A three-pass groove weld made by gas-tungsten arc welding in a 20-mm thick SA508 steel plate is modeled to predict the thermal, metallurgical, and mechanical behavior. The dilution for each pass is estimated as the proportion of base material in the weld metal, based on the predicted cross-sectional areas for the fusion zone (FZ) associated with each individual pass. The temperature predictions are consistent with the thermocouple measurement data and cross-weld macrographs. The predicted microstructures are qualitatively compared with the observed microstructures in cross-weld optical micrographs. The measured hardness is then used to quantitatively validate the predictions for postweld microconstituents (e.g., the ferrite, bainite, and martensite fractions), based on a hardness-microstructure correlation. The predicted residual stresses are compared with those measured by neutron diffraction. The results show that the dilution significantly affects the metallurgical and mechanical properties of weld metal (either as-deposited or reheated), and its consideration notably improves the predictions for microstructure and residual stress in the multipass steel weldment. Furthermore, the increase in dilution promotes the formation of martensite, which enhances the hardness, and leads to lower tensile stresses (or higher compressive stresses) in the weld metal. Such behavior arises due to the higher hardenability of the base material employed in this study, coupled with delayed austenite decomposition on cooling.

The United States Department of Energy's Savannah River Site (SRS) in Aiken, South Carolina, is dedicated to promoting site-level, risk-based inspection practices to maintain a safe and productive work environment. Protective suits are worn by personnel working in contaminated environments. These suits require that cooling be applied to keep the interior temperature within safe and comfortable limits. A vortex tube, also known as the Ranque-Hilsch vortex tube (RHVT), can provide the necessary cooling. As mechanical devices void of moving components, vortex tubes separate a compressed gas into hot and cold streams—the air emerging from the “hot” end reaching a temperature of 433.2 K and the air emerging from the “cold” end reaching a temperature of 241.5 K (Hilsch, 1946, “Die Expansion Von Gasen Im Zentrifugalfeld Als Kälteprozeß,” Z. Für Naturforsch., 1 , pp. 208–214). Routing the cold stream of the vortex tube to the user's protective suit facilitates the required cooling. Vortex tubes currently in use at SRS are preset, through modification solely by and within the SRS respiratory equipment facility (REF), to provide a temperature reduction between 22.2 and 25.0 K. When a new model of vortex tube capable of user adjustment during operation recently became available, prototype testing was conducted for product comparison. Ultimately, it was identified that similar cooling performance between the old and new models is achievable. Production units were acquired to be subjected to complete product analysis at SRS utilizing a statistical test plan. The statistical test plan, data, thermodynamic calculations, and conclusions were reviewed to determine acceptability for site use.

The structural integrity of a reactor pressure vessel (RPV) is important for the safety of a nuclear power plant. When the emergency core cooling system (ECCS) is operated and the coolant water is injected into the RPV due to a loss-of-coolant accident (LOCA), the pressurized thermal shock (PTS) loading takes place. With the neutron irradiation, PTS loading may lead an RPV to fracture. Therefore, it is necessary to evaluate the performance of RPV during PTS loading to keep the reactor safety. In the present study, optimization of RPV maintenance is considered, where two different attempts are made to investigate the RPV integrity during PTS loading by employing the deterministic and probabilistic methodologies. For the deterministic integrity evaluation, three-dimensional computational fluid dynamics (3D-CFD) and finite element method (FEM) simulations are performed, and stress intensity factors (SIFs) are obtained as a function of crack position inside the RPV. As to the probabilistic integrity evaluation, on the other hand, a practically more useful spatial distribution of SIF on the RPV is calculated. By comparing the distribution thus obtained with the fracture toughness included as a part of the master curve, the dependence of conditional failure probabilities on the position inside the RPV is obtained. Using the spatial distribution of conditional failure probabilities in RPV, the priority of the inspection and maintenance is finally discussed.

