Oil & Gas

Coalescing Filter Sizing using Rated and Specified Pressure Loss Components Popular

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Rated & Specified dP Components Rev 1.5.zip

Coalescing Filter Sizing using Rated and Specified Pressure Loss Components


In the oil and gas industry, Flownex is often used to build complex gas flow networks with the purpose of determining pressures, temperatures and velocities at any point and pressure losses of certain components or groups of components as well as the system as a whole.

As such, situations often arise where the pressure loss of a component or network area is known at certain conditions (at a certain flow, a certain pressure and a certain temperature for a certain gas) but calculations have to be performed at other conditions. It is for this specific purpose that the Rated Pressure Loss component was developed and is presented in this case study.

A typical application of the Rated Pressure Loss component is a gas coalescing filter, which serves the purpose of removing solids and liquids from the gas, and as such will become increasingly fouled, resulting in increasing pressure losses. The operational lifecycle of such a coalescing filter is more complicated than it may at first appear and is presented and discussed in this case study. Coalescing filters also serve to remove liquids from the gas flow; however the details of the liquid removal process is outside of the scope of this case study and is not considered in detail.

Similarly, the user often wants to specify a constant pressure loss for a component or area, typically during the design phase when pressure loss quotas are allocated to specific components or areas. The Specified Pressure Loss component was developed for this purpose and is also presented in this case study. 

NOTE: If you are experiencing errors when opening any of the projects in the Oil & Gas section in Flownex, please let Flownex Support know.

Cross Flow Bare Tube Recuperator Popular

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Bare Tube Recuperator Ver 1.6.zip

Cross Flow Bare Tube Recuperator

A recuperator is a specific application of a heat exchanger used to recover heat from a hot fluid. Perhaps the most frequent application of a recuperator is to recover heat from hot flue gas before it is discharged into the atmosphere. Several different recuperator designs are used in industry, however one of the simplest and most cost effective designs is a bundle of bare tubes positioned in cross flow to the flue gas. The tubes may be a single pass or multi-pass design.

A compound component was developed in Flownex® to model a single tube pass recuperator based on bare tubes in cross flow to a rectangular shell. The component is set up such that a minimum of inputs are required to assess the performance of the design. The process inputs are specified at the boundary conditions while the recuperator geometry is specified on the recuperator element itself. Bundles can easily be connected in series for the exhaust gas, as is usually the case, but they can also be connected in parallel. Combinations of series and parallel bundles can also be specified with ease. Similarly, the connection of the tube-side flow paths can be as simple or complex as the user wants. 

Economic Pipe Sizing Using the Generaux Equation Popular

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Generaux Economic Pipe Sizer Ver 1.0.zip

Economic Pipe Sizing Using the Generaux Equation

The Economic Pipe Sizing model implements the well- known Generaux Equation which aims to calculate the most cost effective flow velocity through pipelines from a total cost of ownership perspective. Larger diameter pipes will result in lower velocities and therefore lower pressure losses and hence less pumping costs. However larger pipes are more expensive to purchase, install, operate and maintain. The Generaux equation aims to account for all these competing costs and optimise the fluid velocity accordingly.    

Emergency Vent Flare Ice Build-Up Estimation Popular

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Emergency Flare Ice Buildup Ver 1.zip

Emergency Vent Flare Ice Build-Up Estimation
An emergency vent flare is used when an upset condition occurs or due to equipment failure and the gas stream can’t be processed normally. In some instances, the gas temperature may be extremely low and significant ice build-up may occur on the outside surface of the flare stack. The additional mass and distribution of the mass may be an important consideration during structural integrity calculations of the stack. A very simple Flownex® model is presented which provides the design engineer with a reasonable estimate of worst-case ice build-up thicknesses.

External Heat Transfer Pipe Popular

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External Heat Transfer Pipe Ver 1.61.zip

External Heat Transfer Pipe

Updated for Flownex 8.8 and later

Please note that the original external heat transfer pipe model (ver 1.5) will no longer work properly with Flownex 8.8 and later. Therefore the model has been updated to version 1.6, please download this update.

