Tuesday, June 30, 2020

INDUSTRY TRENDS IN CONTROL VALVE AUTOMATION

Advanced solutions for fugitive emissions monitoring enable process plants to schedule valve maintenance to minimize air pollution from their facilities and avoid fines.

Control valve automation has made major advancements over the last several years. While control valves themselves are largely unchanged, greater emphasis is on automating and precisely positioning these instruments.

This article describes the importance of control valve automation in modern process plants, as well as considerations for ensuring optimal valve performance. When choosing a device or technology to automate valves, many factors come into play. They include specific application requirements, electric certifications, safety integrity level (SIL), digital protocols versus traditional analog communication and more.

Introduction

A valve positioner is a critical component of the final control element of a process loop — the control valve. Positioners convert electrical signals to pneumatic signals to control actuator displacement. This ultimately keeps a valve at an intermediate position in response to a variable process control signal.

Control valve positioner manufacturers must meet rigorous requirements for efficiency, reliability and reduced energy consumption while producing cost-effective instruments that satisfy industry requirements. The need for predictive diagnostics is a demand placed on valve positioners. It is critical to predict failures in the valve, control signal and positioner before they become a catastrophic event and shut down the plant.

Recent advancements

The control valve industry does not innovate as quickly as other technology-centric fields. Instead of major breakthroughs of ingenuity, designers slowly adapt and improve products over time, providing a slow but constant rate of progression.

In the past decade, smart and digital valve positioner developments have outpaced performance capabilities of mechanical and electro-pneumatic systems. Digital communications protocol advancements allow smart controller technology to make progress and integrate more sophisticated functionality.

For example, positioner manufacturers are moving away from designs that require direct contact with the valve stem for feedback to the positioner in favor of noncontact, Hall effect sensor technology. Improvements in device diagnostics play an important role by facilitating the transition from traditional corrective and schedule-based maintenance to predictive maintenance. Diagnostics with valve positioners are becoming much more sophisticated and offer the ability to test valves to determine if maintenance or replacement is required.

Developments such as digital fieldbus protocols and low-power central processing units hastened the evolution of the valve positioner as a computer. Just as process sensors and controllers acquired smart capabilities, valve positioners and controllers followed the same route.

The introduction of intelligent control valve positioners with internal capabilities for trending, diagnostics, alarm status, etc., eliminates the need for external software in many cases. This approach is more fail-safe and secure for end users since setting changes must be made physically at the valve positioner. Moreover, maintaining valve history data in the positioner rather than in the distributed control system software ensures valuable information is not lost if the positioner is removed from service. The ability to locally configure the positioner also eliminates the need for a costly handheld device.

Some of the most significant innovations in automated valve monitoring relate to supply air (i.e., measuring and recording the supply air pressure to the positioner and providing an alarm if it drops below a set pressure), output air (i.e., measuring and recording the output air pressure to the actuator and providing an alarm if it is not present after a period of time), emissions (i.e., detecting a leak in the bellow section of the control valve and closing the valve without outside control if a leak is present), and emergency shutdown (ESD) solenoids (i.e., testing and determining if the solenoid will operate as required in an emergency).

A particularly important enhancement to automated valve technology is the partial stroke test (PST), a feature within the positioner that will move an ESD valve from 100 percent open to a predetermined position (80 percent) and then back to 100 percent. This indicates the valve will move when required. New techniques allow plants to perform PST either from an external source or automatically based on a set interval, with reports indicating pass-fail results of the test.

In addition, the current generation of smart positioners can utilize discrete inputs and discrete outputs to trigger an output for control, while valve friction monitoring indicates the increase or decrease of friction in the valve and the type of hysteresis it is causing.

Ongoing developments in smart and digital valve positioners have had a dramatic impact on plant efficiency, overall profitability and asset life cycle costs.

As far as improvements to instrumentation and system health, valve signature tests can be conducted to accurately evaluate the condition of a valve’s internal components. This helps eliminate unnecessary equipment service, spare parts purchases and valve replacement. Trending and histograms can run in the background to track positioner performance, and an alarm status list can provide a record of alarms. These advanced features enable process plant planners to determine the overall health of their instrument assets and then formulate effective maintenance strategies.

