Synthetic Soil Solution Research Articles

Electrochemical Noise Analysis of the X70 Pipeline Steel under Stress Conditions Using Symmetrical and Asymmetrical Electrode Systems

In this work, electrochemical monitoring of stress corrosion cracking (SCC) behavior of a X70 steel in acidic synthetic soil solution during the slow strain rate test (SSRT) was performed by electrochemical noise (EN) using the conventional arrangement of symmetrical electrodes and electrochemical emission spectroscopy (EES) using the asymmetrical arrangement replacing the second working electrode for a platinum micro-cathode. The statistical method, fast Fourier transform, and discrete wavelet transform were used for analyzing the potential and current signals recorded by both arrangements. The results showed that EN arrangement was more effective to detect the crack initiation at a point close to yield strength despite stress-induced asymmetry in one of the electrodes. For the EES arrangement, the micro-cathode had a strong influence on the electrochemical noise of the current and potential under stress conditions. From the transient features, statistical parameters, and wavelet analysis, a discontinuous transgranular SCC mechanism was found. The resistance values obtained by EN measurements had better correlation with the electrochemical impedance spectroscopy results (EIS) than EES measurements.

Selective Diffusive Gradients in Thin Films (DGT) for the Simultaneous Assessment of Labile Sr and Pb Concentrations and Isotope Ratios in Soils.

A method using diffusive gradients in thin films (DGT) for the accurate quantification of trace-level (μg L–1) Sr and Pb concentrations and isotope ratios [δSRM 987(87Sr/86Sr) and δSRM 981(207Pb/206Pb)] in labile, bioavailable element fractions in soils is reported. The method is based on a novel poly(tetrafluoroethylene) (PTFE) membrane binding layer with combined di(2-ethyl-hexyl)phosphoric acid (HDEHP) and 4,4′(5′)-bis-t-butylcyclohexano-18-crown-6 (crown-ether) functionality with high selectivity for Sr and Pb (TK100 membrane). Laboratory evaluation of the TK100 DGT showed linear uptake of Sr over time (2–24 h) up to very high Sr mass loadings on TK100 membranes (288 μg cm–2) and effective performance in the range of pH (3.9–8.2), ionic strength (0.001–0.1 mol L–1), and cation competition (50–160 mg L–1 Ca in a synthetic soil solution matrix) of environmental interest. Selective three-step elution of TK100 membranes using hydrochloric acid allowed us to obtain purified Sr and Pb fractions with adequate (≥75%) recovery and quantitative (≥96%) matrix reduction. Neither DGT-based sampling itself nor selective elution or mass loading effects caused significant isotopic fractionation. Application of TK100 DGT in natural soils and comparison with conventional approaches of bioavailability assessment demonstrated the method’s unique capability to obtain information on Sr and Pb resupply dynamics and isotopic variations with low combined uncertainty within a single sampling step.

Corrosion Study of Pipeline Steel under Stress at Different Cathodic Potentials by EIS

The effect of different cathodic potentials applied to the X70 pipeline steel immersed in acidified and aerated synthetic soil solution under stress using a slow strain rate test (SSRT) and electrochemical impedance spectroscopy (EIS) was studied. According to SSRT results and the fracture surface analysis by scanning electron microscopy (SEM), the steel susceptibility to stress corrosion cracking (SCC) increased as the cathodic polarization increased (Ecp). This behavior is attributed to the anodic dissolution at the tip of the crack and the increment of the cathodic reaction (hydrogen evolution) producing hydrogen embrittlement. Nevertheless, when the Ecp was subjected to the maximum cathodic potential applied (−970 mV), the susceptibility decreased; this behavior is attributed to the fact that the anodic dissolution was suppressed and the process of the SCC was dominated only by hydrogen embrittlement (HE). The EIS results showed that the cathodic process was influenced by the mass transport (hydrogen diffusion) due to the steel undergoing so many changes in the metallic surface as a result of the applied strain that it generated active sites at the surface.

