Ice Plug Research Articles

Development of Flow and Heat Transfer During Filling a Pipeline with Water at the Pipe Wall Temperature Below the Freezing Point

The paper presents the technique of computing flow and heat transfer of water in a pipeline whose initial temperature is lower than the freezing point of water. A feature of the method is the possibility of calculating the process from the moment of pouring water into a pipe on the inner surface of whose wall a layer of ice is being formed. The system of equations describing the process involves nonstationary energy equations for the water flow, ice layer, and for the pipe wall. It is solved for each section of the pipeline passed by water in a small time interval in the process of filling the pipe and further flow. The Beginning computer program has been created and implemented in the Visual Basic language for numerical analysis of the process. The calculations made with the aid of this program allow one to estimate the possibility of appearance of an ice plug in the pipeline at the given temperature, water flow rate, pipeline diameter, and conditions of external heat transfer of water flow in the pipeline.

Startup of air-cooled condensers and dry cooling towers at low temperatures of the cooling air

The problems of startup and performance of air-cooled condensers (ACC) and dry cooling towers (DCT) at low cooling air temperatures are considered. Effects of the startup of the ACC at sub-zero temperatures are described. Different options of the ACC heating up are analyzed, and examples of existing technologies are presented (electric heating, heating up with hot air or steam, and internal and external heating). The use of additional heat exchanging sections, steam tracers, in the DCT design is described. The need for high power in cases of electric heating and heating up with hot air is noted. An experimental stand for research and testing of the ACC startup at low temperatures is described. The design of the three-pass ACC unit is given, and its advantages over classical single-pass design at low temperatures are listed. The formation of ice plugs inside the heat exchanging tubes during the start-up of ACC and DCT at low cooling air temperatures is analyzed. Experimental data on the effect of the steam flow rate, steam nozzle distance from the heat-exchange surface, and their orientation in space on the metal temperature were collected, and test results are analyzed. It is noted that the surface temperature at the end of the heat up is almost independent from its initial temperature. Recommendations for the safe start-up of ACCs and DCTs are given. The heating flow necessary to sufficiently heat up heat-exchange surfaces of ACCs and DCTs for the safe startup is estimated. The technology and the process of the heat up of the ACC with the heating steam external supply are described by the example of the startup of the full-scale section of the ACC at sub-zero temperatures of the cooling air, and the advantages of the proposed start-up technology are confirmed.

Glacier-surge mechanisms promoted by a hydro-thermodynamic feedback to summer melt

Abstract. Mass loss from glaciers and ice sheets currently accounts for two-thirds of the observed global sea-level rise and has accelerated since the 1990s, coincident with strong atmospheric warming in the polar regions. Here we present continuous GPS measurements and satellite synthetic-aperture-radar-based velocity maps from Basin-3, the largest drainage basin of the Austfonna ice cap, Svalbard. Our observations demonstrate strong links between surface-melt and multiannual ice-flow acceleration. We identify a hydro-thermodynamic feedback that successively mobilizes stagnant ice regions, initially frozen to their bed, thereby facilitating fast basal motion over an expanding area. By autumn 2012, successive destabilization of the marine terminus escalated in a surge of Basin-3. The resulting iceberg discharge of 4.2±1.6 Gt a−1 over the period April 2012 to May 2013 triples the calving loss from the entire ice cap. With the seawater displacement by the terminus advance accounted for, the related sea-level rise contribution amounts to 7.2±2.6 Gt a−1. This rate matches the annual ice-mass loss from the entire Svalbard archipelago over the period 2003–2008, highlighting the importance of dynamic mass loss for glacier mass balance and sea-level rise. The active role of surface melt, i.e. external forcing, contrasts with previous views of glacier surges as purely internal dynamic instabilities. Given sustained climatic warming and rising significance of surface melt, we propose a potential impact of the hydro-thermodynamic feedback on the future stability of ice-sheet regions, namely at the presence of a cold-based marginal ice plug that restricts fast drainage of inland ice. The possibility of large-scale dynamic instabilities such as the partial disintegration of ice sheets is acknowledged but not quantified in global projections of sea-level rise.

Assessment of ice plugging of a cooling water intake by a numerical model

American Electrical Power's Conesville plant had historically prevented ice buildup at a water intake by routing warm water from a once-through cooling system to the intake. In 2012, this system was retired and warm water was no longer available for de-icing. A numerical study was conducted to evaluate design alternatives to reduce ice transport to the intake. An Eulerian–Lagrangian model was used to predict the hydrodynamics and ice trajectories. A porous media model accounted for the ice accumulation in the trash racks. The model was capable of predicting the observed flow pattern. Predicted velocities compared well with measurements using large-scale particle image velocimetry (LSPIV). According to the model, sediment control vanes, placed in front of the intake to alleviate sediment ingestion, favour the ice transport to the intake. Based on model results, a mitigation plan to be implemented during several phases was elaborated.