Heat loss from pipelines is a very common engineering consideration. This relatively simple compound component enables the design engineer to quickly and accurately estimate these heat losses and assists in the selection of the most cost effective insulation option.

The External Heat Transfer Pipe model implements the Churchill and Bernstein (1) correlations for forced convection across a cylinder and the Churchill and Chu (2, 3) correlations for natural convection over horizontal and vertical cylinders. Radiation heat transfer from the external surface is modelled using Flownex’s built-in radiation heat transfer capability included with the Composite Heat Transfer element. Inputs and results are simplified such that only relevant information is presented.

Update: Ver. 1.61 fixed an error relating to vertical pipes under natural convection. Please update to the latest version.

Fired Heater Design Popular

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Fired Heater Design Ver 1.6.zip

Fired Heater Design

Updated for Flownex 8.8 and later

Please note that the original fired heater model (ver 1) will no longer work with Flownex 8.8 and later. Therefore the model has been updated to version 1.6, please download this update.

The design of a fired heater (or similar) package typically starts with a heat and mass balance. This first step is necessary to determine the process parameters which determine most of the sizing of the package. A fired heater package heat and mass balance includes the modelling of the combustion process and the modelling of the heat transfer and fluid flow processes. Modelling the combustion process typically involves the specification of the fuel gas composition, the combustion air composition, the air-fuel ratio and the fuel flow rate. The heat transfer from the fired heater combustion process into the process fluid may be specified in terms of an overall heater thermal efficiency. Typical heat and mass balance calculations do not provide estimations of the physical size of the heater or even the ducting and other components such as combustion air fans. Neither do they enable the calculation of system pressure losses or heat losses. They are also incapable of providing insight into tube wall and process fluid film temperatures which are very important in the oil and gas industry. Flownex®enables the user to perform all these tasks easily and quickly in a single calculation.


The main purpose of this exercise is to size a fired heater (typically an API 560 design) and its associated combustion air fan and ducting. In order to perform this task efficiently, a Flownex®model has been developed which is able to model the combustion, fluid flow and heat transfer processes. As such the model relies on a fired heater compound component and a few scripts to handle fuel and flue gas analyses.


Using Flownex®, the design and sizing of the fired heater, combustion air fan and the associated piping and ducting could be performed inside of an hour. Furthermore, results such as process temperatures, tube wall temperatures, heat fluxes, flow velocities, pressure losses etc. could easily be obtained from the network. As an overall package sizing and design tool, Flownex®has proven to be far more efficient than other detailed design software.


The full case study discussion document is available on the Flownex® web page in the Case Studies section:


Flow Transmitter Orifice Sizing and Uncertainty Analysis Popular

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Flow Measurement Orifice Plate Sizing & Sensitivity Analysis Rev 1.zip

Flow Transmitter Orifice Sizing and Uncertainty Analysis


Fuel gas flow transmitters rely on a variety of measurement techniques, the simplest (and cheapest) of which probably is the orifice plate. The pressure transducers used by flow transmitters are typically calibrated by mapping the minimum to maximum orifice plate pressure drops to the typical 4-20 mA signals it transmits. At zero flow the transmitter would issue a 4mA signal. As a rule of thumb, the minimum flow would therefore be calibrated to approximately 30% above the minimum signal (8.8 mA) whereas the maximum flow would be calibrated to approximately 70% to 80% of fullscale (14 to 16 mA).

For the case at hand, the information is as follows:

  • Maximum fuel gas flow rate = 1500 Nm3/hr
  • Minimum fuel gas flow rate = 350 Nm3/hr
  • Required pressure drop at maximum flow = 5 kPa
  • Required pressure drop at minimum flow = 0.5 kPa

The attached Flownex project enables the design engineer to easily size and evaluate such an orifice plate for minimum and maximum flow conditions. Flownex’s Designer is used to find the required flow rates by searching for the “Volume flow based on ambient conditions” in the upstream pipe component whilst setting the Ambient temperature to the Normal Temperature value of 0°C in the Solver settings. Note that the so-called Normal and Standard conditions are not globally standardised. Once the maximum flow has been found, the Flownex Designer is also used to determine the orifice size to achieve the required measured orifice plate pressure drop.

