When control valve professionals talk about "control valve sizing," they really mean the entire process of selecting the valve that will do the best job of controlling the process. Selecting the right size valve is an important part of the process, but there are other equally important considerations as well.
The control valve's size should be selected so that it will operate somewhere between 60 and 80% open at the maximum required flow rate and whenever possible, not much less than 20% open at the minimum required flow rate. The idea is to use as much of the valve's control range as possible while maintaining a reasonable, but not excessive, safety factor.
If the valve is too small, it will be obvious immediately, that it will not be able to pass the required flow. In actual practice, undersized valves are fairly uncommon. Commonly, the valve is too large. An oversized control valve will cost more than is necessary, but more importantly, an oversized valve will be very sensitive. Small changes in valve position will cause large changes in flow. This will make it difficult or even impossible for it to adjust exactly to the required flow. Any stickiness caused by friction will be amplified by the overly sensitive oversized valve, reducing the precision to which the flow can be controlled.
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In the illustration above, assuming that both valves are capable of positioning within 1%, the properly sized 3-inch valve will be able to control flow within 8 gpm, while the oversized 6-inch valve will only be capable of controlling flow to within 20 gpm.
Cavitation
Liquid applications must always be evaluated for cavitation. Not only does cavitation cause high noise and vibration levels, it can result in very rapid damage to the valve's internals and/or the downstream piping. Especially with rotary valves, the prediction of damaging levels of cavitation is more complex than simply calculating the choked flow pressure drop. As a result of flow separation and the formation of eddies within the valve, localized areas of pressure reduction and recovery can cause damaging cavitation at pressure drops well below that which results in fully choked flow. One proven method for predicting cavitation damage in rotary control valves is based on a correlation between calculated sound pressure level and the potential for damage.
Noise
In addition to the fact that a noisy valve in liquid service will most likely suffer unacceptable rates of cavitation damage, high noise levels usually cause vibration that can damage piping, instruments, and other equipment. Control valves in steam and gas service can generate noise levels well in excess of plant standards, even at moderate pressure drops, especially in sizes above 3 or 4 inches. As a result, the valve sizing and selection process must always include noise calculations.
Installed Flow Characteristic
In nearly all applications, a control valve should have a linear installed flow characteristic (the relationship between controller output and flow in the system). The control valve's inherent (published) flow characteristic interacts with the system's flow vs. pressure loss characteristic to yield the installed flow characteristic. If the installed characteristic deviates significantly from linear, it will be difficult or impossible to tune the loop for both accurate and stable control throughout the entire flow range. A computerized analysis of the installed characteristics should be part of the control valve sizing and selection process.
Actuator Sizing
Sizing actuators for on-off service is fairly straightforward, requiring only that an actuator be selected with a torque output slightly higher than the seating and unseating torque of the valve. The situation is more complex with control valves. The torque output of most rotary actuator's changes with the angle of opening. At the same time, the valve's torque requirement depends both on the opening angle and the throttling pressure drop at that particular angle. To ensure adequate spare torque to guarantee smooth, accurate control, a computerized analysis is recommended.
Selecting Control Valve Style
The choice of control valve style (globe, ball, butterfly, etc.) is often based on tradition or plant preference. For example, a majority of the control valves in pulp and paper mills are usually ball or segmented ball valves. Petroleum refineries traditionally use a high percentage of globe valves, although the concern for fugitive emissions has caused users to look to rotary valves because it is often easier to obtain a long-lasting stem seal with rotary valves.
Globe valves offer the widest range of options for flow characteristics, pressure, temperature, and noise and cavitation reduction. Globe valves also tend to be the most expensive. Segment ball valves tend to have a higher rangeability and size for size, nearly twice the flow capacity of globe valves, while they are typically less expensive than globe valves. On the other hand, segment ball valves are limited in availability for extremes of temperature and pressure and are more prone to noise and cavitation problems than globe valves.
