Tuesday, February 21, 2017

Learning From Catastrophe - Case Study of Heat Exchanger Failure

shell and tube heat exchangers in industrial plant
Shell and tube heat exchangers at industrial plant
Industrial accidents, whether minor or catastrophic, can serve as sources of learning when analyzed and studied. Operators, owners, and technicians involved with industrial chemical operations have a degree of moral, ethical, and legal responsibility to conduct work in a reasonably and predictably safe manner without endangering personnel, property, or the environment. Part of a diligent safety culture should include reviewing industrial accidents at other facilities. There is much to learn from these unfortunate events, even when they happen in an industry that may seem somewhat removed from our own.

The U.S. Chemical Safety Board, or CSB, is an independent federal agency that investigates industrial chemical accidents. Below, find one of their video reenactments and analysis of an explosion that occurred at a Louisiana chemical processing plant in 2013. A portion of the reenactment shows how a few seemingly innocuous oversights can combine with other unrecognized conditions that result in a major conflagration.

Check out the video and sharpen your sense of awareness for potential trouble spots in your own operation.

Tuesday, February 14, 2017

Continuous Liquid Level Measurement Technologies Used in Industry

Industrial pressure transmitter
Pressure measurements can be utilized to determine liquid level
Courtesy Azbil
Although continuous level measurement technologies have the ability to quantify applications for bulk solids, slurries, and granular materials, liquid level technologies stand out as being exceptionally crucial to many facets of the process control industrial sphere. Called “transmitters,” these continuous liquid level measurement devices employ technologies ranging from hydrostatic to magnetostriction, providing uninterrupted signals that indicate the level of liquid in a vessel, tank, or other container.

Hydrostatic devices focus on the equilibrium of dynamic and static liquids. There are three main types of hydrostatic transmitters:
  1. Displacer
  2. Bubbler
  3. Differential pressure
The displacer transmitters utilize a float placed within the liquid container. With its buoyancy characterized to the liquid and the application, the float, a connecting stem, and a range spring or similar counterbalance represents the liquid level in terms of the movement of the displacer (float). The displacement, or movement, of the assembly is converted into an electric signal for use by the monitoring and control system.

Bubbler transmitters are used for processing vessels that operate at atmospheric pressure. This method introduces a purge gas or an inert gas, e.g. air or dry nitrogen, into a tube extending into the liquid vessel. Precise measurement of the pressure exerted on the gas in the dip tube by the liquid in the tank is used to determine the height of the liquid.

Differential pressure (DP) transmitters rely directly on, in a basic explanation, the pressure difference between the bottom and top of the container. Precise pressure measurement is used to determine the height of the liquid in the tank. One of the most advantageous aspects of DP transmitters is that they can be used in pressurized containers, whereas displacer and bubbler transmitters cannot.

Other examples of level transmitter technologies––which are not hydrostatic devices––are magnetostrictive, capacitance, ultrasonic, laser, and radar.
magnetic liquid level indicator gauge with guided wave radar transmitter
Guided wave radar liquid level transmitter
joined with magnetic liquid level gauge
Courtesy Jerguson

In magnetostrictive level transmitters the measuring device, a float, has a series of magnets that create a magnetic field around a wire enclosed in a tube. Electrical pulses sent down the wire by the transmitter head product a torsional wave related to the position of the float, which moves with changes in liquid surface level. The transit time of the torsion wave back to the sensing head is measured and the depth of the liquid, as indicated by the float position, can be determined.

Capacitance transmitters are best applied to liquids that have high dielectric constants. Essentially, changes in the capacitance of the sensor / tank / liquid assembly will vary proportionately with the liquid level. The change in capacitance is measured and converted to an appropriate electrical signal.

Ultrasonic level transmitters emit ultrasonic energy from the top of the vessel toward the liquid. The emissions are reflected by the liquid surface and them time required for the signal to return to the source is used to determine the distance to the liquid surface.

Laser level transmitters operate similarly to an ultrasonic level transmitter. However, instead of using ultrasound signals, they use pulses of light.

Radar level transmitters involve microwaves emitting downward from the top of the container to the liquid’s surface and back again; the measurement is the entire time-frame. One variable radar level measurement echoes capacitance measurements: they both involve dielectric contact of liquid.

The precise measurement of transmit time for a wave or pulse of energy is employed in several of the technologies, the measurement of pressure in others. Each technology has a set of attributes making it an advantageous selection for a particular range of applications. Share your liquid level measurement challenges with an application expert, combining you process knowledge with their product application expertise to develop effective solutions.