Flownex also enables the design engineer to evaluate the influence of temperature and pressure variations (and anything else of interest) on the uncertainty of the orifice plate measurement via the use of Flownex’s Sensitivity Analysis capability.

For the case studied, it is shown that the bulk of the uncertainty originates from pressure and temperature variations. If the calculated mass flow uncertainty of 3.7% is not acceptable, pressure and temperature correction has to be implemented in the transmitter. The orifice plate manufacturing tolerance contributes less to the overall uncertainty but is relatively simple to improve. It is also shown that in typical flow measurement instrumentation, the pressure transducer and transmitter uncertainties are negligible in comparison.

Not only is Flownex capable of designing large, sophisticated flow networks, but it is also able to focus on a single element of design such as a simple orifice plate and then analyse that element in incredible depth. This versatility of Flownex is unparalleled amongst similar products and must make Flownex an indispensable software tool amongst process design engineers.

The full case study discussion document is available on the Flownex® web page in the Case Studies section:


Fouling Factors in Flownex Heat Transfer Models Popular

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Fouling Factors in Flownex Heat Transfer Models Rev 1.zip

Fouling Factors in Flownex Heat Transfer Models


Fouling can have a significant influence on heat transfer processes by reducing the actual heat transfer rate and may therefore need to be taken into account in some cases. In addition, fouling may also influence flow properties such as velocities and pressure drops due to changes in the coil pipe inside diameter and roughness, however this case study only focusses on the influence on heat transfer. Flownex offers impressive heat transfer capabilities as standard, however it is not so obvious how to account for fouling in heat transfer problems. Fortunately, due to Flownex’s scripting capabilities and extensive materials library, this problem can be solved with relative ease.

Two methods to account for thermal fouling are presented. Both may provide results of acceptable accuracy; however it is shown that in extreme cases with high fouling and high heat fluxes, it may be necessary to model the physical fouling layers to improve accuracy. Fortunately, Flownex is perfectly suited to performing this task.

Flownex® offers the user the ability to implement calculations which form part of the solution network. In this way, it is relatively simple to implement the equations required to account for the influence of thermal fouling. What sets Flownex apart from the competition is its ability to model even the temperature profiles through a multi-layered pipe wall subjected to heat transfer.

Immersion Firetube Model Popular

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Immersion Firetube Ver 1.61.zip

Immersion Firetube Model

Updated for Flownex 8.8 and later

Please note that the original immersion firetube model (ver 1.5) will no longer work with Flownex 8.8 and later. Therefore the model has been updated to version 1.61, please download this update. Please note Ver 1.61 fixes an issue with firetube diameters when switching between schedule specification and geometry specification.

Immersion firetubes, as the name suggests, are tubes or pipes fully immersed in a fluid with a burner firing into one end. The combustion gases flow through the firetube and leaves at the other end, normally into an exhaust stack. The immersion tube aims to transfer as much heat as possible to the fluid within the boundaries of inevitable practical constraints.  

Indirect heating processes have been widely used in the oil and gas and several other industries for many decades. Advantages of indirect heating include:

  • the relatively low cost of the equipment
  • separation of the high pressure process fluid from the heating medium via simple pressure piping
  • relatively high efficiencies
  • low maintenance and running cost
  • reduced heat loss
  • long operational life

The heating medium may be water, water-glycol, salt, steam and air for indirect heaters, or any fluid that needs to be heated directly. Water is possibly the most common medium due to its low cost.

The Flownex model presented implements a simple immersion firetube. A more comprehensive discussion and case study on immersion firetubes is also attached.

Natural Draft Exhaust Stack Popular

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Natural Draft Stack Ver 1.6.zip

Natural Draft Exhaust Stack


Although Flownex is capable of modelling natural draft processes out of the box, it is convenient to have a dedicated natural draft exhaust stack component available which may be added to any applicable process. Furthermore, this basic component may be used in conjunction with other combustion compound components to simplify the process flow diagram.