Electrochemical Noise for Detection of Stress Corrosion Cracking of Low Carbon Steel Exposed to Synthetic Soil Solution

Summary of the mechanical properties obtained from SSRT of X52 steel. Environment YS (MPa) RS (MPa) UTS (MPa) E (GPa) Strain (%) EL (mm) TF (h) RA(%) PE (%) Air 368 243 450 245 19.1 4.85 52.31 78.95 17NS4 pH 5 330 212 422 259 15.7 3.99 45.28 72.72 15NS4 pH 8 463 273 545 279 15.5 3.94 45.24 67.90 14NS4 pH 10 372 153 462 209 15.6 3.95 45.44 68.16 15 Table 4. SCC index obtained from mechanical properties of SSRT. Environment RA (%) RAR TF (h) TFR PE (%) PER ELR (mm) ELR Strain (%) SR Air 78.95 - 52.31 - 17 - 4.85 - 19.1 -NS4 pH 5 72.72 0.92 45.28 0.87 15 0.88 3.99 0.82 15.7 0.82NS4 pH 8 67.90 0.86 45.24 0.86 14 0.82 3.94 0.81 15.5 0.81NS4 pH 10 68.16 0.86 45.44 0.87 15 0.88 3.95 0.81 15.6 0.82 was not observed. However, a decreases in YS, UTS, EL and deformation was observed, which can be attributed to diffusion of hydrogen atoms into the steel generating hydrogen embrittlement. 3.4 Surface fracture analysis Figure 5 shows the SEM images of the fracture surfaces of the X52 pipeline steel after carried out the SSRT in air and in the synthetic soil solution (NS4 solution). Measurements of final diameter of fracture were carried out in order to calculate the reduction area (RA). The SSRT of the X52 steel in air presented a ductile fracture, and it is characterized by extensive plastic (permanent) deformation of the material (figure 5a). One mechanism of ductile fracture is known as microvoid coalescence

Plastic Bag Derived-Microplastics as a Vector for Metal Exposure in Terrestrial Invertebrates.

Microplastics are widespread contaminants in terrestrial environments but comparatively little is known about interactions between microplastics and common terrestrial contaminants such as zinc (Zn). In adsorption experiments fragmented HDPE bags c. one mm2 in size showed similar sorption characteristics to soil. However, when present in combination with soil, concentrations of adsorbed Zn on a per mass basis were over an order of magnitude lower on microplastics. Desorption of the Zn was minimal from both microplastics and soil in synthetic soil solution (0.01 M CaCl2), but in synthetic earthworm guts desorption was higher from microplastics (40-60%) than soil (2-15%), suggesting microplastics could increase Zn bioavailability. Individual Lumbricus terrestris earthworms exposed for 28 days in mesocosms of 260 g moist soil containing 0.35 wt % of Zn-bearing microplastic (236-4505 mg kg-1) ingested the microplastics, but there was no evidence of Zn accumulation, mortality, or weight change. Digestion of the earthworms showed that they did not retain microplastics in their gut. These findings indicate that microplastics could act as vectors to increase metal exposure in earthworms, but that the associated risk is unlikely to be significant for essential metals such as Zn that are well regulated by metabolic processes.

Effect of Microstructure on Hydrogen Diffusion in Weld and API X52 Pipeline Steel Base Metals under Cathodic Protection

The aim of this research was to evaluate the influence of microstructure on hydrogen permeation of weld and API X52 base metal under cathodic protection. The microstructures analyzed were of the API X52, as received, quenched, and annealed, and the welded zone. The test was performed in base metal (BM), quenched base metal (QBM), annealed base metal (ABM), and weld metal (WM). Hydrogen permeation flows were evaluated using electrochemical tests in a Devanathan cell. The potentiodynamic polarization curves were carried out to evaluate the corrosion resistance of each microstructure. All tests were carried out in synthetic soil solutions NS4 and NS4 + sodium thiosulfate at 25°C. The sodium thiosulfate was used to simulate sulfate reduction bacteria (SRB). Through polarization, assays established that the microstructure does not influence the corrosion resistance. The permeation tests showed that weld metal had lower hydrogen flow than base metal as received, quenched, and annealed.