Submerged arc welding of SA 516 grade 60 pressure vessel grade steel was conducted with different heat plate thicknesses and the influence of cooling rate on microstructure, Vickers hardness, and impact toughness of heat affected zone (HAZ) of weldment was systematically investigated. Weld cooling rates vary with change in heat input or variation in plate thickness of base metal. Results showed that thin plates accumulate the heat, which cause grain coarsening and loss of acicular ferrite (AF) microstructure, which is further responsible for lower impact strength of welded joint. It is deemed that faster cooling rates due to heat sink in thickness direction with thick plates cause high percentage of AF with finer grain and enhanced hardness values. Improved impact strength with thick plates with same heat input signifies that supplying heat more than required to thin plates may cause microstructural deterioration and responsible for impact strength loss of weldments. Test demonstrates that the cooling rate should be above 15 °C/s to keep impact strength loss within considerable limits.

Most of the microstructural changes in weldment takes place during weld cooling from 800 ° C to 500 ° C ( t 8/5 ) specially in the heat-affected zone (HAZ). Weld strength and cracking tendency can also relate to t 8/5 . A generalized model using dimensional analysis has been proposed for estimation of the weld cooling time (t 8/5 ) for variable plate thicknesses. The proposed model is based on rotatable central composite designed submerged arc welding (SAW) experiments. The model considers material properties, weld parameters, and environmental conditions for submerged arc welding. The model is validated with experimental data and cooling time observed by other researchers. The adequacy of the model was found to be 97% and able to predict cooling time for a plate thickness ranging from 8 to 41.5 mm thickness.

The inner surface of a reactor pressure vessel (RPV) is assumed to be subjected to pressurized thermal shocks (PTSs) caused by the injection of emergency cooling water. The downstream is not homogeneous but typically in a plume shape coming from the inlet nozzles. In this paper, both deterministic and probabilistic methods are used to assess the integrity of a model RPV subjected to PTS. The favor code is used to calculate the probabilities for crack initiation and failure of the RPV considering crack distributions based on cracks observed in the Shoreham and PVRUF RPVs. The study shows that peak K I of the cracks inside the plume increases about 33% compared with that outside. The conditional probability inside the plume is more than eight orders of magnitude higher than outside the plume. In order to be conservative, it is necessary to consider the plume effect in the integrity assessment.

The purpose of this paper is to study the transient temperature responses of a hollow cylinder subjected to periodic boundary conditions, which comprises with a short heating period (a few milliseconds) and a relative long cooling period (a few seconds). During the heating process, the inner surface is under complex convection heat transfer condition, which is not so easy to approximate. This paper first calculated the gas temperature history and the convective heat transfer coefficient history between the gas flow and the inner surface and then they were applied to the inner surface as boundary conditions. Finite element analysis was used to solve the transient heat transfer equations of the hollow cylinder. Results show that the inner surface is under strong thermal impact and large temperature gradient occurs in the region adjacent to the inner surface. Sometimes chromium plating and water cooling are used to relief the thermal shock of a tube under such thermal conditions. The effects of these methods are analyzed, and it indicates that the chromium plating can reduce the maximum temperature of the inner surface for the first cycle during periodic heating and the water cooling method can reduce the growth trend of the maximum temperature for sustained conditions. We also investigate the effects of different parameters on the maximum temperature of the inner surface, like chromium thickness, water velocity, channel diameter, and number of cooling channels.

This is Part II of a study on two-bar thermal ratcheting for Alloy 617. The ratcheting strains were evaluated for conditions with the same temperature range but with different mean stresses, heating and cooling rates, time delays, and thermal histories. These testing conditions were designed to be closely aligned to the development of design rules for strain limits at very high temperatures for Alloy 617. These new design rules have been formulated to address the fact that the effects of plastic deformation and creep deformation on the ratcheting strains are not separable at very high temperatures for this alloy.