Some positioner manufacturers have pioneered advanced solutions for fugitive emissions monitoring, which can help avert failure of the valve’s bellow seal and packing — and the potential for discharge of hazardous gases. These solutions enable the positioner to internally sense the bellow seal housing, open or close the valve, or move it to a predetermined position if the pressure becomes too great. Should the positioner sense a leak, it can initiate an alarm alerting operators to the valve’s status. Through early detection of fugitive emissions via leak monitoring, plants can immediately schedule maintenance to minimize air pollution and avoid fines.

Lastly, energy consumption is a critical concern for industrial equipment. Control systems were once designed with the power supply at 1 1/2 times the current requirements to power individual loops. Plants have gradually increased their power consumption demands on each input/output cabinet to the point that it affects field instruments. Instrument manufacturers responded to this situation by developing new, energy-efficient positioner designs. Earlier valve positioners required approximately 2 to 3 watts (W) to operate, whereas the current generation of positioner requires 1/2 to 3/4 W to operate even with advanced features.

Choosing the right solution

Modern control valve positioner designs allow them to be used as on-and-off devices or for any combination of controlling to include regulation, modulation, mixing or even isolation. Valve positioners are highly engineered instruments and should not be treated as commodities. Addressing control valve performance has a dramatic impact on plant efficiency, overall profitability and asset life cycle costs.

Process plants have two primary requirements for control valves: ease of use and cost-effectiveness. When choosing a device to automate valves, however, a number of key factors come into play:

Specific applications requirements
Explosion-proof
Intrinsically safe
Remote-mounted
High-temperature
Low-temperature
Electrical certifications
FM
CSA
ATEX
usCSA/FM
SIL rating
Safety system

Communication drives automation in complex industrial facilities. Control valve positioners must be able to communicate with all recognized field device protocols, ranging from traditional analog to HART, Modbus, Profibus, FOUNDATION Fieldbus and Industrial Ethernet.

Valve positioner technology that integrates digital communications provides plant operators with greater visibility and control over critical assets. Smart valve positioners offer enhanced capability and practical benefits in relation to improved plant performance and greater operational efficiencies.

The main reason digital positioners are popular is they can do much more than control the valve’s position. The newest positioners can also collect data about the valve to automatically alert users about its performance and assembly.

Looking to the future

A natural response to the increasing economic, environmental and competitive pressures is to modernize automation technology, and many companies are investing in powerful, state-of-the-art control instrumentation as a result.

Technology is available to help process plants streamline operations and make them more efficient. One example is valve automation. Automated valve solution suppliers develop features to meet changing industry requirements. New forms of communications are coming, as well as tools to meet additional diagnostic requirements. The switch from pneumatic linear control valves to electrical linear control valves is on the horizon.

Control valves are a natural fit for digital intelligence and they may be one of the most important elements of a successful plant asset management strategy. With more intelligent valve automation capabilities, end users can better diagnose and repair a problem prior to failure.

Conclusion

Enhanced control valve automation helps all kinds of manufacturers continually improve process efficiency and product quality while safeguarding people, plants and the environment.

The latest generation of smart control valve positioners enables industrial organizations to do more diagnostics locally and better understand overall valve performance at a lower cost.

Any decision to use a positioner on a valve should be made with a knowledgeable and experienced control valve specialists who can advise on the proper type of positioner and installation technique crucial to optimizing the control valve.

Wednesday, June 10, 2020

CHOOSING THE RIGHT STRAINING ELEMENT

CHOOSING THE CORRECT OPENING SIZE

Introduction:

A strainer is installed into a pipeline and functions as a mechanical filter removing and retaining particles too large to pass through yet allowing the flowing media to pass unobstructed. By cleaning the flowing media, pipeline strainers help to protect expensive downstream equipment such as pumps, meters, spray nozzles, compressors, and turbines. Straining of the pipeline flow is accomplished via a perforated or mesh lined straining element, internal to the strainer. This is shown in the illustration below.

Pipeline Straining Example

One of the more common questions asked when specifying a pipeline strainer is: "What perforation or mesh should be used for this application?" Before I go any further, I think it would be wise to discuss the terminology used when talking about pipeline strainers. Typically, the internal perforation or mesh material is referred to as a screen, when talking about "Y" strainers, and a basket, when talking about basket strainers. However, this can cause some confusion since the term "basket" can be used for both the strainer housing and the internal perforated or mesh material. To avoid this confusion, this article will use the term "straining element" when referring to the perforation or mesh material internal to the strainer housing.