Wednesday, February 8, 2017

Safety Cover For Magnetic Level Gauges

Magnetic level gauges provide visual indication of vessel and tank liquid levels. Their application advantage lies in their high visibility, isolation of the indicator from measured media, and options flexibility that permits use in many environments. While armored gauges are available, there is another level of safety that can be added to almost any existing or newly installed gauge.

The video demonstrates the use and toughness of the SafeView™ shield from Jerguson. It accommodates the company's line of magnetic level gauges, as well as those of many other manufacturers.

Your process measurement and control challenges are best solved by working in concert with a product application specialist. The combination of your process knowledge and their product application expertise will develop an effective solution.

Thursday, February 2, 2017

Rotary Vane Actuators for Damper Control

pneumatic rotary vane actuator damper drive
One example of a rotary vane pneumatic damper drive
Courtesy Rotork
A rotary vane actuator is simply a part of an automated damper assembly: its role is to change the position of the damper, converting the motive force of fluid pressure into torque and applying it to a mechanism that will position the damper.

Vane actuators are widely used on quarter turn valves in industrial process automation, but their application also extends to dampers on all types of equipment and installations. Vane actuators are well suited for applications with operation requiring fully open or fully closed damper positions, although some do provide modulating service. A rotation of the actuator drive mechanism through a 90 degree arc, in combination with connecting linkage, quickly moves a damper between open and closed positions. A rotary vane actuator is well suited for driving this type of actuation, with its own 90 degree arc of movement.

A rotary vane actuator is specific to quarter turn opeartion. A pressure tight housing contains a movable vane which is sealed to the sides of the pressure chamber by means of a low friction gasket. Inlets and outlets to the chamber on opposing sides of the vane allow a controller to produce a pressure differential across the vane. The vane will move, in response to the pressure differential, in either direction. A shaft is connected to the vane and the vane acts like a lever to rotate the shaft as the vane is moved by fluid pressure. The torque produced by the actuator assembly is dependent upon the applied fluid pressure.

Hydraulic rotary vane actuators have the ability to handle large amounts of fluid and dynamic motions, exhibiting also qualities of durability and compactness. Pneumatic vane actuators use plant air pressure as the motive force. Both types generally provide fast operation, have few moving parts, and require little regular maintenance. A variety of typical automation accessories and options are available to customize a unit for a particular application.

More information is available from product specialists, with whom you should share your application requirements and challenges. Combining your process and facilities knowledge with their product application expertise will produce effective solutions.

Thursday, January 26, 2017

Advanced Pressure Transmitters for Process Measurement

pressure transmitter for industrial process measurement
Direct mount pressure transmitter
Courtesy Azbil
The measurement of pressure is a common task throughout many industrial spheres. Depending on the application, a wide range of process or machinery operation status can be derived from a pressure reading. Accuracy, ruggedness, and flexibility in application are hallmarks of a useful pressure transmitter.

Azbil North America advanced pressure transmitters offer a combination of features that can make them an advantageous selection for almost any application.

  • Stability of +/-0.1% for 10 years
  • Little to no downtime for calibration
  • Sensor technology that provides day-one accuracy for the life of the transmitter
  • Customizable display
  • Alarm outputs
  • Fast response
  • International standard certifications
The advanced pressure transmitter is available in variety of mounting configurations to suit most applications. More information is contained in the document included below. Share your process measurement challenges with application experts, combining your own process knowledge and experience with their product application expertise to develop effective solutions.

Wednesday, January 18, 2017

Application of Limit Switches on Automated Industrial Valves

industrial valve automation actuator and limit switch
Employed in a wide range of industrial applications,
limit switches are known for ease of installation,
simple design, ruggedness, and reliability.
Courtesy Flowserve Automax
Limit switches are devices which respond to the occurrence of a process condition by changing their contact state. In the industrial control field, their applications and product variations are almost countless. Essentially, the purpose of a limit switch is to serve as a trigger, indicating that some design condition has been achieved. The device provides only an indication of the transition from one condition to another, with no additional information. For example, a limit switch triggered by the opening of a window can only deliver an indication that the window is open, not the degree to which it is open. Most often, the device will have an actuator that is positively activated only by the design condition and mechanically linked to a set of electrical contacts. It is uncommon, but not unknown, for limit switches to be electronic. Some are magnetically actuated, though most are electromechanical. This article will focus on limit switch designs and variants used in the control and actuation of industrial process valves.