Coke drums undergo cyclic operations typically in the temperature range from ambient temperature to about 500 °C (930 °F). During quenching, the coke drum is inevitably subjected to a rapid drop in temperature because cooling water is injected directly into the coke drum through the bottom inlet nozzle. The temperature profile on the shell surface is no more uneven in quenching, and can vary in each cycle of quenching operation. Such complicate thermal profile induces large strains in the shell portion of the coke drum, and eventually causes damage like bulging or cracking. This study makes investigations into the bulging behavior of the coke drum by the thermal elastic-plastic FE-analysis. In this work, a feasible study is conducted on potential causes of bulging. As factors inducing a heterogeneous plasticity in the shell structure of the coke drum, the strength overmatch of welds and the uneven temperature field in quenching as well as quenching conditions are focused. The analytical result shows that strength overmatch in girth seam welds can be one of the causes of plastic distortion under one operating cycle. The lower rising rate of cooling source can induce plastic straining over the whole shell wall, which tends to induce more remarkable plastic distortion.

An alloy commonly used for large pressure vessels, known as SA508 Grade 3, has a microstructure after heat treatment consisting of a mixture of tempered bainite and martensite at fast cooled regions near surfaces subject to water quenching. These two phases are conventionally recognized to consist of fine platelets, each of which is approximately 0.2 μm in thickness, enhancing strength and leading to good toughness properties. We have discovered in our experimental work that there are circumstances where the adjacent platelets of a similar orientation can coalesce as the austenite transforms, to produce much coarser structures which are believed to be detrimental to toughness. An examination of published micrographs reveals that such coalesced regions existed but were not noticed in previous studies. The mechanism of coalescence is described and methods to ameliorate the coarsening are discussed.

It is important that the material used to produce high-integrity pressure vessels has homogeneous properties which are reproducible and within specification. Most heavy pressure vessels comprise large forgings derived from ingots, and are consequently affected by the chemical segregation that occurs during ingot casting. Of particular concern are the compositional variations that arise from macrosegregation, such as the channels of enriched material commonly referred to as A-segregates. By causing corresponding variations in microstructure, the segregation may be detrimental to mechanical properties. It also cannot be removed by any practically feasible heat treatments because of the large scale on which it forms. Here we describe an investigation on the consequences of macrosegregation on the development of microstructure in a pressure-vessel steel, SA508 Grade 3. It is demonstrated that the kinetics of transformation are sensitive to the segregation, resulting in a dramatic spatial variations in microstructure. It is likely therefore that some of the scatter in mechanical properties as observed for such pressure vessels can be attributed to macroscopic casting-induced chemical segregation.

The engineering design of disposal of the high level waste (HLW) packages in a geologic repository requires a thermal analysis to forecast the temperature history of the packages. Calculated temperatures are used to demonstrate compliance with criteria for waste acceptance into the geologic disposal gallery system and as input to assess the transient thermal characteristics of the vitrified HLW Package. The objective of the work was to evaluate the thermal performance of the supercontainer containing the vitrified HLW in a nonbackfilled and unventilated underground disposal gallery. In order to achieve the objective, transient computational models for a geologic vitrified HLW package were developed by using a computational fluid dynamics method, and calculations for the HLW disposal gallery of the current Belgian geological repository reference design were performed. An initial simplified two-dimensional model was used to conduct some parametric sensitivity studies to better understand the geologic system’s thermal response. The effect of heat decay, number of codisposed supercontainers, domain size, humidity, thermal conductivity, and thermal emissivity were studied. A more accurate three-dimensional model was also developed by considering the conduction–convection cooling mechanism coupled with radiation, and the effect of the number of supercontainers was studied in more detail, as well as a bounding case with zero heat flux at both ends. The modeling methodology and results of the sensitivity studies will be presented.

This paper presents the results of a research on the influence of regenerative heat treatment on microstructure and properties of a cast steel after long-term operation at the elevated temperature. The material under investigation was G17CrMoV5-10 cast steel taken out (in the form of a section) from an internal frame of steam turbine serviced for about 250,000 h. Performed research has proven that through the microstructure degradation long-term service contributes to an embrittlement and decrease in yield strength and tensile strength. The heat treatment, however, contributes to an impact energy increase regardless of the applied parameters (cooling rate). It has also been established that the optimum combination of strength properties and impact energy is ensured by the microstructure of high tempered bainite, whereas low strength properties and impact energy were obtained for the microstructure, which was slowly cooled from the austenitizing temperature, i.e., the ferritic-bainitic-ferritic microstructure.

