Constant Tests Research Articles

Initiation and Propagation of Stress Corrosion Cracking of Type 304L Austenitic Stainless Steel in Hot Aqueous Chloride Solution

Abstract A phenomenological study was undertaken of the stress corrosion cracking (SCC) of type 304L (UNS S30403) austenitic stainless steel (SS) in boiling 44 wt% magnesium chloride (MgCl2) aqueous solution. From the morphological information available on the specimen surface after constant elongation rate testing (CERT) and taking into account the real crack shapes, initiation could be modeled using a staircase function, with incubation time and saturation crack density depending upon elongation rate. The propagation rate of a given crack was found to be a sharply decreasing function of the density of deeper cracks.

Optimum array detector for a weak signal in unknown noise

We study the design of constant false-alarm rate (CFAR) tests for detecting a rank-one signal in the presence of background Gaussian noise with unknown spatial covariance. We look at invariant tests, i.e., those tests whose performance is independent of the nuisance parameters, like the background noise covariance. Such tests are shown to have the desirable CFAR property. We characterize the class of all such tests by showing that any invariant decision statistic can be written as a function of two basic statistics which are in fact the adaptive matched filter (AMF) statistic and Kelly's generalized likelihood ratio statistic. Further, we establish an optimum test in the limit of low signal-to-noise ratio (SNR), the locally most powerful invariant (LMPI) test. We also derive the bound for the probability of detection of any invariant detector, at a fixed false-alarm rate, and compare the LMPI and the published detectors (Kelly and AMF) to it.

New Methods For Analysis Of Constant Pressure Interference Testing

Abstract The existing body of theoretical studies on interference testing usually applies for constant-rate conditions at the active well. For constant-pressure situations, which are fairly commonly encountered during injection tests in low-permeability rocks (e.g., crystalline rocks, which are often tested for waste repository projects), alternative approaches must be sought for analysing interference tests. This paper presents a new method for analysis of interference tests with the active well at constant pressure. This new analytical technique makes use of both type curve matching and straight line fitting methods for analysis of such tests. We show in this paper that with a proper grouping of the relevant variables, a constant-pressure interference test can be analysed using constant-rate Cartesian (or semilog) derivative type curves for interference testing. Thus, this method utilizes existing constant-rate solutions for interpretation of constant pressure interference tests. The solution is exact and extends a previously presented approximate solution. Moreover, for rD > 20 and tDr2D > 0.5, we can also use a semilog plot to conduct a straight line analysis of the data from a constant pressure interference test for estimation of interwell transmissivity and storativity. Introduction In an interference test between two wells, the active well undergoes a variety of production or injection tests, with the observation well used only to monitor the pressure transients released into the formation by the active well. Analysis of interference tests are commonly performed using the assumption of a constant rate or of a series of constant rate steps. Such analyses of the observation well data can be performed using wellbore storage and skin at both active and observation wells(l). In the groundwater industry, constant pressure tests are fairly common in tight formations where a constant rate test is dominated by wellbore storage effects for a significantly long time. The constant pressure situation is also well-suited to injection testing, as constant rate methods need a prior knowledge of the formation permeability to select a suitable rate(2). Constant pressure situations are also a useful means of controlling off-site migration of contaminated groundwater(3). Uraiet and Raghavan(4,5), Ehlig-Economides and Ramey(6) and Ozkan et al.(7), among others, have presented a number of tools to aid in analysis of constant pressure tests in a variety of flow situations and reservoir conditions. Analytical methods to interpret constant pressure interference tests in a double porosity situation have been detailed by Grasman and Grader(8). In a very recent study, Hiller and Levy(3) demonstrated the use of an approximate method to analyse the late time data at an observation well, when the active well is being produced at a constant pressure. Their method yields the formation diffusivity directly from the analysis. Mishra and Guyonnet(9) presented a simple but elegant technique to compute formation transmissivity and storativity from analysis of observation well data during constant pressure tests. Their method involves a generalization of the Theis exponential integral solution for constant pressure situations.

Recovery Analysis from Pumping Tests with Stepped Discharge

AbstractRecovery analysis from pumping tests with varying discharge is well‐documented but in practice often wrongly considered to be impractical or even impossible. However, the Theis recovery method for constant rate tests is popular and widely used to determine aquifer transmissivity. The purpose of this paper is to review and promote determination of transmissivity by recovery analysis in tests in which the discharge is not steady but represented by a step function. The equations for a stepped discharge recovery method are presented in a simple form, highlighting the fact that it is a direct extension of the Theis recovery method with the same advantages and ease of application. It is demonstrated that the Theis recovery method cannot generally be used with an average discharge for varying rate tests. Recovery analysis should always be approached with the stepped discharge recovery method, which reduces to the Theis method if the discharge is constant. The stepped discharge recovery method is particularly useful for step tests and for analyzing data from the pumped well, and it should be standard practice to monitor the recovery in all pumping tests on single wells. It is also shown that a different storage coefficient during recovery than during pumping does not result in a shifted straight line in the recovery analysis but in a curve passing through the origin.