Straining Element Types

Determining Opening Size:

The first decision that needs to be made is the hole size of the perforation or mesh. The general rule of thumb is the hole opening size should be one-half the diameter of the largest allowable particle. The largest allowable particle is defined as the size of particle that can pass through downstream equipment without causing damage. For example, if the maximum allowable particle is 1/16 inch than the perforation/mesh opening would be specified at 1/32 inch.

Determine Hole Size

In addition to the size of particles, the quantity of debris in the flowing media must also be considered when determining the appropriate opening size.

Straining elements can only be used to remove insoluble floating impurities. The most common range of particle retention is 1 inch down to 40 microns (.0015 inch). The graph below shows sizes of common particles and compares them to perforation and mesh sizes.

Particle Size Graph

A common mistake is to specify a hole opening that is to small for the application. This can lead to over-straining and should be avoided for the following reasons:

Maintenance costs are significantly increased due to excessive cleaning requirements.
Pressure drop is increased dramatically.
The straining element may become damaged and fail.

In some applications requiring finer filtration, it may be advisable to strain in gradual steps. This is accomplished by placing progressively smaller straining elements in series.

Important:

Straining elements are not designed to withstand the same pressure as the strainer housing. If the straining element becomes fully clogged, it will be exposed to the same pressure as the housing. In most cases, this will cause the straining element to fail. A convenient way to monitor the differential pressure is to install pressure gauges on both the inlet and outlet sides of the strainer. It is not recommended to allow the differential pressure to exceed 20 psi.

Saturday, June 6, 2020

Industry Trends In Control Valve Automation

When choosing a device or technology to automate valves, many factors come into play. They include specific application requirements, electric certifications, safety integrity level (SIL), digital protocols versus traditional analog communication and more.

Introduction

Recent advancements

Ongoing developments in smart and digital valve positioners have had a dramatic impact on plant efficiency, overall profitability and asset life cycle costs.

to operate, whereas the current generation of positioner requires 1/2 to 3/4 W to operate even with advanced features.

Choosing the right solution

Process plants have two primary requirements for control valves: ease of use and cost-effectiveness. When choosing a device to automate valves, however, a number of key factors come into play:

Specific applications requirements
Explosion-proof
Intrinsically safe
Remote-mounted
High-temperature
Low-temperature
Electrical certifications
FM
CSA
ATEX
usCSA/FM
SIL rating
Safety system

Looking to the future

Conclusion

Enhanced control valve automation helps all kinds of manufacturers continually improve process efficiency and product quality while safeguarding people, plants and the environment.

The latest generation of smart control valve positioners enables industrial organizations to do more diagnostics locally and better understand overall valve performance at a lower cost.

Wednesday, May 27, 2020

SELECTING PRESSURE GAUGES : NEW ADVANCES ON AN OLD TECHNOLOGY

Pressure gauges are still useful in many applications, and developments can extend their capabilities.

When a pressure indication is needed and an operator is around to see it, a traditional gauge offers a useful means to get the data, but drawbacks are possible.

While mechanical pressure gauges have been mainstays in the process industry, they have also brought some challenges with them. Still, when a situation calls for a simple and inexpensive device with a local display, a gauge can fit the bill in a variety of applications

Traditional gauges have some serious drawbacks to consider in the selection process. Gauges operate using delicate mechanisms with springs and gears, making them vulnerable to shock and damage . Most operators have seen typical failures with broken glass, bent indicator needles or needles pointing straight down from broken gearing. In many environments, they are considered essentially disposable because of their low cost and frequent failures.

Yet using pressure gauges is still a great way to visually show what is happening in the process. But wouldn’t it be nice to get that information to a centralized location without having to be physically present at the gauge? Old-fashioned clipboard rounds with operators writing down readings take time and can lead to inaccurate information resulting from human error.

Selection considerations

When a pressure indication is needed and an operator is around to see it, a traditional gauge offers a useful means to get the data, but drawbacks are possible.