Valves, devices used for controlling flow, are motion based. The movable portions of valve trim create some degree of obstruction to media flow, providing regulation of the passage of the media through the valve. It is the movement of critical valve trim elements that limit switches are used to indicate or control. The movable valve trim elements commonly connect to a shaft or other linkage extending to the exterior of the valve body. Mounting electric, hydraulic, or pneumatic actuators to the shaft or linkage provides the operator a means to drive the mechanical connection, changing the orientation or position of the valve trim and regulating the media flow. Because of its positive connection to the valve trim, the position of the shaft or linkage is analogous to the trim position and can be used to indicate what is commonly referred to as “valve position”. Limit switches are easily applied to the valve shaft or linkage in a manner that can provide information or direct functional response to certain changes in valve position.

In industrial valve terms, a limit switch is a device containing one or more magnetic or electrical switches, operated by the rotational or linear movement of the valve.

What are basic informational elements that can be relayed to the control system by limit switches? Operators of an industrial process, for reasons of efficiency, safety, or coordination with other process steps, may need answers to the following basic questions about a process control valve:

  • Is the valve open? 
  • Is the valve closed? 
  • Is the valve opening position greater than “X”? 
  • Has the valve actuator properly positioned the valve at or beyond a certain position? 
  • Has the valve actuator driven the valve mechanism beyond its normal travel limits? 
  • Is the actuator functioning or failing? 
Partial or complete answers to these and other questions, in the form of electrical signals relayed by the limit switch, can serve as confirmation that a control system command has been executed. Such a confirmation signal can be used to trigger the start of the next action in a sequence of process steps or any of countless other useful monitoring and control operations.

Applying limit switches to industrial valve applications should include consideration of:

  • Information Points – Determine what indications are necessary or useful for the effective control and monitoring of valve operation. What, as an actual or virtual operator, do you want to know about the real time operational status of a valve that is remotely located. Schedule the information points in operational terms, not electrical switch terms. 
  • Contacts – Plan and layout a schedule of logical switches that will provide the information the operator needs. You may not need a separate switch for each information point. In some cases, it may be possible to derive needed information by using logical combinations of switches utilized for other discrete functions. 
  • Environment – Accommodate the local conditions and hazards where the switch is installed with a properly rated enclosure. 
  • Signal – The switch rating for current and voltage must meet or exceed those of the signal being transmitted. 
  • Duty Cycle – The cycling frequency must be considered when specifying the type of switch employed. Every switch design has a limited cycle life. Make sure your selection matches the intended operating frequency for the process. 
  • Auxiliary Outputs – These are additional contact sets that share the actuation of the primary switch. They are used to transmit additional signals with specifications differing from the primary signal. 
  • Other Actuator Accessories – Limit switches are often integrated into an accessory unit with other actuator accessories, most of which are related to valve position. A visual local indication of valve position is a common example. 
Switches and indicators of valve position can usually be provided as part of a complete valve actuation package, provided by the valve manufacturer or a third party. It is recommended that spare contacts be put in place for future use, as incorporating additional contacts as part of the original actuation package incurs comparatively little additional cost.

Employing a properly configured valve automation package, with limit switches delivering valve status or position information to your control system, can yield operational and safety benefits for the life of the unit. Good advice is to consult with a valve automation specialist for effective recommendations on configuring your valve automation accessories to maximize the level of information and control.

Friday, January 13, 2017

Electronic Line Break Detection - Pipeline Monitoring

electronic line break detector for oil and gas pipelines
Electronic line break detector unit
Courtesy Rotork
There are some process control challenges for which you may need to establish or produce a solution of your own design. These should be applications where a pre-engineered option or product is not available. A manufactured product for your application likely is comprised, not only of appropriate physical attributes suitable for the application, but also the experience gained from numerous successful iterations solving the same problem, challenge, or issue you currently face. There can be expertise, knowledge, and experience provided as part of a hardware item, and bringing that knowledge and experience of others into the solving of a process control challenge is sound practice.

Pipelines, when considered from differing organizational vantage points:

  • A source of revenue
  • A means of transportation
  • A pipe with fluid in it
  • An ongoing operation requiring monitoring and control
  • An extensive physical presence with an associated risk element
Pipelines are all those and more. Regardless of your vantage point, line breaks are decidedly negative events worthy of early detection and rapid response. Part of that solution is available in the electronic line break detection device from Rotork, globally recognized leader in the design and manufacture of valve actuators employed throughout the industrial sphere. The ELB model incorporates a set of features and capabilities that can be used to detect and respond to gas pipeline breaks. It is a self contained unit employing technology to detect line breaks and execute a predetermined response.

Read more about the ELB from Rotork in the document included below. It provides a detailed outline of the operational features of the unit. Share your fluid system control challenges with an experienced application team, combining your process knowledge with their product application expertise to develop effective solutions.