GENETIC AND MORPHOMETRIC DIVERGENCE IN ANCESTRAL EUROPEAN AND DESCENDENT NEW ZEALAND POPULATIONS OF CHAFFINCHES (FRINGILLA COELEBS).

Descendent populations of chaffinches (Fringilla coelebs) introduced to New Zealand about 120 years ago were compared with "ancestral" populations in northern Europe and with those in a broader region of Europe (including Iberia) using protein electrophoresis at 42 loci and 12 skeletal measurements. The New Zealand populations exhibit very small scale differentiation in genetics (Fst = 0.040) and morphometrics, and the haphazard pattern of among-population variation does not align with environmental variation nor is it predicted by the geographic proximity of populations. Thus random drift is implicated in the differentiation among the descendent populations. The New Zealand chaffinches have diverged only slightly in morphometrics from an extant population in southern England, and constant heritability rate tests suggest that random drift alone could account for this small shift. In sharp contrast, the European populations are subdivided genetically (Fst = 0.222) and morphometrically, and this subdivision coincides with the Pyrenees mountains between Iberia and northern Europe which act as a barrier to gene flow between these regions. Iberian populations have smaller skulls and longer wings on average than northern European populations and are characterized by high frequencies of alternative common alleles at Ada and Np. Within both the Iberian and northern European regions, however, populations are effectively panmictic in protein-encoding genes, indicating that homogenizing gene flow is apparently extensive enough to prevent among-population differentiation in allozymes by drift. Variation in body size as represented by PC I is related to environmental productivity across Europe, unlike in New Zealand. These observations jointly suggest that longer term adaptive differentiation via selection for optimal body size has evolved in Europe. Because multilocus evolution is expected to proceed slowly in populations subject to the opposing forces of selection and homogenizing gene flow, I argue that local adaptation within "ancestral" populations in northern Europe may still be evolving.

Investigation into double yield points in polyethylene

The effects of branching on the yield of polyethylene have been investigated using three polyethylene samples with differing degrees of short-chain branching. The experimental results have shown the existence of double yield points for all three samples. The double yield points are evident from the shapes of the stress-strain curves obtained for the three samples over a range of temperatures. Measurement of the residual strains of the samples as a function of the level of maximum strain applied under constant elongation rate test show that the first yield point marks the onset of ‘plastic strains’ which are slowly recoverable at least in part. Deformation beyond the second yield point is effectively irrecoverable and is associated with a sharp necking of the samples. The yield points are interpreted mechanically as the yield of two dashpots and the model used to describe the yield is of two non-linear Maxwell elements in parallel. Transient dip experiments have been used to separate the stress-strain curves of the individual arms and these confirm that the two arms do yield at different strains.

Effect of pH and Chloride Contents on Stress Corrosion Cracking of Austenitic Stainless Steels at Room Temperature

Abstract Constant elongation rate tests and constant load, subcritical crack growth tests were used to investigate the stress corrosion cracking (SCC) susceptibility of metastable (type 301 [UNS S30100]) and stable (type 310S [UNS S30108]) austenitic stainless steels in H2SO4/NaCl aqueous solutions at 25°C. For annealed type 301, at each pH value there was a critical concentration of Cl− ions required to initiate SCC at 25°C. Using the constant extension rate test with notched specimens, the relation between pH and [Cl−] can be expressed as for SCC immunity: pH > 6.9 log [Cl−] + 0.7 By using a sharper, fatigue precrack and a constant load, the critical concentrations of Cl− ions for SCC immunity and active dissolution to occur at 25° can be expressed as: for SCC immunity: pH > 5 log [Cl−] + 3 for active dissolution: pH < 1.6 log [Cl−] + 0.3 SCC occurred at intermediate values of pH and [Cl−]. For type 310S, constant extension rate test results were insensitive to the environment, and the constant load tes...

An in vitro study of the effect endodontic access preparation has upon the retention of porcelain fused to metal crowns of mexillary central incisors

Endodontic therapy often requires cutting access preparations through existing restorations. The purpose of this study was to determine whether endodontic access preparation affected the retention of porcelain fused to metal crowns of maxillary central incisors. Retentive forces required to displace porcelain fused to metal crowns of maxillary central incisors were measured using an Instron constant displacement rate testing machine. Using a paired t test analysis, a significant difference was found between crown retention before and after endodontic access preparation.

