The various valves and instruments along the pipeline must be tested and found functional. Comes with 2-phase capabilities. Many of the legal conflicts arising in large projects have to do with how different codes should be interpreted, or even more common, when to apply which code.
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Calculate flow-induced vibration for a tube in a shell-and-tube exchanger using a rigorous finite element based algorithm. X vib considers fluidelastic instability and vortex shedding mechanisms for both plain and U-tubes. HTRI Xchanger Suite works with many major software packages for physical properties, process simulation, mechanical design, integrated engineering, and fan selection. Fan selection software from the following companies is embedded in X ace. You must have the following equipment to run X changer Suite 7 and eLibrary Calculation modules are fully incremental and calculate localized heat transfer and pressure drop using local fluid properties.
Color coded text allows you to distinguish between user input, default values, and program-calculated input. Extensive output reports provide detailed results including local profiles of all important parameters. Comprehensive online help provides background information, graphs, explanation of input panels and output reports, user tips, and more. Graphs and scale drawings provide in-depth visualization of calculated results. Extensive, user-extendable databank for materials of construction.
Quick Calc tools let you easily perform unit conversions and select exchanger types. X ace Design, rate, and simulate air coolers and economizers including natural draft fans off and forced draft conditions. X fh Simulate the performance of cylindrical and box heaters. X pfe Simulate and design multi-stream axial and crossflow plate-fin exchangers using an incremental model with research-based heat transfer and pressure drop correlations.
X spe Rate and simulate single-phase spiral plate exchangers using an incremental model with HTRI-validated heat transfer and pressure drop correlations. X vib Calculate flow-induced vibration for a tube in a shell-and-tube exchanger using a rigorous finite element based algorithm. Code compliance is mandated by various governmental organizations. Codes can be legal documents, and like other laws, they vary from place to place.
Contractual agreements may typically also have a say on which codes to use, and all in all selecting the right codes and standards is often one of the most important parts of the project.
The different relevant specifications typically overlap, and it is essential to decide what to do when that is the case, for instance that the most restrictive code applies.
Many of the legal conflicts arising in large projects have to do with how different codes should be interpreted, or even more common, when to apply which code. Frankel , gives an overview over different codes relevant to pipeline engineers, and more details can be found there.
As a general rule, though, it is best to stick to international codes and standards as much as possible, and to minimize the use of company- or project-specifications. The different phases in a pipeline project may vary considerably, depending on how large the project is, where it is, whether borders are crossed, whether the pipe goes over land or subsea, who manages it and a multitude of other factors.
The phases shown below can therefore only be seen as a typical example. The main parameters are determined in this phase. They may include approximate pipe length with origin and destination, diameter, type of pipe, mass flow, capital cost, operating expenses with pressure loss and power consumption, main valves and pumping or compressor stations.
Pipe flow simulations are very useful in this study. Both economical and technical feasibility should be considered. The project must be economical, and it obviously has to be technically possible. For overland pipelines, the route should be marked on various sorts of maps. This can most often be done by using existing maps in addition to taking aerial photography and surveys of the pipeline route. Route maps and property plats are created from these. Right-of-way acquisitions are normally not done in this phase, but they are taken into consideration.
In case of rock tunnels, various additional sorts of surveys may be required, such as drilling to determine rock quality. Existing maps are often of little help for subsea pipelines.
Surveying can be quite complicated and expensive, but seafloor mapping technology has developed significantly in recent years. Maps and terrain models are generated using depth data from multi-beam echo sounders mounted on the hull of survey ships, and Remotely Operated Vehicles ROVs are also used. Autonomous Underwater Vehicles AUVs have been used in some recent projects and can be more economical and faster for some surveying tasks.
Many countries have strict laws prohibiting any activities from disturbing unexcavated archeological sites, and most project managers would surely prefer not to encounter any. But archeological sites can be stumbled upon almost anywhere. In a relatively recent development, The Ormen Lange-field off the Norwegian coast, a shipwreck was discovered, and archeological investigations had to be carried out before pipe lying.
Needless to say, planning for such possibilities is not easy. How this is done is to a large extent determined by local laws, and they differ a lot. The process can take the form of voluntary negotiation with land owners, or it can be condemnation, meaning the land is acquired through an involuntary legal process.