Stress corrosion cracking assessment of API X65 steel non‐conventionally heat treated

Stress corrosion cracking (SCC) susceptibility of API X65 steel non‐conventionally heat‐treated was evaluated through slow strain rate tests (SSRTs) using the synthetic soil solution NS4 at 20, 40 and 60 °C. Polarization curves (PCs) and corrosion potential (Ecorr) measurements were also performed. The non‐conventional heat treatment (HT) was made by heating plates at 1050 °C for 30 min followed by water quenching. The tensile strength of the heat‐treated plates increased to values similar to API X80 steel. The SCC index obtained by ratios of mechanical properties indicated that X65 steel without HT is not susceptible to SCC whereas with HT is slightly susceptible to SCC. The SCC mechanism in the soil solution in the heat‐treated plates was influenced by hydrogen diffusion as confirmed by the internal cracks and the brittle fracture observed in the specimens. The electrochemical study suggests that the corrosion process of X65 steel with and without HT occurs via a mix mechanism where the charge transfer resistance is influenced by a mass transfer process. Crevice corrosion features were found in the surface of the steel. It is likely that this type of corrosion could have sensitized the X65 steel and induced cracks when the steel was under tensile stress.

Electrochemical Characterization of X60 Steel Corrosion at Different Overvoltages: A Cathodic Protection Study

This paper presents an electrochemical characterization of X60 steel corrosion using polarization curves. In order to get a surface analysis, a Scanning Electron Microscopy (SEM) was used. Analyses by Energy Dispersive Spectroscopy (EDS) were done to characterize the corrosion products films formed on surface of the steel sample at the different overvoltages studied. The electrolyte was a synthetic soil solution and all electrochemical parameter was measured at room temperature, atmospheric pressure and 24 hours of the total exposure time. It is important to point out that these parameters were measured in the protection potential (versus saturated calomel electrode, SCE) and at different overvoltages. The results of the polarization curves show that the corrosion rate increased as the overvoltage also increased and this behaviour was corroborated by the superficial analysis obtained by SEM; where the corrosion morphology was localized and the aggresivity increased with the overvoltage. In addition, in all overvoltages, the anodic reaction was limited by a mass transfer process. A localized corrosion form was found in all tests.

Effect of cathodic potential on hydrogen permeation of API grade steels in modified NS4 solution

The goal of this work was to simulate the effect of H2S produced by SRB (Sulfate reducing bacteria). This H2S effect was evaluated by different electrochemical tests carried out with the API X60 grade steel. Therefore, Polarization curves, Slow Strain Rate Testing (SSRT) and hydrogen permeation test were carried out using a modified synthetic soil solution – NS4+thiosulphate. In addition, the Slow Strain Rate Testing and hydrogen permeation tests were performed at free corrosion potential (Ec) and cathodic potential equal to 300mV below Ec. These results were compared with the NS4 standard.To conclude, the API X60 steel presented decrease in ductility in the modified NS4 solution at more cathodic potential. This behavior occurred probably because of the increment of hydrogen flux detected in modified NS4 solution in relation to NS4 standard. The contribution of hydrogen embrittlement to EAC (environmentally assisted cracking) is consequently confirmed.

Researches on the Fatigue Crack Propagation of Pipeline Steel

Researches and industrialization of pipeline steel fatigue crack propagation are summarized, especially the X60 and X70 pipeline steel after mechanical damage and in the synthetic soil solution. The results show that the fatigue crack propagation of the pipeline steel has the similar law after mechanical damage or in the synthetic soil solution. It is very clearly that the fatigue crack propagation is deeply depending on the ΔK, and there are all have threshold characters. The mechanical damage and the synthetic soil solution can increase the fatigue crack propagation rate, decrease the fatigue crack propagation threshold ΔKth, accelerate crack propagation rate and shorten the service life of the pipe.

Development and evaluation of geochemical methods for the sourcing of archaeological maize