A generalized radial flow model for hydraulic tests in fractured rock

Models commonly used for the analysis of hydraulic test data are generalized by regarding the dimension of the flow to be a parameter which is not necessarily integral and which must be determined empirically. Mathematical solutions for this generalized radial flow model are derived for the standard test conditions: constant rate, constant head, and slug tests. Solutions for the less common, sinusoidal test are contained within the general solutions given. Well bore storage and skin are included and the extension to dual‐porosity media outlined. The model is presented as a model of fractured media, for which it is most likely to find application because of the problem of choosing the appropriate flow dimension.

Experimental “sytectonic” dehydration of serpentinite under conditions of controlled pore water pressure

We have studied the mechanical behavior of serpentinite under conditions favouring dehydration to olivine + talc + water, at temperatures ranging between 300° and 600° and at total pressures from 100 to 300 MPa. Constant stress, stress relaxation and constant displacement rate testing techniques permitted a wide range of deformation rates and paths to be accessed. Effective confining pressure was held constant during the dehydration process by means of a controlled pore water pressure system. Stress supported by the samples was almost independent of deformation rate at temperatures below those required for the onset of the breakdown reaction. At 500° and 600°C, however, the strength was linearly dependent on the inverse of the deformation rate, and independent of effective confining pressure over the range investigated. Microstructural studies revealed that the weakening was associated with sliding in narrow shear zones containing ultrafine‐grained (0.1 µm olivine produced in the breakdown reaction. The enhanced deformability is interpreted in terms of flow of the olivine in these shear zones by diffusion‐accommodated grain boundary sliding. These experimental results suggest that metamorphic transformations affect the deformability of rocks, and demonstrate enhancement of deformability through the transient existence of fine‐grained reaction products. The results may also be applicable to the mechanics of deformation processes in oceanic transform faults and give some indication of the degree of weakening that might be expected from grain‐size reduction by dynamic recrystallization in plastically deforming rocks.

Theoretical analysis of the transient pressure response from a constant flow rate hydraulic conductivity test

Incorporating a flow pump into a conventional triaxial laboratory system allows fluid to be supplied to or withdrawn from the base of a sediment sample at small and constant rates. An initial transient record of hydraulic head versus time is observed which eventually stabilizes to a constant steady state gradient across the sample; values of hydraulic conductivity can subsequently be determined from Darcy's law. In this paper, analytical methods are presented for determining values of specific storage and hydraulic conductivity from the initial transient phase of such a constant flow rate test. These methods are based on a diffusion equation involving pore pressure and are analogous to those used to describe the soil consolidation process and also to interpret aquifer properties from pumping tests. Examination of the effective stress distributions within the test specimen induced during this type of measurement shows that values of specific storage corresponding to both compression and rebound conditions can be deduced and differentiated simply by reversing the direction of fluid flow. Applicability and limitations of the methods are illustrated with analyses of recently reported flow pump test measurements conducted on a silty‐clay specimen.

A study on the mechanism of iodine-induced stress-corrosion cracking of Zircaloy-4

The iodine-induced stress-corrosion cracking (SCC) of Zircaloy-4 plate specimens has been studied by the constant elongation rate test (CERT) and U-bend test methods. In order to systematically evaluate the effects of stress states on the SCC behavior, four kinds of specimens were prepared from as-annealed Zircaloy-4 plate specimens. The uniaxial tensile and single edge-notched (SEN) specimens fractured in the ductile manner, not by SCC. However, SCC resulted in the plane strain tensile specimens and deep-notched U-bend specimens. As the strain rate was lowered, the susceptibility to SCC increased. The stress-corrosion (SC) cracks propagated by the trans-granular brittle fracture mode for as-annealed specimens, whereas by the inter- and trans-granular mixed fracture mode for reannealed specimens. The SCC processes of Zircaloy-4 in iodine-gas are discussed in terms of effects of stress states, elongation rates and yield stresses. The present experimental results suggest that the iodine-induced SCC processes are based upon the iodine-diffusion model.

