Piping Specialties and PSI Controls Blog: December 2017

Happy New Year from PSI

With 2017 coming to a close, all of us at Piping Specialties wanted to reach out and send our best wishes to our customers, our vendors, and our friends! We hope that 2018 holds success and good fortune for all of you.

Drexelbrook Total Tank Level System

Ametek is a world leader in level measurement technology products. The Ametek Drexelbrook Total Tank Level System is a state-of-the-art measurement instrument utilizing magnetostrictive technology to accurately determine total product level, interface level, and temperature in liquid tanks. Offered in either a stainless steel rigid, and flexible Kynar version, these probes are capable of working in tanks from as low as 2 feet up to 50 feet high.

Magnetostriction is one of many level technology options available to industrial users today. For liquid measurements, especially when a water interface exists, it unquestionably offers the most versatile and accurate solution on the market. Ametek now has an excellent solution to manage multiple variable measurements in storage tanks. Ametek Drexel Brook now offers the Total Tank Level Multi-variable Transmitter to measure both level and temperature with Modbus, 4 to 20 milliamp, and HART output capability.

The ability to measure and track various tank conditions in realtime is critical in today's process environments. The multi-variable capability of the Drexelbrook Total Tank Level System provides simultaneous data for total level, interface level, product temperature, water interface temperature total average temperature, and volume for all liquid components in the tank. Standard industrial level instruments utilizing guided wave capacitive or radar technologies provide 3 to 5 millimeter accuracy. Higher cost tank gauging technologies will provide 1 to 2 millimeter accuracy. Only magnetostrictive technology can provide superior sub 1 millimeter accuracy levels consistently under most process conditions. In addition, the Drexel Brook Total Tank Level System is fully compensated across the entire operating range of process temperatures, up to 257 degrees Fahrenheit.

One of the most challenging applications is the measurement of an interface level between two significantly different density liquids. The most common of these is oil and water. There are only a few technologies that claim to be able to make this measurement. Guided wave radar and magnetostriction are two of the most common. Guided wave radar technology is based on microwave pulses that are transmitted down a probe and are partly reflected by the product surface, as well as the interface level surface. In applications where both liquids have stabilized, guided wave radar technology can accurately determine both the product and interface level. If an emulsion layer forms between the two liquids this can significantly diminish the measured value, or even cause the complete loss of the signal. If this occurs, it is extremely difficult to maintain control of the process. Using a float based magnetostrictive technology, the measurement becomes straightforward. Both product and interface return signals are generated by the reflection of a magnetically induced strain on the measurement wire, which is embedded in the probe. Magnets are positioned on the probe based on their specific gravity matched to the liquids being measured. This ensures that the float will always maintain its position, both on the top liquid level, and at the interface position. The lower measurement signal remains unaffected by the formation of an emulsion. Comparing the two technologies clearly shows the advantage of magnetostrictive technology whenever emulsion layers are present. Guided wave radar can only be used to measure the overall level reliably under all conditions, while the Drexelbrook Total Tank Level System guarantees the continuous and accurate measurement of the overall level, and the interface, even under emulsion conditions.

The Drexelbrook Total Tank Level System easily integrates into existing control systems that have standard protocols, such as Modbus, 4 to 20 milliamp loop, or HART communications. Each instrument can beset up directly through the Ametek STExplorer software which can be downloaded free of charge. This makes installation and commissioning of the instrument easy. Drexelbrook's reliable magnetostrictive level probes have been installed in more than 100,000 systems worldwide. They are proven over years of grueling weather conditions and trusted by some of the largest companies in the world.

Please watch the video below for more information. To discuss a tank level application, contact Piping Specialties by visiting https://www.psi-team.com or call 800-223-1468.

Basics of Process Temperature Sensors: RTDs and Thermocouples

Industrial thermocouples (Marsh Bellofram TCP)

Proper temperature sensor selection is key to getting useful and accurate data for maintaining control of a process. There are two main types of temperature sensors employed for industrial applications, thermocouple and resistance temperature detector (RTD). Each has its own set of features that might make it an advantageous choice for a particular application.