Strontium (Sr)-isotope values on bone from deer mice pairs from 12 field sites in the Chaco Canyon area, New Mexico, were compared with isotope values of synthetic soil waters from the same fields. The data indicate that mice obtain Sr from near-surface sources and that soil samples collected at depths ranging from 25 to 95 cm contain Sr that is more accessible to the deep roots of maize; thus, synthetic soil solutions provide better data for the sourcing of archaeological maize. However, the Sr-isotope composition of mice may be more valuable in sourcing archaeological remains of animals such as rabbit, turkey, and deer. In a separate study, five Native American maize ( Zea mays L. ssp. mays) accessions grown out at New Mexico State University Agricultural Science Center, Farmington, New Mexico were used to determine if soil-water metal pairs partition systematically into cobs and kernels. The sampled maize included landraces from three Native American groups (Acoma, Hopi, Zuni) that still occupy the Four Corners area. Two cobs each were picked from 10 plants of each landrace. Partitioning of the Ba/Mn, Ba/Sr, Ca/Sr, and K/Rb metal pairs from the soil water to the cob appears to behave in a systematic fashion. In addition, 51 rare earth element (REE) pairs also appear to systematically partition from the soil water into cobs; however, the ratios of the REE dissolved in the soil waters are relatively invariant; therefore, the distribution coefficients that describe the partitioning of REE from the soil water to the cob may not apply to archeological cobs grown under chemically heterogeneous conditions. Partitioning of Ba/Rb, Ba/Sr, Mg/P, and Mn/P metal pairs from the soil water to kernels also behaves in a systematic fashion. Given that modern Native American landraces were grown under optimal environmental conditions that may not have been duplicated by prehistoric Native Americans, the distribution coefficients obtained in this study should be used with caution.

Water Extractability of Trace Metals from Soils: Some Pitfalls

Water soluble and/or dissolved metals represent the most ecotoxicologically relevant fraction of metals in the environment. However, water extractions may be prone to errors. This study aims to evaluate the performance of 5 filters as well as Rhizon soil moisture samplers, with respect to metal adsorption and/or release by the filter. In addition, the effect of equilibration time on water extractions of different types of soils was evaluated (silty loam, silty clay loam, loamy sand). Filtrations of synthetic solutions containing 40 μg 1−1 Zn, 20 μg 1−1 Cu, Ni and Pb, 10 μg 1−1 Cr and 2 μg 1−1 Cd were conducted using the different filters. The synthetic solutions either contained (i) no other competitive cations (Ca, Mg, Na, K, Fe, Mn, Al) (A1), (ii) competitive cations at concentrations similar to those observed in soil solutions (A2), (iii) competitive cations at 10 times lower concentrations than those in the synthetic soil solution (A3). Whiteband filters were observed to retain considerable amounts of trace metals (except Cr), both in the presence and absence of other competitive cations. Millipore filters did not exhibit metal retention. Rhizon soil moisture samplers did not retain trace metals from the synthetic soil solution (A2), whereas at lower concentrations of competitive cations (A1, A3) retention of Cu and Pb was observed. Whiteband filters without a predefined pore diameter allowed colloidal material of unknown particle size to pass into the filtrate, making interpretation of results very difficult and comparison between studies using different filters impossible. Millipore filters with a predefined pore diameter are to be recommended for this purpose. However, particular attention must be paid to potential constitutive Zn release by the sintered glass filter holders, the effect of which can be reduced by rigorous acid washing prior to and following every use. Rhizon samplers were also considered to be useful tools with well-defined and sufficiently small pore diameters to withhold colloidal material. However, in the absence or at reduced concentrations of competitive cations (A1, A3) retention of trace metals by the Rhizons, particularly Cu and Pb, was observed. Finally, short equilibration times may be insufficient for full assessment of the water extractable pool of trace metals in the soil.

EFFECT OF P AND SE(IV) ON CALCITE PRECIPITATION INHIBITION

We studied the role of inorganic P and Se(IV) in calcite precipitation inhibition in a Panoche Creek, California, soil. Calcite precipitation inhibition by inorganic P and Se(IV) was first examined in simple Ca2+-Na+-Cl−-HCO3− solutions. In these simple solutions, the presence of small quantities (~0.2 mg L−1) of inorganic phosphate (similar to those typically found in soil solutions) completely inhibited calcite precipitation over the short time period examined. Se(IV) had a similar effect, though its concentration would need to be much higher to exhibit an equivalent degree of precipitation inhibition. A linear relation was found between relative precipitation rate decrease and P [or Se(IV)] concentration in solution when pH and pCO2 were held constant. The inhibition of calcite precipitation by P and Se(IV) was further investigated in more complex real and synthetic soil solutions. Calcite and gypsum saturation states in Panoche Creek, California, soil solutions were examined, and two soil horizons were found to be supersaturated with respect to calcite. Gypsum supersaturation was not observed. Calcite precipitation inhibition experiments using synthetic supersaturated Panoche Creek soil solutions indicated that soil solutions with >0.2 mg L−1 inorganic P could completely inhibit calcite precipitation. Se(IV) concentrations in Panoche Creek soil solutions were too low to significantly inhibit calcite precipitation. Calcite precipitation inhibition by Mg, Si, S, Ba, and Sr in synthetic soil solutions was not observed.