Natural draft processes rely on buoyancy effects to generate draft. However, when modelling an exhaust stack, the stack height also implies a small but significant pressure drop due to elevation. These two effects combine to drive the natural draft flow.

Additionally, the exhaust stack compound component implements convenient mechanisms to specify stack geometry and losses such as the elbow between the vertical stack and the horizontal piping feeding into the stack. It allows for a unity exit loss as well as an additional loss factor that could be used for any additional losses in the stack design such as a velocity seal, a silencer or a spark arrestor.

Natural Gas Combustion Modelling Popular

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NG Burner Model Ver 1.6.zip

Natural Gas Combustion Modelling

Updated for Flownex 8.8 and later

Please note that the original natural gas combustion model (ver 1.5) will no longer work with Flownex 8.8 and later. Therefore the model has been updated to version 1.6, please download this update.

The Flownex® Adiabatic Flame model is based on the NASA Glenn Chemical Equilibrium Program CEA2 and supports a large range of fuels. The development of the natural gas combustion model has only attempted to implement a combustion model for typical natural gas compositions. It would be easy to add capabilities for other fuel components, whether gaseous or liquid.

The development of this model essentially comprised of three basic fields of development; firstly, some effort went into defining fluid tables for the selected natural gas components in such a way that accurate interpolation would result at low partial pressures and at temperatures exceeding those expected during combustion. Secondly, a suite of compound components were developed to assist with the convenient specification and analysis of the gas components. Thirdly, a Simple Burner model was developed by wrapping the Flownex Adiabatic Flame model in a compound component together with a script to enable the specification and calculation of typical natural gas burner performance parameters. 

Flownex deals with combustion gas mixtures via the specification of the mixture mass fractions at the boundaries. Similarly, the combusted flue gas may be analysed at any node downstream of the Adiabatic Flame model. As gas compositions are commonly specified in mol fractions rather than mass fractions, a suit of 5 scripts, each wrapped in a compound component for convenience has been developed. These serve as inputs and outputs of information to and from the Burner compound component. 

The full case study discussion document is available on the Flownex® web page in the Case Studies section:


Pressure Pipe Wall Thickness and Flange Rating Calculation Using a Script and a Generic 4D Chart Popular

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Pressure Piping Thickness and Flange Rating Calculation Rev 3.zip

Pressure Pipe Wall Thickness and Flange Rating Calculation Using a Script and a Generic 4D Chart


In the oil and gas industry high pressure applications are the norm rather than the exception. Process engineers may employ Flownex® to model liquid or gas piping systems as part of their heat and mass balance, and pipe sizing calculations. However, in high pressure applications it is also necessary to design the pressure piping and associated connected flanges to safely contain the high pressure fluid. The process engineer often has to rely on others to determine the required pipe schedules (wall thickness) and flange ratings. This is less than ideal since pipe schedule changes which occur after the process design stage could mean changes in pipe sizes to reduce velocities and / or pressure losses. This will inevitably lead to significant rework of the Flownex® model, initial datasheets and Piping and Instrumentation Diagrams (P&IDs) and add to the cost of the project.

Flownex® does not offer the facility to perform wall thickness and flange checks in a built-in component or script since almost every nation has their own pressure vessel and pressure piping standards. However, Flownex®has a very powerful facility in terms of its scripting capability, and combined with the Generic 4D chart library, all the tools required are available to implement pressure piping calculations according to any design standard. In fact, any data table oriented calculation procedure may be implemented using this approach. This case study demonstrates the implementation of three such international standards – ASME B31.3, AS 1210 and AS 4041 – in a simple script. ASME B31.3 is a widely used US Standard for pressure piping and AS 1210 is an Australian and New Zealand Standard for pressure vessels and AS 4041 is the pressure piping equivalent. It is also further demonstrated how to use the Generic 4D charts as a material property library to be used by the script. The script demonstrates the implementation of:

  • Corrosion allowances
  • Under-tolerance
  • Minimum required wall thickness to safely contain the fluid at design pressure and temperature
  • Calculation of a design margin
  • Selection of an ASME B16.5 flange rating

Using this simple script and Generic 4D chart in any Flownex® model, pressure piping and flanges can be easily checked for compliance with any international standard well before piping engineers are required to verify the structural integrity of the piping system.