Thermocouples consist of a junction formed with dissimilar metal conductors. The contact point of the conductors generates a small voltage that is related to the temperature of the junction. There are a number of metals used for the conductors, with different combinations used to produce an array of temperature ranges and accuracy. A defining characteristic of thermocouples is the need to use extension wire of the same type as the junction wires, in order to assure proper function and accuracy.

Here are some generalized thermocouple characteristics.

Various conductor combinations can provide a wide range of operable temperatures (-200°C to +2300°C).
Sensor accuracy can deteriorate over time.
Sensors are comparatively less expensive than RTD.
Stability of sensor output is not as good as RTD.
Sensor response is fast due to low mass.
Assemblies are generally rugged and not prone to damage from vibration and moderate mechanical shock.
Sensor tip is the measuring point.
Reference junction is required for correct measurement.
No external power is required.
Matching extension wire is needed.
Sensor design allows for small diameter assemblies.

Industrial RTDs
(Marsh Bellofram TCP)

RTD sensors are comprised of very fine wire from a range of specialty types, coiled within a protective probe. Temperature measurement is accomplished by measuring the resistance in the coil. The resistance will correspond to a known temperature.

Some generalized RTD attributes:

Sensor provides good measurement accuracy, superior to thermocouple.
Operating temperature range (-200° to +850°C) is less than that of thermocouple.
Sensor exhibits long term stability.
Response to process change can be slow.
Excitation current source is required for operation.
Copper extension wire can be used to connect sensor to instruments.
Sensors can exhibit a degree of self-heating error.
Resistance coil makes assemblies less rugged than thermocouples.
Cost is comparatively higher.

Each industrial process control application will present its own set of challenges regarding vibration, temperature range, required response time, accuracy, and more. Share your process temperature measurement requirements and challenges with a process control instrumentation specialist, combining your process knowledge with their product application expertise to develop the most effective solution.

What Are High Performance Butterfly Valves (HPBV)?

High Performance Butterfly Valve
(Pratt Industrial)

Industrial process control applications can present stringent and challenging performance requirements for the physical equipment and components that comprise the process chain. The valves employed in fluid based operations need to be resistant to the impact of extreme fluid conditions, requiring careful design and selection consideration to assure proper performance and safety levels are maintained in a predictable way.

Industrial butterfly valves intended for extreme applications are generally referred to as high performance valves (HPBV). While there are plenty of published and accepted standards for industrial valves, one does not exist to precisely define what constitutes a high performance valve.

So, how do you know when to focus valve selection activities on high performance butterfly valves, as opposed to those rated for general purpose? There are a number of basic criteria that might point you in that direction:

Extreme media or environmental temperature or pressure
High pressure drop operation that may cause cavitation
Rapid or extreme changes to inlet pressure
Certain types or amounts of solids contained in the fluid
Corrosive media

Certainly, any of these criteria might be found in an application serviceable by a general purpose valve, but their presence should be an indicator that a closer assessment of the fluid conditions and commensurate valve requirements is in order. The key element for a process stakeholder is to recognize when conditions are contemplated that can exceed the capabilities of a general purpose valve, leading to premature failure in control performance or catastrophic failure that produces an unsafe condition. Once the possibility of an extreme or challenging condition is identified, a careful analysis of the range of operating conditions will reveal the valve performance requirements.

There are numerous manufacturers of high performance butterfly valves. Pratt Industrial manufactures high-quality resilient-seated, high performance, and triple offset butterfly valves. Construction materials include carbon steel and stainless steel. Their TE Series triple offset valve offers premium, zero-leakage seating capability even in severe service applications.

You can always get more information and discuss your special requirements with a valve specialist. They have application experience and access to technical resources that can help with selecting the right valve components to meet your severe service and high performance applications.