The variety of traditional gauges continues to be massive, and key considerations require some analysis.

Ruggedness – Some models are designed for environments in which pipes vibrate or moving equipment may cause impacts. Cases can be armored with rubber covers and beefed-up mechanisms to survive tough environments, but these options add cost.

Material of construction – While the cheapest devices are mostly brass, industrial-grade gauges are usually made of stainless steel or other durable materials. Nonetheless, be sure to know what the wetted and nonwetted parts are made of. Brass or mild steel components can deteriorate in a humid or mildly corrosive atmosphere.

Inlet configurations – Most larger gauges have a male-threaded inlet, usually ½-inch national pipe thread (NPT) or M20. Smaller and cheaper devices may be ¼-inch NPT. Usually the expectation is for screwing into an existing pressure port that has a female thread connection. Some offer more specialized options for more complex mounting situations, such as adding a siphon.

Overpressure and burst pressure limits – These designations can be confusing. An overpressure limit says how much a unit can withstand without damage. In other words, it can take a spike and continue working properly. Beyond that, the Bourdon tube may be permanently distorted or the mechanism pushed past its limits. Burst pressure is where some component fails, usually the Bourdon tube, blowing the case open and releasing process fluid to the atmosphere, which can often be a safety risk. In some cases, the process connection itself fails and it can “launch the gauge” as a flying projectile. In the case where extra isolation is needed, such as using a seal for instance, this can add additional protection for the gauge. However, in the case of a failure, some units will still release the process fluid. If the substance is flammable or toxic, a safety incident will follow. Others are designed to try to contain a release or direct the release, although limits exist.

Accessories & special adaptations

The basic operating limitations of mechanical gauges have prompted the creation of a variety of supplementary devices to overcome some of the problems, so in some cases these may need to be added. Typical examples include:

Snubber – This device restricts the gauge’s inlet pressure spikes and can serve two purposes: It can suppress pressure pulsations and it can improve overpressure protection. In either case, it is applied to the gauge’s inlet and tends to slow response.

Isolator or seal – This device is designed to keep the process fluid from getting into the mechanism. It typically uses a combination of an external diaphragm, which contacts the process fluid and transmits the pressure to the mechanism using a captive fill fluid. Isolators are normally used in situations where products are hazardous or where temperatures are extremely high so the gauge is protected.

Siphon – In situations where a gauge measures the pressure of a condensable vapor, usually steam, a siphon serves as a mechanism to trap condensate and act as a thermal barrier. The live steam places pressure on a slug of condensate in the siphon, which ends up acting as a fill fluid and keeps the device from seeing the full steam temperature.

Many other variations and special construction methods are designed to improve performance or avoid specific problems, including:

Case fill fluid – Filling the gauge’s case with a viscous fluid, such as glycerin, helps reduce needle movement caused by pulsations.

Heat tracing – In situations in which a device is exposed to cold environments, heating the case may be necessary.

Blowout cases and safety glass – Where the possibility of a catastrophic failure is high, some devices are designed to fail and release fragments and fluid in a single direction, usually out the back of the gauge, presumably away from people.

If an application depends on some of these more elaborate precautions, it is probably advisable to investigate some of the new technology improvements available for the industry.

The necessity of having a tube flex in response to pressure change and tying it to a gear mechanism makes for a delicate device easily subject to damage.

Basic design improvements

Since the user case for a basic gauge is still valid, various companies have tried to improve the design without losing the underlying appeal.

Digital gauges – Some companies have developed ways to retain the basic Bourdon tube design but replace the moving needle with a digital display. While the concept is good, the execution often suffers from visibility problems and short battery life. These are not normally practical for a device that is expected to run continuously, so they are often reserved for calibration lab and testing duties where they can be turned on and off when needed.

Electronic gauges – Some of the newest designs combine the benefits of an electronic transmitter with the usefulness of a traditional mechanical design. They use a strain-relief sensor rather than a Bourdon tube, processing the signal electronically rather than mechanically. The needle is driven by a tiny motor, so only one moving part is present, making the mechanism far more resistant to shocks and other extreme operating conditions.