Usually, owners are entitled to compensation at a fair market value. This can be a complicated, lengthy process with many involved parties. In this respect, subsea pipelines are the easiest ones to handle. As already explained, crossing borders generally complicates this task, sometimes to unmanageable levels. This is similar to what was discussed under route selection , but the work is done in greater detail.
Soil borings and various soil testing may in some cases only be possible after the acquisition of right-of way is finished, so it may have to be delayed until this phase. Because different industries use pipelines for different purposes, the design requirements are different and the types of pipe materials vary. In the petroleum and natural gas industry, steel pipe with welded joints is most common. In the water and sewer industries, on the other hand, pipes are normally under relatively low, sometimes atmospheric pressure.
The low pressure has led these industries to prefer low-stress, non-corroding pipe materials as PVC and concrete. Both for low-pressure and subsea pipes, it is common for external loads to exceed the internal ones. Once necessary legal permits and design are approved, construction can start.
For overland pipelines, that may involve clearing a path of minimum 15 m, bringing in the pipe, possibly ditching, trenching, boring, tunneling, and river crossing, followed by welding, coating, wrapping, pipe laying, and backfill with restoration of land. The various valves and instruments along the pipeline must be tested and found functional. There may be additional tests, too, such as pressure and leak tests, and various cleaning procedures may be necessary. For subsea pipelines, the fluid used to achieve the required buoyancy during lying must be removed.
The procedures may include running cleaning and instrument pigs through the pipeline. The whole purpose of constructing a pipeline is of course to have something flow through it, and understanding how the flow behaves is essential. Pipe flow simulation is used to optimize and verify design and to throw light on various operational issues.
It is used not only through all the phases described in the previous chapters, but also for training engineers and operators. During pipeline operation, simulations are used for real time system estimation and forecasting, as well as for operator training. This book is about pipe flow, and it will show how the flow theory can help us to deal with all these tasks.
There are many pipe flow simulation tools commercially available Bratland, , but using them correctly and efficiently requires understanding of what the programs do, how they work, and their limitations. Various reasons to simulate pipe flow. Considering all issues important to maintaining the fluid flow from inlet to outlet is sometimes called Flow Assurance. It is a term encountered frequently when studying pipe flow, particularly when hydrocarbons are involved.
Still, there is no generally agreed on, clear, common definition of what Flow Assurance is. It is obviously possible to define the system boundaries inlet and outlet in different ways. For instance, when considering petroleum production, the inlet could be described as a reservoir or as one or several wells. Alternatively, it could simply mean the pipe inlet. The latter may have been the most common way to look at the problem in the past, but for gathering networks, the trend for multi-phase simulation tools is towards integrated well and pipe network simulations.
Following this trend, many of those involved in developing flow assurance tools are busy creating ever better interfaces so that almost any well simulator can communicate relatively seamlessly with any multi-phase pipe flow simulation package. The same can be said about the outlet end of the pipeline. The trend is to integrate with slug catchers, separators, processing facilities or whatever else the system contains. The complexity of computing pipe flow depends on what the pipe transports and what sort of phenomena we want to investigate.
Various parameters affecting pipe flow computation complexity. The simplest way to classify pipe flow models is probably by specifying how many separate fluids they can deal with simultaneously single-phase, two-phase or three-phase , and by whether they are able to describe time-dependent phenomena transient or purely steady-state.
Let us have a look at what these differences mean in practice. The first pipe flow models dealt with single-phase flow of water or steam, though not both at the same time.
Since many phenomena are multi-phase, such single-phase models have their limitations. Early studies on transient two-phase flow were conducted in the nuclear industry, as it became mandatory to predict the transient flow behavior during potential Loss-of-Coolant Accidents for licensing pressurized water reactors.
Multi-phase flow can also occur in gas pipelines. If even a small amount of liquid condenses on the pipe wall, it will affect the flow. It is essential to know whether condensate forms or not, and dew point specification is frequently part of gas sales contracts. If a small amount of condensate is present, one may get away with simply modifying the friction factor while keeping a single phase model and still get reasonably accurate simulation results.
If the amount of condensate gets larger, computations based on single-phase models can no longer do the job. In some cases it is clear from the start that the flow can only be modeled sensibly with multi-phase software.