Welded, thick-walled piping intersections are widely used in many engineering applications including the offshore and nuclear power industries. These components are often fabricated by multipass welding, which inevitably introduces undesirable residual stresses. In this paper, weld-induced residual stresses in a thick-walled piping intersection were predicted using a validated, full three dimensional, sequentially coupled thermomechanical finite element modeling technique. The moving heat source was simulated by imposing body heat flux onto the newly activated elements progressing along the circumferential weld path around the intersection during each pass. The effect of cooling rate on the final residual stress state, especially at critical areas where the peak residual stresses are located, was then investigated by applying different convective heat transfer coefficients to the exposed piping intersection surfaces. It was found that the magnitudes and overall spatial distributions of residual stresses were very sensitive to cooling rate. Residual stresses on the outer surfaces of the component can be significantly reduced by external cooling. On the other hand, cooling the inner surfaces can dramatically convert residual stresses from tensile to compressive in these regions. The results and modeling technique presented in this paper show that residual stress profiles in multipass welded complex geometries can be efficiently optimized through convenient cooling rate control.

The brittle failure assessment for the reactor pressure vessel (RPV) of a 1300 MW pressurized water reactor was revised according to the state of the art. The RPV steel is 22 NiMoCr 37 (A 508 Cl. 2). The expected neutron fluence at the end of license (EOL) after 32 years of full operation is Φ < 2.3 × 10 18 neutrons ∕ cm 2 . The assessment followed a multibarrier concept to independently prove the exclusion of crack initiation, crack arrest, and exclusion of the load necessary to advance the arrested cracks through the RPV wall. Thermal and structural analyses of the RPV were performed both for the reactor shutdown with postulated upset conditions, as the most severe load case at operation, and for loss of coolant accident (LOCA) conditions. For LOCA transients, a leak size screening of different combinations of cold∕hot leg injection of emergency core cooling was performed, and the leading leak size was determined. A fracture mechanics based assessment was carried out for extended circumferential flaws in the weld joint between the RPV shell and the flange, as well as for axial flaws in the nozzle corner. These flaw geometries postulated at locations of the highest principal stresses and lowest temperatures under the respective transient conditions are representative for the brittle failure assessment of the whole vessel. For a normal operation, the maximum crack driving force takes place at high temperatures preceding the upset conditions. The transient follows a load path decreasing with temperature, producing a warm prestressing effect, which is considered in the assessment. Thus, a large safety margin against crack initiation can be demonstrated. At LOCA, the most severe conditions are determined for postulated cracks in the nozzle corner. Here, applying the constraint modified master curve, which takes account of the low stress triaxiality in the component, the exclusion of crack initiation is proven. Furthermore, two additional safety barriers are proven, the crack arrest after postulated crack initiation well within the allowable depth, as well as the preclusion of the load necessary to advance the arrested crack through the RPV wall.

For the purpose of finding a way to control effectively the residual thermal stresses induced by local heat treatment on spherical vessels, a thermal tracing program is developed successfully based on the transient thermal analysis and controlling method of average temperature of nodes located in an “observed region.” Typical calculation cases reveal that the local heat treatment process itself does cause obvious residual thermal stress that is high enough to cause yield when concentrated heating on small region is adopted, but decentralized heating on a larger region can lower effectively the residual thermal stresses to a rather desirable level. It can be found through a one by one analysis of ten factors, which are possibly influential on residual thermal stress: arc radius of heated region, holding temperature, volume, and wall thickness of the vessel are primary effective factors. The bandwidth of the annular insulated region, the heating rate, and the size of the observed region are secondary factors. Heating pattern, holding time, and cooling rate can hardly affect the residual thermal stress. Considering the primary factors except holding temperature, and taking 30% of yield stress as the expected residual thermal stress level, the recommended arc radius of heated region should be 2.2 R t in minimum.