Electronic gauges avoid many of the problems of mechanical devices. Eliminating the Bourdon tube removes a critical failure point, so overpressure capability is much higher and the possibility for process fluid escape is far lower. Many of the accessories necessary to ensure good performance are also no longer needed since those capabilities are part of the basic design of the new units.

Using sophisticated electronics, these new gauges are also able to monitor their own statuses. No way exists to verify a mechanical gauge is working properly short of removal from the process and testing, but a glance at an electronic gauge can show its operational status by a blinking LED. Even the battery life has been extended thanks to low-power electronics and highly efficient designs.

Wireless pressure gauges, like this model, serve as practical hybrids, incorporating many of the safety and performance advantages of electronic transmitters while providing effective local displays.

In many respects, the most critical drawback of a traditional gauge, its inability to send information to an automation system, has been overcome because these new devices include wireless transmitters able to send the pressure reading and status indications to the distributed control system or other automation platform. This optional function can be used whenever necessary.

One wireless pressure gauge (see Image 2) contains all the features of an electronic gauge while adding the capability to transmit its pressure reading via a WirelessHART mesh network. This additional communication capability adds “future-proofing” so it can be used in a sophisticated networking environment as the Industrial Internet of Things moves into more manufacturing applications. The wireless capability might not be needed today, but it may be soon.

Because this wireless pressure gauge is equipped with an advanced sensor design and additional isolator, it does not require a snubber. Its internal integral sensor isolator also keeps the process fluid from ever reaching the sensor, extending its working temperature range. Since it does not require a special configuration or other accessories, it is often a lower cost option than a traditional gauge in demanding applications.

Matching device & application

This new range of options means it is possible to choose exactly the item needed for a given situation and budget.

Traditional mechanical gauge – Where the process is benign, the budget limited, and a local reading and moderate precision fill the bill.

Electronic pressure transmitter – For more extreme applications, in an automated environment and in which the highest precision is necessary, but it is the most expensive.

Wireless pressure gauge – This new choice fills many of the areas in between. The process and safety parameters can be more challenging, and options exist to communicate wirelessly with the plant systems, today and tomorrow. The price falls between the other two options, providing a useful new process solution.

Pressure gauge technology continues to advance, providing more choices and enabling end users to measure this important process parameter in an optimal fashion.

Tuesday, May 19, 2020

HOW DOES A FLOAT SWITCH WORK?

When it comes to measuring liquid levels in tanks, few instruments are as reliable as the float switch. So what is a float switch? These handy devices can help measure metrics such as presence of absence of liquids in a tank, vessel, or container with dependable accuracy.

It’s important to know that all float switches aren’t created the same. There are many different varieties available depending on how you intend to use them. Still, the basic principle of operation for most float switches remains consistent: opening and closing as the liquid level in an object rises or falls. Float-principle

Reed float switches are commonly set as either normally open dry or normally closed dry. As the float on the normally open witches rises with liquid level, the magnets pull the blades of the reed switch together completing the circuit, allowing power to flow to any attached electronics. With normally closed float switches the reed switch opens up as the float and magnets rise with liquid level, breaking the electrical circuit.

Choosing the type of float switch you want takes some consideration. Low voltage float switch? High temperature float switch? Of course, what liquid you’ll hoping to measure with the float switch also matters. If you’re working with a liquid that is prone to gather deposits, whether it’s lime or calcium, for instance, they can eventually build up to a point that causes float switch failure.

First, though, you’ll need to determine the specifics of your float switch installation, or how you want it to be physically configured, for instance, whether that’s vertically or horizontally. How float switches are mounted makes a big difference in how they operate and interact with liquid. While the simple premise of operation is the same—rising or falling liquid results in a magnetic field, moving into the areas of a reed switch and sparking its activation— the variations between a horizontal float switch and a vertical float switch are worth nothing.

When liquid level rises, the float on a horizontally mounted float switches rises with it so eventually opening or closing the circuit. A vertically mounted float switch is set to activate or deactivate at specific levels. Based on the liquid’s fluctuation above or below the set levels the float switch will work to alert its owner to the changes.

In terms of durability, magnetic reed switches are known to be reliable for years of trouble-free use. Should a customer need a specialized float switch, however, there are several different ways to customize a switch depending on preference. For instance, custom float level switches can be configured with up to seven different switch levels, depending on the series type.