The sulfide stress corrosion cracking of high alloy stainless steels for oil and natural gas wells

The stress corrosion cracking resistance of some martensitic, precipitation hardening, duplex and high alloy austenitic stainless steels for oil or gas wells has been investigated. Different test methods have been utilized: constant load tests on smooth specimens with and without crevices, constant deformation tests on precracked specimens, and constant elongation rate tests on smooth specimens. The tests have been carried out in a NACE environment and in a modified NACE environment. The tests confirmed both the susceptibility to stress corrosion cracking of the martensitic and the precipitation hardening stainless steels and the resistance of the high austenitic stainless steel. Some tests showed the stress corrosion cracking susceptibility of the duplex stainless steel to be worse than expected from traditional tests.

Type-Curve Analysis: What It Can and Cannot Do

Summary. Type-curve analysis has been used for more than 20 years in theoil industry and for more than 40 years in hydrogeology. Yet, what itinvolves and how useful it is in practice is still being debated within theoil industry. This paper attempts to answer some of the questions that aremost commonly raised about type curves and type-curve analysis. What Is a Type Curve? A type curve is a graphic representation of thetheoretical response during a test of an interpretationmodel that represents the well and the reservoir beingtested. For a constant-pressure test, the response isthe change in production rate: for a constant-rate test, the response is the change in pressure at the bottomof the well. Other types of response are also used, such as the time derivative of the bottomholepressure. Type curves are derived from solutions to the flowequations under specific initial and boundaryconditions. For the sake of generality, type curves areusually presented in dimensionless terms, such as adimensionless pressure vs. a dimensionless time. A given interpretation model may yield a single typecurve or one or more families of type curves, depending on the complexity of the model. What Is Type-Curve Analysis? Type-curve analysis consists of finding a type curvethat "matches" the actual response of the well andthe reservoir during the test. The reservoir and wellparameters, such as permeability and skin. can thenbe calculated from the dimensionless parametersdefining that type curve. The match can be found graphically, by physically, superposing a graph of the actual test data with asimilar graph of the type curve(s) and searching forthe type curve that provides the best fit. Alternatively, an automatic fitting technique involving a linear ornonlinear regression can be used. Fig. 1 gives an example of a graphic type-curvematch. The graph of the data is positioned over thegraph of the type curves, with the axes kept parallel, so that the test data match one of the type curves. Reservoir parameters are calculated from the value ofthe dimensionless parameter defining the type curvebeing matched and from the × and y axis shifts. How Can One Select a Type Curve ToMatch Test Data? First, one must find the interpretation model that bestrepresents the dynamic behavior of the well andreservoir during the test. This interpretation modelmust be identified from the test data because it isusually difficult to predict from static information. The most efficient way to identify the interpretationmodel is to use the derivative of the pressure withrespect to the natural log of some function of elapsedtime. A log-log plot of the pressure derivative vs. elapsed time yields a limited number of characteristicfeatures for the various components of theinterpretation model that are easy to recognize. Thesefeatures are illustrated in Fig. 2. The possibilities are(1) a maximum. (2) a minimum, (3) a stabilization, and (4) an upward or a downward trend. Themaximum is found at early times and indicateswellbore storage and skin: the higher the maximum, the more damaged the well. No maximum indicates anondamaged or a stimulated well. The stabilizationindicates semilog radial flow and corresponds to thesemilog straight line on a Horner plot. A minimumindicates heterogeneous behavior. An upward ordownward trend at the end of the data indicatesboundary effects. The complete interpretation modelis then obtained by combining these variouscomponents. Examples of interpretation models areshown in Fig. 3. Once the interpretation model has been identified, one must select the type curves corresponding to thatmodel that are the most appropriate for the range ofavailable test data. What Is the Difference Between theVarious Published Type Curves? For a given interpretation model, the mathematicalsolution to the flow equations is unique, and typecurves derived from that solution should all beidentical. In practice, however, type curves maydiffer by their presentation-e.g., if they use differentdimensionless or dimensional parameters-or by theirrange of application. As a result, some published typecurves may not be usable with the available test data, or may be more or less convenient to use. But evenif they look different, type curves corresponding tothe same interpretation model will give the sameanalysis results if they all cover the range of availabletest data. P. 11^

When Is a Reservoir Limit Test Applicable?

Technology Today Series articles provide useful summary information on both classic and emerging concepts in petroleum engineering.Purpose:To provide the general reader with a basic understanding of a significant concept, technique, or development within a specific area of technology. As discussed in an earlier paper in this series (" Transient, Semisteady-State, and Steady-State Flow," April 1986 JPT, Pages 385–86). after an extended time of production at constant rate in a bounded reservoir, the pressure decrease becomes proportional to time. The period in which this occurs is called semisteady state and is illustrated in Fig. 1. The contributory pore volume, Vp, of the reservoir may be calculated from the slope of the production curve after it reaches semisteady state. For this reason, the constant-rate production test has been called a reservoir limit test. The applicable equation follows.