That is the situation when we want to simulate a well flow of oil, gas and water mixed together. Slugging, a common problem, is very much a multi-phase phenomenon, and flow models may be used to investigate how high the gas velocity needs to be to avoid it. Defining such operational limits, the flow envelope , calls for multi-phase simulations. Some commercially available software packages are steady-state, meaning they can only tell how the pressure, flow, and in some cases temperature, is going to be distributed along the pipe s once some sort of equilibrium state has been established.
They cannot tell us how conditions are on the way to that equilibrium. We see that already in the definition of a steady-state simulator some of its limitations become apparent: It cannot describe transient phenomena like line packing or pressure surges, nor can it produce a meaningful result if the system itself is unstable and therefore never converges towards a steady state.
A fully transient simulator, on the other hand, computes all intermediary steps on the way to the new steady-state when such a state exists. That means transient simulations produce more information, but at the cost of using more CPU-time. Transient programs need some steady-state solver integrated, either in the form of separate steady-state program or by mathematically solving the transient equations for the time derivative being zero.
Many of the transient phenomena of interest are simulated using a steady-state situation as a starting point, so transient simulations may rely on steady-state computations in order to define the initial condition on which the transient simulations should be based.
A commercial program package have several separate parts, it may require several licenses and may also rely on many software and hardware interfaces. Even the simplest possible simulation program must at least provide a way to give input data, typically via a Graphical User Interface GUI.
Typical flow simulation software structure simplified. Simulating a straight pipe containing water can be done with a program containing less than 10 lines of code. Adding all whistles and bells necessary to make the program flexible and user friendly, those 10 lines grow to many thousands. When well structured, the program parts do not all have to come from the same developer. Note that the way programs are structured and which main modules they contain are the same whether the program computes single- or multi-phase flow, steady-state or transient.
Similarly, the same computation modules, say OLGA, can be used with many different simulation packages, even though the license typically has to be bought separately. Computation modules vary between different programs. They generally contain fluid flow equation solvers, and they may contain one or several thermal models. For multi-phase flow, there is also some sort of flow regime identification software. That determines whether the flow is annular, bubbly, slug, or of another type.
At the same time, all multi-phase simulators are very sensitive to getting the flow regime right, even though that is one of the least accurate part of the programs.
The thermal models in use vary greatly, from the simplest isothermal models to detailed transient models of the heat flow both in the fluid, pipe wall and surroundings. The thermal model in chapter 8 discusses this in greater detail.
There is also much variation in how different programs handle PVT-data. Those properties are in reality not constant but vary with temperature and pressure, and an improved model needs to know how those properties are related. It also makes sense to include vapor pressure data to enable the program to give warning in case of cavitation.
In addition, specific heat and surface tension must be known in order to include heat and flow regime estimation. Some fluids are much more complex than water, and several vendors have specialized in developing PVT-data packages.
Note that a simulation program must update PVT-data in all grid-points as the pressure and temperature change during computation. Since one of the main challenges when creating pipe flow simulation modules is to make the program fast enough, it is important for the PVT-data to be handled efficiently. Early phase concept studies may permit relatively inaccurate computations, in some cases favoring steady-state software over more detailed transient simulations.
Note, though, that using the same software through as many phases as possible reduces the need to familiarize with many different interfaces, and depending on how the model is built up, it can also save work. The model should generally be built in several steps, starting by simulating a simplified system. It is best to neglect all nonessential components during the first runs, and get a feel for how the system is performing. Using automated routines for feeding all component data from CAD-drawings into the simulation model, as some software vendors seem to suggest, rarely makes sense, particularly not in an early phase.
Components should rather be added gradually while running increasingly sophisticated simulations. Deciding which details to include and where to simplify is an important part of model building, and it happens to be a kind of task humans tend to be better at than computers.
Hydrates are ice-like structures which form when water and natural gas are in contact at high pressure and low temperature. Paraffins in crude oil or condensate can lead to wax deposits if the temperature drops to the wax appearance point. Both these phenomena depend on pressure, temperature, chemical properties, and fluid velocity. Multi-phase simulations may be used to study how to avoid problems with hydrates and wax, and to some extent how to deal with them if they occur.
Since avoiding problems with depositions can be expensive, it pays to use as good flow and thermal models as possible for such studies. Two different detection principles are currently in use: Neural network-based decision making and calculations bases on flow models. Implementing a leak detection system involves studies of how accurately various sorts of leaks can be detected by the chosen method when fed by signals from available sensors.