High performance butterfly valves are even less expensive than ball valves, especially in larger sizes (eight inches and larger). They also have less rangeability than the ball valves and are more prone to cavitation.
The eccentric rotary plug valve combines the features of rotary valves, such as high cycle life stem seals and compact construction, with the rugged construction of globe valves. Unlike the other rotary valves whose flow capacity is approximately double that of globe valves, the flow capacity of eccentric rotary plug valves is on par with globe valves.
While the selection of a valve style is highly subjective, in the absence of a specified valve or plant preference, the following approach can be used to select a control valve style for applications where the valve will be six inches or smaller:
- Considering pressure, pressure differential, temperature, required flow characteristic, cavitation, and noise, will a segment ball valve work?
- If a segment ball valve is not suitable, select a globe valve. Keep in mind that cage guided globe valves are not suitable for dirty service.
- For applications where the valve will be 8 inches or larger, first investigate the applicability of a high-performance butterfly valve because of the potential for significant savings on cost and weight.
Ensuring Accuracy
Today control valve sizing calculations are usually performed using a computer program. Most manufacturers of control valves offer control valve sizing software at no cost, though most are specific to that manufacturer's valves only. Metso's Nelprof, however, includes a number of generic valves, such as globe valves, ball valves, plug valves, and butterfly valves, to choose from. These generic selections permit the user to investigate the applicability of different valve styles and sizes to a particular application, without showing a preference to a particular valve manufacturer.
Selecting a properly sized control valve is essential to achieving the highest degree of process control for the liquid, gas, or multi-phase fluid. To ensure accuracy, use the following information for control valve sizing:
- If a set of loop tuning parameters only works at one end of the control range and not the other, the valve's flow characteristic is most likely the wrong one.
- If a system has a lot of pipes, use an equal percentage valve.
- If a system has very little pipe, use a linear valve.
- A control valve that is sized to operate around 60% to 80% open at the maximum required flow and not much less than 20% open at the minimum required flow will give the best control.
Looking for control valve installation best practices?
Below we'll cover 7 things you must do when installing a high pressure control valve.
Tubing often looks like the perfect handle to lift a valve. However, lifting the valve by this method can quickly bend the tubing itself or the connection point where the nut and ferrell are. And if you bend it too much it can break that seal to the valve.
The best way to pick up a control valve is either by the valve body itself, the topworks or the lifting hooks on the top.
The second best practice is to install ball valves on both the upstream and downstream side of the control valve.
When it's time to do maintenance on a valve, you will need completely cut off any pressure on the upstream and downstream side. This process is referred to as the double block and bleed procedure, and ball valves make it easy to do.
We often get asked if customers can mount their through-body control valve sideways.
Normally for a through-body valve, the inlet and outlet piping should be horizontal.
However, sometimes, depending on construction of the vessel, the piping the valve is to be installed on is vertical, so if you install the valve without adjusting the piping, the valve would be sideways.
We do not recommend you do this. Here's why.
If you mount the valve horizontally, the weight of the topworks internals and the valve trim pushes the valve stem onto one side of the packing. Because of this, over time you will experience premature wear on the packing and valve stem that could potentially lead to leaks in the valve.
Mounting a HPCV sideways does not allow the lubricating oil on the topworks to travel to the stem. This expedites the wear on the upper stem.
The best practice is to install the valve in vertical orientation so it looks like it's standing upright.
Check and make sure the fail position of the control valve is correct for your application.
Sometimes we are asked "Control valves should always be in what position?" This is an impossible question to answer, because it depends on your application.
If you are using it for back pressure, you want it to fail open so pressure doesn't build. However, you may want it to fail closed to protect downstream equipment if there is a failure.
The easiest way to check your valve's fail position is to look at the position indicator to see if the valve is open or closed before you have any pressure on it.
The good new is if it's in the wrong fail position, you can open up the top works and convert it without having to buy extra parts.