Welding generates thermal distortion and residual stress, and it is well known that they affect the performance of welded structures by contributing to brittle fracture, fatigue, buckling deformation, and stress-corrosion cracking. Welding distortions and residual stresses can possibly be controlled and reduced by using countermeasures. Not only thermal stress behavior but also the prediction of the microstructural phase during welding heat cycles is very important. High-strength steels or martensitic stainless steels are used in many power plant components, and the effect of phase transformation on the mechanical behavior during welding of these steels becomes much larger than that of mild steels and austenitic stainless steels. Simultaneous simulations of the thermal stress and microstructure during welding are necessary for a precise evaluation. In this paper, an analytical method and several applications using actual components are introduced in order to emphasize the effect of the microstructure on the weld residual stress analysis.

In this work, a gouged section of 1080 railroad rail steel is examined using metallographic techniques to characterize the nature of the damage. The gouging was performed by a rocket sled at Holloman Air Force Base, riding on VascoMax 300 steel shoes at 2.1 km ∕ s . The damaged rail is evaluated in detail to examine material phase changes, shear bands, and heat effects. The results are compared to samples of the virgin material, machined and prepared exactly as they are prior to the Holloman AFB High Speed Test Track (HHSTT) runs. The gouged section was examined using optical microscopy, scanning electron microscope (SEM), and other techniques. The resulting microstructure is presented and compared to the virgin material. Material mixing, shear band formation, and significant thermal damage, consistent with a high energy gouging event, are confirmed. In addition, the material phase change evident in this approach allows us to estimate the thermal conditions present during the formation of the gouge. This thermal history establishes a profile by which related research in gouge simulation can be validated against. A one-dimensional heat conduction model is presented that validates the cooling rates required to generate the presented microstructure.

A 155 mm compound gun barrel with full-length integral mid-wall cooling channels was manufactured and connected to a purpose built heat exchanger. Laboratory testing of this system was carried out using electrical heating jackets applied to the outer surface of the barrel and an internal electrical chamber heater to heat the barrel as uniformly as possible along its length. A series of tests were then carried out consisting of first heating the barrel to a uniform temperature of approximately 80°C followed by switching on the heat exchanger and monitoring the rate at which the barrel cooled. The purpose of these tests was to determine the optimum cooling characteristics of the system by studying the effect of different coolant flow rates combined with one or both radiators functioning and also the effect of using different cooling fluid solutions. Having derived the optimum flow rate and coolant solution combination a further cooling test was carried out with the heat exchanger configured to these optimum values and with the barrel heaters operating at maximum capacity. Finally a natural cooling test was undertaken where the barrel was uniformly heated to 160°C, the heating jackets removed and the barrel left to cool overnight. The results from these tests prove that natural cooling is dramatically slower than forced mid-wall cooling.

Analytical solutions for shrink-fit compound gun tubes were used to study the effects of the liner/sleeve interface diameter, the radial interference, and the effect of machining tolerances on tube strength. Finite element analyses were then done of a midwall cooled compound gun tube where a loose-fitting inner tube (liner) is permanently deformed by means of hydraulic pressure to lock it to the outer tube (sleeve). The interaction between the liner and sleeve was modeled with contact elements. The effect of machining subsequent to the hydraulic autofrettage was taken into account. Simulations were first done for smooth tubes with initial clearance of varying magnitude and, second, for the case where the liner has axial semi-circular cooling channels machined on its outer surface. Manufacturing tolerances were found to be much less critical for the hydraulic autofrettage than with the shrink-fit option. The interface diameter seems to be a relatively insensitive parameter. Relatively large initial clearance between inner and outer tubes can be tolerated. The hydraulic autofrettage option therefore seems better than the shrink-fit only option for compound gun tubes. It was demonstrated that the effect of the cooling channels on the stresses in the tube is significant and substantially weakens the inner tube. However, it is still possible to produce a workable design.