Microstructure Dependence of Stress Corrosion Cracking Initiation in X-65 Pipeline Steel Exposed to a Near-Neutral pH Soil Environment

Abstract A study was carried out to understand mechanisms of stress corrosion crack initiation in an X-65 pipeline steel exposed to a near-neutral pH soil environment under a mechanical loading condition typical of a pipeline operating in the field. Microcracks initiated on the polished surface of the X-65 pipeline steel after long-term exposure at open-circuit potential in a near-neutral pH synthetic soil solution. It was found that these microcracks were initiated mostly from pits at metallurgical discontinuities such as grain boundaries, pearlitic colonies, and banded phases in the steel. Strong preferential dissolution was observed along planes of the banded structures in the steel. Selective corrosion at these metallurgical discontinuities is attributed to the anodic nature of those areas relative to the neighboring steel surface. Consistent with previous observations, no increased susceptibility to crack initiation was found at physical discontinuities mechanically introduced into the surface of steel exposed to synthetic soil solution at open-circuit potential.

Effect of precyclic loading on stress-corrosion-cracking initiation in an X-65 pipeline steel exposed to near-neutral pH soil environment

A study was carried out to understand the effect of precyclic loading on stress-corrosion-crack initiation in an X-65 pipeline steel exposed to a near-neutral-pH soil environment. The test specimens were precyclically loaded before corrosion exposure to represent a service history of up to about 20 years, depending on the severity of pressure fluctuation. Microcracks had initiated on the polished surface of the X-65 pipeline steel after long-time exposure at open-circuit potential (OCP) in a near-neutral-pH synthetic soil solution. These microcracks were mostly initiated from pits at metallurgical discontinuities such as grain boundaries, pearlitic colonies, and banded phases in the steel. Strong preferential dissolution was observed along planes of the banded structures in the steel. The selective corrosion attack at these metallurgical discontinuities is attributed to the galvanic nature of those areas to their neighbors. Cyclic loading prior to corrosion exposure had significant effects on microcrack initiation and propagation during subsequent corrosion exposure. Cyclic loading prior to corrosion exposure either reduced or increased the probability of crack initiation and the rate of crack propagation, depending upon the magnitude of the stress cycles. The largest reduction was seen at a peak cyclic stress of about 0.8 of the yield strength. This cyclic-loading-dependent cracking behavior might be related to the alteration of the substructures and the residual stress in the steel as a result of precyclic loading.

Zinc and cadmium mobility in podzol soils

Zinc and Cadmium advection experiments are described which were carried out using columns packed with (a) Podzol B h (b) Podzol B Fe and (c) sand mixed with goethite. Aqueous NaCl and synthetic soil solutions were used as the mobile phases. The column cation and proton exchange capacities (CEC and PEC values) were determined. The CEC values were found to reflect the organic matter (OM) contents of the soils but not to correlate with the observed elution volumes. Differences in the exchange interactions and an overall lack of reaction of Cd and Zn with OM, at the prevailing pH values were deemed to be responsible. The changes in the Zn and Cd elution behaviour observed in the presence of chloride were rationalised in terms of the formation of CdCl + and CdCl 2 species.