The model has been updated to include the following materials:

  • ASTM A106 Grade B with ASTM A105
  • ASTM A312 TP304 with ASTM A182 Gr.F304
  • ASTM A312 TP316 with ASTM A182 Gr.F316
  • ASTM A790-S31803 with ASTM A182 Gr.F51

Furthermore, the Generic 4D charts have been modified to allow data entry in the same units as those found in the ASME standards, i.e. bar-g and MPa-g. Three run-time warnings have also been added to check operating conditions against specified design conditions.


The full case study discussion document is available on the Flownex® web page in the Case Studies section:


The Sizing of Pressure Control and Pressure Safety Valves Including Reaction Force Calculation Popular

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PSV Sizing and Reaction Force Modelling Rev 1.1.zip

The Sizing of Pressure Control and Pressure Safety Valves Including Reaction Force Calculation


Pressure control valves (PCVs), pressure regulating valves and pressure safety valves (PSVs) are an important part of any plant design in the oil and gas industry. Gas products are typically transported at very high pressures to reduce pumping costs and reduce line sizes. Pressure control valves (and the subset of pressure regulating valves) are then used to reduce the pressures to the required levels at the point of consumption. However, if a pressure control valve fails, the plant design must make provision for safety systems to prevent catastrophic events from taking place. The proper selection and installation of pressure safety valves is one option. Alternatively, two pressure control valves may be installed in series in a so called active-monitor arrangement. Furthermore, a slam-shut valve may be installed that is able to shut down the plant in a short period of time.

This case study demonstrates the combination of pressure control and pressure safety valves where the latter is used as the means of ensuring safety should the former fail. The use of PSVs are commonplace in most oil and gas plants, in fact, all international design codes and standards in the oil and gas industry mandate their use at any position in the plant where pressures may exceed design pressures. Pressure increases beyond design values may occur due to mainly three causes:

  1. Process failure – a situation where faulty equipment is no longer capable of controlling the pressure to acceptable limits. This may include a failed control valve, a blocked outlet, a tube rupture, a loss of utility such as cooling medium or power, gas blow-by etc.;
  2. Locked-in thermal expansion – a situation where a vessel or length of pressure piping may be locked-in upstream and downstream and a resident heat source then causes the internal pressure to rise beyond design limits; and
  3. External fire relief – a situation where an external fire may add heat to a vessel or pressure piping, resulting in a similar scenario to the locked-in thermal expansion case.

A side-effect of the installation of a PSV is the resulting reaction force that may be created when the PSV opens. Since most PSVs “pop” open rather quickly, very high reaction forces may result and must be checked by the design engineer.

This case study demonstrates how Flownex® has been used to size a PCV as well as a matching full-flow PSV and easily calculate the resulting reaction forces. Checks for design code compliance are also performed.

The full case study discussion document is available on the Flownex® web page in the Case Studies section:


Thermal Oxidiser and Recuperator Heat and Mass Balance Popular

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Thermal Oxidiser Ver 1.0.zip

Thermal Oxidiser and Recuperator Heat and Mass Balance
A thermal oxidiser typically consists of a burner system which creates a high-temperature environment in a chamber into which a waste stream is injected to oxidise the hazardous waste stream. Due to the high temperatures required to perform the chemical destruction, recuperators are often used to recover as much of the waste stream heat as possible. In this case, the recuperator used is a steam generator. A model was developed in Flownex® using previously developed compound components to simplify certain tasks such as gas composition specification and gas property analysis. The model uses an iterative approach to establish the heat and mass balance of the entire system by adjusting the fuel flow, the air flow and the water flow in succession until the desired oxygen levels and steam quality are obtained.