Cryogenic formation of brine and sedimentary mirabilite in submergent coastal lake basins, Canadian Arctic

Two informally named basins (Mirabilite Basins 1 and 2) along a submergent coastline on Banks Island, Canadian Arctic Archipelago, host up to 1m-thick accumulations of mirabilite (Na2SO4·10H2O) underlying stratified water bodies with basal anoxic brines. Unlike isostatically uplifting coastlines that trap seawater in coastal basins, these basins formed from freshwater lakes that were transgressed by seawater. The depth of the sill that separates the basins from the sea is shallow (1.15m), such that seasonal sea ice formation down to 1.6m isolates the basins from open water exchange through the winter. Freezing of seawater excludes salts, generating dense brines that sink to the basin bottom. Progressive freezing increases salinity of residual brines to the point of mirabilite saturation, and as a result sedimentary deposits of mirabilite accumulate on the basin floors. Brine formation also leads to density stratification and bottom water anoxia. We propose a model whereby summer melt of the ice cover forms a temporary freshwater lens, and rather than mixing with the underlying brines, it is exchanged with seawater once the ice plug that separates the basins from the open sea melts. This permits progressive brine development and density stratification within the basins.

Ice plugging of piping: from the theory to the practice - 25 years feedback from EDF PWRs

Ice plugging or freeze sealing refers to the process of applying an external refrigerant in order to cause the formation of a solid internal plug from the frozen fluid contained in the pipe. Freeze sealing is most often used to isolate for maintenance purpose a section of a piping system where no other means of isolation is available. Applications for freeze sealing at nuclear power plants are mainly to: -) Enhance maintenance capabilities during outage; -) Provide blocking in lines where valves or stops are not placed; and -) Eliminate the necessity of taking a full system out of service during plant operation. Liquid carbon dioxide and liquid nitrogen are used as refrigerant. Freeze sealing is practiced on both austenitic stainless steel and carbon steel. It may be applied on large diameter piping (800 mm) and under elevated pressure. Within EDF and EPRI, extensive works on freeze sealing technology have been carried out early as beginning of 1980 years. EDF experience on freeze sealing applied to PWR systems and technical recommendations are presented in this paper. Several metallurgical questions regarding use of freeze sealing are also discussed, such as: -) Embrittlement risk of steel at low temperature (-195 C), -) Assessment of acceptable defects size under freeze sealing conditions, -) Effect of residual martensite (austenitic stainless steel) on mechanical properties at low temperature. (authors)

Development of the Residual Stress Improvement Method for Small-Diameter Butt-Welding Pipe (Improvement of Residual Stress through Application of Freezing Process)

To prevent stress corrosion cracking (SCC) initiation at the inner surface of the butt-welding region of a small-diameter pipe, a residual stress improvement method has been developed. In this method, the local expansion process is applied to the butt-welding region with ice plugs. During the local expansion process, tensile yielding is generated in the butt-welding region. The tensile yielding generated at the inner surface is larger than that of the outer one. After this process is applied, compressive residual stress can be introduced at the inner surface due to larger tensile yielding. In this study, residual stresses at the inner surface of the butt-welding region were measured, and SCC initiation tests in the accelerated environment (in boiling 42% Magnesium Chloride) were performed. The measured residual stresses and the results of SCC initiation tests proved this method effectively reduces residual stresses and prevents SCC initiation.

Freeze-thaw dynamics and the implications for stratification and brine geochemistry in meltwater ponds on the McMurdo Ice Shelf, Antarctica

AbstractA high resolution record of water column temperatures was measured in a coastal meltwater pond on the McMurdo Ice Shelf, Antarctica. The maximum temperature gradient measured through the water column was 35°C, with an annual temperature range of 52.1°C within the pond. For most of the year the pond shows reverse temperature stratification with the lowest temperatures measured at the surface of the pond, with the exception of brief periods of normal stratification over winter caused by regional warming events. During freezing, the freezing front propagated downwards from the pond surface, excluding major ions and releasing large amounts of latent heat, both of which had a dramatic effect on the thermal and compositional evolution of the pond. Thawing is dominated by changes in surface air temperatures and the differential absorption of solar radiation. A new conceptual model of the physical freeze-thaw process has been developed that explains the presence of an ‘ice plug’ during melting, which reduces wind-induced mixing, forms a physical barrier to chemical processes, and encourages thermal and chemical stratification. It may also explain the persistence of anoxic and hydrogen sulphide bearing basal brines in summer stratified ponds that are otherwise fully oxidized.