Reversibility of damages to forest floor plants by episodes of elevated hydrogen- and aluminium-ion concentrations in the soil solution

Herbs and grasses may episodically be exposed to elevated concentrations of potentially toxic elements as H+ and Al3+ due to considerable temporal variability in the chemical composition of soil solutions in the uppermost layer of the soil profile. Greenhouse experiments were performed to test the effect of episodes of different length (1 and 2 weeks) and concentrations of H+ and Al3+ (pH 3.8, 4.0, 4.2 and 4.5; 0, 20 and 70 μM Al) on root and shoot growth, designed to elucidiate the reversibility of growth inhibition. Three forest floor species were studied-Galium odoratum and Lamium galeobdolon, having similar pH distribution ranges in the field and Poa nemoralis which also occurs at slightly lower pH. The plants were grown for 5 weeks (episode and recovering time) in a synthetic soil solution in a flowing solution system without recirculation. The species reacted in three different ways. Galium odoratum was the most sensitive species and seemed to be irreversibly damaged (ceased growth) by 2 week episodes of pH≤4.0 and Al≥20 μM at pH≤4.2. Lamium galeobdolon was about equally sensitive during the episodes but it had a much greater ability to recover. Poa nemoralis was rather insensitive to the episode treatments tested. It is concluded that episodes of elevated H+ and Al3+ concentrations may be decisive for plant performance. It is therefore important to consider the extreme environmental conditions which plants may be exposed to in the field, in addition to long-term averages of e.g. soil solution concentration of potentially toxic elements, when studying species distribution and performance in relation to soil chemical properties.

Detrimental Sulfate Effects on Formation of Al‐13 Tridecameric Polycation in Synthetic Soil Solutions

AbstractThe chemistry of Al in soil solutions and in surface waters is complex and has included evidence of the tridecameric polycation, known as Al13, in an acid forest soil. The Al13 polycation is the dominant species formed when Al solutions are partially neutralized under controlled laboratory conditions, and solution culture studies have shown Al13 to be highly toxic to root growth. Doubt has been raised, however, as to the occurrence of the Al13 polycation in natural systems. The objective of this study was to examine the effects of solution composition, comparable with soil solutions extracted from acid soils, on the formation of the Al13 polycation using both 27Al nuclear magnetic resonance (NMR) and spectrophotometric methods. The presence of Ca, Mg, K, Cl, and NO3 during partial neutralization had no effect on the formation of the Al13 polycation. However, SO4 at ≥50 µM during partial neutralization to a OH/Al ratio of R = 2.0 precipitated the major proportion of Al and interfered with the formation of the Al13 polycation. The addition of similar concentrations of SO4 after neutralization had no effect on the measured Al13 concentration. The presence of ≥250 µM SO4 resulted in no detectable Al13 polycation present after the solution had been neutralized to R = 2.5. We suggest that in view of the ubiquitous nature of the SO4 anion in soil solutions and surface waters, the Al13 polycation is unlikely to be formed in measurable quantities.

Aluminium Toxicity as a Factor Limiting the Distribution of Allium ursinum (L.)

Solution experiments and analyses of soil solutions from the field were made to elucidate whether the Al concentration in the soil water of dystric cambisols could be a factor restricting Allium ursinum to less acid soils. Two size classes of A. ursinum were exposed, for 4 weeks to a synthetic soil solution of pH 4·3 containing 0, 20, 40 and 70 µM Al, using a flowing solution culture system. An Al concentration of 20 µm, at a Ca/Al molar ratio of 12·5, was toxic to the plants, as shown by a cessation of root extension and slower root dry weight production. Compared to mature plants, seedlings developed Al toxicity symptoms after shorter exposures to Al and negative effects on the shoots were displayed at smaller Al concentrations in solution. The high sensitivity of this species to Al, and the maximum soil solution concentration of available Al present at the most acid sites that support A. ursinum, indicate that Al and the Ca/Al ratio may determined the field distribution.Copyright 1993, 1999 Academic Press

Effects of pH and aluminium on growth of Galium odoratum (L.) scop. in flowing solution culture

Growth of Galium odoratum in a synthetic soil solution was studied at pH 5.0, 4.5, 4.2, 4.0, 3.5 and 3.2 without Al and at pH 4.2 with 0.35 mM Al. The plants were treated for 5 weeks in a flowing solution culture system. The H + concentration was found to limit performance and growth at pH 4.2 or lower, pH 3.2–3.5 was lethal. Aluminium at 0.35 mM inhibited shoot and root growth. It was concluded that high H + concentration (pH 4.2) in soil solution, as a result of soil acidification, may be responsible for observed decreases in frequency and cover of G. odoratum in southern Sweden over the last decades. High Al concentrations can be an additional negative factor for the species performance.