Wet or dirty gas doesn't always affect the valve itself, but it does affect the pilot or level controller communicating with it. And if device is not working, the control valve won't work properly.
Examine the vent port of the control device (pilot or liquid level controller). If the vent port looks like it has dirt stuck around it, your supply gas is probably wet. After exhausting the wet gas, dirt will begin to stick to the moisture.
If this is the case, move your tubing to pull supply gas from a high and dry spot or consider using compressed air for instrument supply.
When installing a control valve with a flanged connection, tighten the bolts in a star pattern, just like you do on a car wheel.
One side cinched down too much doesn't create a good seal. Also, any time you are replacing a flanged valve, make sure to replace the flange gaskets. Using a damaged flange gasket can lead to issues.
When installing a valve with a threaded connection, use Teflon tape or pipe dope (or both) on the threads. This helps seal the connection to prevent leaking and protects the threads.
Recently, many producers in the Permian and Mid-Con have begun using 2 High Pressure Control Valves in dump valve applications on their separators.
These producers are seeing decreased down time and reduced operational costs as a result of this method.
This dual dump design provides redundancy, so you don't have to stop production to perform repairs. The reason is obvious'if the trim from one valve fails, you can isolate it and divert the flow to the second valve.
This solution also allows for greater variability in production volume. You can install two smaller valves rather than one large valve. You can flow both dump valves in early high-volume production. As production rates decline, you can move down to one valve and repurpose the other on a different application.
Seats, seals and O-rings are small but critical pieces for oil and gas control. These elements play an important role in control valves, regulators, and temperature controllers. They're made from different types of rubber materials, called elastomers.
You may also hear them called soft goods or rubber goods.
Each material is designed to perform best under certain conditions. Elastomer wear is inevitable, but by selecting the correct material, you can run production longer before the elastomers require replacement. So, how do you know what to select?
Download our Free Guide to Valve Elastomers
Let's look at three important questions to ask when selecting your oil and gas elastomers, as well as the four primary elastomer materials that we offer in our products.
A control valve is made of different elastomers, each designed to perform best under certain conditions. There are three primary data points you need to identify in order to determine which elastomer to select for a given application: Operating Temperature, Level of Potential Corrosion, and Level of Potential Wear.
This one is straightforward: What is the temperature of the liquid or gas flowing through your production process'specifically the temperature the elastomer will be exposed to?
This is the first point you can use to narrow your selection.
Production running at a maximum temperature of 425° F may be limited to a single elastomer option; however, based on temperature alone, a 200° F operating temperature could still use any of these options.
Corrosion in oil and gas production occurs when acid gases, such as H2S and CO2, and chemicals contribute to the elastomer and metal deterioration of the production equipment and controllers.
Though elastomers cannot corrode, when their integrity is compromised, it can cause improper valve function, or even total valve failure. This is why the selection of elastomers is so important.
When you're dealing with corrosive conditions, you'll need to consider important resistance rating categories like CO2, H2S and Methanol. Some are clear'such as using HSN for high levels of Methanol, or Aflas® for high H2S presence. Others, like CO2 have similar resistance across each elastomer.
One cause for elastomer wear (or erosion) is high levels of actuation. This could be from something like a high-producing well where your control valves need to actuate multiple times per minute to control the flow.
The main cause of elastomer erosion, however, is when abrasives like sand are in the flow stream. Sand will quickly wear out internal components and cause further damage to equipment. This is another reason that elastomer selection is so key to production.
If you are experiencing recurring issues with your elastomers'for example if you're replacing the elastomers in your valves more than once a month'you probably need to use different materials. Kimray has narrowed down our options to help make the selection easier.
Buna/Nitrile is a synthetic rubber commonly used in elastomers. It's also known as Buna-N or Nitrile.
It's good for most applications with a typical amount of wear and corrosive elements present in the production flow. No matter which kit or selections you make, many elastomers across our product lines will likely have some components made of Buna.
