7075 Al alloy (low in Fe, Si, and Cr), having equiaxed grains, under tension (mode I) and torsion (mode III) loading in a solution of IN A1C13 has been performed. The SCC results in the two loading modes, including fractography, appeared to suggest that the predominant processes of SCC were hydrogen embrittlement in mode I and anodic dissolution in mode III, in agreement with prior work on a commercially produced 7075 alloy, but that severe corrosion during longer tests renders those results unsuitable for threshold determination in this very aggressive testing environment.