Canadian cryospheric response to an anomalous warm summer: A synthesis of the climate change action fund project “the state of the arctic cryosphere during the extreme warm summer of 1998”

As of 2003, the warmest year on record in Canada (and globally) was 1998. Extensive warming was observed over the Canadian Arctic during the summer of 1998. A collaborative, interdisciplinary project involving government, universities, and the private sector examined the effect of this unusual warmth on cryospheric conditions and documented the responses, placing them in a 30–40 year context. This paper represents a synthesis of these results. 1998 was characterized by a melt season of exceptional length, having both an unusually early start and late finish. Extremes were noted for cryospheric variables that included ground thaw penetration, snow‐free season, lake‐ice‐free season, glacier melt, and the duration and extent of marine open water. The warm conditions contributed to the break‐up of two long‐term, multi‐year ice plugs in the north‐west Canadian Arctic Archipelago, which allowed floe ice into the Northwest Passage. Synoptic events and preconditioning were observed to play an important role in governing the response of some variables to the warming. It was also noted that response was not uniform in all regions. This study provided an opportunity to examine possible cryospheric response to future, warmer conditions. It also provided a chance to assess the capability of current cryospheric monitoring networks in the Canadian Arctic. This study has suggested the manner of cryospheric response to low frequency, high magnitude events occurring within the broader milieu of large‐scale forcing.

The distribution of diatom flora in ice caves of the northern Yukon Territory, Canada: relationship to air circulation and freezing

In the late 1980’s and early 1990’s, various media in karst environments in the Northern Yukon Territory were examined for their diatom content. Cryogenic cave calcite powders, grus and various ice formations (ice plugs, ice stalagmites and floor ice) were collected from three freezing caves and one slope cave to make an inventory of the diatom content, and to explain the spatial distribution of the diatoms within the caves. The results show that approximately 20% of diatoms in the caves originate from external biotopes and habitats (e.g., river, lake, stream), with the remaining 80% of local origin (i.e., from subaerial habitats near cave entrances). The results also indicate that the greater abundance of diatoms is found in the larger caves. This is explained by the fact that the air circulation dynamics are much more important in caves that have a larger entrance. Also grus, ice plugs and ice stalagmites have the lowest diatom diversity, but greater relative abundance, indicative of growth in specific habitats or under specific conditions. Overall, these results are a contribution to the study of particles transport in ice caves.

The control of ice slurry systems: an overview

This article outlines some typical control strategies for the basic components of an ice slurry system. From this review it became apparent that the control of terminal units is not fundamentally different from the control of classical single-phase secondary cooling systems, except from the fact that it must be based on the use of local pumps and the ON–OFF operation of actuators to avoid ice plugging problems. The safe control of the ice generator can be ensured with a simple thermostat, although the resulting ice concentration control would be approximate. It was also demonstrated that any ice accumulation in the storage tank would not prevent the ice slurry system from functioning safely. As a final precaution, it was not recommended to operate an ice slurry generator at low solute concentrations and temperatures greater than −3/−4 °C due to the risk of plugging up the distribution loop and causing mechanical wear to the ice generator.

An Experimental Study for the Liquid Freezing Phenomena in a Pipe During Ice Plugging

The ice plugging process consists of placing liquid nitrogen around a pipe and removing heat until the water in the pipe freezes and provides a solid plug or seal against fluid movement. This technique enables us to repair or inspect a pipe system without shutdown of entire system. A set of test apparatus for investigation of the liquid freezing phenomena during ice plugging is prepared. This study shows the characteristics of the liquid freezing and the heat transfer with various pipe and freezing jacket conditions. And in case there is flow of the fluid inside the pipe, the flow rate which can be able to form the ice plug is identified with the effect of the pipe diameter and freezing jacket length on the plug formation. The permissible maximum flow rate for the complete plug formation is approximately proportional to the freezing jacket length at the same pipe diameter condition.

Faunal and Archaeological Remains as Evidence of Climate Change in Freezing Caverns, Yukon Territory, Canada

Animal and plant remains, some associated with prehistoric artifacts, were collected in freezing caverns (glacières) of northern Yukon Territory. Radiocarbon dates show that the oldest remains are Middle Wisconsinan ca. 38 000 BP). The absence of material of Late Wisconsinan age likely indicates that the caves were infilled by ice during this cold period. Climate warming and ice melting during the Holocene allowed animals and prehistoric hunters to regularly visit these caves. Ice plugs were evidently smaller during the early Holocene than they are now.

On the Prediction of Local Ice Formation in Pipes in the Presence of Natural Convection

Pipe freezing is a pipeline maintenance technique which is used to isolate sections of a liquid-filled pipeline by freezing the contents to form a solid pressure-resistant plug. This paper describes the development of a numerical model of natural convection and solidification in a vertical water-filled pipe. The natural convection-driven flows are examined in detail and the interaction with the forming ice plug is studied. The results are compared with experimental data. The numerical approach is contrasted with a simpler one-dimensional analytical method and criteria are proposed to aid the choice of modeling technique under different conditions.