Highly Saturated Nitrile, or HSN, is a special class of nitrile with more chemical resistance, thermal stability and greater tensile strength. It's resistant to petroleum oils, ATF, sour gas, amine/oil mixtures, oxidized fuels, lubricating oils, CO2 and low levels of H2S. Another advantage of HSN is its excellent resistance to Methanol injection.
FKM (Viton') is the ASTM short form name for fluoroelastomer. Kimray uses Viton', which is a registered trademark of the manufacturer, but also widely used for the material in general.
Viton is a great option primarily for higher operating temperatures. However, with those high temperatures, you'll need to avoid hot water or steam applications, as the material will quickly break apart under those conditions.
Aflas® is the trademark name for a unique fluoroelastomer that is highly resistant to a wide range of chemicals, acids, strong bases, amines, and steam.
Let's contrast a few of these:
Again, Buna is good for most applications with a typical amount of wear and corrosive elements present in the production flow. Viton can operate at higher operating temperatures than Buna. (Note: avoid hot water or steam applications)
While Viton can operate at higher operating temperatures than standard Buna, Aflas has many additional advantages.
Aflas is highly resistant to a wide range of chemicals, acids, strong bases, amines, and steam. It also has outstanding heat-resistance and electrical insulation properties, but is proportionately more costly than Buna or Viton. Aflas is typically targeted at special applications such as high levels of H2S, high temperatures, and amine plants.
Here are some key indicators that you need to change elastomers from standard Nitrile/Buna to another material:
Here are some examples of the ideal elastomer materials in specific applications:
NITRILE/BUNAHSNFKM/VITONAFLASSaltwater DisposalMethanolHighHeatH2SPetroleum FluidsPetroleum FluidsAcidsPetroleum FluidsGeneral PurposeGlycol DehydrationPropane GasolineHigh HeatWaterLow LevelH2SSteamCO2AmineAcidsBasesDownload our Free Guide to Valve Elastomers
Bending metal tubing is a critical function for pneumatic devices in the oil and gas industry. In this video, we'll equip you best practices, tips, and tricks to ensure that your tube bending and fitting installation is accurate, consistent, and safe.
We'll start by looking at a fitting which includes four parts: the body, nut, front ferrule and back ferrule.
Generally, you don't want to take these apart ahead of time to avoid the possibility of getting any dirt or debris inside. It's good to know what the parts are, so when you're putting it together, you know how to layer the components.
For all fittings on control valves and equipment, we suggest using a thread sealant such as Loctite rather than Teflon tape to avoid the potential of any tape getting inside the equipment.
We recommend planning out a path ahead of time so you can avoid tubing that crosses paths if possible. Taking some time up front to figure out your paths can save you material and make your bends easier. On our packages, we like to keep all the tubing as close to the valve body as possible to keep it out of the way.
If you're installing a straight connector, you can fully tighten it when you install it since there's only one way the tube can go in. However, to give yourself a bit more flexibility, don't fully tighten any 90° or elbow fittings until the tubing has been installed.
For this high pressure control valve package, we're going to start by connecting the upstream side of the valve to the sense line.
Apply sealant to the connection. Since it's a 90° elbow fitting, we won't tighten it all the way yet.
One of the first things you can do on your tubing is make an end reference mark. This mark will make sure you always know which side of the tube is your reference side, which will go to the left of your bender.
This first measurement will be taken from the where the tubing touches the bottom of the nut to the center of where the bend will be. I'm going to use a piece of scrap tubing to get an estimate of where this bend needs to be.
Insert your tube into the fitting, then measure and mark where you'll make the 90° bend. This mark will be the centerline radius (CLR) or bend radius. CLR is determined by the die size of the tubing benders.
It can be helpful to mark the whole circumference of the tube so that no matter how it's inserted into the bender, you can still see the line.
You can easily put this tool in a vise as we're doing to help keep it steady and leave your hands free to control the tubing.