Materials Behavior in Alternate (Hydrogen) Water Chemistry in the Ringhals-1 Boiling Water Reactor

Abstract In-plant studies on the intergranular stress corrosion cracking (IGSCC) of sensitized austenitic stainless steel (SS) have been performed at the Swedish Ringhals-1 boiling water reactor (BWR). The studies have covered the present [full-temperature (normal)] water chemistry (PWC) and the alternate (primary) water chemistry (AWC) with hydrogen addition. The test techniques applied were constant extention rate testing (CERT) and electrochemical potential (ECP) measurements. The program was covered by extensive environment monitoring. The results verify earlier laboratory studies which show that sensitized austenitic SS is susceptible to IGSCC in PWC, but not in AWC. Other pressure-bearing BWR construction materials are not adversely affected by AWC. The boundary conditions in Ringhals-1 have been established for an AWC, which is defined as an environment that does not produce IGSCC in sensitized SS. The results are compared with a similar program at Dresden-2, and the points of agreement and discord...

SCC testing of pipe materials in BWR environment

A test loop has been installed in Ringhals 1 BWR, including facilities for Constant Elongation Rate Testing (CERT) and Electrochemical Potential (ECP) measurements in primary reactor water at reactor operation temperature. The loop is designed as to minimize transport time for reactor water from the reactor pressure vessel to the specimens being tested. Thus the testing environment is representative of the primary piping systems of BWRs, also with regard to short-lived constituents like hydrogen peroxide. The test program, which is in progress, has covered seven tests during start-up conditions or during power operation with presently current reactor water chemistry. In this presentation only CERT testing results on heavily sensitized austenitic chromium—nickel stainless steel are presented, although many other materials have been tested. Results show sensitized austenitic stainless steel is more prone to intergranular stress corrosion cracking (IGSCC) in actual than in simulated BWR environment and that start-up environment is chemically more aggressive than power operation environment. Reproducibility of the CERT technique as used is excellent.

Modeling nonlinear viscoelastic response

AbstractWe present a model for calculating nonlinear viscoelastic response which we call the “phases model” (PHM). In terms of a mechanical model representation the PHM is a generalized Maxwell model with nonlinear elements where each Maxwell element is referred to as a phase. The viscous material properties are represented in the model in terms of flow curves of the individual phases. The collection of flow curves form the flow diagram. We show how to calibrate the flow diagram from a family of constant rate test curves by means of a simple straightforward procedure. We give an example of such a calibration for a certain rigid polyurethane. We applied our model to the calculation of nonlinear viscoelastic response to varius loading programs in uniaxial tension, and to the creep of a simply supported beam, and obtained good agreement with experimental data.

Strain rate history effects and observations of dislocation substructure in aluminum single crystals following dynamic deformation

Single crystals of aluminum are deformed in shear at a number of constant strain rates in the range 10 −5–1600 s −1 and to strains of about 20%. These constant-rate tests are supplemented by a series of jump tests in which a sharp increment in strain rate is imposed during the quasi-static straining. Thin foil samples of the strained specimens are examined by transmission electron microscopy (TEM). The constant-strain-rate tests show a linear increase in flow stress with the logarithm of strain rate up to 500 s −1, followed by a more rapid increase at higher strain rates. TeM observations after deformation at quasistatic strain rates reveal a cellular dislocation arrangement that develops into well-outlined subgrains as strain increases. Cells are also visible after dynamic deformation, but these cells are about one-quarter of the size of those produced by quasi-static deformation and their walls are not as well defined. Furthermore, results indicate that, as the cell size is reduced, both the flow stress and the strain rate sensitivity increase. The jump tests show a pronounced strain rate history effect and their results permit the calculation of an activation volume applicable to quasi-static straining. Results of this calculatin, which is based on macroscopic measurements and on the theory of thermally activated deformation of metals, are compared with an activation volume based on the dislocation densities measured after deformation.

Radiation chemistry related to nuclear power technology

A brief review is given to the radiation chemical problems, especially with the emphasis on water radiolysis, in the nuclear power technology. Radiation chemistry in aqueous system is pointed out to be closely related to the problems such as corrosion of Zircaloy, the formation of insoluble corrosion products or crud, stress corrosion cracking of stainless steel in BWR and the radioactive waste managements. The results of the constant extention rate tests on sensitized 304 stainless steel under irradiation are shown, and the computer calculations were carried out to simulate the model experiments on the release of crud from the corroding surface under irradiation and also the water radiolysis in core of BWR.