Experimental Evaluation on the Thermal Stress Due to Ice Plugging of Tubes in Nuclear Power Plant

Ice-plugging of tube in nuclear power plant has been widely used for the purpose of preventing flow of the tube temporarily like a valve. Most common plugging method employs Liquid Nitrogen Gas of . According to the change of tube materials and its dimension, the thermal stress caused from the application of the frozen gas can be varied. In this research, a series of experiments have been carried out to inspect the effect of tube geometry on thermal stresses induced due to ice-plugging. Two typical dimension of stainless and mild steels of 3 and 6 inch diameters were used for the experiments. Each critical spots were checked using strain rosette gages. Another inspection was made on the pressure and temperature of the fluid. It is shown that significant thermal stress level which can cause plastic deformation of failure has not been noticed in this series of experiments.

Hydrate dissociation rates in pipelines

Recent laboratory and field data suggest that hydrates form very porous pipeline plugs which transmit pressure freely, while hydrates act as significant flow obstructions. The blocked flow causes an ocean pipeline to rapidly equilibrate to the ocean temperature at 4°C. When the hydrate plug is dissociated through total depressurization of the pipeline, the hydrate plug will be converted to an ice plug which significantly dissociates longer than the hydrate. This work formulates the first dissociation model in rectilinear coordinates. It indicates that there may be an optimum pipeline pressure for the most rapid dissociation of all solid phases resulting from hydrate pipeline blockages. Surprisingly, the high ice thermal diffusivity provides the highest heat flux when some ice is present.

Analytical study of the effect of natural convection on cryogenic pipe freezing

An analytical model of freezing a liquid inside a vertical pipe is described. Natural convection in the liquid is included by incorporating an integral solution for the heat transfer coefficient for convection driven by a heated vertical plate. The resulting model can be applied to different pipe sizes, temperatures and liquids and was used to predict the formation of an ice plug under varying freezing conditions. A method of scaling the effect of pipe diameter and initial water temperature on natural convection during freezing is proposed. The factors which limit the situations in which the model can be applied are discussed

On the Prediction of Stresses in Pipes Caused by Ice Plug Formation

Stress development in pipes due to local fluid freezing is investigated through a simple analytical model based on thin axisymmetric shell theory. Particular attention is given to modelling the interaction between the pipe wall and the ice formed within the freezing jacket. The developed analysis accounts for the interface shear traction and relies on rational assumptions regarding its distribution in order to interpret and reproduce observed pipe behaviour. It is validated by comparing its predictions to available exact and numerical solutions as well as experimental data. Finally, it proves a valuable tool in understanding the ice plug-pipe wall interaction mechanism which controls stress generation and distribution.

Residual stress relief of welded joints in pipework using ice plugs

Summary This paper describes a residual stress relief method for butt welded joints in pipework made using ice plugs. Named by the authors the Twin Ice Plug (TIP) method, it is basically as follows. Two ice plugs are formed inside the pipework and isolate a section including a welded joint. The internal pressure of the isolated section increases as the ice plugs grow, imparting tensile strain to the pipe wall of the section. When the pressure reaches the target level, it is released, and the residual stress decreases. The paper describes details of this process, measurement of the internal pressure outside the pipework, control of the internal pressure, and the effect of residual stress relief. The internal pressure of the isolated section is estimated by the strain measured by strain‐gauges affixed to the outside surface of the section. Section pressure control is exercised by control of refrigerant (liquid nitrogen) supply and pipe wall heating. The maximum internal pressure attained by this method is 4...

アイスプラグを利用した配管残留応力除去方法

A stress relief method using ice plug for butt weld joint of piping is described. The method is as follows. Two ice plugs are formed inside piping, and isolate a section which include weld joint. An internal pressure of isolated section increases as ice plugs grow, and it gives tensile strain to pipe wall of the section. After the pressure reaches target level, the pressure is released and the residual stress decreases. The stress relief method is named by authors as Twin Ice Plug (TIP) method. This paper described details of this process, measuring of internal pressure from outside of piping, controlling internal pressure, and the effect of stress relief.The internal pressure of isolated section is estimated by the strain measured by strain gauge on outer surface of the section. A control of a pressure of the section is done by controlling supply rate of refrigerant (LN2) and heating pipe wall. The maximum internal pressure reached in this method is 40 MPa for 4BSch4O (O.D.=114.3 mm, t=6.0 mm) stainless pipe and 22.5 MPa for 6BSch4O (O.D.= 165.2 mm, t=7.1 mm). The residual stress of as GTA weld joint of stainless pipe is measured, its maximum value is more than +300 MPa. The effects of this method are confirmed by measuring residual stress of 4BSch40 6BSch40 joints that are treated by this method. The residual stress of inside surface decreases and changes to compression, and that of outside surface also decreases to under 100 MPa.