Lift the short arm of the bender and insert the tube into the jaw of the bender. Align both zero markers on the tool, then adjust the tube until your mark is aligned with the 'L' position. For 90° bends, you always align your mark with the 'L'. Our reference side is on the left, so that's why we use the 'L'. If the reference side is on the right, you would use the 'R'.
Tighten the tube latch and make your bend. The '0' on the arm (or roll support) will be your indicator for the degree of bend you're making. Pull the arm down until you reach the 90° mark.
You may need to bend slightly more than your target angle to compensate for angular springback, which is how the tube will spring back a few degrees when released. Don't over bend it too far'you can always go back and add more, but you can't reduce an angle after it's made.
Now we'll be cutting our bent tube to length. Insert the tubing in one fitting and make a mark where it aligns with the shoulder of the fitting body.
A tubing cutter works by rotating around the tubing and gradually tightening the cutting wheel until it cuts through the tubing.
Position the mark in the cutter. Turn the handle until the wheel touches the tubing. Then turn the handle an extra 1/16-turn. The marks on the handle indicate an 1/8-turn, so use that as a reference.
Rotate the cutter around the tube. After every second rotation, turn the handle about a 1/16th of a turn until the tube is cut through.
After cutting the tubing, use a deburring tool to remove any sharp edges or burrs from the tubing. This is an important step to ensure that the tubing fits securely into the fittings without causing any damage.
To keep track of the amount of rotation, you can mark the tubing and nut in its starting position. Hand-tighten the nut and then turn another 1 or 1-¼ turns with a wrench. Overtightening can put too much pressure on the fitting. Do this for both fittings.
For our second connection, we'll be using a straight connector and one elbow. First, apply sealant to the connection. Fully tighten the straight connection then hand start the elbow connector leaving a half turn to make the installation easier later.
For this piece of tubing, we'll need two 90° bends. Measure to get a rough estimate of the length of tubing you'll need.
Cutting a long piece of straight tubing is difficult to hold on to while cutting, so you can lightly put it in a vise if you need. We'll do a final length cut later.
A quick trick you can use to get measurements for a bend like this is to use your tubing set in the connector and some scrap tubing in the other connector. Line them up by eye and use a straight edge or a level to get a more accurate measurement. Make your mark on the center line.
Using the same techniques as the other bend, insert the tubing, align the zeros and put your mark at the 'L'. Clamp down with the latch and bend to the 90° mark.
For our second 90° bend, accuracy is more important now because we must reach our fitting perfectly. Return the bent tube to the fitting, and slightly move the scrap piece of tubing so it can rest in its final position. Mark the center line on your tubing for your second 90° bend.
Before clamping the latch down all the way, make sure that your tubing bender is square with the bend you previously made. Check the level of the tool, then check the level of the previous bend.
Secure the latch, bend the arm down to bring the zero to the 90° indicator, maybe a little more, then release.
With the tubing back in the fitting, mark the final length based on the start of the shoulder of the fitting body. Make your cut, again tightening after every second rotation. Deburr the end and you're ready to install.
Hand-tighten the fittings, mark a reference point and turn 1 to 1-¼ turns.
On this example, we'll be making a 90° and an offset bend.
First, we'll measure for the first 90° bend. Use a piece of scrap tubing in one fitting and your actual tubing in the other. Use a level to mark where your centerline will be.
The length of tube before our mark is less than the allowable amount for this tubing bender. Since we know we will need the shortest amount of tubing possible before the bend, I'll simply adjust it so the reference end of the tubing is aligned with the latch.
If you want to learn more, please visit our website Cage guided valve.
A best practice when you're making two bends on a single tube is to make a reference mark on the top of the tubing, so you get the correct orientation of the bends.
Set in a scrap piece of tubing and measure the distance from the center line of the scrap piece to the center line of the fitting. In this case, 3'.
For this piece, the offset just needs to clear the bonnet or any obstructions. Make your mark and bend the tube, but for this bend, we're not bending it to a certain angle, we're bending it to achieve that 3' offset height.
For this bend use the mark you made earlier to help you align the tubing correctly for your next bend. You'll need more precision on this second bend, so use a level to get your angle correct. Tighten the latch and make your bend.
This might be a little bit of a trial-and-error process, just don't bend it too much. Bend it close, get a measurement and adjust from there.
The reason we're doing it this way instead of mathematically is because it's just not necessary for the type of connections we need to make here.
If you want to calculate the exact distance for an offset with two 45° bends, multiply the offset height by 1.414. That will be the length of tubing needed between the two centerlines of both 45° bends.
With our offset bend ready, mark the final length of tubing near the shoulder of the fitting. Make your cut and deburr the end. Once the piece is in place, make reference marks on the fittings and tubing to fully tighten the connectors.
For this connection, we're going to use two straight fittings. The tube will have two 90°s. We'll start by fulling tightening the fittings using sealant.
Take a rough measurement of the amount of tubing you'll need. Each side will need to come out of the fitting and make a 90° bend.
Set the piece of tubing in the fitting and a scrap piece in the other. Use another piece of tubing to mark the location of the first bend. Fortunately for this one, we can simply eyeball the placement.
Make your bend as we have before ' insert the tubing with the latch part way down, line up the zeros, align your mark to the L, tighten the latch, and make your bend.
With the piece back in the fitting on the body, make your second mark on the tube according to how it lines up with your scrap piece.
This bend will need to be level with the previous one. Check the level of the tool, then level the previous bend before making your second 90°.
Mark the tubing where it meets the shoulder of the fitting to make your final cut.
After deburring, insert the tube, hand-tighten the nut and then turn another 1 or 1-¼ turns with a wrench.
In natural gas production, managing your gas pressure drops is critical. If mishandled, these drops can jam up your system and cause downtime.
A pressure drop across a valve means that the media is flowing the normal direction'from up to downstream. If you didn't have a difference in pressure between upstream and downstream'in other words, if those pressures were equal'there would be no flow across the valve.
Production fluid, be it oil or natural gas, naturally flows from high to low pressure. That's how the flow is determined in any kind of separation equipment or system.
The pressure drop across a valve may also be called the "differential pressure."
Pressure drop across a valve is determined by the control points both upstream and downstream of the valve. If the valve is in a dump application, the pressure drop will be determined by two things:
Pressure drop does affect flow rate, but does not always reduce it.
Again, every valve flowing media will have a pressure drop, which is what creates the flow. Whether the pressure drop reduces or increases flow rate depends on if the drop moves higher or lower.
Here's the general rule:
If the pressure drop gets higher (meaning there is an increase in differential pressure), there will be more flow across a valve (to a point).
If the pressure drop gets lower (meaning there is a decrease in differential pressure), there will be less flow across a valve.
For example: A 1' trim in a 2' stem guided valve would be able to flow more with a 100 PSI drop than if it had a 50 PSI pressure drop. This is because there's more pressure in the flow media pushing on it to force it through the 1' trim.
Note, however, that this increased flow from increased pressure cannot go on indefinitely. At a certain point, you will reach what's called choked flow.
There comes a point where if you're increasing the pressure drop by lowering the downstream pressure, you're not going to increase the flow rate. The fluid will reach its maximum velocity at the vena contracta, and after that point, it will enter a state called "choked flow."
The higher the pressure drop is, the more flow you can get across a given orifice size. If you want to increase volume using the same valve and equipment you have, but you are in choked flow, you won't be able to.
This creates problems in your system because you can't pass the amount of volume that you need. And depending on the application you might be starving another piece of equipment that needs volume to operate correctly.
If you partially close a valve, would it increase the pressure? That depends on your volume.
If you partially close a valve and you are flowing a relatively high amount of volume, upstream pressure may increase if it's not opening far enough to release pressure.
If the valve is partially closed and you are flowing a relatively low amount of volume, it could release enough volume so that pressure decreases.
There are many variables that determine what your pressure drop is, including the application and the flow conditions the valve is exposed to.
That said, our Cage-Guided High Pressure Control Valve can handle higher pressure drops than many valves because of its balanced trim.
This is because with the working pressure of the valve, there is the potential of a high pressure drop, and the valve's operation allows it to work in those high pressure drop applications.
To get your valve out of choked flow, you must decrease the pressure differential. If you are worried about not passing enough volume through the valve in choked flow, you need to increase your valve trim size or you can increase your upstream pressure.
One important distinction to make: Once you're in choked flow, decreasing downstream pressure to increase the pressure differential doesn't do anything to increase flow rate.
If you increase upstream pressure, you're adding more energy to push it across the valve so that can increase the flow rate because it increases the pressure drop.
In other words, when you're in choked flow, you can push more production fluid or gas through but you can't pull more through.
If you add pressure from behind (upstream), you can push more through, but if you take away pressure downstream to create a higher differential, it's not going to allow more flow through the valve.
Cavitation is the formation and collapse of air or gas bubbles in a liquid.
The bubbles are formed when liquid undergoes a rapid change of pressure and falls below the vapor pressure. These bubbles collapse when the pressure recovers.
This can all happen in a very short span just after the vena contracta'the point in the valve where the diameter of the flow is at its smallest, and fluid velocity is at its maximum.
Because it happens inside a valve or pipeline, cavitation is not easy to spot. Here are two symptoms that may be caused by cavitation:
There are three things you can do to prevent cavitation in your valves:
Cavitation happens a lot with high pressure drops and high velocities. If you're experiencing a high pressure drop, another problem to watch for is flashing.
While cavitation is more common in liquid, flashing is more common in gas production.
Flashing happens when you reduce the pressure on a liquid hydrocarbons to the point that they "flash" into vapor.
For example: If you dump your oil emulsion quickly from a high pressure to low'say, 500 PSI down to 60 PSI'it can flash, meaning the rich, light, high-gravity oil condensate in your production vaporizes, and you lose that resource forever.
The pressure on your operation's production vessels is what keeps this oil condensate in liquid form.
This is why producers drop gas pressure in 'stages.'
Staging is the process of reducing pressure in stages rather than all at once. Reducing pressure all at once can not only cause freezing, but cavitation and flashing. More oil and condensate can be recovered in liquid form and not be lost to vaporization when staging pressure drops.
This is usually a concern in gas-producing wells. These operations are usually labeled as 'natural gas production''meaning gas is the largest resource the producer is recovering by volume.
However, these wells still produce oil, sometimes called 'white oil' because of its light color, and it can create significant revenue for these producers.
Many producers use a gas production unit (GPU) on their natural gas wells to heat the well stream before reducing the pressure, helping to mitigate freezing. In this set up, the oil and condensates can be recovered in the separator portion of the GPU.
The dry gas, meanwhile, flows out of the top of the vessel. The gas is sent downstream into a sales line. Some of the dry gas is used to power the instrumentation on the GPU.
Note staging is the reverse of the process of compression. The purpose of a natural gas compressor is to re-pressurize natural gas to push it downstream.
When the gas reaches a compressor, producers want the condensate to be 'knocked out' so it doesn't damage the compressor.
In many industries, engineers will create a blueprint for equipment and control layout, called a Piping and Instrumentation Diagram, or P&ID. In this video, we'll walk through codes and symbols specifically for oil and gas production equipment so you can read and understand P&IDs in the industry.
Process diagrams can be broken down into two major categories:
A P&ID is complex while a PFD is more of an overview of a process.
A flow diagram is a simple illustration that uses process symbols to describe the primary flow path through the production equipment. It provides a quick snapshot of the operating unit and includes all primary equipment and piping symbols that can be used to trace the flow of the well stream through the equipment. Secondary flows, complex control loops and instrumentation are not included. These PFDs are more helpful for visitor information and new employee training.
Field technicians, engineers, and operators use P&IDs to better understand the process and how the instrumentation is interconnected.
Sales personnel and OEMs (original equipment manufacturers) use P&IDs to spec equipment and build the vessels.
Not all P&ID elements are standardized, but the instrumentation symbols follow a standard set by the International Society of Automation (ISA). The ANSI/ISA's S5.1 standards are what this guide will be using to communicate consistently.
After some practice, you'll become familiar with many of these codes and symbols, but if you're just starting out or need a visual resource to reference, make sure to download our P&ID Reference Guide, which features a full list of symbols.
Download P&ID Symbols Guide
Stand alone, physical instruments are indicated by a tag number with a circle around it.
Tag numbers are a series of letters and numbers that identify a device as what it is controlling, the type of device being used, and the number assigned to it on the P&ID.
For example, 'PC' is a Pressure Controller, while 'PIC' is a Pressure Indicator Controller.
This chart shows common abbreviations for what you would see and how it would be written on a P&ID. However, there are many other abbreviations that you will see such as this more comprehensive industry list.
The number below these letters is the numerator to help identify a specific component on a project within the control loop. When there are multiples of the same device used in a diagram, this number helps viewers to reference that specific instrument.
If you were looking at a list of the controls, you could look at the control loop number to find that specific device on the P&ID.
Companies have different protocols for where these numbers originate. ANSI/ISA-S5.1 Table A.1 and A.2 dictates typical loop and instrument identification/tag numbers structure and allowable letter/number combinations for loop numbering schemes.
A viewer can use these critical tag numbers to reference additional process information for that instrument, which helps product sizing, material selections and other variables.
You'll notice that some components such as check valves, ball valves and isolation valves do not use tag numbers. Typically, the information given with these will be limited to their symbol and the line size.
The circle combined with the presence or absence of a line determines the location of the physical device.
No line means the instrument is installed in the field near the process.
A solid line means the instrument is in a primary location in a central control room (accessible to the operator).
A dashed line tells us that the instrument is in an auxiliary location in a central control room (not accessible to the operator).
A double solid line means that it is in a local control room or on a local control panel
Located in or on front of secondary or local panel or console
Visible on front of panel or on video display
Normally operator accessible at panel front or console
A double dashed line means it's in an auxiliary location in a local control room or local control panel.
These symbols may be supplemented with information on the name of the local control room or the local control panel, just outside the symbols, for example, COMPRESSOR, i.e., the local control room or local control panel for a compressor.
Shared display means you can see the same information in several locations across a network and it can be accessed anywhere. Shared control means you can change the parameters of that device remotely.
Some instruments are part of a Distributed Control System, or DCS, where a user can select a specific controller or indicator and see it in one location, such as on a terminal screen.
With today's computerized systems using virtual controllers like in PLCs and DCSs, new P&ID symbols had to be developed. If you take the same tag number symbol for a physical instrument and add a square around it, it now means that it is part of a shared display and shared control in a DCS.
Different symbols for line types tell us about the instrument. Users can identify how instruments connect to each other and what type of signal is being used.
For example, a solid line indicates piping, while a dashed line tells us that there is an electrical signal. Familiarize yourself with these different connection symbols by downloading our reference chart.
Piping symbols have various important uses you'll want to be familiar with. For example, one important symbol to note here would be the concentric and eccentric reducers. This will help you identify when piping changes sizes. You'll see these sometimes immediately upstream or downstream of a control device. This information is helpful for understanding flow capacity and sizing.
P&ID symbols can sometimes change from company to company. This is especially true with control valve symbols. This chart of common control valve symbols can be downloaded for reference, but always consult the P&ID legend if available.
Here are the symbols for pumps, tanks, and other types of equipment. The most common pumps used in oil and gas industry are screw, progressive cavity, and reciprocating pumps. The most common tanks are dome roof tanks.
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